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elektor saptember 1980 - UK 03contents

selektor 9-01

8K RAM + 4,8 or 16K EPROM on a single card 9-04Many readers have requested that the 4K RAM card for the Elektor SC/MPsystem be updated. The new card presented in this article contains a totalof 8K of RAM, up to 16K of EPROM and can be used with either of theElektor SC/MP systems or the Junior Computer.

precision power unit 9-08

electronic linear thermometer 9-12Conventional mercury thermometers are, of necessity, rather fragile andtherefore break very easily, always at the most inoppotune time. Electronicthermometers, on the other hand, are not as fragile and can enjoy a muchlonger life. The 'readout' can be a great deal more accurate with infinitelybetter legibility. The electronic thermometer featured here can be builtby anyone to fit almost anywhere which is certainly rot true of theconventional type.

the Josephson computer 9-15hun

instructionsutetuns: npder logic circuits

aLnadrgaerecc'amblpeuttoeresxraecuntec*mnosirset thfan"aer million

adsevti,iospemr

byseemm,a.ciot smzt

ms20 times faster than this is currently beingfrom a brand new branch in technology,

namely, the Josephson technique

VOX printed circuit board 9-22

ejektor measuring multipath 9-26

high speed readout for elekterminal 9.28With minor a modification to the Elekterminal it is possible to 'store' theentire contents of the display (TV screen/ on a cassette tape.

musical box 9-30

electrolytology 9-33There is nothing new about the fact that electrolytic capacitors possessinductance due to the method used in their construction. At highfrequencies their impedance will be largely determined by this parasiticinduction. An electrolytic capacitor even acts as a band pass filter andthus also has a resonant frequency.What fewer people will be aware of is that the capacitance is clearlyfrequency dependent. Elektor takes a closer look 'inside' electrolyticcapacitors this month.

curve tracerThis article describes an economic curve tracer for transistors and diodesNo really professional new instrument, of course, but an extremely usefulaid to quickly carry out a general test either to compare transistors orselect them.

9-36

using the vocoder 9-38Several months ago (Elektor no. 56, December 19791, Elektor publisheda 10 channel vocoder. When building a vocoder there are a few 'obstacles'which ought to be taken into account. Readers who have already built oneand are familiar with it will find that this article provides usefulinformation on how to improve on the vocoder's technical qualities.

market 9-45

advertising index UK 22

contents=II (Di I

TSMO

EDITOR:. van der Horst

UK EDITORIAL STAFFT. Day E. RogP. Williams

TECHNICAL EDITORIAL STAFFJ. BarendrechtG.H.K. Darn

E.P. H0i111136

teat '"rG.

NacntrnannWalraven

selektor Weldor septomber 1)1130 - 9-01

Bright outlook for liquid crystalsReliable, long -life l'quid-crystal displaysare now familiar features of mass-produced watches and pocket calcu-lators. But the wo k of the university,government and industrial researchteams that made them available so

' cheaply is by no means at an end, forthe growing complexity of devicesmeans more stringent specifications ofmaterials. Liquid crystals of a newly -developed type promise to hold the keyto further important innovations.Digital electro-opticdisplays using liquidcrystals are now commonplace inwatches, pocket calculators and clocks;and, thanks to advertising, the termsliquid crystal and liquid -crystal displayare now familiar to all. The success ofsuch devices is entirely dependent uponthe quality of the thin, fluid film ofliquid -crystal material that is used topresent the figures and is shown in thephoto.Progress Jr making satisfactory liquid.crystal displays was held up fore longtime simply because liquid -crystalmaterials with good, stable character-istics were not available, but thingssuddenly changed with the discovery ofthe cyano.biphenyl class of liquidcrystal.

Immediate demand

The potential of these liquid crystalsscorned to be excellent, and it was borneout by an extensive test Programme atRSR E. There was an immediate demandfor the new materials. BDH Chemicals,at Poole, in the South of England,solved the problems of production andmade them in large quantities, pureenough to guarantee reliable perform-ance in display devices.One interesting feature of this collabor-anon between a university, a govern-ment research laboratory and a chemicalcompany is that the research, in bringingtogether two scientific disciplines,chemistry and physics, has led to morein the nature of mutual stimulus than toproblems of communication and under-standing.

Liquid crystals

What are liquid crystals? They havebeen known for many years, havingbeen discovered by the Austrian botatistReinitzer in 1888. He observed that theorganic chemical cholesteryl benzoatemelted sharply at 145°C but did notform a clear liquid. Instead, it gave acloudy fluid which became clear onlywhen heated to 179°C. The inter-mediate phase was eventually recog-nized as a liquid crystal. Soon, other

Photomicrograph ens mectic liquid crystal lies article on page 2) with a magnification ofabout 200. The liquid -crystal phase was formed by cooling a thin I ilm of isotropic liquid (blackbackground) and is highly order. in spite of beim) able to flow. In other words, though liquidcrystals ere fluid they have some of the optiul properties of solid crystals. This mai. itPossible, using mimetic liquid crystals which can be electriully controlled, to produce thefamiliar sort of display seen in the lower part of the piMure.

CH,0 -0- N = N -0- OCH,

0

CH,0 -0-C14=N-0-000.CHa

CH,0-0-HC?1>CH-0-0CH,

Figure 1. Soon after the discovery of the I irstliquid crystals, it was found that other organiccomp:panda behaved in a similar way.A common feature of the materials was thatthe molecules were long and narrow, a.contained ring system.. double bondslending rigidity to the molecules.

organic compounds were found tobehave in a similar way, and a commonfeature 01 011 the materials was that themolecules were long and narrow. More-over, they all contained ring systemsand double bonds which lent themrigidity (see figure 1).It is not unreasonable that compoundsmade up in such a way should behave asthey did. Their crystal lattices consist ofa rigid, three-dimensional, ordered arrayof the rodlike molecules; when thecrystals are heated, thermal vibrationseventually overcome the intermolecularinteractions, the molecules become freeto move in any direction and the rigidcrystal ceases to exist. With less elon-gated or more nearly spherical mol-ecules, the material is a true liquid, withtotal disorder of the molecular system.But with rod -shaped molecules there isa strong tendency for their long axes tostay parallel, over considerable molecu-lar distances, even after the crystal hascollapsed. This brings about a fluid butnevertheless quite highly organizedphase.Because of the molecular order which

2

=

101

H t

C I

Ibi

Figure 2. Reversible transition from a nemetic liquid crystal la) to the disordered isotropicsquid lb).

go2 MO

persists, the material in this phase hasmany of the optical properties of acrystal, yet it can flow; that is why weuse the term liquid crystal. Only whenwe heat the material to a higher tem-perature is the truly disordered, liquidstate produced (see figure 2).It is quite common for the molecules inliquid crystals to retain a parallelarrangement, in layers. When this hap-pens the crystals are known as smecticliquid crystals and are rather viscous;they have not, so far, been of muchcommercial use. A great deal moreimportant are the so-called nematicliquid crystals, which are much morefluid and possess a non -layered, Parallelmolecular arrangement.

Optical attireAnother form of the nematic liquidcrystal is found when the molecules ofthe compound are optically active, thatis, when they can take up either a right.handed or left-handed structure, relatedone to the other as an object is to itsmirror image. Through the asymmetryof the intermolecular force fields inliquid -crystal phase made up entirely ofright-handed or of left-handed mol-ecules, the molecules are no longerarranged mainly in parallel in threedimensions; inwead, the moleculararrangement may be thought of as inthe diagram in figure 3. Here, the mol-ecules lie parallel to one another insheets, but there is no ordered arrangeman, of their ends. Crystals with thissort of structure are known as

cholesteric liquid crystals.Passing upwards through a stack of suchsheets, we find that the long axes of themolecules lie progressively in a single-handed sense, forming a right-hand orleft.hand helical arrangement with a

well-defined pitch. Because of therelationship A = Pn, where his the wave-length of the incident light, P is thepitch and n is the refractive index(usually about 1.5), such crystals havethe property of selectively reflectingcoloured light, when P is within therange of wavelengths of visible light Forthis reason, suitably pitched cholestericliquid crystals are used in digital ther.mometers and for various forms of sur.face thermograph}, the pitch and thecolour of the reflected light change withtemperature.Obviously, the existence of materialsgiving fluid but ordered states of matterprovides a considerable challenge toinventively minded people to find otherapplications for them. The need to heata solid to form the nematic or cholas.rent phase was a severe drawback, butin turn it challenged organic chemists toprovide materials that formed thosephases in the ambient temperaturerange. The aim was eventually achieved,but at first the materials had certaindrawbacks.

Room tempereture

The first room -temperature phases we e

3

Figure 3. Portrayal of the molecule, arrange-ment in a cholesteric liquid crystal. The arrowrepresents the direction of the molecular longexit in each sheet.

4x '.0-A -n -0-Y

CH0(CH).-0--0-CN

CH,(CHe).0

(a)

(b)

(0)

CHACH,).-0-0-0-CN (d)

Figure 0. The first mom -temperature limit,cry. phases wme formed hy compounds, ormixtures of compounds which all had thegeneral form Mown in lel. where the linkinggroup A was of the tillm-NM110/-, -CO.0- a. so on. Such linkinggroups made Me compounds unstable orcoloured, a. this problem was eliminatedbe linking Me two rings directly in a biphmylstructure. To avoid shortening the nematicmmperature range, cyano and sat:ir.atn:ILIItyl

eru;:s ro're 71-74Ir'M'd -a k o xy.4..cmnoMphmyls as in 101 11. 101. The

Pdmphenyl derimtives such as WI wore Mandeveloped.

formed by compounds. or mixtures ofcompounds, which all had the generalform shown in lal in figure 4, where-A-B-, the linking group, was of thetype -N=CH-, -N=N101-,-CO.0- and so on. But these linkinggroups made the compounds chemicallyor photochemically unstable, orcoloured them. The best group was theester linkage -COO-. Nevertheless, theexistence of these roomdemperaturenematics allowed physicists to explorethe potential value of such materialsand, from the early 1960s, it seemedcertain that they would be exploited.The disadvantage of the central groupwas recognized and it was eliminatedby linking the two rings directly inbiphenyl structure. Shortening the mol-ecules might seriously restrict the tem.perature range of phases, so, fromprevious experimence. a cyan groupwas used as one of the end groups. Thegroup for the other end was chosen tobe a saturated alkyl group or an alkoxygroup. In this way, the idea of the4.alkyl. and 4.alkoxy-4'-cyanobiphenylswas born. Their structures are shown in(blend (c) respectively (figure 41.One of the first materials synthesizedwas that shown as (b) in the diagramwith a chain of five carbons. It meltedat 21.5°C and was nematic until 35°C;the nematic phase was maintainedindefinitely at roomy temperature anddown to 4 C ire supercooled state. Thenematic phase was colourless, the com-pound highly stable chemically andPholochemically, and the material wasnon-toxic and apparently devoid ofharmful properties. A wide range ofthese compounds was mad, Severalmelted at low temperatures and thecompounds of the form lc) in the dia-gram had the higher -temperature changeof phase from nematic liquid crystal toisotropic liquid.

1

wile.e

Derivatives

From this range of compounds, mix-tures could be produced that behavedas a system melting at around 0°C orjust below and remaining nematic untilover 50°C. This temperature range wasjudged to be too narrow and led to thedevelopment of analogous pderphenylderivatives such as that shown as inthe diagram.The nematic phases of these materialspersist at temperatures up to well above200°C, but by incorporating suitableamounts of compounds such as (d)with, say, n = 4, in mixtures of thematerials (b) and lc) new systems wereobtained with wider nematic rangesfrom -10°C to 60.5°C, -12°C to 72 Cand so forth.With their wrongly dipolar cyano groupat one end of the molecule, these com-pounds have a high positive dielectricanisotropy, which means that the elec-tric permittivity along the long axis isgreater than it is across the short axis;so, in the nematic phase, the moleculeshave a strong tendency to align parallel

selektor elektor september 1.80 - .3

to the direction of the field. This is justwhat was needed, for the availability ofsuch wide,range nematic systems on a

, commercial scale front BDH Chemicalsallowed electronics companies to makeelectro-optic displays capable of excel-lent performance and long life.

Twisted nernatic devices

The watch or calculator display is

simply a thin sandwich of the nematicliquid crystal between two glass platescoated on their inner surfaces with atransparent, conductive film of an elec.node material such as Ins°, or SnOt.By treating the electrode surfaces in asuitable way, the molecules of the liquidcrystal are made to lie parallel to thembut their directions are arranged at a

right angle across the film. The inter-vening molecules in the film, which is 6to 12 pm thick, take up a quarter helicalarrangement, as shown in figure 5. Iflight entering the sandwich is polarizedin a plane parallel to the long axes ofthe molecules at the film's surface, it is

guided through a right angle as it passesthrough the film and it emerges through

right angles tothe one through which it enters. So, inits so-called off state the cell transmitsbrightly and can be used to producebright reflections if a back -mirror is

used. But when a small voltage, of about2.5 V in a 12 -pm cell is applied acrossthe film, the molecules turn rapidly toalign at a right angle to the electrodes.Light is no longer guided as it passesthrough the cell, which appears black.It is obvious that if only parts of the cellare activated electrically dot example,groups of seven bar electrodes in a

figure -of -eight arrangement) we have away of presenting black information ona bright background without having togenerate light energy within the device.When we switch the field off, the mol-ecules rapidly realign to form thetwisted state. This is the basis of the dis-play in which the cyano-biphenyl liquidcrystals have been so successful. The

' only movement is molecular, so theresponse times are very fast, and, witha power consumption in the microwattrange, batteries have a long life.

GmlesTeric devices

Biphenyl liquid crystals provide us witha means of making stable cholestericmaterials. We need only introduce abranched carbon chain for X instead

Of CHsICHz)n- or CHsICHz)n0-,and provided it makes the systemactive optically, for example, with a

kri-CHaCHzCHICHOCHz- group, thematerial will be cholesteric.Materials of this sort were made at Hull,

Off On

Polarizers

Electrodes

Electrodes

P '

Bright

0 U

U U[10 0

U g

D rk

Nora 5. The change in molecular arrangement when a twister! mimetic liguid-crystal isswitched electrically from the bright off state lied to the dark on °edition (right). When thefield is switched off, relaxation from the on to off state takes plac rapidly through forcesStarting at the surfaces.

and they went into commercial prod-uction. Incorporating them in thenematic hosts shown in Oa) and lcl ofthe diagram above produces cholestericswith a range of pitch values that dependupon concentration. Such compoundsare added in very small amounts tonematic liquid crystals used in thetwisted nematic device to ensure thatwhen the device is switched off, thequarter helix always regenerates withthe same sense, so avoiding patchesthrough reverseddwist areas. In greaterconcentration, they are added tonematics to form quite high -pitchcholesteric phases for use in anotherform of device which does not needpolarizers. In such devices, the twist ofa cholesterin of positive dielectricenisotroPY can be unwound electricallyto yield a nematic phase, which thentwists back to a cholesteric when theelectro-motive force is switched off.There is an optical contrast between theswitched -on and switchedoff states,which can be made more pronouncedby dissolving dichroic dyes in the liquidcrystal, thereby making it possible toproduce a negative colour contrast inthese cholesteric-nematic phase changedisplays, with numbers in white on acoloured background.

New material

The cyano-biphenyl and cyanoderphenylmaterials have provided the essentialmeans of producing the reliable liquid -crystal display devices which are nowpreferred to light -emitting diode dis-plays, particularly for batteryoperatedinstruments. But devices are becomingmore and more sophisticated, whichmeans more stringent requirements ofperformance and properties of theliquid-crygal material, so there is Will

a great deal to do.For example, in multi -function calcu-lators and watches, matrix addressingof the display greatly reduces the num-ber of individual electrical contactsneeded for the electrode elements.Mixtures of the cyano-biphenyl liquidcrystals with other nematic materialsallow this to be achieved, but for idealperformance we need materials withoperating -voltage thresholds that arelargely independent of temperature.Mixtures of a new type of nematicmaterial developed at Hull have nowbeen found at RSRE to be less depen-dent on temperature than any earliermaterials are, and they may well be thekey to further success.Cholesteric materials of negative dielec-tric anisotropy are the basis of positive -contrast colour displays, with colourednumbers on a colourless background,making use of dyeoholestericoematicphaseohange. Such devices are at theirbest if the materials are of the type witha low birefringence, that is, with refrac-tive indexes that have much the samevalues in the directions of the long axesand the short molecular axes. Workgoing on at Hull, RSRE and BDHChemicals aims to combine thewdesirable physical characteristics inliquid crystals that are stable Co roomtemperature.Prof. G.W. Gray, in Spectrum no. 167

(570 SI

409 - eleWor september 1980 8K RAM .46 or 16K EPROM on a single care

The extremely popular 2114 RAM IChas four times the memory capacity ofthe type used for the original 14 k) RAMcard. This means that a card with twicethe memory capacity can be con.structed with half as many ICs. It willbe apparent that this leaves a certainamount of 'free space' on the actualboard. Why not fill it up with EPROM?By doing this we can kill two birds withone stone - there is no Elektor EPROMcard as such for any of the Elektorcomputer systems.

The decoder 11051 divides the entireaddress range into 4k 'pages'. Eachmemory section (including the RAMarea) can be placed anywhere within the64k address range. When 2708s areused for the EPROMs, they can bepositioned on any page by connectinga single link from IC5 to both inputs ofNI. Two pages are required if 2716sare used and this involves installing twowire links between IC5 and N1. If,however, 2732 s are used, one completepage can be allocated to each EPROM. '

8K RAM + 4,8 or16K EPROMon a ale cardMany readers have requested thatthe 4 k RAM card for the ElektorSC/MP system be updated. Thenew card presented here containsa total of 8 k of RAM, up to 16 kof EPROM and can be used witheither of the Elektor SC/MPsystems or the Junior Computer.

The 2700 series of EPROM was chosenas the 2708, 2716 and 2732 are all pincompatible (I k, 2k and 4k EPROMSrespectively). Obviously, to be 'univer-sal' certain connections have to made'programmable' (see circuit diagram infigure 11. The address decoding and thelogic level on the chip select inputsdepend on the particular type ofEPROM used. These connections can bealtered by means of wire links on theprinted circuit board (figure 21.

EPROM .

wPeIVO P. input 17 address order

2708 A10 A11 (02626-27-262716 Al2 A11 IC2527-26.28 be at an even page2716 Al2 A11 1026.28.26.272736107 deleted Ism text,

beginning at an odd page

Tablet. This table shows the conemtionsto the A and B inputs of IC7 for the different typesof EPROM.

Table 2RAM

2707

EPROM

2716 2732

1k0.1000.. IC25 = 3000 ...33FF 3000 ...37FF1k1 v 1400...IC26 a 3000 ...37FF 4000 47FF1k2= 1600...1BFF 1027 a 3600 ...3BFF 3800 ...3FFFtk3= 1000... 1 FEE 1038= 3000 ... 3F FF 4800 ... OFF F1k4 = 2000 ... 23F F1k5 v 2400 ... 27F Ftk6= 2800... 213FF1k7 a 2000... 2F FFconnect pins 9 ancl 5 oannett pin 14 connect pins 19of IC5 to inputs of of IC5 to anc13 of IC5 toN2 inputs of N1 inputs of N1

000 3FFF4000..,. OFFF5000 ... BEFF6000 ...BEEF

connect pins 19,3,11and7o5IC5 to pins9...12of IC7(107 is deleted!).

Table 2. An example of the possible address format when the RAM sectio is sequentiallyfollowed by lb. EPROMs

This will be explained in detail further

The next step in the address decodingis to enable the individual memory ICs.As far as the RAM is concerned this willbe in sections of 1k Itwo ICs per sec- i

tion). The EPROMs, on the other hand,will be in sections oft k, 2k or 4k (for2708s, 2716s and 2732s respectively).The RAM section is taken care of by the3 to 8 line decoder IC6. One half of asimilar IC, IC7 (2 to 4 line decoder) isused to select the EPROMs. Wire linksare included to preprogram the A andB inputs of IC7 for the particular typeof EPROM to be used (see table 1). Theorder of addressing will be slightlydifferent when 2718 s are used, but thisshould not cause any problems inpractice, provided the EPROMs areprogrammed (and installed) in thecorrect order. Table 2 gives an exampleof the relevant addresses and connec.bons for when the RAM section is

placed on pages 1 and 2 followedsequentially by the EPROM sections.The memory card iscompletely bufferedto keep the Iced on the bus system toa minimum. The address bus is bufferedby ICI and IC2. These are uni-directional buffers which have PNP inputsrequiring a very low input current. Thesame is true of the data bus buffers(IC3 and IC4). These are bidirectional,the direction of data transfer being con-trolled by the logic level on the com-mon select line. When this line is lowthe buffers enable the transfer of infor-mation into the RAM section, and whenthe select line is high the data con-tained in the RAM/EPROM sections canbe read out.While the memory card is not beingaddressed the data bus buffers are held

85 RAM 4.8 or 16K EPROM on e sinple card eleMor September 1980 -9-05

I 11111111111 11-''''FITIITITTIT}7

I 11111111111

ollllllllllTl 111111111111

111-11-11iiI,U11

a Ha

I. 1111111111 II

igg

B HE

IIIIIIIIIIII

a In

08D O

A1

4. 4

Figure 1. Complete circuit diaprem of the RAM/EPROM card. The connections which need to be mounted for the various types of EPROM meclearly shown.

806 elektor »Member 1980

2 1

SR RAM. 6,8 or 16K EPROM on a single card

Figure 2. The printed circuit board and component layout for the RAM/EPROM card. There is room Mr 8 k of RAM and up to 16 k (EPROMon the (double sided/ board.

Parts li t

Capacitors:

Cl 1 µ/10 V tantalumC2 100 n

Semiconductors:C1,IC2 70.201C3,IC9 70.243CS. 01.C6,IC7 - 701.1155C8. 79.08C9... IC29 2119 (RAW

IC25... IC28- 2708, 2716or 2732 (EPROM sea text)

IC29 74.00

All parts ave.le komrechnoma.)

in the write mode (via gates N3 and N51 section when a WRITE signal is present other microprocessor systems.to ensure that the card is unable to (via N4). The two wire links shown atinterfere with the data bus. When the the inputs to N4 enable the memory Arranging the memory blockscard is being addressed, the buffers are card to be used with the Elektor SC/MP The way in which the address decodingswitched to the read mode. Data can system or the Junior Computer (both is done on this card makes for a largethen only be entered into the RAM inputs connected to 31a), or with most degree of flexibility - provided you

September 1980 -907OK RAM 0 OA or 16K EPROM on a shale caul

know what you're doing! The first thingto realize is that IC5 divides the addressarea into 4k8yte blocks, and that Ni(with inputs V and WI selects one ormore of these for the EPROMs, whereasN2 (inputs X and Y) selects two 4k8yteblocks for the RAM. In general:

IC5output

ekBytaaddressblock

2x dkflyte RAMarexa selec,;ed

0 0000 ... OFFFIF FF

01000

23 2000 3FFF

2

5 5000 5Ff F0

6 6 000 6FFF70110 7FFF

6

F F000 FFFF

F:,,r.tfr,',.7npt:r,t,`,",:e7LL.Vock, somes

RAM arae

Two 4kByte blocks are required.one for IC9 ...IC16 and one forIC17 ... IC24. One of these blocksmust be on an eve -numbered Page(0. 2, 4, etc.) and then other on an oddpage. For example, X = 4 and V = 5would define a consecutive RAM areafrom 4000... 5F F F.

EPROMs twee 2706

For four of these 1kByte EPROMs, a4kByte address field is required. This isselected by connecting one of theoutputs from IC5 to N2 I'V'); the otherinput to N2 (nail is either connected to

V or, via a wire link, to positive supply.The 4k8yte field is further subdividedby IC7 (connected to address lines Al 0and All), to select the EPROMs asfollows:IC26 V000 V3FF1C26 V400 V7FF

elleFlyta EPROM 2x ekeyte EPROMarea forv2708a are: for 27,,1,6s

5

IC27 V800 VBFF1C28 VC00 VFFF

EPROMs sype 2710

An 8kByte address field is required inthis case (4 x 2kBytel. The same

principles apply as discussed above forthe RAM area: V must be connected toan numbered output from ICS, andW to an odd -numbered output. Forexample, if V = 2 and W = 7. the fourEPROMs will correspond to thefollowing address fields:IC25 2000... 27FFIC26 7000 77FFIC27 2800 2FFFIC28 7800... 7FFFNote that IC25 and 1C27 form a 4kBytepair, as do IC28 and 1828.

EPROMs type 2232

Each of these ICs corresponds to a

4kByte address field - in other words,to one output from IC5! In this case,no further subdivision of this field is

required, so that IC7 becomes reduthdantl N1 is not required either, but itstwo inputs (V and WI must be connectedto +5 V by means of wire links.The four 4kByte blocks required can beprogrammed by wire links direct fromthe corresponding outputs of 105 to theholes intended for pins 9... 12 of IC7lk n). Pin 9 (k) corresponds to 1C25,pin 10 III to IC26, etc. This means thatif, say, IC28 is to be located on the lastpage, a wire link must be taken fromoutput F of IC5 to pin 12 (n) of the IC7Position.

Wire links and unused positionsAn important point to note is that

used inputs should not be leftfloating. This was already mentionedabove, as regards NI and N4. The sameobviously applies to N2, if the totalRAM area is not to be used as yet:unused inputs must be connected eitherto +5 V or to an unused output fromIC5.Particular care should also be taken withthe wire links at the inputs to IC7 andIC28 IC27. These depend on thetype of EPROM used, as follows:2708: P.O,S-T, e -f, ac.2716: P.R, &T. e -g, ad.2732: e -g, a -b.Finally, it should be noted that thesupply common (0 V) connection to theboard must be applied via two sets ofconnector pins: 4 a/c + 16 a/c and32 a/c. These two sets are not inter.connected on the board!

996- elektor septerober 1980 Promo power unit

When calibrating voltmeters anaccurate reference voltage is, ofcourse, essential. As far as digitalvoltmetert are concerned thereference voltage will have to bevery accurate indeed for suchmeters to be of any significantvalue. If close tolerance precisionresistors are incorporated in theDVM's input attenuator, thereference voltage should meetaccuracy requirements outside thebasic measuring range. Thus, areference voltage is required withan accuracy that corresponds atleast to the tolerance of thedivider resistors. The precisionpower unit described hereproduces several reference voltageswith an accuracy of 0.1%! Tomake full use of the degree ofprecision achieved, the unit hasbeen incorporated into a highquality power supply.

As we all know it is virtually impossible The voltage across RSET is buffered byto const anructa precision voltage source opamp before being fed to thewith standard components. Close internal series pass transistor. The ICtolerance devices (both active and contains integrated 0.1% tolerancepassive) are very difficult to obtain. If resistors between various pins which canresistors are connected in series and be interconnected to provide a combi.parallel to produce the required value, a nation of values. Resistors with valuestolerance of 0.1% is out of the question. of 5k, ID k, 2k and 6k are locatedThe solution, therefore, is to find between pins 9 and 7, 7 and 6, 6 and 5integrated components with 'everything and 8 and 4 (ground) respectively. Theincluded'. The majority of so called output current is determined by.LLIMprecision voltage regulators suffer from (100 !IA) and the current flowingthe disadvantage that they can only through RSENSE and can be calculatedprovide one output voltage. Elektor's from:

design team, however, have discovereda little known IC from NationalSemiconductor which is able to produceseveral accurate voltages and hasexcellent characteristics and can also beincorporated into a power unit as a'normal' regulator IC. This device hasthe part number LH 0075.The block diagram of the Precisionpower unit is shown in figure 1. As canbe seen, it is very similar to conventionalcircuits of this kind. Pre -stabilisation hasbeen included to limit the input voltageto the regulator IC. This protectivemeasure is quite justified consideringthe cost of the IC. Both voltage andcurrent can be adjusted separately. Byincluding a pair of series pass transistorsan output current of up to 2A can beproduced. A description of the technicalspecifications for the unit is given intablet.The internal nructure of the IC is

shown in figure 2. A constant currentsource is fed to a zener diode via a fieldeffect transistor. This produces a highlyaccurate, temperature stable reference

voltage with a variation of 0.003VDIThis reference voltage is then used toproduce two further constant currents(ISET and I Lim) The output voltage isdetermined by the (1 mAl currentflowing through resistor RSET and canbe calculated from the formula:

BOUT' ISET RSET

The IC can also be used as a pro.grammable current source when pin 9 isconnected to ground via a 25 k resistor.The output current will then be deter-mined by the values of Rum andRSENSE. A potentiometer could beused for ALMA so that the outPotcurrent can be made adjustable..

Circuit diagramThe complete circuit diagram of theprecision power unit is shown in figure3. The maximum secondary voltage ofthe mains transformer is limited to 30 Vso as not to exceed the input require.ments of IC2. The transformer voltage isrectified by 81 and smoothed by Clbefore being fed to the pre -stabiliser IC1.LED DI indicates that the circuit isswitched on.By including a tenet diode (D2) in serieswith the ground lead of ICI, its outputvoltage is 'raised' to 30.2 V to providean adequate (and safe) input level forIC2.The output voltage of the circuit can beadjusted by means of potentiometer P2which is connected as shown in figure A.The output current limit is set by Pl.R2 and R6. Resistor R6 is included in

Table 1

Technical Data

Variable Output voltage:Fixed Output voltage:

Accuracy:Voltage regulation:Ripple suppression:Rosetta.e current limit:Lod regulation:

OV to a asv.1,6 V,2 V,6V,I1V,8 V,10 V,12 V,15 V.18V

0.19,WM 0.0089/V80.3Oro vA1.1. 0.0)6%

Table 1. Techniol spoil iotion of . precision power unit. As the f igures show, the unit isindeed precise.

precision power unit elektor september 1980 - 9-09

0- OII

(AK

rectification smoothing FOSIBbiliSIIIi0 precision...4.n 00610 .1

Figure 1. Block diagram of the Elektor precision power unit. T. stabilisation section consists basically of one IC 0.600751, two poten-tiometers and a selector switch.

parallel with P110 reduce the maximum 2output current to 2A, while R2 acts as acurrent sense resistor. The outputvoltage is selected by a multi -positionswitch (see figure 4) connected, as

mentioned before, to the internalprecision resistors of IC2. This switchconnects the various resistors in series orParallel as required.Transistors TI and T2 increase thecurrent output capability of the supplyand the resistors in their emitter leads1R7 and RE3) ensure that the current isdivided equally between them.Resistor R3 is included as a dummyload for the unit and diodes D4 and 05protect the circuit from negativetransients.The output voltage and current can bemonitored by including a moving coilmeter and a double pole switch. If theunit is to be used to power HF circuitsan extra 100 nF capacitor should beconnected directly across the output. Figure The internal diagram of the 1.110073 and its pinout. The use is electrically insulated.

3

Byer. 3. The complete circuit diagram of the unit. The output yolMge can . preset to serious values between l .5 ... 18 V ormin becontinuously variable between 0.2... 26 V. The output cement can be limited to anything .tween 0 2 A.

9.10 - elektor sutamber

4 Parts list

Figure 9. The wiring of the voltage seleuor it 53. Three wafers are used a., therefore,the wiring must be thoroughly checked.

mistOrs51.51e. 11.10.5W

I 11/2 W53 - dB/HO=1k5115=12k110.1C0k117,1113. WWI WPt ds2 25 k linP3=25 k pram,PI= 1 k preset

Capacitors

= 2200 0/90 VC2,C9 . 100 n 5151/1C3 202/25 V tenmlurn

llprecision power unit

SemiconductorsO 1 . LEDD2 5V2/900 reW miter diodeD3 = DUG 10A 1501106,D5. 1N61302TI,T2 = 2N3055ICI = 7512.4IC2. LH 00)5 (National/B I EI9IC3250/2200 or

100 V/9 A bridge rectifier

MisullaneousTrl 30 V/3 A transtormerF1= 0.63 A Doane fuseSt =double pole mains twitch52 = double pole toggle switchS3 =11 way. 3 pole water switchNI = I rnA moving tail meter

5

Figure 5. Printed circuit board and component layout fot the precision voltage unit. Thesocket for 1C2 can be made up from 'socket WV,

ram power unit elektor september 1960 -911

6 7

10 15 po

/9

*

Figure 7. The new scale forme 1 met movingcoil meta,.

Construction and setting upThe printed circuit board and com-ponent layout for the precision powerunit is shown in figure 5. The socket forIC2 can be made from 'socket strip' bycutting off four strips of three contacts.A suggested front panel layout for theunit is shown in figure 6. Once this hasbeen attached, and the meter scalesubstituted for the one shown infigure 7, the unit can be wired as shownin figures 3 and 4.All wiring should be carried out with agreat deal of care and attention to detailas one mistake could burn a hole inyour pocket.After the wiring has been checkedthoroughly (several times!), the outputvoltage of IC1 should be measuredwithout IC2 inserted. If this voltage isany higher than 32 V there is somethingwrong with the pre -stabilisation circuitwhich could result in damage to IC2.If the voltage is correct the unit can beswitched off and IC2 inserted. Again,check several times that the IC is

positioned correctly. With S2 in the'voltage' position, S3 switched to one ofthe preset ranges and a voltmeterconnected across the output, the unitcan be checked and P3 adjusted to givethe correct reading on the scale of M1.The current range can be adjusted withthe aid of a known load resistor. Switchthe unit off, turn Pt fully anticlockwiseand switch S3 to the 10 V position.With a load resistor of 10 S2/10 Wconnected across the output (or a

universal meter switched to the IA -range- or higher) rotate P2 until the meterneedle stops moving. According toOhm's Law a current of 1A will thenflow through the load resistor. Themeter scale can be adjusted by means ofP4.Once the above checks have been carriedout successfully the unit can be installedin a suitable case and is ready for use. N

Mime 6. Proposed front panel layout for the unit.

electronic Omar manometere.tz -stainer semarnber segoefregroilie

linearthermometera semiconductor used as a temperature sensor

The conventional mercurythermometer has been with us fora long time, mainly because itserves its purpose very well. Itdoes however suffer from anumber of major disadvantages.They are, of necessity, ratherfragile and therefore break veryeasily, always at the mostinopportune time. A relativelylong period is required for them tostabilise and they are not theeasiest thing in the world to read.Electronic thermometers, on theother hand, are not as fragile andcan enjoy a much longer life. The'readout' can be a great deal moreaccurate with infinitely betterlegibility. Furthermore, they canbe built by anyone to fit almostanywhere which is certainly nottrue of the conventional type. Theactual sensor, in this case asemiconductor diode, is very smellallowing it to be mounted inpreviously impossible situations. Afurther advantage is that, due toits linear characteristics, expensiveequipment is not required tocalibrate the unit.

Various types of sensors are availablefor the purpose of constructing a fullyelectronic thermometer. Temperaturesensitive resistors are often used, witheither a positive temperature coefficient(FTC) or a negative temperature INTCI.A temperature coefficient that ispositive means that the resistanceincreases with the temperature whilewith a negative coefficient the resistancewill decrease with temperature.The disadvantage of thermal sensitiveresistors, however, is that they are notlinear. The characteristic whichrepresents the curve of the resistance asa function of the temperature is not astraight line, but slightly curved. There.fore, unless elaborate compensationnetworks are included, a resistor canonly be used within a small temperaturerange, for then the small part of thecurve used can be considered to be astraight line. For greater temperatureranges a different sensor will have to beused. With respect to fairly high

temperatures of up to 1000° C thermo-couples are needed. These, however,demand a rather specialised technique(cold welding compensation, compen-sation of temperature influence as a

result of current pawing through, etc.)and are therefore not suitable fordomestic use.Temperature sensors using semicondoc.tor diodes or transistors do not stifferfrom these drawbacks. They can beapplied within a wide temperature range,are nor complicated in structure and are '

as compact as the other sensors.The temperature sensitivity of thesemiconductor sensor is based on theprinciple that the forward voltage willchange with temperature when theforward current is maintained at a

constant level. An example of this isshown in figure 1, when the forwardvoltage is a function of the temperaturein the SAX 13 diode. It will be seenthat it can exhibit PIG or NTC charac-teristics depending on the value of theforward current. At a current of 1 rnAthe diode has a distinct negativetemperature coefficient which reducesas the forward current is increased. Atefigure approaching 75 rnA the 'forwardvoltage is practically temperatureindependent which can of course bevery useful. When the forward current isincreased beyond this point the diodethen behaves with a positive temperaturecoefficient. All very interesting but notof great importance to us in thisinstance.What is significant, however, is that allthe lines in figure 1 are straight. Infestthis linearity continues at cemperaturesbelow freezing point. Thus, the BAX 13would make an ideal temperature sensor.Furthermore, most of the common

1

lin11111111111

.1 1

J. Borgman

Figura 1. forward voltage of tha PAX 13 it shown plotted as a function of tamperatura atfour different forvoird currents. It can be seen that et any salmi of forward currant the Plot ISa straight line.

Awes. linear thermometer Oahu, septemher 1980 -9.13

2

Figure 2. The circuit diagram of the linear thermometer. Using the 'Nal 48 ass sensor, the temperature can be displayed welt the aid ofmoviu it meter or a digital voltmeter with 'floating' inputs.

sule meter MI temperature range R8 liedM

0- 300. 30

0.300 PR0-100

- 30- 30 30C

1 k3k

-0,3-0,3

.0,3 V+0,3 V

0- 50o- 50

0-300 AA0500 AA

- 50 50C- 50 50C

1.87 k1 k

-0,5-0,0

.0,5 V

.0,5 Vwoo 01 rwk -100...+100C 1k -1 +1 V

2 x 3k3 in parallel.

TAW . A number of alternative values for R8 tegeth with the measurement ranges obtainedfor various moving coil meter ea...

types of diodes have similar character.!sties providing the forward current iskept as constant as possible.

The circuit diagramThe circuit diagram shown in figure 2was first published in the 1979 SummerCircuits issue and many readersrequested a printed circuit board for itwhich is now available. A suitable diodeto use as a temperature sensor can bethe common 1 N4148. I ts f orward voltagedrops by about 2 mV per rise in °C.If a diode is to be used as the basis fortemperature sensing it is important thattwo main conditions are met in thecircuit. Firstly, as previously mentioned,the forward current through the diodemust remain as stable as possible.Secondly, the circuit measuring theforward voltage of the diode must havea high impedance.

The sensor diode, Of, is included in abridge network which is supplied withthe reference voltage from a 723 IC. At0°C the bridge must be completelybalanced, that is, there must be novoltage difference between the twoinputs of IC2. The 741 will, in fact,ensure this itself since 07 is connectedto the inverting input and constitutes afeedback path. The IC will maintain ormake the voltage across R7 equal to thevoltage at its non -inverting input.When the temperature of the sensordiode is 0°C, the voltage across R7 willbe equal to the voltage across R6 pluspart of the pre. P1. The output of IC2isthenadjusted to MO by Pt ,effectivelybalancing the bridge. The display of thethermometer is a meter in the output ofIC2. The meter has been connected in abridge rectifier circuit and it will there.fore read in one direction only. Thisthen makes the adjustment of PI a

simple matter.Any variation in temperature will resultin a change in the forward voltage of thesensor diode 01. Since the voltage acrossR7, D1 and P2 is the reference voltageof the 723, and therefore constant, anychange in the forward voltage of D1 willresult in a voltage variation across 07.This will be immediately detected byIC2 which will react by passing a smellcurrent, via the meter, to P2 to compen-sate for the change. Any variation of thecurrent through DI, due to changes inforward voltage, will therefore beavoided by the reaction of IC2. Thusthe path through the meter bridge circuitand R8 is a servo control loop tomaintain the ct through DI at aconstant level. Theurncurrent level throughR8 (the current which counteracts thechange in voltage across 071 reflects thetemperature of the sensor diode. Themeter will, of course, indicate this andcan be provided with a scale graduatedin degrees.

As mentioned, the meter is connected ina bridge rectifier circuit. This meansthat the meter will always read in thesame direction, regardless of whetherthe temperature of DI is above or below0°C. In other words, the meter will givean identical reading for bah 410°C and-10°C. Some indication is needed toshow whether the temperature is aboveor below zero.So far, only the reference voltage sectionof the 723 has been used. Since this ICalso contains an opamp with a transistoroutput, this could be used for theindicator circuit, with the addition of afew other components. The champ is

910 - elektor september 1980

3 1

electronic Sneer Warmomator

P eru list:

Resistors:

R1 -47k820 n

R3,R0 u 100 k115 o 210R6=10 k

=110RB " tax,

Capacitors:C1= 100p02 - 220 ./25 V

Semiconductors:T1 = BC 5178O 1 ...135 =18411808 - LEDICI u 7231C2 - 741

Miscellaneous:

Moving co meter Bee text,.B1 o 8400000 12V/100 m.

bridge rectifierTR -12 V/100 rn. mains

transformerPW86 box type BOC aaoWest Hyde or Vero.. WM2518-H Electroyelue.

used as a comparator with the outputof IC2 and the reference voltage beingconnected to the nverting andinverting inputs respectively. Assumingthat the circuit is calibrated for zerodeflection of the meter at 0°C, a fall intemperature will result in an increase inthe output level of IC2. This will takethe non -inverting input of the opamphigh and with it the output. TransistorT1 will turn on, lighting the LED. Whenthe temperature rises above zero. thereverse process will occur and the LEDwill be extinguished.If a digital voltmeter with a 'floating'input is available, the meter describedabove may be omitted. The DVM maybe used tomeasure the voltage across118 in the feedback loop. This willcorrespond to the current passingthrough it and therefore to the tempera.tore of the sensor diode. If this option isused the output of IC2 can be directlyconnected to R8, since the meter, itsbridge rectifier and the temperaturepolarity indication circuit (131 ... 84,T1 and 061 need not be used. It will beobvious that neither of the terminals ofthe DVM must be earthed. The polarityof the temperature (above or below 0°C)

Figure 3.11re punted count board and component layout for the Imam thermometer.Proyis.n has bean made to mount small trenslorrun on the board.

will be indicated by the positive ornegative sign of the DVM display.

Construction and calibrationThe construction of the LinearThermometer should not Present anydifficulties if the printed circuit board isused. The layout for this is shown infigure 3. Room on the board has beenallowed for the small 12 V 100 mAmains transformer required. Thecompleted printed circuit board may befitted in a type OOC 430 plastic casefrom West Hyde or the 65.251811 fromVero. The mounting holes on the boardhave been drilled to fit either of thereboxes.For the temperature sensor the 1144148diode is recommended. This may bemounted at a reasonable distance fromthe circuit board if desired. For airtemperature measurements, the diodecan be used without any form of cover,provided it is protected from accidentaldamage by some means. To measure thetemperature of electrically conductivefluids, the diode will need to be electri.tally insulated. The insulation should beas thermal as possible for obvious

reasons.Depending on which type of meter ischosen, it may be necessary to adjustthe values of R8A and ROB as well asthe limits of the measuring range.Table 1 gives some guidelines for thispurpose. The connection points for aDVM are shown in figure 2.Before calibration can begin, a quantityof ice must be produced from distilledor demineralised water (available at thechemist's). The ice is crushed and placedin a position where it can melt slowly.The sensor diode is then put in themelting ice and P1 is adjusted fora zeroreading on the meter. This then is

freezing point calibrated, now for theother end of the wale. With P2 inrentral position, the sensor diode can beplaced in boiling water (also distilled ordemineralised). The voltage across R8can now be set to exactly 1 V by P2.This should complete calibration but ifa reliable reference thermometer is tohand, further checks can be made on acomparison basis.

the Josephson computer

Large computers can consist of over a hundred thousand logic circuitsand are able to execute more than a million instructions per second.Fast as this may seem, a computer 20 times faster than this is currentlybeing developed by IBM. It stems from a brand new branch intechnology, namely, the Josephson technique. Its most striking aspectis that it can only function at extremely low temperatures, at whichmost life has come to a complete standstill, for it is then that electronsmove with an increased velocity.

superconductors supercede semiconductors

elektor se.ember 1980 -9-15

There are two ways in which to expanda computer's capacity: either by includ-ing more logic circuits, or by enablingthem to work at a higher speed. TheJosephson computer, the 'super brain'of the near future, draws its strengthfrom its rapidity.The speed at which a computer carriesout its instructions is measured in thecycle time or clock generator period.The large computers in operation todayhave a cycle time of around 30-50ns(nanosecond = one millionth of a sec-ond). The world's fastest computer,which oddly enough is not an IBMdesign, but a CRAY (small scale special -

industry), has a cycle time of 12 ns.With the ad of the Josephson techniqueit is hoped to reduce this to 1 ns. Inactual fact, the first prototypes willprobably have a cycle time of 2 ns, buteven this amounts to their being20 times faster than the large present-day computers. Apart from their speed,the prototypes performance will re.amble that of the IBM 370/168, oneof the biggest existing computers.

die Josephson short cAchieving such a

ycle time

eomputer

116Ja(s' 016A' in hruisleall

414: IQ '40 LSI . 436.668611100.111.

Fewer. An electron microscopic photo of pert of a Josephson chip. Smiler to the methodused v. sernicondumor technology, circuits may be photolithogrephically miniaturised. TheJosephson technique, however, has nothing to do with semiconducting. This is an experimentalOR trot which switches in 50 picoseconds 150.10'2 seconds). Peen faster ranching times areposse. (photo IBM.

is not only a mat-ter of searchingfor high-speedlogic circuits. It

also involves solving the problem Per-taining to the transport of countlesselectrical signals. In one nanosecond anelectrical signal can only travel about15 cm, which means if that is to be thecycle time, the dimensions of the entirecomputer will have to be no more than15 cm. For this reason, the Josephsoncomputer as designed by IBM will be13.5013.7 x 14 cm.The question is now: will the hundredthousand logic circuits required by anextensive computer be able to fit intosuch a tiny space? Yes, by means oflarge scale integration ILSI) whichmodern technology has fortunatelyalready achieved. Several tens of thou-sands of chips can be integrated. How-ever, if they belonged to the semi-conductor type, the circuit would bedoomed to disintegrate after a verybrief lifespan, as they would dissipateseveral kilowatts.Thus, what is needed is a technologyincluding similar miniaturisation possi-bilities, but which at the same timeproduces higher speeds and much lessdissipation. All this is achieved by theJosephson technology. Figure 1 showsthe result: a Josephson chip.

Superconductors and electrontunnelsIn 1962 while still a university student,the British physicist Brian D. Josephsonlaid the theoretical foundation for theJosephson effect named after him. It isbased upon two physical phenomena:superconductivity and electron tunnel-ling.Superconductivity was discovered in

9-18 - alaktor septemher 1980

1911 by a university professor at Leiden,Heike Kamerlingh Onnes. He noted thatcertain metals (superconduceors) lose allresistance to electric current flow whenthey are cooled to below a certain tern-perature (which is different for eachsuperconductor). The resistance literallydrops down to zero ohms. KamerlinghOnnes found that superconductivity willonly take place if the current is main-tained at a certain level. If it rises abovethat value, the metal will start to actas an ordinary conductor, despite itsbeing sufficiently cooled. It also ap-peared to be possible to disturb thesuperconductivity with a magneticfield.It was only in 1957 that a satisfactoryexplanation for this phenomenon couldbe given. One of the people responsiblewas John Bardeen, one of the threeinventors of the transistor. What itcomes down to is that in the super-conducting state an electric currentmust not be regarded as a stream of'single electrons, but of pairs' (Cooperpairs, named after another founder ofthe theory). The electrons belonging tosuch a pair now move in step with eachother, so to speak, and no longer needto 'cling' to the atom nuclei. With eachother's help they shoot between thenuclei. Superconductivity stops whenthe electron pairs become separated forsome reason. This may be due to enincrease in temperature or current, ordue to a magnetic field. Strictlyspeaking, superconductivity is only validfor direct currents; as for alternatingcurrents, they cause a slight deviationfrom the 'ideal' superconductivity untilfar into the high frequency range.Whereas superconductivity was ex.plained long after its discovery, withelectron tunnelling the tunnel effect)it was quite the opposite. The theoryhas been in existence for some timebefore the phenomenon .could bedemonstrated during the sixties. It hasnothing to do with superconductivityand infect also occurs at everyday tem.peratures. It is the tunnel diode, oftenapplied as a gigahertz amplifier or as afast switch, which makes use of theeffect.Contrary to what might be expected,a thin insulator between two conductorswill allow an electric current to pass.Thus, despite the tact that its ohmicresistance is infinite, current will flow.This involves quantum mechanics andso is rather complicated. Basically, itmeans that the electron should notonly be regarded as a particle, but also

as a wave phenomenon. It 'rebounds'as it were against the barrier formedby the insulator, but being a wave itpenetrates it slightly, provided that theinsulator is not too thick.

Josephson: superconductingtunnellingJosephson combined the two physicalphenomena by applying the electron

tunnelling theory to electron pairsresponsible for superconductivity. Thisis because an electron pair can also beconsidered as a wave. Remarkably, thethin insulator, which really should notallow any current to pass at all, was nowfound to act eat superconductor. Thisoccurred when the metals around itwere in a superconducting state.This effect is called the Josephsoneffect. A year later is was also observedin the American Bell laboratory.A thin insulator between two super.conductors is called a Josephson junc-tion. This is the principle behind theJosephson computer. Since supercon.ductivity only takes place at very lowtemperatures, the entire computer iscooled by submerging it into liquidhelium. Its boiling point is around4.2 degrees Kelvin (-269°C). Thus,more than anything else, the Josephsoncomputer has to 'keep its cool'. Thereare additional applications for theJosephson effect outside the computerfield. It can, for instance, be used tomeasure tiny magnetic fields and volt-ages, and can also be applied in micro-wave technology.

The Josephson junction used asa switchAs we have just seen, a superconductingmaterial can be brought out of this statein three different manners: by an in.crease in temperature, an increase incurrent and by the creation of a mag-netic field. This is not only true ofsuperconducting metals, but also of theJosephson junction - even more so, infact. That is why Josephson called it a'weak super conductor'. When it is

. Josephson computer

brought out of its superconductingstate, it does not start acting as a normalconductors, like metal, would, but as anordinary tunnel junction. In practice,this means that the Josephson junctionthen demonstrates a resistance of a fewhundred ohms, so that it is possible toswitch its resistance from zero to a fewhundred ohms. The Josephson com-puter uses this phenomenon.Switching from a superconduceing to aresistant state, and vice versa, happensat a speed that few physical processescan match. The switching time is around6 picoseconds (a picosecond is onebillionth of a second), less than 1% ofthe 1 ns cycle time IBM seeks to achievein the Josephson computer. By way ofcomparison, the fastest semiconductorswitches take ten times longer.

This incredible speed is not the onlyadvantage the Josephson junction hasto off.. Its dissipation (heat develop.ment) when ice superconducting stateis nil, even where current of 0.1 mA isflowing. For, after all, its resistance isalso nil! In fact, dissipation will be verylow, even in the resistant state, as Mecircuit's supply voltage will be approxi-mately 10 mV.A Josephson computer including a

16 Mbyte memory capacity is thereforeexpected to dissipate a mere 7 watts ofelectrical power. What a difference,compared to the amount of kilowattsproduced by presentAay computingmonsters!This does not mean that a Josephsoncomputer will not lead to high elec-tricity bills. On the contrary, cooling itto 4.2 Kelvin will require about15 kilowatts. Cooling techniques havefortunately long since been developed.

2

to.

Figure 2. The Josephson computer vtill have an unusual appearance. M. of it will he taken uphe Me cimiinfl system required to maintain 4.2 K 1-289.C1. This requires Clot of enemy:15 KW, seharaaa the computer itself needs only 7 Will. Ai .rtipressor for the coaling:

c.ling system, C: interface a. supply operate at room temperature; D: in- and outputconnectio. Di Me actual computer: F, liquid helium at 4.2 K.

Mon com elelstar september 1980 -9-17

3

Figure 3. The structure of a Josephson'unction 131.1 and its voltage/current ratiocurve 1301. The Josephson junction consistsof two superoondmors (shaded areas1 with avery thin insulator, the Josephson barrier,

The operation of a cooling installation(cryostat) hardly differs from that of adomestic fridge. Its design is such, thatroar be switched off for as long as ahundred hours at a time without anydetrimental effect to the superconductivity. Figure 2 outlines the installation.It consists of a cryostat able to hold460 litres. A compressor takes rare ofthe cooling. The actual computer, theblock of less than 4 litres, is submergedin the cryostat.

The U -I curveThe relationship between the currentpassing through a component end thevoltage across it can be expressed inthe form of a graph: the U -I curve. TheU.I curve of a Josephson junction is

shown as a circuit diagram in figure 3aand ass graph in figure 3b. It is ratherunusual, as it has two curves. It looksas though at certain I current values thevoltage U can assume two differentvalues!What happens if the current through aJosephson junMion is allowed to riseabove zero? First we remain within thelefthand plot of the curve. The current

4

- vAlv,

16143

Figure 4. The influence of a megnetio fieldon the voltege/ourrent ratio cum 1441. Thediagonal is the Md line caused by includingload resistor 11,1410.

increases, but the voltage is still 0 volts.Its resistance is nil and it is in thesuperconducting condition. This con-tinues until the current rises above!max, for as soon as this happens thejunction will cease to be in a super-conducting state. Thus, we jump Iliter.ally) to the right branch of the curveand there is a voltage across the junc.tion. If the current is allowed to dropdown below Imac we continue toremain in the right branch of the curve,for there is still a voltage across thejunction. The superconducting con-dition will only occur again, therefore,if the current is reduced to below Imip,or if the voltage is brought down tobelow Up,9, which comes down to thesame thing.

Thus, the Josephson junction can bemade to switch from a superconductingstate to a resistant state by increasingthe current passing through it vettbriefly. Switching back to a super.conducting state is achieved bydecreasing it very briefly. The Josephsonjunction has a memory function: thesuperconducting and resistant statesboth being stable, they can be fixed.This distinguishes it from a transistor,

for in the tatters ease at least twotransistors are required to store a singlebit. In this manner, a memory com-ponent is prevented from dissipatingpower in either of its two conditions.

MagnetismBy varying the current passing througha Josephson junction, we can switch itfrom its superconducting state to a

resistant state and beck again. But thisisn't always convenient, as in elec.tronics we prefer to switch a currentwith the aid of another independentcurrent or voltage. Ideally, theJosephson junction should have a

base. or aate.electrode, or somethingsimilar. Fortunately, this appears to bepossible and not even all that compli-cated.Use is made of magnetism. The values'max end Umin Ise elm Irpip) are foundto depend on the size of the magneticfield. This is shown in the curve infigure 4a. The maximum super-conducting current in.. drops tolrpjtif when a magrietic field is applied.The minimum voltage in the resistivestate 1.1.it will then drop to Umin 8.Thus, the Josephson junction can bepreset at a fixed current I. If a meg..ic field is applied, it will switch fromits superconducting state to normalconductance. Similarly, it will switchback to superconductivity when themagnetic field is removed. For this tohappen, there must be a voltage U, ofbetween Urpip (a and Umin across thejunction. This is done by switching it inseries with a load resistor RL, as drawnin figure 4b. The diagonal I ,-Ub infigure 4a is a load line, like the onesfound in transistor graphs. It indicatesthe various current/voltage combi-nations which are possible after the loadresistor has been added. Switchinghappens along this line.Since the supply voltage Ub is veryIOW 1a few millivolts), very little poweris dissipated in the resistor. In theresistant state about 0.5 pW is con.sumed. Often self inductances areemployed for the load in the Josephsontechnique.How is a magnetic field generated?Simply by emitting an electric currentalong the Josephson junction, for eachcurrent has its own magnetic fieldaround it. Since the junction is highlysensitive to the magnetic field, a smallto is all that is necessary. Figure 5gives an enlarged view of the way inwhich a Josephson switch can beintroduced into a chip. Above theJosephson junction there is a controlchannel through which the controlcurrent lo flows. The arrows indicatethe magnetic field created by thecurrent. Current I through the junctionis affected by the much smaller controllc. The Josephson switch is a currentcontrolled current switch. In 1965 theIBM technician, Juri Matisoo, succeededin making and testing such a switch.

- elektor saptemher f 660 the Josephson computer

Standard component: the SQUIDIt would be an advantage if the junc- 5tion's sensitivity to magnetic fields wereat a maximum, for then the controlcurrent could be low. This is achievedby making the surface area of thejunction as large as possible. However,this also has disadvantages: for not onlydoes a large junction naturally occupymore chip space, but it will also switchmore slowly. The Josephson junctionhas a capacitance, a slowing -downfactor, which increases with junctionsurface area.This dilemma has been solved by thedevelopment of the SQUID, a kind ofJosephson 'standard component' withtwo or more small Josephson junctions.In the SQUID use is made of the coop-eration of different Josephson currents.This cooperation is rather complex andmay be compared with the interferenceof wave forms (light, for instance). It isconnected with the fact that Josephsoncurrents tend to be unevenly diNributedover 8 Josephson junction M the tares- Figure S. Highly enlarged outline of a Josephson switch. The current I is swAched under thepp. of a magnetic field. Figure 6 influence of magnetic ield (indicated with arrows) inducted lay the control current ly.

6

Figura 6. When a magnetic field 0 is created the current through a Josephson junction is notevenly distributed. At certain levels magnetic I orce, Melo. current through the junctionmay even become nil ICI.

illustrates this. It shows what thecurrent distribution in increasinglymagnetic field looks like when thecurrent through it is equal to themaximum superconducting currentmax. As the magnetic force augments,lrymx will decrease and may even equalOats magnetic flux of 0, At that levelin magnetic force, the Josephson cannotattain a superconducting state, howeversmall the current flow through it. If themagnetic field is further increasedhowever, lmao will rise again. Notdrawn is how !max will agaM equalzero, if the magnetic field force is

further increased. This is why the mag-netic field to maximum super-conducting current ratio forms such apeculiar, periodical curve (figure 71.Now the two Josephson junctions maybe made so that at a certain magneticfield force, one junction can easilybecome superconducting and the othernot at all, while at another level thesituation will be exact reverse. The twojunctions are both controlled by thesame control current. Thus, the controlcurrent sends the controlled currentinto a certain direction: either via oneJosephson junction, or via the other.This is what occurs in a SQUID, aSuperconducting QUantum Inter-ference Device'. It enables the sensttivity via large Josephson junction tobe combined with the speed of a smallone. SQUIDs can be made in all sortsof versions and may include more thantwo Josephson junctions.

Logic circuitsSQUIDS form the pillars of theJosephson computer. They enable allthe known logic circuits in semiconduc.for technology to be made: inverters,gates, flipflops. An AND gate, for

the Josephson computer

instance, may be made by controlling aSQUID with not one control currentbut two. Then the two control channelswill be created above the junctions. TheSQUID will switch only if both thecontrol currents are large enough. Sucha type is also called a 'current injectiondevice', as shown in figure B. Similarcircuits make OR gates possible.As for flipflops,these can be constructed

various ways. One of the moninteresting mak. use of inducedsuperconducting loopcurrents, for suchcurrents flow indefinitely!

Alternating voltageA remarkable characteristic inherent tothe Josephson junction is its perfectlysymmetrical non -polarised structure.This means it can be conn.ted eitherway around. What is more, a Josephsoncircuit may be equally well fed with analternating voltage, which is the case inthe Josephseon computer. The greetadvantage here is that the supply voltagewill then function eta clock signal. Inother words, its stomach is also its heartand so quite a few electrical connectionsmay be omitted. This also helps to resetcircuits.The power supply of the first prototypecomputer will consist of a 500 MHzsine -wave oscillator producing 7 wattspower. It is 'on dry land' and so is notcooled. On each of the more than tenthousand chips included in theJosephsoncomputer, there will be a number ofvoltage controllers to limit the voltageto an upper threshold of 12 millivolts.The sine -wave will then have become asquare wave. BY voltage limiting inmany places interference between signalpaths is avoided.The synchronisation of such a highspeed computer poses a serious problem.During a two nanosecond clock periodan electrical signal will only travel30 cm, Highly specialized techniques areneeded to ensure that processes occursimultaneously in the way they should.

The materialAlthough it should not be taken lightly.a Josephson computer is not difficult tomanufacture. This is because familiartechniques may be used on a large scale,such as the manufacture of semiconduc-tor IC's. Although the materials used aredifferent, the procedure is very similar:layers are evaporated, patterns areapplied photolithographically andetched. Complicated semiconductorprocesses like diffusion and implantationare not even necessary for Josephsonchips. On the other hand, more layersare applied (Mn to fourteen, instead ofthree to six) and the tunnel barrier (theinsulator between the superconductors)is very hard to make, because it has tobe so thin.The materials used in a Josephsoncomputer have to comply with twoobvious requirements; they must be

7

Figure 7. As a result of the uneven distri.hution drawn in figure 6, this remarkablerelationship between current through ajunction and the magnetic field t isestablished. Such an effect is used in the'Josephson standard component', Me

SQUID.

capable of sustaining freezing tempera-tures and great changes in temperature.After all, a Josephson computer is builtand probably repaired at room tempera -tore. Because of the fluctuations intemperature, the materials used musthave similar expansion coefficients,among other things, which reduces thechoice of possibilities considerably.The latter aspect is quite a headache forIBM technicians, It is truethat enormousprogress has been made Ithe error factorafter 400 temperature cycles has alreadybeen brought down from 99% to 0.1%),

°moor remember moo -.19

but there are to many chips that thesensitivity to temperature changes is stillfar too great.Josephson chips are based on silicon,like the semiconductor type. Silicon waschosen because its use in the semi.conductor industry is well established.Some experts believe that more is

known about silicon than about anyother material on earth.Contrary to semiconductor chips, thesilicon heretakes no part in the electricalprocess. Thus, its semiconducting charac-teristics are not at all involved, for theJosephson computer silicon is merely aninsulator. The fact that it is also a goodheat conductor is an extra advantage.Different insulating and protective layersare made from another material used insemiconductor technology: siliconoxide. The superconducting layersconsist of the metal niobium or of aIced alloy (with bismuth, or withindium and gold).The Josephson banners made from ladand indium oxides are subjected to verytough requirements. They are no thickerthan 4 to 6 nanometres, about thirtyatom diameters (the other layers areabout 100 nm thick (Furthermore, thedensity of that layer is highly critical.as the maximum superconductingcurrent depends on it exponentially.What it comes down to is that the layermust be made in such a way that theaverage density may only vary from thestandard by less than an atomic di-ameter. This is like covering an acreswith a layer of soil three centimetresthick without it varying anywhere by

Figure 8. A current injection device, om of the methods to produce a logic AND gate by meansof the Josephson technique. The este works with mozose.son junetions,shown as weirecircles in Me dark horizontal rectangle. The left.hand junction has five times the surface area ofits right.hand counterpart. The smenendimensions are arOund 2.5 ;AT, Whi. is as tiny as an LSIsemiconductor dun 11810 photo/.

9.20 - elektor samernhar1980 tkedosephson computer

more than a millimetre. This featrequired brand new evaporation 9techniques.

Soldering with mercuryThe chips couldn't be connected untilanother new technique was developed,for of course the Josephson chipscouldn't just be mounted onto printedcircuit boards. Apart from the undesir-able cooling effects, the computer withits more than ten thousand chips wouldbe far too big.Flow it is put together is shown infigures 9 and 10. Figure 9 displays amodule about 30 x 25 x 15 mm. Thechips here are packaged very closelytogether. Not only do the substrates ofthe chips consist of silicon, but so doesthe rest of the module. Without anyother form of case, the chips aremounted onto the small cards 'facedown, according to the 'bonding' process(from the semiconductor technology).

Figure 9.11 is very important that the Josephson chi. be mounted closely togeMer. This littleblock measures .0.30 x 25 x 15 mm. Every said contains four or eight chips of 6.0.1.6mmIshe.d areal which ere mounted face downward. Roth the large card and the Wia.nal cards'consist of mono crystalline silicon, along which delicate copper wiring patterns hare beenaffixed by photolithagrephiml means.

10

Figure 10. This is how the entire compular is put together using the blocks shown in figure 9. It contaires more than ten thousand chins and is,as illustrated in figure 2, submerged entirely in liquid helium. From the rear side flat cable rum ta the interlace and to the supply whichoperate

at room temperature.

Mei Joseneson computer slakter santemluir PM -9-21

This makes the heat transfer to theliquid helium highly efficient.The chip cards are connected to thelarger card by means of minuteconnectors. These have 'micropins'.A rnicropin is 0.2 mm long and0.075 mm in diameter. Larger pinswould cause the magnetic field to betoo large, which would slow down thesignal transfer and cause cross -talk. Theindividual distance between the micro'pint is half a millimetre, (an ordinaryOIL -IC's pins are 2 mm apart). Themicropins are connected, not withsolder, but with mercury, as thissolidifies at low temperatures (below-40°C). At room temperature, theliquid mercury is stored in drops witha 0.4 mm diameter in specially madecavities.Four modules (which sometimes wry insize) in figure 9 are combined to form aIN module', Twenty one such modulesconstitute the entire computer shown in

. figure 10. More than the thousand chipshave been collected in a block of lessthan 14 x 14 x 14 cm. The CPU and thefast 32 K byte scratch memory are bothincluded in one of the twenty oneW modules. The other twenty areoccupied by the large 16 M byte mainmemory. Once it is submerged in liquidhelium, this block outshines all present-day computers.

Why a Josephson computer?It is almost certain that a Josephson

computer can be built. Already,complete 16 K RAMS and CPU chipshave been made according to theJosephson technique. Problems left tobe solved involve developing a sufficientresistance to temperature changes, asmannered above. Furthermore, suitablefast I/O systems still have to be created,for without its 'hands and feet' even themost cold blooded of brains will not beup to much. At this stage, however,these problems seem unsurmountable.Whether a Josephson computer will everbe a market product is hard to say. Themicroprocessor is threatening to put anend to the golden age of the large.sizecomputer. Fewer calculations are dealtwith 'centrally in favour of the small,Specialised microcomputer systems. Itdoes not look as if the world is desper.ate for even larger and faster computers.Nonetheless, IBM must see some futurein its Josephson computer, as otherwiseit would not have put so much time andeffort land money!) into research.There are still a number of fields wherethe present-day computing monsterslack ability. Computer simulations ofphysical or economic processes, forinstance, could be far more accurate andtake place on a larger scale. Computersimulations are also important inweather forecasts and in some fields ofpurely scientific research (nuclearphysics). And of course then it couldhave military applications.Another field which would welcome ahuge computing capacity is pattern

recognition, in which the computerinterprets sound (speech) and videosignals (written text. video and radar). Athird possibility is provided by the greatdata banks which must be accessible formany users at once.In any case, IBM is already speculatingupon fields which are still reserved forthe ordinary semiconductor micro-computers and which one day, in thedistant future, could well be taken overby Josephson technology ...

Sources:Spektrum der Wissenschaft, Jell 1900:

Superleitende Compuhr',Juni Mods.;

IBM Research High/gets, June 1979:'Experimental IBM circuits are theworld's fastest',

IEEE Spectrum, May 1979:'Computing at 4 degrees kelvin',W. Anacker (IBM). 14

TemperatureA word on temperature, which is a

peculiar concept. It is quite differentfrom heat. Heat can but cause a changein remperature, no more In modernphysics temperature no longer has muchto do with cold or heat. Rather it is

considered as a gauge of the tremblingpertaining to atomic nuclei. Atomicnuclei do not stay in a fixed position,but move around a fixed point. Using aIMIe imagination. a particle of mattermay be seen as a swarm of mosquitoes.The swarm remains stationary, whereasthe individual mosquitoes are highlymobile.The more atomic nuclei in movement,the higher the temperature. To thephysicist, therefore, temperature isinherent to matter- it is one of itscharacteristics.If the temperature of a piece of matteris lowered, the atomic nuclei startmoving less wildly. This is true of allmaterial. If the temperature is lowenough, the atomic nuclei will becomeimmobile. Since temperature is a

measure for atomic mobility, it is notstrange that the temperature at whichthe nuclei become immobile is the samefor all kinds of matter.

Standing still is as immobile as you canget. This brings us to the conclusionthat a lower temperature will thereforenot be possible. For this reason, thetemperature at which atomic nucleistand absolutely still is called theabsolute zero. It is somewhere around-273.40C. It can also be expressed as0 K (in the past: 00K1. K representsKelvin, the absolute temperature unit.

The tunnel effectThe tunnel effect is based on the factthat a thin insulator applied betweentwo conductors will allow an electriccurrent to pass. The phenomenon is

explained in quantum mechanks. Whatthis boils down to is that particles donot have a certain fixed mass, speed,energy, Mc., as was believed in classical(newtonian) physics. A random distri-bution is involved. You could say thatin classical physics a particle used to beconsidered as a hard little globulemoving in perfect orbits at a well definedspeed, whereas in quantum mechanicseverything is much 'hazier'. Here aparticle looks more like a cloud, notclearly circumscribed, but ending'somewhere'. The averagesof the various

chance distributions of mass, speed andeneMY will however still be the same asin classical physics.Classical physics has no explanation forthe tunnel effect. According to it theparticles - electrons - would all havetoo little energy to be able to penetratethe thin insulator barrier. Quantummechanics states, however, that althoughthe average energy of the variousparticles would be deficient, neverthelessit is possible for one particle to haveenough energy. Some particles musttherefore be almost immobile, whereasothers are highly mobile.In other words, according to quantummechanics, the panicles are no longer allidentical.

t422 - elektor september 1990 VOX printed circuit board

WI printedcircuit board

The VOX switch published in theDecember 1979 issue of Elektorattracted a lot more attentionthan expected and it is for thisreason that a printed circuit boardhas now been produced.

A brief recap of the original article willbe useful to those readers who areunfamiliar with the purpose of a VOXswitch. Basically it is a voice operatedelectronic switch, normally used tooperate a transmitter/receiver. It canhave other uses of course, but its mainpurpose is to allow the hands to be freewhen using the microphone. As soon asa sound is picked up by the microphonethe VOX will switch the transmitter/receiver to 'transmit'. At the end of thespeech passage the VOX will switchback (after a short delay) to 'receive'.The delay is presettable and is includedto cater for breaths and hesitations.This VOX is fine but there are drawbacksin practice, Sound picked up by themicrophone can include squeaky chairs,doors closing or even beer cans poppingopen, should this occur in the vicinity.It is not of course desirable for the trans-mitter to switch on in these instances.The Elektor VOX switch avoids thisproblem by the addition of a filterdesigned to exclude all frequenciesother than those in the speech band.The filter can be made 'active', to acertain degree, to the characteristics of a

particular voice pattern, since both thebandwidth and the centre frequency areadjustable (with P2 and P3 respectively).The two other potentiometers are topreset the input sensitivity (PI) and thelength of the delay (P4). In practice, therange of Pt should be adequate sincethe gain of the microphone preamp Alcan go up to 100 X.Delay time however can be a matter ofpersonal preference. With the values ofP4, R20 and C7 as given in figure 1 thedelay time is adjustable between 0.5 and2.5 seconds. The range can be altered bychanging the values of any or all ofthe. components.The layout of the printed circuit boardfor the VOX is shown in figure 2.Everything in figure 1 is included on theboard with the exception of the twostereo potentiometers, the relay and themicrophone.For a more precise description of theVOX circuit readers are referred to theprevious article published in Elektor 56(December 1070).

Parts List

RIRM,R4,RI0,R13,R16 10 kR2,RI7. 47 kR5,146,R7.RI4,RI9 - 22 k118,R11 =139,R12.1k2R15a 100kRIB - Ok7R20 220 kR21,R22 = BIM

Capacitors:DI - I ir INIKN)CZCS .22 nC4,Cb,C10 - 100 nOn 242/16 VC7 - 4st7/16 VMOP 220 g/16C11.100PC12.27n

Semiconductors:

TI,T2,T3 TUNTO = TUPD1,172,173 = DUSICI a TL OSO

05251

Miscellaneous:

141,PO 1 M presetP2. 1 M lin.P3.10k1o9.

= 5 turns 0.1... 0.25 CuLwire on WM. bead

VOX printed cir uit hoard Wok., sr...ember 1980 - 9.23

.1v

Figure 1. The circuit diagram of the voice operated control switch.

2

,gure 2. The VOX printed circuit board layout.

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Multipath distortion occurs when the signal oftransmitter reaches the receiver along more

the e'patt, f igure one illustrates this. If

thedifference in distance between two ofthose signals is equal to an odd number ofhalf wave lengths, then these are out of phaserelativ wherech other. This and cam in ig-

ure 2 the direct la) Me reflected(b) signals of figure 1 have been drawn. Ifthey are both equal in strength, then one can.cels the other. This is an extreme cam a. itdoes not occur that often. There is usually adifference in amplitude laMonreen a direct a.reflected. signal and, often, more than one

signal reaches Me receiver. On theother h., the singnals add when the difference in distance corresponds to an evennumber of half wave lengths. Let us now comeider the complete music or speech moduletedtransmission signal. It will be seen that thingsare quite differs.. After modulation thereare a large number of signals of various fre.quencim and Me chances are that one ormore frequencies will occur in the total spec.

An AM synchronous demodulator does notProduce distortion in the envelope detector.Normal or synchronous SSIB Isingle side band)will of course not cause any problems. Themultipath signal pro... lalo a Porto/front/usdemodulator remains u.istorted but is

coloured by antihaselike effect. So far so

ood. It isn't dealing with FM that fennasty effects start cropping up, The originalsignal, which has a constant amplitude whenthis modulation method a umd, os changedby multipath conditions into a signal on whichAM is also pres.ent. After limiting in the re-

ceiver, the unwanted AM signal becomes a PMIPhase Modulated) signal , which mmns thatthe deviation will increase with the odul.don frequency.The I1 signal is then the worst affected a.during Pereo reception the Presence of ....-path will be immediately audibte. Amplitudeminimum levels may also occur an the unmodulated arrier, distorted ill cause monosignals to be badly too after demo-dulation.

measuring muldpaihMultipath Distortion

Multipath distortion; an unpleasantphenomenon, especially with FM stereo.Often the only thing you can do tocombat it is to empirically rotate theaerial. What's important is that the die -torsion produced by the receiver caneven be recognized as e multipath pro-blem. For quality FM receivers, there-fore, a multipath meter is highly desir-able. The standard recipe for such anindicator can be improved on as this orwile will show.

00111,0 taatO oat

Build.. or otherrefiestove op.

o .noono 0

2rz.,,..,:to:,::::ttegseri when the trans...signal reaches the receive two

trum which will show signs of minimum am.plItude or maximum feel as a resultof multipaM. The amount o nterferenceincurred depends on the kind of modulationapplied a. on the way in which demodula-tion takes place on the recePer.If during AM lAmplitude Modulation) a fewside band components are amplified or room,

this will merely cause the demodulatedsignal to be 'coloured'. lf, wever, the mo-dulation depth at pmk ofamptude is greaterMan 10096, the envelope detector which is

present in the majority of broadcastingceivers will start to produce when amount ofdistortion. The mme is true low ampli.turd levels occur in the carrier wave, Listenersto short wave radio will be familiar with Misphenomenon. Where distant radio stationsare concerned, short wave signals constantlyreproduce themselves along various pathsmrough Me ionosphere.

Although an effective AM suppression in anFM re ceover is cewainly useful to have, it is

impossible to counteract multopath clostortiononce it has arisen. For this reason top qualityFM receivers, more often than not, are equip-ped with a multipath indicator during manu-facture.

Multipath indicator CircuitIn f inure 3 the block diagram of an FM recei-ver has been drawn in which Me ordinary Smeter is expanded vv. the additional Mc.ty of roultipath indication. With the switchin position 1, it operates as a multipath roan

cator and, on position 2 as an S meter.The input signal of the indicator circuit is

derPed by detecting the outputs of all the IFfin Mere Al, A2 and P2/ and adding

them. why not just the output PIMP of B2FBecause A3 will already be limited to average

*yr.. elektor september 1980 - 9-21

strength signet L and will therefore not10ttri a very reliable source of information for 2the S meter:The added signal of the three IF amplifiers isjust right .r the amplitude of the signal re-ceived as far as the PC component is conc...nod. Therefore, for the S meter i.ication,this signal may be fed directly through an PCnetwork to the meter.Whenever multtpath distortion occurs, the ad-ded signa l Ipoint AI will .ntain an AC tom.ponent during modulated transmission, Thesimplest way to construct a multiparo meter

4 is tO amplify the PC (AM and rectify it, asshown in figure 3. This mwhod neverthelesshes one big drawback. The indication is de-pendent on the unpin.. modulation,Owing modulation in nothing is indcMed and this proves to be quite a nolmnce inpractice. The logical solution, therefore, is tomake um of Me 19 kHz pilot tone (alwaysavailable in the signal). This may be achievedby replacing the circuit inside the dotted area Figure 2. The direct la) and reflected (b) signals may often M in exact antiphare when they

of figure 3 by figure.. T. amplifier Ad reach the receiver aerial and cancel each other completely.

3

Figure 3. An FM receiver aguipedOn .2 it acts es an S meMr.

a multme amr in the normal method. When switched to II' the meter indicates inultipath distortion.

Iwiro Increased win/ is Preceded by 19 kHz 4band f ilte. After detection this will result in acontinuous multipath indicWion which is

completely independent of the normal transrnitter modulation.An even better solution is given in figure gh.The voltage drop across the diodes does notmen come into visaede too, the 1 kHz com-ponent is first from the detected andadded IF signals. This is now mixed with anartif icially produced IP kHz signal which maybe derived 1 mm the PLL stereo decoder for

as The two input signals of the mixergive a direct representation of multipeth digtortion. Thus, after the mixed product hasbeen low pass filtered .n be fed to themeter without my further modification, N

. kH

Figure 4. A fairly simple alternatire IMO to the dotted area in 1More 3 and a slightly morecomplMated and effective version 1413).

9-28 - elektor seplember 1980 high speed readout for elekternsinal

With a minor modification to theElekterminal it is possible to 'store'the entire contents of the display(TV screen) on a cassette tape.The majority of the connectionscan be wired to the existingexpansion sockets. For theremaining connections just threeof the copper tracks between theUART and the CRTC on the mainboard of the Elektermirml have tobe broken.

The heart of the extension circuitconsists of two multiplexers, ICI andIC2. The information at one or theother set of inputs is passed to theoutputs of the multiplexers dependingon the (logic) state of the select input.The data lines of the keyboard andthose of the memories are each connec-ted to a separate 'group' of inputs.When the relect input is taken low thekeyboard data will be passed through tothe outputs, and when the select inputis high the date from the memories willpass through. To be able to store thememory contents on tape, therefore,the select input will have to be takenhigh. This is accomplished as follows:

When the start button, St of figure 1, isdepressed. the C output of FF1 goeslow. As the Q output of FF1 is high, thememory WRITE signal is inhibited byN4. When one of the keys on the ASCII

thespace key or control key, a strobepulse (KS) will be generated. Theleading edge of the strobe pulse willcause the data from the keyboard to beentered into the UART in parallel. Withswitch 51 in figure 2 closed, thisinformation will be passed out of thetransmitter section of the UART andback into the receiver section in series.Once a complete character has beentransferred in this manner the DataAvailable (DAV) output, pin 19, of theUART will go high for a short period oftime. The trailing edge of this pulse willset the RS flipffop formed by Ni andN2 which in will take the selectinputs of theturnmultiplexers high. Thememory dare, together with the RAT,/signal, will now be present at themultiplexer outputs. Shortly after theDAV pulse, an RAI/ pulse is generatedwhich acts as a substitute for the strobepulse. This means that the data held inmemory will be shifted in and out ofthe UART repeatedly. This informationpassing out of the UART in series cannow be stored on cassette. Since the

corder will have to be running beforerea key is depressed, the character whichstarts the cycle will also be recorded.This is why it is advisable to use thespace key or a control key, as these willhave very little effect on the actualdisplay.A DAV pulse is generated after eachcomplete byte has been shifted out(and back in again). The leading edge ofthis pulse also increments the memory

address counter so that the date storedin the next memory location becomesavailable. When the WRITE pulse occurs(immediately afterwards) the PARTwill operate once more.The entire cycle is repeated until thecomplete page has been 'dumped'. Theend -of -page' pulse CU/ inhibits boththe DAV pulse and the RATY pulse viaFF2, N6 and N7.By pressing the reset button (S2 offigure 11 FFI and the RS flip-flop(1,11/N2) are both reset and theElekterminal. can be operated normallyonce more. The information stored oncassette can be re entered via the serialinput.

The modifications1. Break the copper track between

pin 6 of IC19 (11111 and pin 3 ofIC1... IC6.

2. Break the copper track betweenpin 16 of ICIO (CRTC) and pin 19of IC8 (UART).

3. Break the copper track betweenpin 3 of 1016 (N12) and pin 23 ofIC8 MARTI.

4. Connect points Al, A2, B1, 82, Cland C2 of figure I to the correspond.ing points in figure 2.

5. Connect pin 27 of ICI 0 (0) infigure 2 to the point marked WP infigure 1.

6. Connect the following:in figure 1: in figure 2:pin 3 of 101 to paint MO (IC6)pin 6 of IC1 to point M1 (IC5)pin 10 of IC1 to paint M2 (IC4)pin 13 of ICI to paint M3 (IC3)pin 3 of 1C2 to point M4 11C21pin 6 of IC2 to point M6 (ICI)

7. Disconnect points 000... KB6 be- ,

tween the keyboard and IC8 in fig-ure 2 and re -connect as follows:K80 from keyboard to pin 2 of ICIKB1 from keyboard to pin 5 of ICIKB2 from keyboard to pin 11 of ICIKB3 from keyboard to pin 14 of IC1KB4 from keyboard to pin 2 of IC2KB5 from keyboard to pin 5 of IC2KB6 from keyboard to pin 11 of IC2

8. Finally, connect the outputs of thetwo multiplexers in figure 1 to theUART (IC8) in figure 2 as follows:pin 4 of IC1 to pin 26 of IC8pM 7 of ICI to pin 27 of IC8pin 9 of ICI to pin 28 of 1C8pin 12 of ICI to pin 29 of IC8pin 4 of IC2 to pin 30 of IC8pin 7 of IC2 to pin 31 of IC8per 9 of IC2 to pin 32 of 108

Wok au* readout for wekterminel els., september 1980 -9.89

Fioure 1. The complete extension circuit.

Figure 2. The original circuit, with the various connection points elearlar marked. The points where copwor tracks must he broken are shownins. Me dotted circl.

9.30 - Mater sepoubm 1980 musiul box

Readers who collect musical boxes will probably think that an'electronic musical box' sounds as crazy as a gas telephone or a steamradio. After all, what made the musical box so enjoyable was windingit up and listening to its familiar tune. The circuit presented here showsthat electronics can be used to replace the wear -prone internal workingsof a musical box. In fact, an advantage over its old-fashionedcounterpart is that this circuit is able to play no less than 27 tunes.Applications can also include toys, video games and doorbells.

musical boxAs can be seen from figure 1, the actualmelody generator is a single IC IIC4/. Itis the AY -3-1350 from GeneralInstrument Microelectronics, a companywith an excellent name for solid statemusical devices. The circuitry aroundIC4 generates the clock signal, selectsthe melody required and amplifies theoutput level.To select a panicular tune, one of theconnections marked A ... E will hawto be grounded and pin 15 of themelodic chip must be connected to oneof the points marked 1 ...4. There areseveral ways in which the desired code

can be presented to the IC. One methodis to use wire links, another is to incor-porate snitches and a combination ofthe two is also possible. The printedcircuit board has been designed toaccomodate either of the two methodsshown in figure 2.If the circuit is cted exactly asshown in figure 1 and

construwire links are

placed between points K .. N andR ... V Ise. figure 2a), the followingprocedure will take place.When one of the pushbuttons, SA SEis pressed, one of the points markedA ...E will be connected to ground via

Tablet

figure Pt

4

gure 28 melody

53

s A 'A.A..'Se William Tell- C Hallelujah Chorus

ED Star Spangled Banner- SE E Yankee DoodleKR SA A Sohn Brown, BodyKS Se ClementineKT Sc C God Save The QueenKU Sp D Colonel BogeyKV Se E MarseillaiseL8 SA A America, AmericaLS Se B Deutschland LiedLT Sp C Wedding MarchLU Sp eeeshoseo's 9rhLV Se E AuguoineMR SA A A Sde MioMS So 8 San. LuciaMT Sp C The EndMU Sp D Blue DanubeMV Se E Brahm, LullabyNA SA A Heirs Bells (specially composed)NS Se B Jingle BellsNT Sc C La Vie en RowNU Sp D Star WarsNV Se E Beethoven's 9th

Descending Octave ChimeSp Weominster Chime

musical box elektor missend., 1980 - 941

o

a

Fieure 1. The complete circuit of the 'electronic musical box..

2a 2b

® 0 0 0

Figure 2. Using wire links, as shown in figure 2e, five melodies can be me.selected. If this is considered too much of a restriction, two five -wayswitches can be used, as shown in figure 213.

9 32 - elektor septernber 1989 musical box

Parts list

Resistor,RI .136,110 - 10 kR7= 100kR8,RI 7 = 2L7RI0,R12,R16 3k3R11=270R13,R16,R18 33 kR15=5130 kR19=07 kR20 = 100 St

PI =10k presetP2= 1 NI presetP3 = 500 0 preset

Capacitors:CI... C5 = 10 nCRDELCII =IRO nC7 = 220 PC9 = 220 nCIOD12 =10 il/18 V

Soviconductors:DI .. 1311.1317,D13 [WS012 ... 015 10 V/400 rnte

moorEA a - 5V6M00 mW AmerTI TUPT1 BC 517T3 = TUNICI 0003IC2,1C3 0066ICA = AV .3.1350

Miscellaneou

SA . . SG =

s:

PUShbutIon 99939

52 = 5 position wafer switchS3 -6 position wafer switchLS= 8 010.5 W lOuclapeaker

(see text)

one of the diodes 01... 05. Eachpushbutton has a total of five melodiesat its disposal. The choice can be cutdown to one by means of a wire link.Thus, one of five predeterminedmelodies can be selected per switch and,in addition, two well-known chimesmay be 'played' by depressing SF or SG.Table one shows the melodies which areavailable and the combination ofconnections required to select each one.The code numbers and letters cope.spond to those given in the circuit andin the component layout shown infigure 3.The second method is to use a pair ofmulti -way switches, in which case thearea inside the dotted line in figure 1may be omitted. This will enable anyone of 25 melodies to be selected. As

can be seen from figure 2b, pointsA ... E can be grounded by means of asix position wafer switch, S3. Switch S2connects one of the points K N topoint P. The melody will be initiatedupon depressing SF. Resistor 136 andthe electronic switch ES5 are notnessary for this latter option. Theyceare shown outside the dotted line asES5 is contained in a separate IC toE51 ES4.The oscillator is formed by C7, StandPI together with part of ICA. The pitchof the melody being played can beadjusted by PI, the length of each notecan be adjusted by P2, leaving P3 toregulate the volume.Two 4.5 V batteries are all that is

required to power the circuit as thequiescent current consumption is only a

few rnicroamps. Transistor T1 and thesaner diode D18 are included to dropthe voltage down to 5 V for those partsof the circuit requiring a lower voltage.The nominal loudspeaker impedance is80, but if one with a higher impedanceis to be used, the value of R20 can bereduced accordingly. Switch SI is stillto be mentioned. Its function is toselect between a 'piano' sound withslow decay (position (all and a constantvolume 'organ' sound (position (13/1. Itshould keep the children amused forhours! 14

electrolytologg

Capacitors area vital part of electronics,so it is important to realise exactly howthey work. In its simplest form thecapacitor consists of two flat metalplates which are separated by an electri.cally insulating substance calleddielectric (see figure 1). When a voltageis applied to the plates (figure 21, thefollowing happens. The electrons(negatively charged particles) whichoriginate from the negative pole of thevoltage source, will repel the electronson plate lb) when they reach plate (a)(since similar charges repel each other).The electrons on plate (b) will beattracted to the positive pole of thevoltage source. Electrons are therefore

an inside look at capacitors

There is nothing new about thefact that electrolytic capacitorspossess inductance due to themethod used in their construction.At high frequencies theirimpedance will be largely

induction. An electrolyticcapacitor even acts as a band passfilter and thus also has a resonantfrequency.What fewer people will be awareof is that the capacitance is clearlyfrequency dependent. This has todo with moving ions in theelectrolyte, which will bediscussed later.

being moved - in other. words there iseilseziongcucrir,:nrgte:ilo:nicriig;letnencsilaatree

disappearing from plate (b), a potentialdifference occurs across the plates.Whenever this voltage is equal to that atthe source, the electron flow will stop.The capacitor will then be fully charged.It should be mentioned that there is nocurrent flowing from plate (a) to plate

iefitairngbrr. rires are separated bynsulThe

current is of a temporary nature(until the capacitor is fully charged). Bycontinuously reversing the polarity ofthe applied voltage he current can bemaintained. That is why a capacitor willonly pass alternating currentThe amount of current depends on theamount of charge which is displacedinside the capacitor, which in turndepends on the applied voltage and onthe value of the capacitor. The relation.ship between voltage and charge is

expressed in capacitance. The greaterthe capacitance, the more charge is

displaced for a given voltage and more

maw, samarnbar 1980 -EMS

AC is allowed to pass through.There are various methods of increasingthe value of capacitance. In the firstplace by having a larger plate surfacearea, secondly by using a thinnerdielectric and thirdly by using animproved dielectric. In order to obtainthe greatest possible capacitance fromthe smallest possible size, manufacturershave examined various techniques.Capacitors are normally made from verythin sheets of metal foil separated by athin dielectric. The thinner the dielec-tric, the greater the capacitance,' but atthe same time the maximum voltagethat can be applied has to be reduced toavoid breakdown. To increase the

capacitance even further, several layersof metal foil and dielectric can be piledon top of each other (see figure 3). Thisis called a layered capacitor.The dielectric may consist of paper,plastic or a type of ceramic material.Thus, there are paper, polyester,polycarbonate and ceramic capacitors.Each type of dielectric givesown special characteristics and makesthe capacitor suitable for certainpurposes.In addition to the layered construction,there is the more common woundmethod where the metal foil and thedielectric are rolled up (see figure 3b). Acapacitor of this kind will have a higherparasitic induction than the layeredtone.Up to now these have all been foliatedcapacitors, being made up from thinstrips of metal and insulating material.In spite of the extremely thin metal foiland dielectric used, dimensions increaseat an alarming rate at high capacitancevalues and working voltages. For thisreason, the maximum value of foliated

2

Figure 1. In its simplaat from a celseenerconsists of two flat metal planes which are Figure 2. By connecting a voltage to theSeparated by an electriully insulating materiel plates, charge can Ise produced doe to the(sometimes eirl. electron movement.

9.. - elektor september 1900 ale trolytolo.

3a

=Figura 3. To obtain large capacitances in small dimensions, sageeel layers of metal foil and dielectric can be placed on top ol each other 1.1.

Auto.. Method is to roll up the metal foil and dielectric I MA.

capacitors is restricted to a few micro- 4farads. For larger values electrolyticcapacitors must be used.

The electrolytic capacitorThe plates of the electrolytic capacitoralso consist of very thin metal foil. Thematerial will be either aluminium ortantalum. Taking the aluminium type asan example, it will be found thatbasically the electrolytic capacitor hasthe same structure as an ordinarycapacitor: two plates and an insulator.Since the electrolytic capacitor is

polarised, it has an anode plate (positive)and a cathode plate (negative). Thecathode contains not only the metal foil,but also an electrolyte (electricallyconductive fluid). In figure 4 thesimplified structure of the electrolyticcapacitor is shown. The cathode onlyserves to pass current to the electrolyteby way of its large surface area.The dielectric consitsts of aluminiumoxide, a good insulator with a highbreakdown voltage (800 million voltsper metre!). This means the dielectriccan be very thin enabling large capaci.tames (even up to 1 farad) to bereached in relatively small dimensions.The layer of aluminium oxide is obtainedby anodising the aluminium foil.Anodising is an electrochemical process,whereby the aluminium is dipped intoan electrolytic bath (figure 5). A voltageis applied (the activating voltage)between the bath and the aluminiumwhich acts as the anode (positive). Theoxygen ions (negatively charged), in thesolution, combine with the aluminiumand the density of the layer ofaluminium oxide created depends onthe value of the activating voltage. Thedensity of the dielectric can thereforebe controlled very accurately. Theoxidised aluminium foil is then readyfor use as the anode of the electrolyticcapacitor.Nowadays, all electrolytic capacitors arewound. The foils of the anode and thecathode are separated by a layer ofpaper for two reasons. Firstly, toprevent a short circuit between the twoaluminium foil layers and secondly, toact as a holder for the electrolyte(sponge effect).

.Figura In the case of the electrolytic capacitor, the cathode plate is not only made up ofefz,,,i,l,,t ots.1:ekiroelucles an electrolyte lelectrically conduMive Th dielectrict consists

a ad through enodisation

To increase the capacitance of electro-lytic capacitors the anode plate is

etched before oxidisation to Provide agreater surface area (see figure 61. Asthe cathode is made up from a fluid, itwill adapt itself to the rough surfacearea of the anode. Modern productionmethods for electrolytic capacitorsalmost always follow this constructionmethod. The electrolyte need notalways be a fluid, often a form of 'paste'is used. Hence the terms 'wet' .pacitors.As mentioned before, the electrolyticcapacitor is polarity conscious, with theanode elwaYs being positive with respectto the cathode. The voltage across thecapacitor must never exceed theoxidising voltage, as this would causethe anodisation process to continue andthe electrolytic capacitor to explodedue to the heat produced. If the electro-

lvIZ:hcr aitnoordes 'n'treeicn irnecl:'t=tothe cathode) the aluminium foil of thecathode plate will be subject toanodisation and again the capacitor willcome toe bad end. For AC purposesspecialwhiCh

attiPLIatrp:IIV;;I'c'OLcapeciecyf

been developed.

The electrolytic capacitor and itsimpedanceWe have already seen that the windingmethod produces an unwanted sideeffect - that of induction. At higherfrequencies especially, the parasiticinduction contributes greatly to the im-

5

Figure 5. Anadisation is an electrochemicalpoems. whereby the aluminium is dipped inan electrolytic bath and "plated' with a layerof oxide by means of an electric current. Harethe aluminium acts as the anode.

/IBAFigure S. A 2500 times enlargement of...aluminium. as used in electrolytic...plots. Due to the etching the...oral surface area ie(Simms Data Book 1900/81).

mennalylegy

pedanceso(AC resistance) of the electro.lyric capacitor. With the exception ofbipolar types, capacitors are only suit-able for DC anyway, so is there a prob-lem? The answer is yes, for when an ACsignal is superimposed on a DC level thiswill create considerable problems. Con-sider for instance, what happens in thesmoothing circuit for mains supplies,when circuit voltages are disconnectedor when two amplifier stages are ACcoupled. In these caws it is impossible

1 to merely rely on the given value of thecapacitor.

7

Figure 7. The equivalent circuit of theelectrolytic capacitor.

In addition, the electrolytic capacitorhas a resistance produced by the electro-lyte. This resistance is highly dependenton temperature. The frequencydependence of the impedance is clearlyshown in the equivalent circuit of theelectrolytic capacitor (figure 7). Basi-

cally, the electrolytic consists of a

capacitor, a resistor and an inductorconnected in series, By way of illus-tration, the impedance curve of anelectrolytic capacitor of 100 µF/63 Vhas been plotted at different tempera-tures in figure 8. At frequencies of up to60 BO kHz (at 20°C) the impedanceis mainly determined by the R and C inthe equivalent circuit, and at higherfrequencies by the R and L. The curvealso shows that the electrolytic capacitorhas a resonant frequency, where itsimpedance will be at a minimum. Inother words, it acts as a band pass filterfor high frequencies (LCR series loop).

AC and DC capacitanceAs stated, the cathode of an electrolyticcapacitor is made up of an electrolytic

8

Figure B. The impedance characteristics of an demo!1Siemens Data Book 1980/811.

c capacitor various frequencies

measured capacitance in

Ty, 0Hz 50 Hz 00 Hz 11300Hz

47 oF, 350V 5,91,1,, 49,210396

47,90096

43,290%

6800 oF, 25V 878020%

737000%

7330100%

667090%

5110oF, 25 V 829111%

759101%

74910099

69993%

100 oF, 25 V 13311096

122101%

121

100%110

oco,

4,7µF, 25V 9171139% 1 0:91

3,92

atakter ssetamber 1980 -8.35

fluid (or paste) Current conduction ina fluid takes place rather differentlythan in a solid. In solids only electronsmove about, whereas in fluids ions alsotake pert Because of their small sizeand mass, electrons are very mobile andcan keep up with the speed of voltagevariation. This is not the case with themuch larger and heavier ions. These aremuch slower, especially at lowtemperatures. If the temperaturebecomes low enough for the electrolyteto solidify, the ions will be frozen, as itwere, and will not take part in theconduction. Only the electrons will thenbe able to displace the charge (a charac-teristic of solids). The result is a greatlyreduced capacitance.Since ions are less mobile, they will havedifficulty in penetrating the deepestpores of the etched anode, as they donot have enough time. For this reasonthe deepest pores will not be effective inthe operation of a capacitor under asuperimposed AC,which means a smalleranode surface area to operate on. Thus,the effective value of an electrolyticcapacitor under DC conditions will begreater than with AC. In other words,the capacitance is frequency dependent.Electrolytics therefore have a DC and anAC capacitance. The AC capacitance ismeasured according to DIN standardswith a 50 Hz signal of <O.5 V (lowenough to prevent destruction) and at atemperature of 20°C. The IEC standardprescribes a measuring frequency of 100or 120 Hz. The DC capacitance isdetermined by timing a single dischargefrom an electrolytic capacitor chargedto a nominal voltage.The DC capacitance is usually 1.1 to 1.5times greater than the AC value. Thegreatest differences are found withelectrolytic capacitors having a lowmaximum working voltage. Thedielectric in these is very thin and so thedimples in the rough anode are rela-tively deeper after anodisation than inthe case of capacitors with a highmaximum working voltage.After the 'd igif arad' article was published(Elektor 54, October 19791, severalreaders drew our attention to the factthat the values of electrolytic capacitorsmeasured with this innt have tobe interpreted with care.strumeThis is becausethe digifarad measures capacitanceaccording to a method which is verysimilar to that used to determine theDC value.Since the AC value is indicatedon most electrolytic capacitors, thedigifarad will more often than notoverestimate the value. This is notnecessarily incorrect, but it will have tobe taken into account when thecapacitor is used.By way of illustration, several values ofelectrolytic capacitors at differentfrequencies are given in the table. N

Literature: -

Siemens Data Book 1980/81,Aluminium and Tantalum ElectrolyticCapacitors.

9.36 - Weldor servemher 1980 transistor currv tracer

The designFigure 1 gives the layout of a designwhich escaped notice in last year'sSummer Circuits '79 Ino.13). This is acheaply constructed curve tracer fortransistors and diodes. No 'really pro-fessional test instrument, of course, butan extremely useful aid to quickly carryout a general test either to comparetransistors or select them. Naturally,hobbyists will have to have an oscillo-scope (with separate x and y inputs),because the curves will be displayed onthe oscilloscope screen.Since it is impossible to tell whichtransistor characteristic is more import-ant than another, there is no such thingas the 'most important curve.. Transistorhandbooks speak of the most read curve.

to the V input and the ground connec-tion of the oscilloscope 'hangs' resistorR7. This is the TUT's collector resistorand the voltage across it is naturallyproportional to the collector current ofthe transistor tested. In this way, an 'lcwill appear on the vertical axis of theoscilloscope. The TUT's emitter is

connected to the X input so that thecollector/emitter voltage IUCEI can beread horizontally on the screen.

What causes the curves to appear on thescreen? Two signals are fed to the TUT.A5 step position staircase waveform isfed to the base and during each step asawtooth is fed to the collector. Thismeans the collector voltage changescontinually at a certain base drivecurrent. This occurs at quite a speed so

transistor curve tracer

There are never enough simplecircuits which provide useful andlow.cost additions to the 'homelab'. This particular designpossesses all the advantages tomake it a glorious example of itskind. It offers oscilloscope ownersa neat, additional measurementfacility. It is easy to build,contains common parts and isinexpensive. Reason enough todesign a printed circuit board forit.

Ic/UCE characteristics directly onto the screen.

This involves the I c/UCE characteristicswhere the collector current is plotted asa function of the collector/emittervoltage at different drive currents.Figure 2 gives an example of such a

characteristic. At the se time it(roughly) indicates the drive currentsthe curve tracer uses. The currentamplification may be directly derivedfrom the IC/UCE characteristics and,after a few calculations, to may thetransistor's output impedance. Thelatter siraffected by the curve's slope.Generally speaking, the more horizontaland straight it is, the higher the collector/emitter impedance.Back to the schematic. The transistorunder test is indicated as 'TUT' as usual.Between the points which are connected

that the oscilloscope screen simul-taneously shows 5 characteristics for5 different base drive currents. Thestaircase signal and the sawtooth wave-form are controlled by means of anastable multivibrator. The AMV

of

of T1 and T2 and generatesa squarewave with a frequency of approximately1 kFlz.The sawtooth is obtained very easily byintegrating the square we is R5 andC5. Creating the staircase voltage is a

little more complicated. During thepositive half -cycle of the square waveprod cad by the AMV, C3 is charged toa ma imum which is equal to the supplyvoltage. During the negative half -cycle,C3 will turn on transistor T3 and thusthe voltage at T4's emitter (connected

B. DarntonFigure 1. The circuit Mamma of the curve tracer.

transistor curve tracer elektor september 1980 - 9-37

2

Figure 2. lo/Ude curses of a transistor. In our circuit five different base drives are measured.

Figure 3. This is how the curves eltlwer onthe oscilloscope screen.

to the TUT's base via RB) will becomea little lower. By loading C4 intermit-tently; each successive negative half -cycle will reduce the emitter voltage of14 in steps until 14 starts to conductturning on T5. 04 is soon dischargedand a new cycle starts.The number of stages which make up asingle cycle is determined by the ratioof CO to CO and is 5 here. By adjustingthe value of CO the number of stagesland thus the number of curves indicatedon the screen) can be changed asrequired.

In practiceThe photo in figure 3 shows how thecurves appear on the oscilloscope screen.The circuit's only flaw now comes tolight - the characteristics are tracedfrom right to left, instead of the otherway around. Unfortunately, nothing canbe done about this. In practice it doesnot present a problem. What is serioushowever, is that the tracer is onlysuitable for NPN transistors. NPN typescannot be tested with it If this is

considered to be a drawback, however,there is a cheap solution: two printedcircuit boards may be built instead ofone. The circuit requires few com-ponents, so why not? The second circuitwill then be a PNP version.For T1 ...T4and T6 use TUPs, T5 will bee TUN, C6,DO and the supply leads will beswitched around. Furthermore, such aPNP version will trace the curves fromleft to right, only now the T axis will benegative so that they will appear upsidedown on the screen. A little strangeperhaps, but you'll soon get used to

As mentioned above, diodes may also betested. Thew are connected with the

Figure 4 The printed circuit board of Me curve tracer. anode to R7 Ill and the cathode to theSupply zero IX). The I/U characteristicsof the diode in question will now appear

Parts list on the screen. Figure 4 shows theprinted circuit board. It is highly

Resistors, Capacitors: Semiconductors: compact and can be built in less than noR1,110 slk7 CI,C2,64. 100n time.R2,R3,R5= 05k 03. 22 n T5= TOP Last word.Since the circuit only requiresR6 - 21s2 05 si toe DI - DUG a few mA, the supply will not have toR7= 330 II Ce = 1006/10V be very 'heavily' tested. However, theR8= 000k supply voltage must be well regulated

f ritt kp p ly N

9.38 - oloktor sopternhor 1980 using the Elektor Vocotler

dieElektor VoeoderSeveral months ago (Elektorno. 56, December 1979), Elektor 1

published a 10 channel vocoder.When building a vocoder thereare a few 'obstacles' which oughtto be taken into account. Readerswho have already built one andare familiar with it will find thatthis article provides usefulinformation on how to improveon the vocoder's technicalqualities. To start with it is a goodidea to check the initialadjustment.

F. Visser

Each channel in the vocoder containsthree presets. Two of these are intendedto eliminate leakage of the Voice andCarrier signals to the vocoder's output;the third sets the dynamic range of thevoltage control circuit lin the analysersection, where the audio signals are splitup into small bands and are convertedinto DC control voltages). This is

portant if the vocoder is to respond to awide range of input signal levels andreproduce the speech sounds as accu-rately as possible. In passing, it shouldbe noted that this high 'responsiveness'may cause a disturbing side effect whenthe vocoder is used during live perform-ances, where there is usually a high levelof in nce.terfere In such cases thevocoder will analyse and synthesize theentire complex sound. producing anundesirable cacophony. Further on inthis article, methods will be suggestedto suppress these side.effects. For themoment, however, let us concentrateupon setting up the vocoder properly. mines the vocoder's dynamic range. Unfortunately, they are also moreThe best way to start is to adjust The offset should not be more than difficult to obtain and more expensive.potentiometers P1, P5 and P9 in the 5 mV. If this cannot be achieved it may If all the Unnt buses are now Connectedband pass, high pass and low pass filters be advisable to modify the offset to the Uin buses, there is no danger ofrespectively. These presets compensate compensation slightly, as shown in undesirable offset voltages turning onthe output offsets of the filters that figure 1. In the original design HA 4741 the OTAs in the synthesizer section (orfollow the rectifiers in the analyser type opamps were used, as these have cutting them off - if the offset issection. To a large extent, this deter- a smaller offset than the TL series. negative).

.0 PICIO,C.000

uson0 the El.., Vocoder

2

IC3 701PIO PIC, C.000 IOW

0

"'a

65713

elektor seotember IWO -939

The vocoder's dynamic behaviour is

further determined by the followingadjustment: the cutoff point of theOTAs. This can best be done with theaid of an oscillator and an oscilloscopeor an AC millivoltmeter. The (sinewave) oscillator is oonnected to thecarrier input and is tuned to eachsucceive filter frequency in the syn.thesizessr section. The signal voltage is

set to about 10 V p -p, measured an

pin 7 of A4, A14 and A24. The Uigpotentiometer on the front panel is

turned up fully and now the oscillo-scope or millivoltmeter is used to checkthe output of A10, A20 or A30. Thepreset potentiometers P4, P8 and P12are adjusted to the point where theoutput signal just Mops decreasing (seefigure 2).Finally, the leakage from control inputto audio output of the OTAs must bereduced to a minimum. Usually. it willnot be possible to eliminate this entirely- but it is worth while trying (evenreplacing the OTAs, if necessary). sincebreak -through of the speech signal tothe vocoder output seriously affects theoverall performance. Figure 3 shows themeasurement setup; P2, P6 and P10 areadjusted for minimum break -through.Best results will be obtained when theleakage of the single phase rectified sinewave signal, applied to the speechip,t0, is not greater than 5 my p -p atthe vocoder output. In practice, this willnot be easy to achieve. It has beenfound that only 200 out of every 1,000OTAs manage it!If an oscilloscope and an oscillator areavailable, it is a good idea to check thepass -band and gain of all the filters.Obviously, any deviation with respect tothose particular aspects can lead to anundesirable colouring. If, however, goodcomponents are used (and mounted inthe correct positions!), any error shouldbe so small as to be negligible.

How to use the vocoderHaving set up the vocoder properly, thenext question is whet to do with it. Itsmost con application is as a 'voiceprocessormmo'. A recent 'hit' in the chartsis 'Funky Town' by Lipps Inc, in whichthe voices of two members of the group

POWs are transferred to the sound of a syn-thesizer. The introductory lyrics aredifficult to understand (even forAmericans!). One reason for this couldbe that the key chosen for the melody israther high and, as our previous article

m1.10;on the vocoder stated, it is importantthat the frequency spectrum of the

ex carrier signals overlap that of the speech-1C11),I1

input. If the carrier consistc almostexclusively of high frequency com-ponents and the modulation signal (inthis case the voice/ is in a lower fre-quency range, only the higher har-monics of the voice will be super-imposed on the carrier signal, as shownin figure 4. Furthermore, a woman's

940 - Elektor SEptenlber USIOO the Elektor Vocader

3 PRIXTOOCIOCUIT BOARD

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voice appears to be used as the modu.lation signal on this recording, with a'Formant range that is less suitable forthe classical vocoder with a relativelysmall number of channels. Later on in'Funky Town' the melody is played ina lower key and a male voice sings thelyrics. The improved intelligibility is

very noticeable!The Elektor vocoder has the advantagethat it can offer a reasonable solutionto the problem of 11011-0VeriOPPing1:111811Cy spectra. By connecting thevoltage control outputs ottheanslysarto channels one or two places higher upin the spectrum instead of to the con-trol input of the corresponding syn-thesizer channel, the significant spectralinformation is moved up, as it were, toa range that encompasses the highercarrier frequencies This technique,known as 'form ant shift', will be dealtwith in depth later on in this articl.In addition to the vocoder's use as a

voice processor there are many ways inwhich sounds can be superimposed ondifferent kinds of carrier signals. Thebest way to get to know the vocoder isto systematically carry out experiments,using a microphone and a simple saw -tooth or pulse generator.

The microphoneAs far as the microphone is concerned,a high quality type is best: it the modu-lation spectrum is free from coloration,the end product will also be good. Noteveryone will be able to afford a high-priced microphone, of course, so a fewsuggestions on how to obtain goodresults with a reasonable quality morn -phone may prove useful.In the first place, it may prove usefulto give the microphone pre -emphasis- in other words, emphasize certainfrequencies, where necessary, or atten-uate them This is done by means oftone controls or with separate filters.One of the most important correctionsto be made is to attenuate the low fre-quency range. It is difficult to giveprecise figures for this, as it of COVI,Vdepends on the type of microphoneused and also on the distance between .

the mouth and the microphone. Thecloser the microphone, the more lowfrequency components will reach theanalyser, not to mention the sound ofbreathing and MI.,. COOWOOn,O

Sometimes, depending on the high fre-quency spectrum of the carrier signals,it may be advisable to boost or atten-uate the treble range. As a rule, a

standard Baxandall tone control with aturnover frequency around 1 kHz is

fine.

The carrierMany sound sources may be used ascarrier material, but a simple function

Elektor Voogd., elektor septerriber 1980 - 9-01

6

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generator with a control range betweenabout 20 Hz and 1 kHz would be idealfor the first experiments. Thesuitable wave forms to experiment withare triangle, square wave, sawtooth andpulseforms. Should such a generator notbe available, you can always build onebased on one of the many Elektor cir-cuit designs.

Monitoring the resultsThe best way to judge the results is touse headphones. The system can also beused to drive a conventional audiosystem with loudspeakers, but head.phones are preferable as they avoidacoustic feedback problems.

A few simple examplesWhen the microphone, generator andheadphones are connected (figure 51and everything is switched on, the firstexperiments may be carried out. If youdon't want to fall back on sentences like

it is perhaps useful to have a text infront of you. Experienco has taught usthat not everyone possesses the 'gift ofthe gab' at such moments!The frequency of the generator is set atabout 50-60 Hz. using a pulse wave-form. The result will be a resonant,clear, synthesized voice. If the fre-quency remains unchanged, the resultsounds like the 'Cylon effect'. Cylonsare robot-like creatures from theAmerican TV series and film: 'BattlestarGalactica'. A vocoder was in fact used

to produce their robot voices.By raising the carrier frequency whilecontinuingvoice can be made to change in pitch. Itwill become less intelligible once thefrequency is above 500-600 Hz; thiseffect was mentioned earlier, when dis-cussing the Funky Town recording.It should be clear that the pitch of thesynthesized vocoder product dependsexclusively on the carrier's pitch. Thenext test to be described will demon-strate this.The frequency is set toe low value, forinstance 100 Fin, and now the pitch ofthe voice is changed by singing insteadof speaking, or by producing othersound varying in pitch. You will noticethat the resulting timbre will change,as if a band-pass filter were being used,but that the fundamental frequency willremain the same. This is because thegenerator is still set at a fixed fre-quency. Nevertheless, this is a source ofregular misunderstandings. Witness thefact that the vocoder is often comparedto a harmonizer or to a pitch shifter- equipment used to shift the funda-mental frequency and the spectrum ofspeech or music.If the same good intelligibility isquired at higher frequencies, 'tormentshift' can be used. The Elektor vocoderis one of the few vocoders on theprofessional market that offers thisinteresting facility. Formant shift liter-ally means shifting the intelligibilityinformation to a higher or lower freequency range. By coupling the outputvoltages of the analyser to the controlinputs of synthesizer filters which do

not have the same F0, the measuredtorments are transposed to anotherplace in the spectrum. If, for example,the voice at the speech input is muchlower than the fundamental frequencyof the carrier signal, the result can bemade more intelligible by shifting thetorments to a higher carrier spectrum.The synthesized 'voice' will becomeclearer and at the same time assumean entirely different character. Thisphenomenon can be used with greatsuccess to produce 'funny' voices.The higher the analyser spectrum is

moved up, the more the voice willsound like Donald Duck. If the analyserspectrum is transposed down, thespeaker will sound as if he suffers fromthe proverbial hot potato. Quite a

different way to manipulate the form -ants is 'torment inversion'. To obtainthis effect the analyser and synthesizerchannels are cross -coupled. Not sur-prisingly, the result will be practicallyunintelligible. All transient sounds, suchas K, P, T and hissing sounds will besuperimposed on the low end of thecarrier spectrum, whereas the low fre-quency information in the speech signalwill control the high end of the carrierspectrum. Furthermore, of course, theferments will be thoroughly mixed.A good example of this is the '0' soundwhich comes out as a 'U'. In spite ofthe fact that the result is virtuallyunintelligible, this effect can be usefulwhen making (complex) musical sounds.This is illustrated in figure 6.The results obtained so far throughspeech synthesis will all sound robot.like. In the first place, this is due to

402 -.teeter sautsiettor lea°

the pulse signal used as a carrier: it con.tains a lot of higher harmonica, creatinga slightly grating, 'mechanical' sound.If a sawtooth is used instead of a pulseshaped signal as a carrier, the result willbe softer. This illustrates that thecarrier's complexity affects the timbre.To attenuate the robot sound furtherthere are all sorts of other tricks.By modulating the carrier signal, forinstance with a low frequency sinewaveor triangular signal, a much more life-like 'human' sound is produced. Othermodulation effects may involve a lowfrequency random signal or, even better,a control signal that is derived from thefundamental frequency of the originalspeech. This can be simulated by tuningthe generator to the voice pitch andthan adjusting it by hand to follow theinflections. When an accurate frequency/voltage converter ("pitch extractor') is

used a very natural sounding voice canbe synthesised, which shows that theintonation of the voice is a very essen-tial part of human speech. A fewsuggestions to obtain carrier modulationare given in figure 7.

Unvoiced consonaMsUp to now, the unvoiced consonantsIS, SH, SK, SY, K, T, P, F, etc.) have beenneglected. These cannot be successfullyreproduced by only using a sawtoothor pulse as a carrier. To synthesizeunvoiced consonants, a detection systemis required with the aid of which noisecan be added to the carrier signal atthe right moment. Since the Elektorvocoder does not (yet) possess thatVoiced/Unvoiced detector, anothertrick will have to be used for themoment.A wry clever expedient was developedby Harald Bode, vocoder manufacturer,and he has now taken out a patent forit. Bode constructed a sort of 'bypass'circuit for high frequencies derived fromthe analyser section. In the case of theElektor vocoder this has been providedby means of potentiometer P17 on thehighpass filter. This contains the highfrequency range of the speech spectrumwhere most unvoiced sounds are pro.duced. By adding this signal directlyto the output, a reasonably complete'speech' signal may be obtained.Nevertheless, it is worthwhile to listento the unvoiced sounds as they arereproduced when pulse or sawtoothwaves form the carrier signal. By pro-ducing hissing and 'plop' noises in themicrophone while switching the gener-ator from triangle to squarewave tosawtooth to pulse waveshaPes. you canhear how important it is to have a widecarrier spectrum for unvoiced sounds.Using a triangular wave, which only haseven' harmonics, the result will be verypoor, whereas the pulse which containsall the harmonics will produce some-thing remotely like an S or an F.Whistling into the microphone with a

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fixed pulse frequency as a carrier willalso show how much high frequencyenergy it possesses.

The vocoder for musiciansThe experiments just carried out mayseem a little too simple, but theyemphasize the basic operation of thevocoder. Once the user really feels heunderstands exactly what is happening,the variety of applications will only belimited by his imagination. Whenused for musical applications, thevocoder will be restricted to keyboardand string instruments. After all, a saxo-phone player can hardly be expected toblow and talk and sing all at the sameticoalGuitar and bass guitar players willdiscover that more often than not thedynamic range of their instrument willnot be sufficiently wide to produceintelligible or clearly articulated sounds.

Depending on the effect that they wishto achieve, it may be advisable to con-nect an effects box between theirinstrument and the vocoder carrierinput, with which additional high foe'querncy components may be added tothe original sound. Examples of suchdevices are phasers, flangers, boosters,distorters, fuzzers, frequency doublers,etc,It may also be interesting to connectthe guitar to the speech input of thevocoder, while using an organ, Wingquartet or synthesizer as the carriersignal, This of course requires strictcoordination between the variousplayers. Chords or a melody will beplayed on the keyboard instrument,whereas the guitar is used to play amelody or a rhythmic pattern - prefer-ably monophonic, so no chords. Thenewly generated sounds will have theenvelope shape and some of the spectralcharacteristics of the guitar. Many other

using Ole ElsOtor Vow.

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Alektor septernber - 043

The vocoder at live performancesWhen performing with the vocoder onstage during a concert, a few aspectsneed to be treated with care.There are basically two characteristicsin the vo.der, which could turn theperformance into an absolute catas-trophe.In the first place us Sensitivity Or'responsiveness' which was mentionedearlier. Like so many devices, the GreatCompromise will have to be sought.Providing the vocoder with a widedynamic range may create chaos innoisy surroundings. This is because thevocoder makes no distinction betweenwhat it hears and what it is supposed tohear. Not in front of the vocodernEverything that enters the analyzer isprocessed in the usual fashion andappears synthesized at the output ofthe equipment and those of you whohave experienced the result know whata terrible din that can be!The only suitable methods to suppresssuch sensitivity to undesirable noises isto use a highly directional microphonewhich is spoken into from as short adistance as possible or to use two micro-phones in antiphase. The latter methodis illustrated in figure 8.When two (identical) microphones areused in this way it is important to speakor sing in front of one of them at asshort a distance as possible. A plop capand a bass roll -off filter are indispens-able. Another advantage of this methodis that acoustic feedback may be notice.ably reduced. Feedback sensitivityhappens to be another drawback of thevocoder, as a result of the phase shifts inranges where the syntheses tutors over-lap.

The vocoder in the studioThe above -mentioned precaution tocurb nasty side effects are of course lessimportant in recording studios and may

musical instruments may of course beequally well combined.For electronic pianos the same appliesas for the guitar. Here too, the use ofsome kind of effects device is rec-

ommended.Organists and synthesizer players have amuch easier time. A nice effect whichcan be produced on most keyboardinstruments is the bass effect, bymaking explosive noises with the mouthin the microphone and letting themdecay. Wind instruments like the tuba,trombone, etc. can be imitated with alittle practice. Electronic synthesizers,like the Elektor Formant, offer anextremely wide range of possibilities.Apart from generating carrier sounds,the synthesizer can alto be used toproduce signals to control the vocodersynthesizer inputs directly, and theanalyser outputs of the .coder can beused to control numerous units in themodular synthesizer.

8

1.04- Mikan semember IPSO using the Elektor Voeoder

9 10

= _r

even be totally unnecessary. Thevocoder is an instrument which is highlysuitable for use in the studio, providedthat a few details are taken into account- particularly when dealing withexisting recordings. The vocoder is not amiracle machine with a 'talent button'or a 'success filter', but an instrumentwhich one must learn to use, preferablyin the initial stages of a musical pro.duction, where required. If krocoding.is postponed until all the material isrecorded on the various tracks of a

multi track recorder, there is a chance

SPE

FOR cpepyr.

that the material may not be spectrallywholly suitable and that the synchronis-ation between the Voice and Carriersignals may not be sufficient.The problem in the sound studio isoften that time is money' and so a

producer will sometimes get a littleimpatient if the vocoder does notobtain astounding results at first bat.Vocoding is then postponed until thefinal mixdown stage, where it is oftenmuch more difficult to obtain thedesired effect.Fortunately, more and more sound

technicians seem to understand thatthe vocoder needs to be played. like anyother instrument, and that learning toplay may take some time.Finally, figure 9 provides a few examplesin which the vocoder can play an

infer.. kV pant, especially if morevoltage control equipment is available.Figure 10 gives a few suggestions forperipheral devices to make the vocodermore versatile. The voiced/unvoiceddetector, in particular, is scheduled forPublication in the near future.

elektor pptember 1980 - 8-45

T. Mod -1 WM U mries ///.standing units, account tor eighteen of theseand are unique for their built-in handles. Inaddition to the usual handles either side ofthe front panel, each side panel is formed toan elegant shape incorporating Profile MesuMtantial handle. giv.effortless Sitting and carrying, honever he,the contents.These distinctive mses are mar...red inthree vvidths. two depths and heights of 3,4

Large 7 -segment characters a. 6U, have a smart blue and naturalCharacters up to gig min high may be elm- anodimd 1 ini. and mke a wide range ot mrdtrortically controlled using a new ranw of gui.s, .95 connectors,and other accessories.7 segment display units from ImpectronLimited. The displays can he clearly read ult Unit 9 Park St kW Est.,to 35 metres away. Units in Me 5. SeriesoIs rate using simple lowsoltage sig.. to Telephone: th,,(296(042961create local magnetic fie. .hind the

11624 MIsegments. each segment is simply a rotatingmagnetic bar, finished in matt black on oneside a. bright reflective yellow on the other.After creating a desired character. no power isconsumed until a change is next required.

Bemuse moving parts are kept a minimum,and there are no filament lamps, operationallife is extremely long. Fn feature isthe use of semi -hard magnetic corm theelectromagnetic drives, whi. allows highvelociw character changes driven from rapidpulse trains.Two sizes of unit are available initially, withcharacter sizes of 40 x 32 rnm (Type SO) a.80 x 40 mm (Type St). Each unit includes abuilt-in driver circuit whi. coMrols thesegments using 16 V dc signals. MaximumPoWer oonsumption oCcurS during charaCterchange end units are rated at 0.07 Watts.Inspection Limited,Foundry Lane,Horsham,W. Sussex. BHT SPX.

090.23011

(1623 M)

A case with a differenceWen Hyde Developments have remarryenlarg. their Mod -1 renge.This now amoumsto some 62 different enclosures and .assisunits.

Tape -stereo -radio -clock displayJust introdiced by Fairchild's Op (lyricsProduct Group is the F LB 4010 4 -digit LCD.ThO gg.pin tepostere0,100, display .aturesf.r reg. 10 mm high P...., Pomo.Other sy.ols evaila. include a stereo modeindimtor, a tape mode inclicator,tapa directionindicators, end AM -FM radio mode indicators.Transflector and reflector PertiOnt are

available. With transilective LCD operationthe display has Me ability to allow light topass through the cell from the rear as well as

133 F=2..e

-reflect light incident on the front. The glass -f rit seal used is highly reliable and thebiphenyl liquid costal material very stable. Atypical connection system would consist of aPC board, a .ir of conductive elastomerconnectors on which the diming( is placed. A.zel would Men hold the easembly together.Operating voltage is typically 3 Vrms 565form of a square neve at 32 Hz. Contrastratio is typimIN / 1.

Fairchild Camara B Instrument (UK) Limited230 High Street,Potters Bar,Hera ENS 5BU,Telephone (0707)51111

(1625 M/

Microwave frequency counterElex announce the Eldora. Model 99018-GHz microwave freqmncy counter.The Eldora. 950, from 51.0,1w a standardoperating ran. from 20 Hz to 18 GI. with-25 dem sensitivity. Options extend thisrange to 26 Gt. and provide .nsitivitY tO-30 dem. Input protection to 2 nous is

incorporated and the instrument features a+25 dBm overload spscification.

A large 11 digit parer display provides highreadability While the basic 1 Hz resolution canbe reduced to increase measurement time.This is a microprocessor based instrumentMM the MP U controlling Me measurementand mquence as well as Me display a. controlfunctions. Remote control of mode, resolutionand reset are prOVided through an optiOrielIEEE 486 interface from which rem. canalso be output. The remote .ntrol interfacecan also be used for presetting any desir.number from 0 to 99.19£199999 for receiverLO monitoring.Elea Systems Ltd.,Croswell How,Bracknell,Berkshire.Ter (0,744) 52929,

(1625M)

Photodiode for optical sensingoperationThe Syrnot 320/1 range of photovoltaicphotocliodm now includes the SP - ION ty.measuring 10.1 x 10.1 min and having an

active area 91.16 mr/12. The ...voltage at25°C 5 0.039. and the photonurrent is

500 me) nest conditions 1000 Lux). Darkcurrent is typically 1.5 mA (reverse voltage20) and the capacitance is 2,000 pf. Peaksensitivity is at 830 nM wavelength.The package is equipped with flying leads.covered in vinyl tubing.

This photodiode is sui.ble for a wide rangeof optiml sensing appications where theshape is a.amageous, including stroboscopes,light reflection, smoke detection, motiondetection, detection, toys and electronicgemesThe prototy. Price is 2.45; .0.1 primfor 1.000 pieces is £ 1.20 end,Symot Limited,22e Heading Road,Henley on Themes,Oxon itS9 IAG,

(04.9 121 2663.

1162101

9.46 -Minor SeMember 1980

Low -profile p.c. relayA new subminiature relay designed gm°.sally for printed circuit board aPPlicatiOnS isthe lightest relay of its kind available. Weighingonly 12 5 ammes Me Type SF lowgrofilerelay offers a choice of either double -poledoublthrow or 4 -pole double.throw contactconfigurations, a. contact ratings of 2A d.c.or 50 W. at a maximum of 60 V dc. intoresistive oad. The bifurcated crosstoar

pansre of gold over silver palladiumare designed for long operational

life and high reliability.In .dition to Me standard or Oasis relay.designated SFA, oMer more specializedversion. are available including non -polar.self°tching ISSLI andpdarity self tatchingISHII types. Further a variety of alternativecontact forms may be incorporated to meetindividual user requirements.

SW)

The taffy's p 1. termin° are ananged Meindustry standard dual inhise 0.1 in. gridformat, and it has been designed for instahlation using variety of techniques. includngflow soldering. Electrical characteristics of theSF series of low -profile p.c.b. relays include

it spanning voltages of 5.6.12, 24 or 28 Va.., power consumpbon of pproximeb.0.56W a. an operational temperaturemope from -309C to $709C. It measures28.40/n x210 mm x 7.5min nigh whenmounted . p.c. board.Diamond H Controls Lot,Vulcan Rood North,Norwich N86 6AN.Telephone: (06031 45291/0

11635 MI

Fest response temperature sensorsTwo temperature sensors featuring fastresponse times haw been announced by Texas

Instrum teents ted. The new devices,designad TSLI102 and TSF 102, feature apositive temperature coefficient a. aremernprts of a Mmily ofthe prevously

announvic sMPh0nc u

TSM 102.iThe ad.es

two older devices have been inproduction for over a year. All members ofthe family have a nominal room temperature(269 Cels)usl resistance of 1800 ohms and areavailable in t 196, t 296, t 396, t 5% and t 10%tolerances. The deviws are produced using aPlanar process. The resistance element usesMe spreading...stance principle which rests°

itnurersis'tet7onpeic o of the tempera

The TSF 102 is equipped with a 'thermalantenna or flag which provides close coupling

Ohe device to the object to be monitored.urs to small thermal mass the TSF 102 and

TSU 102 offer improved thermal resPonseover the TSP 102 a. TSM 102 for pli-cations requiring it. Thew devices elf o offer amuch srnSff r package Mr applications such asmedical thermometers where physics)) size is aconsideration. The slope of the temperatre/resistance responsenume for all devices in thefamily is easily linearised by the addition of aseries or a shunt Med esistor.Texas InstrumentsMenton...Seer ford, 441(41 70A,

and1, 023447406

11638M/

Energy measurementDigital power integrators are now available inNorthern Design's NO 26 series of custominstruments. nital by

lathe r

to monitor a.control internal mixers inubber a.PM. industry, they are equally suit., forenergy management in any process industry.SpecifiwIly intended for industrial appli-cations, these instruments give a Wrestreadng - in watt or kilowatt hours-of theenergy consumption of a process or machineoperating off single or three phase powersystems. They are supplied in dn style Pao.mounting case 172 x 144 mml and feature a

one inch high four digit display, an a

Set Off. control. T allows the operatorto preset a power levelhis (such as the no.lmdpower consumption of a mixer/ so that theMtegrators measures only the energyconsumed in the process, deducting energymss io me process plant. Optional features)nciude analogue and digital out.ts, plus a

nandby facility to store readings inthe went of power loss.

DernbNorthern Design,

ridge Place,INepP(ngRoadBradford 80.3 OEE,INest7orkshirt, England.Ter (02741 306710

11631 MI

The first push-pull RF power feteO F designers will be interested in the firstO F Push,. VNIOS power devices justP1159

by Siliconix for bro.°ndapplications from 2 to 200 MHz.The new OF devices combine the well knownadvantages of puMmull o.ration. such as

ewn order harmonic suppression, with theproven advantages of VMOS devices, such ashigh power at high efficiency, low noisefigures, no thermal tuna.. niShogging when paralleled, the ability towithstand infinite VSWIS a. geat,/simplified designs.The DV 281200 (DV 11121 delivers 120 watts

inim. a. the DV 28800 IDV 1111180 bows Also available is the DV 2.00mV 1110/ 40 wans driver. All these devicesdeliver rated output at 28 Volts and provide a

Theypower operated0 dB at 175 MHz.

They can each be in Clam A, B o. Cand are well suited for a variety of broadbandOF amplifier applications. The most obvious

advantage to the .sh.pull pack. is thereduced amplifier size a bility todirectly connect impedancend matching trans-formers° the devices.

ititataLs

These new pushmull transistors are easilybroadband. within the VHF bands. Thelower frequency limit is governed only by theMnsformer design. Mouse the transconduc.tame is virtually constant over widefrequencyexcursions, the input loading taquirementrernains relatively constant within the Inregion. Thus the input VSWO quite stableover an unusually broad bandwidh.VirtuaIN no external fe.back is required toensure stability. Thus overall efficiency is

unusuallyereby sign

high and out-ohband stability )s

thificantly enhanced. Low ex.nalfe.back also means that gain is flat across amey wide bandwidth. OF desigoers erefinding VIMOS particularly

lowerbecause

baseband noise is 10 to 15 dB lower than incomparable bipolar devices.This new family of OF VMOS deviws exhibitsa reversegain of -35dB or more. So variationsin output loading have little effect upon theMost of the amplifier. Equally important,VMOS power amplifier circuits have ...Tedthe ability to wiMsmnd 20 ) 1 VSWIII at anyphase angle.

Silkonrt Limited,Plorriston,Swarm .6 6NE,Tel: (07021 74681.

11620M1

Miniature multi -way connectorwith integral locking featureH & T Components announos the availabilityof a series of lowoost, miniature ...wayconnectors combining compactness withextreme reliability.The RPC connector seri. has .en introducedby H & T Components for applimtions in

equipment such as communications, radar,instrumentation and data collereion systems.It has been resigned. meet requirements forhigh density intermnnection with high powercap,iiity. T. lightweight, plasticshroo.dRPC plug and socket mmsures only 15 mm indiameter x 55 inm ovehall, excluding itsflexible protective ,roud for the cable en,.It is rated at 5 A. a. proofed to 500 V ac.Probably the most imporMnt feature of theRPC connector, however, is its integral'one -touch' locking system. This consists of aimking arm which is part of the bOsremou.ing, which mates the two connectorelements positively a. securely to preventacci.ntal disconnection.

a tro-fit

The RPC series offersalmost 2110 user options,enabling it to meet a wide range of individualapplication requirements. It is constructed inmoulded grey or black reastic, and is availablewith from two to seven contacts in either goldor silver plated brass or phosphor bronze. Itoffers the choice of panel or p.c.b. mounting,and is supplied with a choiceof 3older bucket'or pc.b. terminations.SS T Components,Crowdy's Hill Estate,ICembreVSvindon.Wiltshire SW SerS,Tel: Swindon (07031 693681-7.

11622 511

Low-cost hand-held digitalmultimeterThe new Alpha V. Me Ireest and smallest inthe comprehensive range of digital mul.timeless from Gould Instrumems Division,is a low-cost, hand.held instrument combiningversatility a. ruggedness. The Alpha V has a35 -digit liquid -crystal display, a. the25 measuring ranges cover the five basicfunctions of DC voltage, AC voltage... cur -re, AC current, a. resistance. Cooing onlyf 85.00 Italto V.A.T.), the Alpha V is being

offered with an introdureory discount of5% on quotations of from two to nine unitsand 10% tor larger quantities.The Alpha V has a maximum reading of 1.9and a maximum rmolution of 100 rsV. DC ac-curacy on the 2001,10 range is 110.5% 0.5%Dl full scalel. DC and AC voltages are eachcorer. in five ranges from 200 mV to 1 kV,and DC a. AC current in five ranges from2 mA to 10 A. The five resistance ranges gofrom 200 to 20.2. Range a. functionselection si by two rotary switches 011 116*

clearly coded front panel, which make theinstrument vary easy. use.The multimeter is powered by a 9 V carbon -zinc or allreline battery IPP3 or equivalere),the latter giving a rypical lire of 200 hours.frettery-low indication is provid00 by themultimeter's display, which shows 'BAT'when less than 10% of umful batrery liferemains. Automatic decimal -Point, Preeriry

and overrenge indication is also provided.The cam is of high -impact ABS plastic, andthe display is shock -mounted behind a toughPolymr.nate PintiC .relow. The .tterya. the protection fuse are easily accessible,a. a single oalibration control is provided.Estimated mean time between failures is in

excess, 20000 hours.The 6,10(0 6(650 V measures only 07601.1117 inl x 76 mm 13.07 in/ x 38 mm 11.5 in)and weighs 282 g. Accessories supplied withthe basic instrument include standard red andblack tmt leads, battery and handbook. 0,eraccessories available are a soft protmtivemrrying case, high -voltage probe, r.f. detec-tor, and a special set of test leads rat. at2 kV RMS and 20 A.Gould Instruments Division,Roebuck Road,

Essex.Telephone: 01500 I000

11637 MI

Low cost digital storageoscilloscopeDesignated the Model MS -1650, this versatileinstrument combines a 10 MHz real timeosciiioscope with a digital storage systememploying a 1024 x 8 bit memory.Digital storage offers several advent.. over

0161.1 september 1980 - 9-47

the more common tube storage, notably thereriable Prereigger a. postoreger vievaing -simulmneous display of real time waveformsand previously recorded waveforms for

detailed and unambiguous comparison -.rmanent hard copy record by output to aperipheral device, such as a pen recorder.

OscilloseoPea employing digital store.techniqum premnt the user with a num.r ofpractical advantages when observing one shot.transient or slow speed signals - display,quality and clariry . not deteriorate withtime and the display is completely without

MS1650 can protect its stored signal data byan internal optional nickel -cadmium battery,which retains memory data when the es.mains power is switched off or inadvertentlyremoved.

rer 1

411.1.1111111111111111111111M1

The MS -1650 regital storage oscilloscopeincorporates a rectangular CRT, and is ro.barely mnreructe0 with a die.cast front paneland integral carrying handle, tilt stand. Itweighs only 9 kg, measures 2. x 138 x 400mm, and costs just 1,.0 with a two yearguarantee.House of Instruments,34136 High Sue,Saffron Walden,Essex, CS 10 IEP.

(07001 22612.

11632141

Miniature Dustproof PresetsThe H0521A ia a low cost miniature cermettrimmer. with an almost in.structibleadjustment cap for applications throughoutall rypes of electronic circuitry. T. mmdiamemr makes the trimmer small enough tofit virtually any applimtion. Despite costingonly 15 p in 1000 off quantities -a carbontrack version 1HO 651A/ is avail,. at 9,5 pfor less demanding situations.

Anil. International,SOO North Service Road,Brenscood - Essex. CS/140SG,tel. (0277(230988

11629 MI

9.111- september 1980

Weller rework stationThe 05100 9EC is a complete soldering anddesoldering

as

operating from a wqmPower supply and generating its own de-sol.ring suction from a builvin vacuumpump, The unique feature of the unit is thatMe working temperature of the solderingand demirPring instruments can be continu-ously adjusted tween 50° and 050°C witha tolerance of 2°C. The latest precautionsfor avoiding interIeren. voltages haw beenincorporated to enable use on highly sensitiwcomponents without risk. The station consistsof a basic power supply control unit andvacuum pump If.tow compressed air mayalso be used/. a two stage foot switch, twosafety stende. a Temvonic soldering iron, anda Temtronic desoldering pencil with paneparent solder collector and replaceable filter.

lorwl1W,,,

Oar

Tani -eve id.,OPton 9552,Beading,903.294Telephone: (0730129046

11557 MI

Tuneable inductorsToko's range of tuneable inductors nowincludes the 12VX series of high inductancetuneable coils - available with rimary/taoand secon.ry up to 68 nominal.although tuning 30% of this canna valuebe dug core adjustment.

The 1 IVXA is designed for bias oscillators,tuneable traps. MODEM applWations endsuitable for all types of LC filter designs,svhere the versatility of a tuning adjustment

00C. vie

u an invaluaMe advantage, since it is eater 5.15-1.4.014:-.7./44to use standard value capacitors.

Mu IfAmbit International,200 North Service Rood,Brentwood Essex. CM10 0,39Cl. !02111230909,

115501.1/

Communications aerial switch unitTelecommunications Accessories Limitedhaw launched an aerial changeover designedMr use in high security installations. Thedevice allows the operator to change fromone aerial to another in the event of mai.conne.no,ree, thus maintaining radio

Switch o.ration W by a 12 -volt relay and theunit has a loss of less n 1 dB over thefrequency range500 MHz.

Telecommunications Acce.pries Limited,Theme Incluitrial Estate, Bodes Wax,Theme. Oxon 093323Greer BranTon Thorne 363IN/3.

1150101

Math processor chips boost micro-computer performanceIntel bathere two new math processorchips, 8231 dived point/ and 8232Ifloeting Pont.. which incre.e the P.M..-ene. of a microcomputer system by a f.torof up to 100 tim. wWert

car chipsout

mathematical operations. Both ips actas d.i.ted peripherals interfacing directlyto hwelts 8080, 8085 and 80M3 microcom-Posen in addition to all other generetpurposeprocessors with 8Wit data buses,The 8232 will .rform 60 Gt dem hie's..cision or 32 -bit single preCWanpoint addition,subraction, multiplicationand division. Double precision opewion ismost likely to be used In scientific tinmints such as chromatographs and spet o.grephs sn. they require calculations to becanted out over a wide dynamic range with

a high level of accuracy.Single -precision 132-bitl operation will heused on these occasions when speed is a moreimportant COnsideration than absolute accu-racy. The process.. time depen. on thedata, however, a typical single -precisionmultiply takes .roximatNy 100 micrwN.M. The BP., floating point algorithmif a subset of the proposed IEEE float..Point standard velich is the same as usedfor Intel, fleeting point arithmetic librarysoftware a. the ISBC 310 ariMmetic pro-cessor board, In fact, this standard is usedin all Intel hardware a. software to ensurethat programs written in different languages

a run on different systems will alwaysyield the same result.The 8231 is intended for use in process a.industrial control applications requiring a realtime mathen.ics capability over smallerdynamic range. It operates in a fixed pointmode. performing 16 a. 32 -Wt addition,subtraction multiplication and division. Otherfunctions v.. can be performed by the8231 include the calculation of sine, cosine,tangent. cosecant, secant, cotangent, squaresoot, logarithm, natural logarithm, 8PP...is-Pali and posPerS.Both the 8232 and 8231 math processor chipscontain e 16.ti1 arithmetic logic unit, a pro°rammer" algorithm contro101. an 8 by18 -bit operand stack, a 10 -level markingregister stack, command a. control registersand a read only memory containing all thecontrol software. All transfers .t.en thehost processor (including operand, rem.,status and coMmand information. take pWceover an 8.0auidireetionei data bus.Both chips are manufactured using Intel'sHOGS technology and are available in 20 -pin.6 -in -line packages. Ea. requires M2 Vend 1-5 V power supplies.

INTEL Corporation ONO Ltd.,Oen.. Towns Road, Cowley,

Oxford OXil 3N0.Tel: Oxford rosa, 771031

0.320)

alektor septamber 1980 - UK 13

Lightweight polypropylene toolbox Wile design ensures that the tie: flange baseThe new 151 Cantilever tool box from 11.0 lamps do not move during operation, thus re.is made from rugged polypropylene and has clueing lamp failure.overall dimensions of 500 x 220 x 220 mm. Lamp replacement is easily achievable fromFour tool trays each 480 x 75 x 35 mm fold acme ofout when the lid is opened. The top two traysare provided with movable dividrs. A fold 72.flat lid a. two safety .ches nom.. an HFeeding,.tp,eetremely lightweight Package. in Oxon. RG9 IAO,brown and fawn with white coMParamentool trays it is an ideal alternative to heavymetal tool bows.

.**ftLiit/

The Sacco 151 Cantilever Tool Box costsL 12.50 + VATToolrenge LTO.,Upton Road,Reading RS3 WA,

Tel: Reading 10734129446 or 22245

1157310/

Flatter flat pack relayMiniature pc, type LZN relays from IMOOrman are now flatter. Th.e highly reliableultra lovv prof ile (11.5 men) fiat pack W.miniature relays, available in two or four poleemploy the international grid terminal ar.rangement. The LZN has triple gold lash.silver contacts rated 3A@ 24 VAC, these twinbalurcated contacts plus the unique card lifeoff system for the contact drive ensures re-liable switching of louv voltages. Operatingvoltages are 8.48 V DC. These competitiv.priced flat packs have extremely long life, inexcess of 100 million operations minimum,lovv coil resistance plus reliable low

all:switching makes the LZN int.l for the alarminduNry where these consideration, are so im-POrtant.

Illuminated push button switches .0 Pewee', ...et.,offer RFI shielding 309 Edgware Road,

The capital OF 335 Wries Of iliuminA. FF.London W2 IBS,Tel: 01 723,2231/4w d 01 402-7333/6.

button switches is now available from SymotLimited, 1575 AnSingle or dual lamp units are offer. in.a.e over combinations up to 4 poles.The normal rating is 2 amok 250 VAC.Steel housings, 1 inished with a Week oxidebezel are ..ard and stainless steel clipsensure pose retention from fro. of panel.The panel cutout dimensions are 0.028 inchesx 0.972 inches. DIL switches sealedMomentary and alternate action switches with Dual in line switches, type 338, are now.mplementaw indicator only units are avail- offered by Symot Limit.. The principalable. Lens modules can be full -screen or Dori- advantage claimed for these switch. is thezontally or vertically split and a simple ada. terminaf sealing technique which is designedter provides full shielding. Lenses are to prevent contamination from flux andavailable In all Venda. colours. The lens mob solder.

These DIL switches embody a single .intcontact system. with self mleaning wipingaction Which results in a low and stablecontact resistan.. The tial inure of lessthan 50 milliohms at 2 V DC, 10 mA, isguaranteed for over 10,000 switching oper-ations.

Temperature coefficient is 'fully .cu-mented over the range -25°C to .130°C.

Am. InternadonalSOO North Service,Brondwood Seeex. 01.914 dSGtel. 102771230909

(1580 Ml

UHF cavuty filtersoko, 232MT series of helical resonators

reprewnts a substantial price roughfor communi.tions quality UHF filters.Originally developed for applications rangingfrom UHF BF filters to the first IF of SHF(satellite broadcasting) systems, the seriesare

available in the range 380 - 480 MHzwith eiMer two or four chambers.The insertion loss is only 1.8 dB max for fourPOle units, wi a shape factor 16/60 dBI ofbetter than 5m1, Mr... anF band-width of 25 MHz at 60 dB, an ultimatestop.. of some - 70 dB.

Gold flashed terminals and heat resistantplastics have been [flown to increase thereliability of these svvitches, which are ratedat 50 V DC, 100 mA. non switching a.5 V DC,100 mA in the switching mode:The terminal pitch is 2.50 mm ..82 mm.

mired,Reeding Road

Henleywninemes,Oxon. RG9 IAGTel: 10691212663

11572 MI

Meld°, member 1900 - UK 19

3'i2 DIGIT LCD MUMETER KIT

Build the Practical Electronicshandheld DMM.This superb productoffers prof essonal precision withextended battery life. FNe functionoperation (AC and DC VOLTS, ACand DC CURRENT, RESISTANCE)with ability to check diodes. 0.5" LCDdisplay with 'Battery Low' warning.Auto.polarity. Auto -zero. Full protectionagainst transients and overloads withability to withstand mains on any range.0.5% basic DC accuracy and 15different ranges. It measures AC/DCvoltages from 0.1 mV to 500V. AC/DCcurrent from 0.1uA to 2A. Resistance fromVtft to 2M11. 200 hour battery life.

The Kit contains all parts needed toconstruct the multirneter plus assemblyinstructions, battery and test leads.

We also offer a calibration serviceODD 5 VAT) and a trouble -shooting andcalibration service (22.50 + VAT). Various othercomponent parts are also available as lifullysted.

The multim isassebledand calibrated at ater costalsoof 239.70b+ PAP + VAT.

Lauer Ekctronics Ltd., Unit I, Thomasin Road, 19.6112on.Essex. Telephone No: Basildon (0260)727383.

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7.954.95

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1270.62

9.726.27

FULLY ASSEMBLEDOHM (INC. LEADS)

3970 125 6.14 47.09

. lager Electronics, Unit 1, ThometErt Road, Baskl,Dan. auumttnearatLeoommoracm.64netc47.290

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scimputer (1)This first book of a series describes how to buildand operate a simple microprocessor systembased on the National Semiconductor Micro-processor (INS 80601. The system may beextended to meet various requirements - thesewill all be discussed in the SC/MPUTER books.PRICE/UK £3.70 inc P&POVERSEAS SURFACE MAIL £3.90 Inc P&P