development of a call alert system for paging mine …...stuart lipoff, paul o'brien 9....
TRANSCRIPT
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DEVELOPMENT OF A CALL ALERT SYSTEM FOR PAGING MINE PERSONNEL
John Trornbly, Program Director
Stuart Lipoff, Paul O'Brien
prepared for
1 UNITED STATES DEPARTMENT OF THE INTERIOR BUREAU OF MINES
ARTHUR D. LITTLE, INC. CAMBRIDGE, MASSACHUSETTS
FINAL REPORT
On Contract No. HO 262026
) Arthur D Little,Inc I
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USBM H0262026
DEVELOPMENT OF A CALL ALERT SYSTEM FOR PAGING MINE PERSONNEL
John Trombly -- Program Di r ec to r S t u a r t L ipo f f , Pau l O'Brien
ARTHUR D. LITTLE, I N C .
Cambridge, Massachuset ts 02140
C-79492
USBM CONTRACT FINAL REPORT (H0262026)
UNITED STATES
DEPARTMENT OF TIEE INTERIOR
BUREAU OF MINES
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REPORT DOCUMENTATION PAGE
1. Report No. 2. 3. Rocipieat'r Accarion No.
4. Title and Subtitle Development of a C a l l A l e r t System f o r Paging Mine Personnel
7. Author(s)
John E. Trombly, Program D i r e c t o r S t u a r t L i p o f f , Paul O'Brien
9. Performing Organization Name and Address
Ar thur D. L i t t l e , Inc . 1 5 Acorn Park Cambridge, Massachusetts 02140
12. Sponsoring Organization Name and Address O f f i c e of t h e A s s i s t a n t D i r e c t o r - Mining Bureau of Mines, Department of t h e I n t e r i o r Washington, D. C. 20241
r
15. Supplementary Notes
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5. Report Date
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6.
8. Performing Orgmiution Report No.
79492
A
10. Projtct/Tark/Work Unit No.
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11. Contract or Grant No. H0262026
13. Type of Repon
F i n a l Report
L J
14.
- 16. Abstract
System o b j e c t i v e s and des ign c r i t e r i a f o r a n in-mine ULF r a d i o paging system a r e d i scussed . Coding fo rmats , frequency and bandwidth s e l e c t i o n c r i t e r i a l e a d i n g t o t h e system des ign a r e d i scussed . The p ro to type c a l l a l e r t t r a n s m i t t e r and pocket page r e c e i v e r is func t ioa - a l l y desc r ibed . The r e p o r t inc ludes c i r c u i t d e s c r i p t i o n s , schemat ics , p a r t s l is ts , p r i n t e d c i r c u i t f a b r i c a t i o n and assembly drawings. The r e p o r t concludes w i t h a n e s t i m a t e of t h e manufacturing c o s t f o r each assembly.
17. Originator's Key Words Mine Communications, Personnel Pagers , Radio Paging, Pager Phones, Pager Telephones, Paging.
18. Availability Statement
19. U.S. Security Classif. of the Report
U n c l a s s i f i e d J J
20. U.S. Security Clasrif. of Thir Page
U n c l a s s i f i e d 21. No. of P a g a 22. Price
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FOREWORD
This r e p o r t was prepared by Arthur D. L i t t l e , Inc. , Cambridge, Massachu-
s e t t s under USBM Contract No. H0262026. The c o n t r a c t was i n i t i a t e d under
the Coal Mine Health and Safe ty Program. It was administered under the
t echn ica l d i r e c t i o n of t h e P i t t sbu rgh Mining and Safe ty Research Center
with M r . Harry Dobroski a c t i n g a s the t echn ica l p r o j e c t o f f i c e r . M r .
George Honold was the c o n t r a c t admin i s t r a to r f o r t h e Bureau of Mines.
This r e p o r t i s a summary of t he work r e c e n t l y completed a s p a r t of t h i s
c o n t r a c t during the period June 1976 t o Jtine 1977.
No invent ions o r pa t en t s were developed a r d no app l i ca t ions f o r inven-
t i o n s o r p a t e n t s a r e pending.
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TABLE OF CONTENTS
LIST OF TABLES
LIST OF FIGURES
I. INTRODUCTION AND S W Y
A. OBJECTIVE
B . SYSTEM DESCRIPTION
C. FINDINGS AND CONCLUSIONS
11. THE CALL ALERT SYSTEM
A. BACKGROUND
1. Page Queuing
B. TECHNICAL DESCRIPTION
1. C a l l Alert Transmit ter
a . In t roduct ion
b. Nomenclature
c . Power Supply
d. Visual Pager I n t e r f a c e
e . Transmit ter Logic
f. Modulator
g. Transmit ter Power Output Stage
h. Local Operation
2. C a l l A l e r t Receiver
a. In t roduct ion
b . Nomenclature
c. Power Supply
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TABLE OF CONTENTS (Continued)
d. Receiver Front End
e. Demodulator
f . Decoder
111. MANUFACTURING COST ESTIMATE
A. SUMMARY
B. CALL ALERT RECEIVER
C. CALL ALERT TRANSMITTER
APPENDIX 1 - COST ESTIMATES
APPENDIX I1 - PARTS LISTS
APPENDIX 111 - VISUAL PAGER SCHEMATIC DIAGRAM
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LIST OF TABLES
TABLE 1 CALL ALERT SYSTEM CODES
TABLE 2 UART PIN ASSIGNMENTS
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L I S T O F FIGURES -
FIGURE 1
FIGURE 2
FIGURE 3
FIGURE 4
FIGURE 5
FIGURE 6
FIGURE 7
FIGURE 8
FIGURE 9
FIGURE 10
FIGURE 11
FIGURE 1 2
FIGURE 13
FIGURE 1 4
FIGURE 15
FIGURE 16
THE CALL ALERT SYSTEM, BLOCIK DIAGRAM
POCKET PAGE RECEIVER
CALL ALERT TRANSMITTER
TRANSMITTER SWITCH PANEL
D I F F E R E N T I A L PHASE S H I F T KEYING
OCCUPIED BANDWIDTH, 3 H z
OCCUPIED BANDWIDTH, 30 H z
OCCUPIED BANDWIDTH, 300 H z
UNMODULATED REFERENCE
BLOCK DIAGRAM - CALL ALERT TRANSMITTER
BLOCK DIAGRAM - CALL ALERT RECEIVER
TRANSMITTER SCHEMATIC
RECEIVER SCHEMATIC
RECEIVER ASSEMBLY DRAWING
RECEIVER COMPONENT ASSEMBLY DRAWING, BOAZiI) 1
RECEIVER FABRICATION DRAWING, BOARD 1
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L I S T O F FIGURES ( C o n t i n u e d )
FIGURE 1 7 ~ / B RECEIVER ARTWORK DRAWING, BOARD 1
FIGURE 18 RECEIVER COMPONENT AS SEMB1,Y DRAWING, BOARD 2
FIGURE 19 RECEIVER FABRICATION DRAWING, BOARD 2
FIGURE 2 0 ~ / B RECEIVER ARTWORK DRAWING, BOARD 2
FIGURE 2 1 VISUAL PAGER SCHEMATIC
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I. INTRODUCTION AND SUMMARY
A . OBJECTIVE
For a number of y e a r s , c o a l mines small and l a r g e have made e x t e n s i v e
use of p a r t y l i n e pager te lephones t o communicate i n t o and between
working a r e a s a s w e l l a s t o supe rv i so ry sites above and below ground.
These phones page t h e c a l l e e by means of a se l f -conta ined loudspeaker;
normal communications a r e t hen c a r r i e d on by a convent iona l te lephone
hand set. The a c q u i s i t i o n range depends on how a u d i b l e t h e speaker is,
a s w e l l a s on t h e number of phones i n a given a r e a , and t h e chances of
a c a l l e e be ing i n t h e i r v i c i n i t y .
C l ea r ly , t h e r e a r e o p e r a t i o n a l drawbacks t o t h e system. To remedy the se ,
t h e u se of v i s u a l pager u n i t s h a s been proposed, and engineer ing models
of such u n i t s a r e c u r r e n t l y under develop~ment. These, i n t h e i r s i m p l e s t
form, a r e d i s p l a y pane l s which, when se le (c t ive1y a c t i v a t e d , show symbols
t o d e s i g n a t e paged i n d i v i d u a l s who have no t been reached v i a t h e v o i c e
paging s y s t e m .
These d i s p l a y pane l s en l a rge t h e paging a r e a and can b e i n s t a l l e d where
phones a r e n o t needed. Unless t h e s e d i s p l a y pane ls a r e read by a l l con-
cerned, they too, l i k e t h e pager phone wi:Ll sometimes f a i l t o n o t i f y an
i n d i v i d u a l t h a t h e is be ing paged.
The u l t i m a t e system i s a w i r e l e s s scheme which can s e l e c t i v e l y page any
one of a number of m in i a tu r e pocket r e c e i v e r s c a r r i e d by key mine per-
sonne l ; thereby prov id ing each of t h e s e i r ~ d i v i d u a l s w i t h a pe r sona l
a l e r t i n g s i g n a l t h a t he should c a l l i n . Such w i r e l e s s schemes can cover
a l a r g e working a r e a , and a r e a lmost imposs ib le t o ignore .
From a system engineer ing p o i n t of view, a l l t h r e e paging techniques:
phone, v i s u a l , and wireless perform b a s i c a l l y t h e same func t i on ; and
they b e n e f i t g r e a t l y by be ing made modules of a complete paging system
which uses any o r a l l t h r e e modes of communication. F igure 1 i l l u s t r a t e s
t h e system concept . This shows t h e e x i s t i n g pager phone hardware, t h e
v i s u a l pager hardware developed by ADL f o r t h e Bureau, and t h e a d d i t i o n a l
equipment necessary t o add t h e wireless page c a p a b i l i t y .
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DISPATCHER'S CONTROL CONSOLE
VISUAL PAGER
VISUAL PAGER SYSTEM --- - - - - - - - - - - - - - - - - - - - - - - - - - ---------I-------- ------- - - -
CALL ALERT SYSTEM
I WIRELESS
I I I TRANSMITTER
I I UNDER DEVELOPMENT AT ADL L --------,-,,,,,-,,,,,,,,,,,,,,-,,,
BLOCK DIAGRAM C A L L ALERT SYSTEM
W I T H PROTOTYPE VISUAL PAGER
Figure 1
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The o b j e c t i v e a s o u t l i n e d i n t h i s f i g u r e is t o p rov ide a n add-on wire-
less pager system t h a t i s f u l l y compat ible w i th t h e e x i s t i n g v o i c e pager
phone equipment and w i th t h e v i s u a l paging system p rev ious ly developed.
B. SYSTEM DESCRIPTION
The c a l l a l e r t system, a s d e l i v e r e d t o t h e Bureau of Mines, is comprised
of t h r e e p ro to type pocket page r e c e i v e r s , a compact page t r a n s m i t t e r
and an i n t e r connec t i ng c a b l e t o i n t e r connec t a v i s u a l d i s p l a y w i th t h e
t r a n s m i t t e r . The system can b e expanded, wi thout mod i f i ca t i on , t o page
a t o t a l of 1 5 r e c e i v e r s and then t h e c a p a c i t y of t h e system is on ly
l i m i t e d by t h e v i s u a l page r ' s d i s p a t c h e r ' s conso le . The pocket r e c e i v e r s ,
shown i n F igure 2, a r e designed t o accommodate 32 d i s t i n c t codes with-
o u t modi f ica t ion . I f t h e de s ign c a p a c i t y is perce ived t o b e a l i m i t i n g
f a c t o r , t h e r e c e i v e r s can b e expanded t o a f i e l d of 128 codes w i th only
a ve ry minor modi f ica t ion .
The r e c e i v e r , as dep i c t ed i n F igure 2, is completely s e l f - con t a ined .
The enc lo su re houses a f e r r i t e loop antenna, a u r a l and v i s u a l a larms,
two p r i n t e d c i r c u i t c a rd s and a rechargeable n i c k e l cadmium b a t t e r y
designed t o p rov ide approximately 40 hours of cont inuous s e r v i c e be-
tween charges . Two c o n t a c t s a r e provided a t t h e bottom of t h e r e c e i v e r
f o r charg ing from a 12-vol t source .
When the r e c e i v e r is switched on, t h e a u r a l a la rm sounds t o i n d i c a t e t o
t h e wearer t h a t t h e b a t t e r i e s are charged and t h e r e c e i v e r i s opera-
t i o n a l . I f a page i s rece ived corresponding t o t h e code s t o r e d i n
t he r e c e i v e r , t h e a u r a l a la rm sounds f o r about 2 seconds and t h e l i g h t
e m i t t i n g d iode i l l u m i n a t e s s t e a d i l y . The LED can be reset by dep re s s ing
t h e s l i d e swi tch .
The r e c e i v e r ' s address code i s programmed by i n s e r t i n g w i r e b r i d g e s i n
a header l o c a t e d on t h e upper p r i n t e d c i r c u i t c a rd . This d i p header
i s v i s i b l e i n t h e upper l e f t -hand p o r t i o n of t h e disassembled r e c e i v e r
i n F igure 2 .
The c a l l a l e r t t r a n s m i t t e r is shown i n F igure 3. The enc lo su re houses
a w i r e wrapped card assembly, r echa rgeab l e b a t t e r y and a swi tch pane l
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f o r i n s t a l l a t i o n and system t e s t . The t r a n s m i t t e r can be operated on a
stand-alone b a s i s , completely independent of t h e v i s u a l pager system f o r
t e s t purposes. I n normal opera t ion , however, t he t r ansmi t t e r is con t ro l l ed
by a d i spa tche r ' s console, us ing an e x i s t i n g pager phone l i n e a s a communi-
c a t i o n s l i nk . The t r a n s m i t t e r der ives decoded s i g n a l s by plugging i n t o a
s tandard v i s u a l d isp lay o r a b a t t e r y / r e c e i v e r box such a s shown i n Figure 1.
The t r a n s m i t t e r ' s b a t t e r y is designed t o accommodate up t o 7,000 pages
between charge cyc les . A s t h e b a t t e r y is deple ted , the t r a n s m i t t e r
l o s e s power without d i s a b l i n g t h e v i s u a l d i sp lay t h a t t h e t r a n s m i t t e r
may be i n t e r f a c e d with.
The t r a n s m i t t e r may be con t ro l l ed manually from a switch panel , p ic tured
i n Figure 4 , l oca ted j u s t i n s i d e the hinged f r o n t cover. The switch
panel permits code s e l e c t i o n , antenna tuning and remote/ local con t ro l .
C. FINDINGS AND CONCLUSIONS
The c a l l a l e r t system has been success fu l ly demonstrated a t t he ADL
bu i ld ing complex and grounds a s w e l l a s a t t h e Bureau of Mines t e s t
mine i n Bruceton. The primary performance c r i t e r i a f o r a paging system
a r e , of course, paging range and f a l s i n g r a t e , p a r t i c u l a r l y when t h e
r ece ive r is ope ra t ing i n an a r e a of i n t ense electromagnetic in t e r f e rence .
The paging range meets with ou r o r i g i n a l system goals of 500 t o 1000
f e e t a s a funct ion of surrounding s t r a t a and electromagnetic no i se .
Typical paging range a t t he Bruceton mine was est imated t o be 700 f e e t ,
according t o the Technical Pro j ec t Monitor.
One f a l s e page was de tec ted during con t ro l l ed t e s t s a t Bruceton, b u t
only whi le the t r a n s m i t t e r end les s ly repeated a s p e c i f i c code. Since
t h e t e s t was conducted during a 20 minute per iod , during which 2,200
pages were t ransmi t ted ; one f a l s e page i s equiva lent t o a f a l s i n g r a t e
of one every 73 days i f 30 pages per day is assumed t o be a t y p i c a l
r ad io paging r a t e .
The c a l l a l e r t r e c e i v e r is most suscept i 'b le t o f a l s i n g a t t h e f r i n g e
of a s i g n a l l i n g a r e a and only i f t h e r ece ive r passes through a f i e l d
below t h e r e c e i v e r ' s capture range dur ing t h e course of t h e page. Both
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condit ions must occur s i n c e not only muslt t h e r ece ive r synchronize wi th
the incoming da ta stream, but the code must match the f i v e b i t code
s t o r e d by the rece iver . I n add i t ion , pa.r i ty and framing condit ions
must be met.
I n a d d i t i o n t o paging performance, system goals emphasized design of
a compact l ightweight and rugged paging rece ive r . Figure 2 c l e a r l y
i n d i c a t e s the small s i z e of the r ece ive r , made poss ib le by extens ive
use of LSI technology, without r e s o r t i n g t o hybrid c i r c u i t s o r o ther
manufacturing techniques no t commonly employed by the mining communica-
t i o n s indus t ry .
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11. THE CALL ALERT SYSTEM
A. BACKGROUND
Since the choice of an ope ra t ing frequenlcy based upon f i e l d t e s t s was
beyond t h e scope of t h i s p r o j e c t , t h e 3 kHz band cu r ren t ly i n use by
Col l ins Radio was s e l e c t e d t o minimize contingencies . It is bel ieved
t h a t t h i s band o f f e r s t he advantage of optimum range t raded aga ins t t he
disadvantages of high ambient no i se and l a r g e phys ica l antenna s i z e .
It is f u r t h e r hypothesized t h a t the use of t h i s low frequency w i l l per-
m i t a simple, low power and low c o s t r ece ive r design.
Conventional r a d i o paging r ece ive r modulation schemes have employed
baseband modulation of audio tones onto t h e c a r r i e r frequency. S i z e
and c o s t economies i n these s ta te -of - the-ar t pagers have employed
mechanical tuning fo rk f i l t e r s i n the audio frequency range of 300 Hz - 3 kHz. These conventional baseband audio tone techniques were judged
t o be unsui tab le f o r our Ca l l Alert System. A t a c a r r i e r frequency of
3 kHz, baseband tone modulation of even 300 Hz would r equ i re such a
l a r g e r e l a t i v e occupied bandwidth about t he 3 kHz c a r r i e r , t h a t t h e
system range would be expected t o s u f f e r . Furthermore, t he use of
mechanical f i l t e r s which a r e s e n s i t i v e tro shock is not compatible with
the mine environment. The use of audio tone frequencies below 300 Hz
wi th a c t i v e f i l t e r techniques is poss ib l e , b u t t he l a r g e phys ica l s i z e
and high c o s t requirements of t h e requi red capac i to r s make t h i s approach
u n a t t r a c t i v e . Furthermore, t he s ignal l i ing t i m e per page f o r these low
frequency tones m y be expected t o be s u b s t a n t i a l .
D i g i t a l coding schemes on the o the r hand o f f e r f l e x i b i l i t y i n system
performance; permi t t ing s e n s i t i v i t y , code s e t s i z e , s i g n a l l i n g time,
and f a l s i n g performance t o be e a s i l y t raded o f f a g a i n s t one another . I n
add i t ion , d i g i t a l decoders permit s t ra ight forward homogeneous in t eg ra t ed
c i r c u i t custom designs which i n t u r n enhance s i z e and cu r ren t d r a i n
performance.
Phase S h i f t Keying (PSK) is a s p e c i a l case of FSK t h a t is i d e a l l y s u i t e d
f o r t h i s app l i ca t ion . By choosing the d i f f e r e n t i a l scheme shown i n
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Figure 5, t h e modulator is e a s i l y implemented and t h e demodulation pro-
ce s s is s t r a igh t fo rward , provided phased-lock loop techniques a r e employed
t o recover t h e da t a . The coherent demodulation provided by t h e phase-
locked loop i n s u r e s maximum system range a s p red ic t ed by s i g n a l d e t e c t i o n
theory. Furthermore, PSK provides an approximate 6 dB reduct ion i n re-
qui red rece ived power f o r the same CW system performance.*
The occupied bandwidth r equ i r ed by t h e s i g n a l of Figure 5 was measured
us ing a synchronous modulator connected t o an HP3580A spectrum analyzer .
The modulator i n p u t s i g n a l cons i s t ed of a 50% duty c y c l e square wave of
modulation frequency 3, 30, and 300 Hz. The spectrum analyzer photo-
graphs are a t t ached as Figures 6, 7 , and 8. F igure 9 is a photograph
of an unmodulated c a r r i e r f o r r e f e rence . Note t h e fo l lowing f e a t u r e s
of t he spectrum: The c a r r i e r frequency is nu l l ed o u t , t h e f i r s t set of
s idebands is +/- t h e modulation rate and 4 dB down from the c a r r i e r ,
the o t h e r s idebands are spaced mul t ip l e s (of t h e modulation r a t e and f a l l
o f f r a p i d l y wi th inc reas ing spac ing from the c a r r i e r . To a good approxi-
mation, t h e occupied bandwidth is equal t o fou r times t h e modulation
r a t e . In genera l , t h e c a r r i e r w i l l n o t d i sappear f o r a modulation b i t
s t ream wi th a duty c y c l e d i f f e r e n t from 50%; b u t i n t h i s case , t h e
occupied bandwidth w i l l a l s o be less s o t h e above approximation is a
good upper bound.
The 30 Hz modulation r a t e has an occupied bandwidth of 120 Hz and thus
would permit t he c a r r i e r and i ts modulation products t o be placed be-
tween t h e 180 Hz >phase power l i n e harmorric n o i s e p reva len t i n t he
mines. The 30 Hz d a t a r a t e permits an e i g h t b i t s e r i a l word t o be t rans-
mi t t ed i n about 260 m s , not an unreasonable de lay i n comparison t o a
d i s p a t c h e r ' s keying i n t e r v a l when ope ra t ing t h e console .
The system p r o t e c t i o n aga ins t f a l s e alarms w i l l , t o a l a r g e e x t e n t , determine
t h e acceptance of t h e system by t h e use r s . Commonly used rates f o r c o w
*Bennett and Davey, Data Transmission, McGraw-Hill, New York C i ty , 1965.
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Occupied Bandwidth of Differential PSK Modulation
Vertical Amplitude Scale is 1 d B / ~ i v
Figure 6 ~dulation Rate 3 Hz, Horizontal Scale 5 Hz/Div
Figure 7 qlation Rate 30 Hz, Horizontal Scale 50 Hz/Div
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Vertical Amplitude Scale is 1 ~ B / D ~ V
Figure 3 Modulation Rate 300 Hz, Horizontal Scale 500 H.z/~iv
Figure 9 Unmodulated Reference
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mercia l r ad io common c a r r i e r paging should a l s o apply t o the mining
app l i ca t ion . Industry s tandard l i m i t s a.re 0.1% f a l s e s per t o t a l pages
t ransmi t ted . The system design should i.nsure t h a t f a l s i n g r a t e s f o r
random no i se f a l s i n g a r e no t s ign i f i can t . compared t o s i n g l e b i t f a l s i n g
on a v a l i d page intended f o r another pager.
1. Page Queuing
While pos t ing a sequence of pages i n the Visual Pager system, a f l e e t -
f ingered d i spa tche r could pos t pages a t t he maximum system r a t e of 200 m s
per page. Consequently, a queuing delay occurs while t h e t r ansmi t t e r
s e r i a l l y outputs a page. A v i s u a l pager processes the d a t a i n r e a l time
and the re fo re has no need t o s t o r e t h e pages. The burden f o r s t o r i n g
pages a s they a r e generated by t h e d i spa tche r is placed on t h e C a l l A le r t
t r ansmi t t e r .
When viewed from a systems perspec t ive , fou r s o l u t i o n s t o page queing appear
f e a s i b l e . I n the f i r s t approach t h e l eng th of t h e pager code could be
shortened t o a t o t a l of s i x b i t s t o dispose of t h e delay. The f i e l d of
addresses would b e reduced t o about four unique codes. Although as few
a s four addresses may b e s u f f i c i e n t t o eva lua te the C a l l A l e r t System, no
f l e x i b i l i t y i s provided f o r f u t u r e expansion.
The second approach considered would r e t a i n the aforementioned da ta r a t e
b u t would only s t o r e t h e c u r r e n t page f o r t ransmission. The t r a n s m i t t e r ' s
i npu t p o r t would go i n t o a busy mode whi le a page is t ransmi t ted and
a d d i t i o n a l pages posted by a d i spa tche r would be ignored, u n t i l the
cu r ren t t ransmission is completed. Sincre considerable time could exp i re
between pages, t h i s approach o f f e r s a reasonable t r adeof f .
The t h i r d approach considered would s t o r e a l l of t h e pages a s they were
posted by the d ispa tcher . The capaci ty of t h e memory would permit t h e
e n t i r e r o s t e r of 15 poss ib l e pages t o be s t o r e d i n t h e sequence of
t h e i r post ing. The t r ansmi t t e r would s e r i a l l y s t e p through t h e memory
s t a c k u n t i l i t a r r i v e d a t a page f o r t ransmission. The page would be
t ransmi t ted and a po r t ion of t h e memory reservzd t o count t he number
of times t h a t page was outpulsed would be incremented. I f t he page
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was incremented n t imes, where n i n t h i s case is equa l t o perhaps 5 , i t
would be e r a sed from t h e memory s t a c k . Following a page cyc l e , t h e
t r a n s m i t t e r would s t e p t o t h e next page i n sequence i n t h e s t a c k . I f
t h e d i s p a t c h e r repea ted t h e pos t i ng of a page s t i l l c u r r e n t i n t h e s t a c k ,
t he counter would be r e s e t t o n = 0, r a t h e r than r e - en t e r ing t h e page.
The con ten t s of t h e memory would no t overflow wi th t h e repea ted e n t r y
of t h e same page. When t h e t r a n s m i t t e r completes ou tpu l s ing of a l l
pages c u r r e n t l y i n t h e s t a c k , power would be switched o f f u n t i l a new
pos t command is rece ived from t h e d i spa t che r .
The l a s t approach cons idered is a t runca ted form of t h e process ing scheme
desc r ibed above. Rather than s t o r i n g t h e e n t i r e f i e l d of 1 5 p o s s i b l e
pages, only two pages a r e s t o r e d . One i s c u r r e n t l y be ing t r ansmi t t ed
whi le t h e second page, i f i t i s pos ted , i,s s t o r e d . Each page is re-
pea ted ly t r ansmi t t ed , a s descr ibed e a r l i e r . I f a t h i r d page i s posted
s e q u e n t i a l l y , t hen the f i r s t page rece ived by t h e C a l l A l e r t t r a n s m i t t e r
i s bumped. It should be noted h e r e t h a t t h i s arrangement permi ts a
reasonable p r o b a b i l i t y of t r a n s m i t t i n g a t l e a s t t h r e e s e q u e n t i a l pages,
even a t t h e hands of a f l e e t - f i n g e r e d d i spa t che r . As t h e d i s p a t c h e r
keys t h e t h i r d page, 600 m s have e l apsed , s o t h e f i r s t page has a l ready
been t r ansmi t t ed . The disadvantage, of course, is c l e a r . The f i r s t
page i s bumped and t h e r e f o r e i s only trainsmitted once.
W e cons ider t h e programmable processor approach t o be beyond t h e scope
of t h e p r e s e n t C a l l Alert c o n t r a c t . W e do f e e l , however, t h a t t h e
second approach o f f e r s a reasonable a l t e r n a t i v e s i n c e i t s i m p l i f i e s t h e
hardware i n t e r f a c e , lowering product ion c o s t s wi thout incumbering page
process ing from t h e d i s p a t c h e r ' s viewpoint. With t h e above d i scus s ion
a s background, b lock diagrams f o r t h e t r a n s m i t t e r and r e c e i v e r were
developed and a r e i l l u s t r a t e d i n Figure 10 and 11, r e s p e c t i v e l y . A
d e t a i l e d f u n c t i o n a l d e s c r i p t i o n of t h e C a l l A l e r t System is included
a s t h e i n t r o d u c t i o n t o t he Technical Desc r ip t i on below.
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B. TECHNICAL DESCRIPTION
1. C a l l Alert Transmi t te r
a. In t roduc t ion
The c a l l a ler t t r a n s m i t t e r is a se l f -conta ined u n i t , housed i n a water
t i g h t s teel enc losure w i th dimensions of approximately 8" wide by 10"
h igh by 4" deep, exc lus ive of t h e ca r ry ing handle and mounting bracke t .
Connector J1 i s l o c a t e d t o t h e l e f t of t h e f r o n t pane l and in t e r connec t s
w i th a v i s u a l d i s p l a y ' s accessory connector v i a a fou r f o o t c a b l e pro-
vided wi th t h e t r a n s m i t t e r . Loop antenna connector 52 is loca t ed t o
t h e r i g h t of t h e f r o n t pane l and con ta in s two s p r i n g loaded c o n t a c t s
designed t o accept strand@d o r s o l i d w i r e t o /I10 gauge.
The t r a n s m i t t e r ' s c o n t r o l swi tch pane l and 4.5 A-H rechargeable ge l - ce l l
b a t t e r y can be r e a d i l y accessed by removal of t h e two screws t h a t r e t a i n
t he hinged f r o n t pane l . The fo l lowing switches are loca t ed on t h e pane l
d i r e c t l y above t h e t r a n s m i t t e r ' s b a t t e r y :
Remote/Local Switch
Code S e l e c t Switches (5)
Antenna Tuning Switches (5)
A f u s e ho lde r is a l s o mounted t o t h e swi tch pane l and w i l l accept a 6
amp 3AG fuse .
I f t h e ~em/Loc Switch i s placed i n t he remote p o s i t i o n , t h e t r a n s m i t t e r
w i l l accept and process pages rece ived from a v i s u a l pager . When a
v a l i d code is r ece ived , t he t r a n s m i t t e r w i l l cont inuously c y c l e t h e
page code f o r N pe r iods , where N is equa l t o t h e s e t t i n g of t h e t ransmi t
cyc l e s swi tch l oca t ed on t h e w i r e wrap c a r d j u s t above t h e swi tch pane l .
This swi tch may be sc rewdr iver ad jus t ed t o t r ansmi t from one t o n i n e
cont inuously repea ted pages. Since a complete page is t ransmi t ted i n
530 m s , a sequence of n i n e repea ted pages w i l l r e q u i r e approximately
4.8 seconds t o process . This process ing t i m e is important t o t h e d i s -
pa tcher and should be considered by him as; pages a r e posted. I f t h e
d i spa t che r pos t s a second page be fo re t h e t r a n s m i t t e r ha s completed a
code cyc l e , t h e second page w i l l be ignored by t h e t r a n s m i t t e r .
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The rechargeable b a t t e r y housed w i t h i n t h e t r a n s m i t t e r ' s enc lo su re w i l l
power t h e u n i t f o r approximately 7,000 pages, provided each page code
is t r ansmi t t ed on ly once. Typ ica l l y , a page w i l l be repea ted s e v e r a l
t imes. A s an example, i f t h e t r ansmi t c y c l e s sw i t ch is set t o 5 , t h e
b a t t e r y w i l l be dep l e t ed fo l lowing 1 ,440 past-page sequences. A t a
r a t e of 30 pos t i ngs p e r day, and w i th t h e t r ansmi t c y c l e s sw i t ch s e t t o
5 , t h e b a t t e r y should be recharged a t i n t e r v a l s of 1-1/2 months.
The t r a n s m i t t e r may be opera ted independent ly of t h e d i s p a t c h e r ' s con-
s o l e and t h e v i s u a l d i s p l a y f o r t e s t purposes . I f t h e Rem/~oc swi tch
is p laced i n t h e l o c a l p o s i t i o n , t h e t r a n s m i t t e r w i l l con t inuous ly re-
p e a t t h e page code programmed by t h e Code S e l e c t swi tches l o c a t e d on t h e
swi tch panel . Caution is advised when ope ra t i ng t h e t r a n s m i t t e r i n t h e
l o c a l mode, s i n c e a f u l l y charged b a t t e r y w i l l be dep le ted i n about one
hour i f t he an tenna i s tuned t o resonance.
The correspondence between t h e page keys of t h e d i s p a t c h e r ' s conso le ,
t r a n s m i t t e r code and r e c e i v e r code is i n d i c a t e d i n Table 1. The t r ans -
m i t t e r code is n o t d i r e c t l y equ iva l en t t o t h e r e c e i v e r code because t h e
system employs d i f f e r e n t i a l phase s h i f t coding. The t r a n s m i t t e r code
is e a s i l y mapped i n t o t h e r e c e i v e r code i f i t is recognized t h a t a
change from t h e prev ious b i t t r ansmi t t ed is i n t e r p r e t e d a s a l o g i c zero
by t h e r e c e i v e r . I f t h e c u r r e n t b i t be ing t r ansmi t t ed is t h e same as
t h e prev ious b i t , r e g a r d l e s s i f t h e b i t is a one o r ze ro , t h e r e c e i v e r
p roces se s t h e b i t a s a l o g i c one.
The c a l l a l e r t system is designed f o r a capac i t y o f 32 d i s c r e t e page
codes. S ince t h e d i s p a t c h e r ' s conso le is designed f o r a maximum of 15
v i s u a l pages, s l i g h t l y l e s s than h a l f t h e capac i t y of t h e c a l l a l e r t
system i s u t i l i z e d . During remote ope ra t i on , t h e f i f t h d a t a b i t i s
always t r a n s m i t t e d a s a l o g i c one. However, dur ing t h e " loca l" mode,
t h i s b i t may be manually programmed by t h e f i f t h Code S e l e c t Switch.
Antenna tun ing swi tches a r e l o c a t e d on tthe swi tch pane l and a r e used
t o op t imize performance of t h e t r a n s m i t t e r a t i n s t a l l a t i o n . Power
t r a n s f e r t o t h e loop is a t maximum when t h e antenna is opera ted a t
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CALL ALERT SYSTEM CODES
TABLE 1
I
Arthur D Little Inc.
Visual Display
Symbol Code 1 2 4 8 - - - -
0 0 0 0 0
-F d 1 0 0 0
5 0 1 0 0
3: 1 1 0 0
L.5 0 0 1 0 r-- 3, 1 0 1 0
rzj 0 1 1 0
3; 1 1 1 0 - ,A. 0 0 0 1
E 1 0 0 1
E 0 1 0 1
E 1 1 0 1
E 1 0 1 1
0 1 1 1
1 1 1 1
Transmit ter Code
Parity S t a r t I Program Istop
1 2 3 4 5 1 I - - - - - I I
0 l o o o o l ~ l l I
0 ~ 1 0 0 0 1 ~ 1 1
0 ~ 0 1 0 0 1 1 1 1 I
0 , 1 1 0 0 1 ; 1 1
0 1 0 0 1 0 1 1 1 1 I
0 ' 1 0 1 0 1 1 1 I
0 ' 0 1 1 0 1 ~ 1 1 I
0 ' 1 1 1 0 1 , 1 1 1
0 , 0 0 0 1 1 1 1 1
0 ~ 1 0 0 1 1 ; 1 1
0 ' 0 1 0 1 1 1 1 1 I
0 l l l o l l ~ l l I
0 ~ 1 0 1 1 1 ( 1 1 1
0 ' O l l l l , l l I
0 , 1 1 1 1 1 ; 1 1
Receiver Code
P a r i t y , S t a r t I Program l Stop
1 1 2 3 4 5 1 I - - - - - 1
0 ~ 1 1 1 1 0 ~ 1 1 I
0 1 0 0 1 1 0 , l l
0 l l o o l o ~ l l I I
0 1 0 1 0 1 0 , 1 1
0 ~ l l o o o l l l 0 1 0 0 0 0 0 ~ 1 1
I I 0 ( 1 0 1 0 0 ( 1 1
0 1 0 1 1 0 0 ~ 1 1
0 ' 1 1 1 0 1 I 1 1 I
0 l o o l o l ~ l l 0 ~ 1 0 0 0 1 , 1 1
0 ~ o l o o l l l l 1
0 1 0 0 0 1 1 ( 1 1 I
0 ~ 1 0 1 1 1 ~ 1 1
0 l 0 1 1 1 1 ~ 1 1 -
Receiver S . Id, if
79492-
0 1
0 5
0 2
0 4
0 3
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resonance. This may b e s t be observed by monitor ing t h e c u r r e n t wave-
form dur ing t h e t un ing procedure w i t h a p o r t a b l e b a t t e r y opera ted 0s-
c i l l o s c o p e . Connect t h e scope ground t o t e rmina l 2 of 52 and t h e probe
a few inches away from t e rmina l 2, toward t h e loop. This loop connec t ion
w i l l f u n c t i o n a s a c u r r e n t shun t and prov ides a convenient method of
observ ing antenna c u r r e n t . The loop may be tuned by f i r s t swi tch ing
t h e t r a n s m i t t e r t o t h e l o c a l mode. The c u r r e n t waveform is then ob-
se rved wh i l e t h e antenna tun ing swi tches a r e opera ted u n t i l t h e c u r r e n t
sw i t ch ing t r a n s i t i o n s occur a t t h e zero c ro s s ing of t h e c u r r e n t waveform.
The c u r r e n t swi tch ing t r a n s i t i o n s w i l l be v i s i b l e a s d i s t i n c t , f a s t
r i s i n g o r f a l l i n g s t e p s and should be a d j u s t e d t o co inc ide w i th t h e
o s c i l l o s c o p e ' s b a s e l i n e . The swi t ch bank i s designed t o accommodate
an an tenna induc tance between 75 and 300 ph.
b . Nomenclature
The t r a n s m i t t e r schematic is shown i n F igure 12 . A l l components a r e
mounted t o a w i r e wrapped board assembly w i t h t h e excep t ion of t h e
connectors J1, 52 and t h e b a t t e r y . I n t e g r a t e d c i r c u i t s are i d e n t i f i e d
by a U followed by a one o r two d i g i t number. Wire wrap socke t s a r e
i d e n t i f i e d a t t h e top of t h e socke t wi th t h e i r a p p r o p r i a t e U de s igna t i on .
Most d i s c r e t e components a r e mounted on d i p headers which a r e des igna ted
w i th a Z followed by a s i n g l e d i g i t number. The power ou tpu t t r a n s i s t o r s
a r e mounted t o a rear p l a t e b u t a r e wi red d i r e c t l y t o t h e ca rd assembly.
The swi t ch pane l is wi red d i r e c t l y t o t h e ca rd and con t a in s a l l swi tches
i n d i c a t e d on t h e schematic w i t h t h e except ion of t h e Transmit Cycles
swi tch which is plugged i n t o a d i p socke t , d i r e c t l y on t h e card .
c. Power Supply
During remote ope ra t i on , 12 vdc is a v a i l a b l e con t inuous ly a t J 1 - H (VB)
from a v i s u a l d i s p l a y system, Figure21J4-H (VB).t A s t h e d i sp l ay powers
up i n response t o d. c. a p p l i e d t o t h e pager phone l i n e , VS swings p o s i t i v e
and t h e 2N3904 swi tches on. The 2N6109 conducts and a p p l i e s 11 .5 v o l t s
t o VDD, t h e l o g i c supply. S ince t h e c u r r e n t d r a i n i s less than 20 m a ,
t h e v i s u a l page r ' s b a t t e r y is n o t exces s ive ly loaded.
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The 2.2 uf capac i to r (22) i s i n i t i a l l y discharged and U9B p i n 4, the
master r e s e t l i n e , is high. The Schmidt t r i g g e r formed by U4C and U9B
c r e a t e s a power up r e s e t pulse about 50 Ins long. U9 p i n 4 switches low
a t t he end of t h i s period, r e s e t t i n g U5, U7 and U8.
d. Visual Pager I n t e r f a c e
The v i s u a l pager i n t e r f a c e clocks da ta from Figure 21, J 4 t appearing on J1
connector p i n s B C D l t o BCD8 i n t o a s t o r a g e r e g i s t e r (U5) fol lowing a v a l i d
pos t code. Gates U2B and U4A monitor t h e ,4 b i t bus f o r a pos t command
(0011). I f a pos t word is de tec ted , t h e D i npu t t o D-flop U3A goes high
and t h e fol lowing s t r o b e pulse on J1-E c:Locks U3A. A s t h e Q output of
U3A switches s t a t e , t h e s e t i npu t of U3B goes high, s e t t i n g t h e Q output
of U3B.
The r e s e t input of U3B a l s o remains h igh u n t i l jam input counter U7 is
p rese t . I f a second s t r o b e does not fo1:Low the i n i t i a l pos t s t r o b e ,
then U3B w i l l r e s e t when U3A is r e s e t . 'fiis occurs when the v i s u a l pager
r e t u r n s t o i t s power down quiescent mode. However, i f a second s t r o b e
pu l se occurs while a pos t command is s t o r e d i n U3A, then counter U7 is
p r e s e t and U3B remains s e t . The Q output remains high and sources suf-
f i c i e n t base cu r ren t to t h e 2N3904 t o keep t h i s t r a n s i s t o r conducting.
Based on t h e previous d iscuss ion , i t s h o i ~ l d be c l e a r t h a t the t r a n s m i t t e r
remains powered up even though a v i s u a l d i sp lay has s h u t down, provided
the t r a n s m i t t e r rece ives a pos t command :followed by a second d a t a s t robe .
Post f l o p U3A enables the inpu t t o quad l a t c h U5, permi t t ing the second
d a t a s t r o b e t o clock d a t a p resen t on the bus i n t o U5.
e . Transmit ter Logic
I f S1A is switched t o the remote positioin, d a t a present a t the output
te rminals of t h e quad l a t c h (U5) is passed through the 2 channel multi-
p l exe r U6 t o the Z output bus. The mu1t:iplexer 's p a r a l l e l output is
terminated a t t he Universal Asynchronous ~ e c e i v e r / ~ r a n s m i t t e r (UART)
t r a n s m i t t e r i npu t s TBR1-4. The UART p in assignments and a b r i e f des-
c r i p t i o n of t h e func t ion of each p i n is :included i n Table 2 .
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I
PIN SYMBOL DESCRIPTION
1 VCC *5 volts Supply 2 IM6402-N C No Convectton
1M6403-Control 4 11 Stage Divider ~ ~ g h 4 Stage LOH 1 1 Stage
3 GND Ground 4 RRD A Htgh level on RECEIVER REGISTER
DISABLE torces the recelver ho ld ing reg~ster outputs RBRI-RBRB to a high cmpeda~ce state
5 R BRB The cooteots of the RECEIVER BUFFER REGISTER appear on these three-state outputs Word formats less than8 charac- ters are rtght justified to RBR1
6 RBR7 See Pin 5 - RBRB 7 RBR6 See Pln 5 - RBRB
RBR5 See Pin 5 - RBR8 See Pin 5 - RBRB See Pln 5 - RBRB See Pln 5 - RBR8
RBR1 See Pln 5 - RBRB
PIN SYMBOL DESCRIPTION I
2 1 MR A high lekel on MASTER RESET clears PE FE. OE andDR toa low levelandsets the t r a n s ~ ~ t t e r output to a high level
2 2 TBRE A htgh level on TRANSMITTER BUFFER REGISTER EMPTY indicates the trans- m~tter butter reglster has transferred its data to rne transmltter reglster and IS ready for new data
2 3 TBRL A low level on TRANSMITTER BUFFER REGISTER LOAD transfers data f rom Inputs TBR1-TBR8 rnto the transm~tter buffer reglster A low to hlgh transltton on TBRL indicates data transfer to the trans- mltter register If the transmltter register is busy. transfer is automat~cally delayed SO that the two characters are transmitted end to end
2 4 TRE A h ~ g h l e v e l o n T R A N S M I T T E R 6 REGISTER EMPTY ~nd~cates completed
transrntsston of a character lnc lud~ng StOPt3ltS
2 5 TRO Character data, start data and stop blts appear serlelly at the TRANSMITTER REGISTER OUTPUT
26 TBRI-TBR8 C h a r a c t e r d a t a IS l o a d e d i n t o t h e TRANSMITTER BUFFER REGISTER vla Inputs TBR1 -TBR8 For character formats less than 8 blts the TBRB. 7. and 6 Inputs a r e i g n o r e d corresponding t o t h e programmed word length
1
PIN SYMBOL OESCRIPT ION
13 PE A hlgh level on PARITY ERROR ~nd~cates rece~ved partly does not match parity pro- grammed by control bits When part!^ IS inhibited this output 15 low
14 F E A h lgh level o n FRAMING ERROR Indicates the flrst stop bit was invalid
15 OE A h igh level on OVERRUN ERROR rndicates the data received flag was not
B cleared before the last character was \transferred to the recetver buffer reglster
16 SFD A high level on STATUS FLAGS DISABLE forces the outputs PE FE OE. DR TBRE to a h ~ g h tmpedance state
17 IM6402-RRC The RECEIVER REGISTER CLOCK IS
IM6403-OSCIN 16% the receiver data rate 18 DRR A low level on DATA RECEIVED RESE:
clears the data recelved outputDR. to a low level
19 OR A h ~ g h l e v e l o n D A T A RECEIVED lnd~cates a character has been rece~vea and transferred to the recetver buffer regrster
20 RRI Serlal data o n RECEIVER REGISTER INPUT IS c locked in to the receiver register
L
PIN SYMBOL DESCRIPTION
2 7 TBR2 See Pin 26 - TBRl 2 8 TBR3 See Pln 26 - TBRl 2 9 TBR4 See Pln 26 - TBRl 30 TBRS See Pin 26 - TBRl 3 1 TBR6 See Pin 26 - TBRl 3 2 TBR7 See Ptn 26 - TBRl 3 3 TBRB See Pin 26 - TBR 1 3 4 CRL A high level on CONTROL REGlSTEc
LOAD loads the control reg~ster 3 5 PI A high level on PARITY INHIBIT ~ n h t b ~ t s
parity generation. partty checking aqa forces PE output low
36 SBS A high level onSTOP BIT SELECT se1ec:s 1 5 stop blts for 5 character torrnat and 2 stop b ~ t s for other lengths
3 7 CLS2 These Inputs program the CHAR ACT E R LENGTH SELECTED (CLS1 IOH CLSi low 5 bits) (CLS1 high CLS2 loth 6 bits1 (CLS1 low CLS2 high 7 bits) (CLS1 high CLS2 high 8 bits)
38 CLSl See Pln 37 - CLS2 39 EPE When PI is low a htgh level on E V E h
PARITY ENABLE generates anc cheers even parity A low level Selects @ad pa..:?
40 tM6402-TRC The TRANSMITTER REGISTER CLOCK IM6403-OSCOUT IS 16X the trensrntt data rate
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When jam inpu t down counter U7 is p r e s e t by a d a t a s t r o b e , t h e "0" output ,
p i n 12, swi tches low, r e l e a s i n g t h e r e s e t from b f l o p UlOA. The next
low t o high 3KHZ c lock t r a n s i t i o n s e t s t h e Q output of UlOA. The Q
t r a n s i t i o n causes t h e UART t o load i t s t r a n s m i t t e r b u f f e r r e g i s t e r
from p a r a l l e l i npu t s TBR1-5. Two c lock cyc le s l a t e r , t h e UART begins
s e r i a l l y t r a n s m i t t i n g t h e d a t a , inc luding s t a r t , s t o p and p a r i t y b i t s
a t TRO (p in 25). The e i g h t b i t word begins wi th a l o g i c low ( s t a r t
b i t ) and always ends wi th a l o g i c high,, two b i t s long , c h a r a c t e r i s t i c
of t he p a r i t y and s t o p b i t s .
The t r a n s m i t t e r f l a g s t h e end of a trarlsmission by r a i s i n g TRE (p in 24)
h igh . This ou tput i s simply inve r t ed and passed on t o t he Receiver
Ready Input (RRI, p i n 20). The r e c e i v e r s e c t i o n of t h e UART is used
t o gene ra t e a one word delay be fo re t h e next t ransmission. This de lay
al lows r e c e i v e r s t o resynchronize i f th~ey pass through a dead spo t o r
a r e l oca t ed i n a low s i g n a l l e v e l a r e a . A t t h e end of a r ece ive cyc l e ,
d a t a ready output (DR, p in 19) swi tches h igh and counter U7 is clocked.
D-flop U l O A c locks TBRL (p in 23) and t h e t r ansmi t cyc l e is repea ted
u n t i l U7 is f i n a l l y clocked t o zero. The a c t u a l number of cyc l e s
i t e r a t e d is s e t by Transmit Cycles swi tch S2 and may be s e t from one t o
n ine .
f . Modulator
A 3kHz c lock (3086.42Hz) i s generated by count ing down from 1 MHz c r y s t a l
o s c i l l a t o r t h a t i s a l s o used a s t h e master c lock f o r t h e UART. Pro-
grammable b ina ry counters U 1 1 and U12 d i v i d e t h e 1 MHz clock by 162 and
U13A d i v i d e s 617.84 Hz by two t o genera te t h e 3086 Hz c a r r i e r frequency.
D-flop U13B and ~ n d / ~ r ga t e U14 toge the r form the phase s h i f t keyed
modulator. Two phases of the c lock , 180' o u t of phase a r e p re sen t a t
t he Q and ? ou tpu t s of U13A. E i t h e r the Q and ?j c locks a r e s e l e c t e d
by t h e complex g a t e and appear a t ZA o r ZB a s a func t ion of t h e s t a t e
of U13B. This D-f l op c locks t h e s e r i a l d a t a appearing a t TRO synchronously
wi th the 3kHz c lock and t h e r e f o r e c o n t r o l s t h e phase of t he c lock gated
t o U14 ou tpu t s ZA and ZB.
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g. Transmi t te r Power Output S t;age
Complex g a t e U14 is d i s ab l ed u n t i l a p o s t command is s t robed i n t o D-flop
U3A and U3B i s s e t . While U14 is disablled, ou tpu t s ZA and ZB a r e low
and both MPSAO5 d r i v e r t r a n s i s t o r s remain o f f , conserv ing power u n t i l
a p o s t command i s de t ec t ed . When U14 i.s enabled , t h e t r a n s m i t t e r is
keyed a s b u f f e r U15 A and D r e c e i v e t h e c a r r i e r 180" o u t of phase w i th
r e s p e c t t o each o t h e r . P a r a l l e l connected i n v e r t e r s U15 B-F provide
adequate c u r r e n t ga in t o d r i v e t h e two MPS-A05 swi t ch ing t r a n s i s t o r s .
Transformer T 1 p rov ides c u r r e n t ga in and l e v e l t r a n s l a t i o n t o t h e
complementary ou tpu t s t a g e . The t rans former a l s o minimizes power con-
sumption du r ing t h e qu i e scen t power o f f mode. The c o l l e c t o r c u r r e n t
of t h e d r i v e r t r a n s i s t o r s i s approximately 200ma and t h e base c u r r e n t
t o t h e complementary p a i r is one ampere. The d r i v e r and ou tpu t s t a g e s
a r e bo th sourced from the i n t e r n a l 12-vol t b a t t e r y . The c o l l e c t o r s
o f t h e complementary p a i r d r i v e a sw i t chab l e s e t of po ly s ty r ene capa-
c i t o r s t o se>ries tune t h e loop an tenna as descr ibed earlier i n t h e
i n t r o d u c t i o n . The t r a n s m i t t e r ' s ou tpu t may be open o r s h o r t c i r c u i t e d
w i thou t a danger of de s t roy ing componerlts i n t h e ou tpu t s t a g e . The
o u t p u t t r a n s i s t o r s w i l l d i s s i p a t e about 10 w a t t s each when t h e ou tpu t
is s h o r t e d , however, they a r e mounted t o t h e r e a r p l a t e t o main ta in an
adequate j unc t i on temperature s a f e t y margin, even i f t h e ambient tempera-
t u r e reaches 60°C.
h . Local Operat ion
The t r a n s m i t t e r w i l l r e p e a t t h e code programmed by t h e Code S e l e c t
Switches e n d l e s s l y i f ~ e m / ~ o c a l Switch S1 i s p laced i n t h e l o c a l posi-
t i o n . I n t h i s mode, S1A d i s a b l e s t h e c y c l e coun te r U7, SIB bypasses
t h e power up c i r c u i t and SIC permi t s t h e f i f t h d a t a b i t t o be s e l e c t e d .
S1A a l s o swi tches t h e mu l t i p l exe r t o s e l e c t d a t a from t h e code s e l e c t
swi tches .
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2. C a l l A l e r t Receiver
a . I n t roduc t ion
The c a l l a l e r t r e c e i v e r i s a 3 kHz phase s h i f t keying (PSK) r e c e i v e r
of t h e tuned r a d i o frequency (TW) type. The r e c e i v e r is preprogramed
wi th a s e t of i n t e r n a l swi tches t o respond t o i t s unique 5 b i t d i g i t a l
code by a c t i v a t i n g an a u r a l and v i s u a l a l e r t . Contained w i t h i n t h e
r e c e i v e r housing a r e t h e rechargeable n i c k e l cadmium b a t t e r i e s and t h e
f e r r i t e loop antenna. The u n i t is designed f o r b e l t o r pocket mounting
on t h e person and no e x t e r n a l connect ions a r e r equ i r ed f o r normal use.
Recharging is accomplished by two e x t e r n a l b a t t e r y te rmina ls l oca t ed on
the bottom of t h e u n i t and a r e c u r r e n t l im i t ed f o r i n t r i n s i c s a f e t y
a g a i n s t s h o r t i n g .
b . Nomenclature
The r e c e i v e r schematic diagram is a t t ached a s F igure 13. The cons t ruc t ion
of t h e u n i t is such t h a t t h e components a.re spread between two double
s ided p r i n t e d c i r c u i t boards and t h e ca se . Components mounted t o t h e
c a s e a r e s u f f i x e d wi th d i g i t s 1 t o 99 (e .g . C12), components mounted t o
PC Board ill a r e s u f f i x e d wi th d i g i t s 100 t o 199 (e .g . R104), components
mounted t o PC Board #2 a r e su f f ixed wi th d i g i t s 200 t o 299(e.g. 4204).
Figure 14 d e p i c t s t he o v e r a l l assembly of the r e c e i v e r , i nc lud ing place-
ment of t h e b a t t e r y s t r i n g s . P r i n t e d c i r c u i t ca rd assembly, f a b r i c a t i o n
and ar twork drawings a r e included i n F igures 15 through 1 7 f o r board
number one and F igures 18 through 20 f o r board number two.
c . Power Supply
A l l c i r c u i t s i n t h e r e c e i v e r a r e opera ted from 5 vdc. This vo l t age i s
suppl ied from BT1 and BT2 a s fol lows: BT1 feeds a l l c i r c u i t s except
t h e LED v i s u a l a l e r t , CR3. CR3 is suppl ied from BT2. This arrangement
w a s chosen t o op t imize t h e b a t t e r y form f a c t o r f o r t h e ca se used;
however, i t does o f f e r t h e advantage that: i f t h e LED is l e f t on and
BT2 is permi t ted t o run down t h e r e c e i v e r w i l l s t i l l func t ion w i t h t h e
a u r a l a l e r t .
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T
rfP : v 3
L - J l?Y
t
- r--- --I
T - 7
, - - - - - - La,
\ /
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Switch SWlOO removes a l l power (both b a t t e r i e s ) from t h e c i r c u i t when
opera ted b u t does n o t b reak t h e c i r c u i t t o t h e charg ing con t ac t s .
Charging i s accomplished by means of an e x t e r n a l charger which a p p l i e s
12 Vdc t o t h e charg ing c o n t a c t s . The i n t e r n a l c u r r e n t l i m i t i n g r e s i s t o r s
R l and R2 approximate a 10 mA c o n s t a n t c u r r e n t sou rce cha rge r f o r t h e
b a t t e r i e s . The b a t t e r i e s a r e r a t e d t o wi ths tand t h i s charge r a t e in-
d e f i n i t e l y and should be f u l l y recharged a f t e r 16 hours .
d . Receiver Front End
The r e c e i v e r f r o n t end c o n s i s t s of i n t e g r a t e d c i r c u i t s U101, A & C and
U102. This s e c t i o n of t h e r e c e i v e r acc'epts t h e i n p u t s i g n a l from t h e
an tenna , a m p l i f i e s and f i l t e r s i t be fo re apply ing i t t o t h e demodu-
l a t o r .
The antenna assembly i s a h igh Q (about 30) p a r a l l e l resonant LC c i r c u i t .
The e x a c t resonant f requency is trimmed w i t h t h e " s e l e c t a t test" capa-
c i t o r C107. U l O l i s b i a sed w i th Rl21 a t 5 PA and under t h e s e cond i t i ons
t h e loop antenna a m p l i f i e r , U l O l A , runs w i th a n open loop g a i n of about
60 dB. The DC qu i e scen t b i a s p o i n t f o r U l O l A & B , and a l l of U102 is
set a t about h a l f supply by R120 and Rl21. Th i s b i a s p o i n t i s decoupled
w i th C115 t o ground. The ou tpu t of U l O l A is coupled by DC b lock ing
c a p a c i t o r C109 t o t h e a c t i v e bandpass f i l t e r c i r c u i t of U102.
The a c t i v e bandpass f i l t e r is a t h r e e a m p l i f i e r s tate v a r i a b l e f i l t e r
u s ing a l l t h r e e s e c t i o n s of U102. The state v a r i a b l e f i l t e r was chosen
t o p rov ide a Q of 30 wh i l e minimizing t h e s e n s i t i v i t y t o component
v a r i a t i o n s over frequency and t o l e r ance . The c e n t e r frequency of t h e
f i l t e r is trimmed by t h e " s e l e c t a t t e s t " r e s i s t o r Rl14. The midband
g a i n of t h e a c t i v e f i l t e r is l i m i t e d by t h e d i v i d e r i n p u t r e s i s t o r Rl13
s o t h a t t h e a c t i v e f i l t e r remains i n t h e l i n e a r r eg ion even when U l O l A
i s d r i v e n i n t o f u l l c l i p . This approach i n s u r e s t h a t n o i s e and s t r o n g
s i g n a l s a r e c o n t r o l l e d i n t h e amount of energy t h a t can be coupled i n
t o t h e demodulator which reduces t h e p r o b a b i l i t y of f a l s i n g on
ex t raneous s i g n a l s .
The ou tpu t of t h e a c t i v e f i l t e r i s bu f f e r ed w i t h a s i n g l e a m p l i f i e r
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s e c t i o n c o n s i s t i n g of U102C w i t h a nominal ga in of 20 dB. The ou tpu t
of U l O l B i s coupled t o t h e demodulator through C102.
e. Demodulator
The demodulator c i r c u i t c o n s i s t s of U100, U l O l B and U103A. This c i r c u i t
f unc t i ons by demodulating t h e c a r r i e r PSK phase t r a n s i t i o n s i n t o 5 Vdc
c o n t r o l l e d p u l s e width l o g i c l e v e l t r a n s i t i o n s .
U l O O i s a phase locked loop i n t e g r a t e d c i r c u i t . The v o l t a g e c o n t r o l l e d
o s c i l l a t o r (VCO) i s nominally tuned t o t h e 3 kHz c a r r i e r frequency by
C l O l and Rl02. This frequency i s trimmed a t t e s t by s e l e c t i n g Rl03.
R104 i n s u r e s t h e o s c i l l a t o r s t a r t i n g under wors t c a se b a t t e r y cond i t i ons .
The loop i s locked through a p ropo r t i ona l p l u s i n t e g r a l c o n t r o l loop
f i l t e r c o n s i s t i n g of Rl00, Rl01, and C100. The f i l t e r is s e l e c t e d s o
t h a t t h e minimum bandwidth c o n s i s t e n t ?with t h e 30 b i t p e r second s ig -
n a l l i n g r a t e is used. The va lues were s e l e c t e d emp i r i ca l l y t o s e t
in tersymbol i n t e r f e r e n c e t o ze ro a t thle maximum 30 baud s i g n a l l i n g r a t e .
The f i l t e r damping was s e t t o a t l e a s t one c y c l e of r i n g i n g t o i n s u r e
t h a t both a p o s i t i v e and nega t i ve going t r a n s i t i o n a r e a v a i l a b l e re-
g a r d l e s s of t h e d i r e c t i o n of phase change. The phase d e t e c t o r ou tpu t
is bu f f e r ed i n t e r n a l l y i n U l O O and is supp l i ed t o t he audio ou tpu t
p i n 10.
The phase locked loop ou tpu t d i v i d e s a t p i n 10 i n t o two s e p a r a t e pa th s
i n t o t h e comparator, U l O l B . The f i r s t pa th through R106 i s f i l t e r e d
by C103 t o remove t h e 3 kHz c a r r i e r . 'The o t h e r pa th through R105 t o
C104, p rov ides a l onge r i n t e g r a t i o n i n t e r v a l compared t o R106 and
C103. So t h e average DC l e v e l of t h e phase locked loop appears a t
p i n 6 of U101. When a phase t r a n s i t i o n occurs i n t h e phase locked
loop , t h e comparator U l O l t r a n s l a t e s t h e 50 mV loop ou tpu t i n t o a
5 VDC pu l s e . The comparator ou tpu t a t p i n 9 of U l O l is f u r t h e r f i l t e r e d
t o reduce t h e 3 kHz c a r r i e r by R l l l and C l l O and app l i ed t o t h e mon-
s t a b l e U103A.
The nega t i ve going t r a n s i t i o n appearinrg a t p i n 5 of U103A t r i g g e r s t h e
monostable. The t iming i n t e r v a l is se,t by t h e RC product of R112 and
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C 1 1 1 . The t iming i s ad ju s t ed t o be eqiual t o one nominal b i t i n t e r v a l
a t t h e 30 baud r a t e . The monostable irs f u r t h e r configured t o be re-
t r i g g e r a b l e t o any phase changes t h a t occur i n t h e c a r r i e r be fo re i t
r e s e t s . I n t h e qu i e scen t s t a t e t he mo~nostable ou tpu t a t p i n 7 of
U103A is high.
f . Decoder
The decoder c i r c u i t c o n s i s t s of U201, 'U200, U203, U202, and U103B. The
decoder func t i ons by accep t ing t h e s e r i a l b i t s t ream from t h e demodulator
and prov ides an a la rm s i g n a l t o t h e i n t e r f a c e c i r c u i t r y i f t h e rece ived
code sequence matches t h e preprogrammed pager code.
The fo l lowing convent ions w i l l be assu~med f o r coding: A phase t r a n s i t i o n
i n t h e t r ansmi t t ed s i g n a l causes a "0" t o be i n p u t t o t h e decoder, no
t r a n s i t i o n causes a "1" t o be i npu t . 'The b i t i n t e r v a l s a r e equa l l y
spaced f o r a l l b i t s . The code format l cons i s t s of a s i n g l e s t a r t b i t of
a "0" fol lcwed by t h e f i v e d a t a b i t s , followed by a s i n g l e p a r i t y b i t ,
ended by a s i n g l e s t o p b i t of a "1". 'The code is en t e r ed i n t o t h e pager
us ing SW200 where a sw i t ch c l o s u r e i s (a "1" and a n open is a "0". The
code w i l l be s t a t e d a s b i t p o s i t i o n 1 through 5 a s noted on U200 from
l e f t t o r i g h t .
For a d d i t i o n a l r e f e r ence , a l i s t i n g of t he p i n s and func t i ons of U201
is i n d i c a t e d i n Table 2.
The s e r i a l b i t s t ream from p i n 7 of U1103 is i n p u t t o t he Universa l
Asynchronous Receiver Transmi t te r (UAR'T) U201 i n t o t h e r e c e i v e r i n p u t ,
p i n 20. The UART t iming is c o n t r o l l e d by q u a r t z c r y s t a l Y200 and t he
d i v i d e r s t r a p p i n g on p i n 2 of U201. Tlhe UART s e p a r a t e s t h e s e r i a l b i t
s t ream i n t o t h e f i v e p a r a l l e l code b i t s and makes them a v a i l a b l e on
p i n s 12 through 8 a s noted on t h e sche~matic. I n a d d i t i o n , p a r i t y and
framing e r r o r o u t p u t s a r e made a v a i l a b l e on p in s 12 and 14 r e s p e c t i v e l y .
A d a t a ready s t r o b e i s provided on p i n 19 which is r e s e t by i npu t t o
p i n 18. The r e c e i v e r ou tpu t s a r e n o t r e s e t by p i n 18, only t h e s t r o b e
is r e s e t , s o t h e d a t a and t h e e r r o r ou tpu t s remain l a t c h e d u n t i l t h e
n e x t code sequence of 8 b i t s i s rece ived ( s t a r t , 5 code, one p a r i t y ,
one s t o p ) .
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The f i v e p a r a l l e l code b i t s a r e rou ted through t h e c i r c u i t r y about U200.
This I C and t h e code s e l e c t Switch U200 permit s e l e c t e d code b i t s t o be
i nve r t ed . The programming i s such t h a t t h e c o r r e c t code w i l l produce
a l l "1"s a t t he t r a n s m i t t e r i n p u t t o t h e UART, p i n s 26 through 30.
The converted code p ins from SW200 a r e loaded i n t o t he t r a n s m i t t e r s e c t i o n
of U201 by t h e d a t a ready s t r o b e from p i n 19 t o t h e load i n p u t p in 23.
When t h e code sequence has been s e r i a l l y clocked o u t of t he t r a n s m i t t e r
a t p i n 25, t he empty output of t h e t ransimit ter a t p i n 24 provides a
r e c e i v e r d a t a s t r o b e c l e a r i n t o U201 p i n 18.
The remainder of t h e l o g i c func t ions a s fol lows: The i n i t i a l "0" s t a r t
b i t from the p i n 25 t r a n s m i t t e r ou tput of U201 is ignored by t h e U202
f l i p f l o p because of t h e pu l se de lay ou tpu t from t h e b u f f e r r e g i s t e r
empty output p i n 22 of U201. I f t h e remainder of t h e o the r code and
p a r i t y pu l se s ou tpu t from p i n - 2 5 have no high t o low t r a n s i t i o n s U202
w i l l be clocked on through p i n 11 and ou tpu t s t o t h e alarm i n t e r f a c e
w i l l be provided. Addi t iona l ga t i ng from t h e number one b i t p o s i t i o n
a t p i n 5 of SW200 is provided i n t o p i n 9 of U203 t o i n s u r e t h a t t h e
decoding only occurs i f a l l t h e code outputs a t SW200 a r e high ( i . e . no
low t o h igh t r a n s i t i o n s p l u s number one b i t high means a l l a r e h igh
s i n c e t he l a s t s t o p b i t is always h igh ) . Decoding w i l l be i n h i b i t e d
by a framing o r p a r i t y e r r o r on p ins 1 3 o r 14 of U201.
A c o r r e c t decoding sequence causes t h e "0" f l i p f l o p U202 t o l a t c h wi th
p i n 1 3 h igh and p i n 12 low. The p i n 12 output is routed t o t h e LED
d r i v e r Q200 and t u r n s on t h e LED. The p i n 1 3 output t r i g g e r s U103B
f o r an approximate 1 second i n t e r v a l determined by C116 and R123. The
output of U103B a t p i n 9 feeds t h e a u r a l a larm through t h e d r i v e r
t r a n s i s t o r 4100.
The alarm w i l l sound only once and t h e LED w i l l remain l a t ched on u n t i l
U202 is r e s e t by SW100C.
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111. MANUFACTURING COST ESTIMATE
The c o s t es t imates f o r t h e ind iv idua l assemblies t h a t comprise t h e c a l l
a l e r t system a r e a t t ached a s Appendix I and a r e based on our prototype
design. S p e c i f i c f e a t u r e s of t h e prototype w i l l no t necessa r i ly f i n d
t h e i r way i n t o a production system, p a r t i c u l a r l y i n view of t h e t e s t
funct ions b u i l t i n t o t h e t r ansmi t t e r .
The c o s t es t imates i n Appendix I a r e based on t h e fol lowing assumptions:
The c a l l a l e r t r e c e i v e r w i l l be manufactured i n l o t s of
one hundred u n i t s .
The c a l l a l e r t t r a n s m i t t e r w i l l be manufactured i n l o t s
of t e n u n i t s .
This is f a c t o r y c o s t ; t h a t is , t h e c o s t of ma te r i a l s
and d i r e c t l abor only. The l abor c o s t s inc lude overhead
f o r f ac to ry space and s u p e r ~ i ~ s i o n . We assumed an average
of $12 pe r hour f o r a l l types of d i r e c t labor .
a These p r i c e s do no t i nc lude t h e c o s t of development,
s a l e s o r adminis t ra t ion . For a low-volume, job-shop
type of manufacturing s i t u a t i o n , which t h i s i s , t h e
f ac to ry cos t would be marked up 200-300 percent t o ge t
t h e sel l , o r l ist p r i ce .
a The c o s t of production engineering and documentation
is no t r e f l e c t e d i n these p r i ces . Complete p a r t s lists
and f a b r i c a t i o n drawings a s w e l l a s t h e design of a
p r i n t e d c i r c u i t board f o r t h e c a l l a l e r t t r a n s m i t t e r
w i l l b e requi red be fo re a production run of any s i z e
could be s t a r t e d .
B. CALL ALERT RECEIVER
Although p r i n t e d c i r c u i t boards were used i n t h e pro to type design of
t h i s u n i t and t h e i r c o s t savings a r e r e f l e c t e d i n t h e c o s t es t imates
i n Appendix I, f u r t h e r c o s t reduct ions a r e poss ib l e by t h e e l iminat ion
of custom f a b r i c a t e d p a r t s . For in s t ance , i f t h e ex tens ive ly modified
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commercial enclosure is replaced by a custom designed i n j e c t i o n molded
enclosure, and t h e purchased c l i p assembly i s replaced by a custom
designed aluminum d i e cas t ing , then a l l t h e cos t s f o r f ab r i ca t ed p a r t s
would b e el iminated. This would reduce t h e f ac to ry c o s t from approxi-
mately $167 t o $125. I f t h e antenna is produced on a semiautomatic
c o i l winder i n s t e a d of a labora tory type c o i l winder, then t h e f ac to ry
cos t would b e reduced another $9. These cons t ruc t ion and labor savings
should be i n s t i t u t e d be fo re a s i g n i f i c a n t production volume is s t a r t e d .
C. CALL ALERT TRANSMITTER
The t r a n s m i t t e r w i l l never be manufactured i n a s h igh a volume a s t h e
r ece ive r , bu t i t w i l l s t i l l be cos t e f f e c t i v e t o change from w i r e
wrap cons t ruc t ion t o p r i n t e d c i r c u i t wir ing. This would e l imina te the
cos t of I . C . sockets and component c a r r i e r s as w e l l a s t h e l abor c o s t s
f o r w i r e wrapping. The t r ansmi t t e r manufacturing cos t would change from
approximately $594 t o $330.
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APPENDIX I
COST ESTIMATES
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APPENDIX I1 -
PARTS LIST -
Arthur D Little, lnc.
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APPENDIX I I [ I
V I S U A L PAGER DILAGRAM
Arthur D Little Inc.
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FIGURE 21 I
5 6 a u I +