two wire stepper motor positioner

8/9/2019 Two Wire Stepper Motor Positioner

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GLOLABTwo Wire Stepper Motor Positioner

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Introduction______________

A simple and inexpensive way to remotelyrotate a display or object is with a positionerthat uses a stepper motor to rotate it. Themotor is driven by a circuit mounted nearthe motor and by a control circuit at aremote location. Power for the motor and itsdriver circuit and for the signals that controlthe speed and direction of the motor are allcarried over a single two conductor cable.This is a device that will remotely positionan object on command to any desiredrotation at an adjustable speed in smallsteps. The object can then be left in thatposition until a different rotation is desiredor it may be continuously rotated in steps.

How it works_____________

MotorsAlmost any two phase (sometimes calledfour phase) unipolar stepper motor with avoltage rating of from 9 to 24 volts and a

current rating of 900 milliamps or less maybe used. A unipolar motor has two centertapped windings with six leads and has itsvoltage and either its current or resistancemarked on the nameplate. Another motorcharacteristic is its stepping angle which isalso marked on the nameplate. An angle of1.8 degrees or less is preferred becauseeach step is smaller but 7.5 degrees or evenmore can be used. Although many surplusmotors come without a wiring diagram, youcan easily find the correct connections withan ohmmeter. Figure 1 is a diagram of atypical stepper motor. The windingresistance will be a few hundred ohms orless. To find the center tap first measurebetween any two leads. If you measure anopen circuit try again until you get a readingand then record its value. Number theseleads 1 and 2. Connect the meter to lead 1and a lead other than 2 until you get anotherreading and then number it 3. If this value isthe same as the 1-2 value then lead number

1 is the center tap. If it is twice the 1-2 valuethen lead number 2 is the center tap. Makea note of which lead is the center tap as thislead will be connected to the +V power.Repeat the above procedure for theremaining leads numbering them 4, 5 and 6to find the center tap of the second winding.The motor voltage is not very critical. Alower than rated voltage may be used with aresulting lower torque. You should expectyour stepper motors to run very warm oreven hot because power is applied to twowindings at all times. You may have seenspecifications or applications that use aresistor in series with the center tap of eachwinding. Their purpose is to maintain amore constant torque at high speeds andare not necessary for low speed operation.When resistors are used, a higher thanrated voltage is applied and the excessvoltage is dropped across the resistor. Athigh speed as the motor impedanceincreases more voltage drops across themotor and less across the resistor tomaintain a more constant torque. A constant

current driver circuit would do the samething.

Control circuitFigure 2 is a diagram of the control circuitbuilt on a 1.45 X 1.8 inch PC board. IC1 isan LMC555 CMOS timer that generates a200 microsecond wide clock pulses to stepthe motor and control its speed. The speedcan be varied by changing the pulserepetition rate with R1. The negative goingclock pulses at pin 3 of IC1 drive the gateof Q1, an IRL530N power FET thatmomentarily turns OFF and disconnects thedriver board from ground. These powerinterruption sends pulses to the motor drivercircuits that cause the motor to step. Motorspeed is controlled by the rate of theinterruptions and direction is controlled bythe polarity of the voltage applied to thedriver circuit through interconnect lines L1


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and L2. Bipolar MPSA05 NPN transistor Q2and MPSA55 PNP transistors Q3 and Q4invert the pulse from pin 3 and pull the drainof Q1 UP when it is OFF. Pushbutton S2starts and stops the motor by turning theclock on and off. Toggle switch S1 sets itsdirection by switching polarity. Power for themotor is provided by DC wall transformer T1and filter capacitor C2. Five volt regulatorIC2 and filter capacitor C3 supply power toIC1.

Driver circuitFigure 3 is a diagram of the motor drivercircuit built on a 1.7 X 2.2 inch PC board.The motor is driven by four IRL530N power

FETs having very low ON resistance of 0.1ohms resulting in very little voltage drop andalmost no heat. These FETs have a logiclevel gate threshold making them ideal foruse in circuits powered by 5 volts. Theywere also chosen for their specifications of60 volts at 15 amperes. FETs Q2, Q3, Q4and Q5 are driven by CD4013 dual D typeflip flop IC3A and IC3B, each having dualphase outputs that latch either Q2 or Q3 ONand either Q4 or Q5 ON, depending on thestate of the flip flops. Current flows throughone half of each motor winding at all times.Each flip flop has its data input crosscoupled to the other flip flops outputthrough a CD4070 exclusive OR gate inIC4. The cross coupling between flip flopscauses them to change state alternatelywhen simultaneously triggered. Thesequence of change, IC3A before IC3B orIC3B before IC3A, is controlled by theexclusive OR circuits that feed data intopins 5 and 9 of IC3. This sequence changecontrols the direction of the motor. A DOWNor UP level passing from L1 through D3 todirection control pins 2 and 6 of IC4determines weather it will invert or non-invert the data applied to its input pins 1 and5.

Both the clock and the direction controldata are carried to the driver board over thesame wires that power the motor. If L1,figure 3 is positive then the motor will rotateleft when IC3 is triggered by a clock pulse. IfL2 is positive then the motor will rotate right.

The motor steps when the voltage across L1and L2 goes DOWN and then goes UPagain producing a clock pulse. The UPtransition feeds through D4 or D5 and R8,depending on the polarity of L1, L2, intoclock input pins 3 and 11 of IC3. Zenerdiodes D4 and D5 serve the dual purpose ofcoupling the clock pulses into IC3 andacting as a transient voltage suppressor.High voltage spikes caused by switching,that may appear across L1, L2 will passthrough the forward conduction of one ofthese diodes and through the reverse zenerbreakdown of the other, thus clamping theL1, L2 voltage to a maximum of about 33volts. C4 delays the rise of the clock pulseso it arrives later than the direction controlpulse at IC4. D2 improves the discharge ofC4 through R9. Power is supplied to themotor and the circuits through bridgerectifier BR1 which rectifies the L1, L2 inputinto a positive output. Power for IC3 and IC4also passes through 5 volt regulator IC5 andis further filtered by C6. D6 clampsinductive spikes from the motor.

Some unpredictable motion may occurwhen the direction is changed. This iscaused by a pulse or pulses that aregenerated when the polarity is switched.

These pulses appear to the circuits as clockpulses. This is usually not objectionablewhen the positioner is used to rotate adisplay or similar object.

Construction____________

Control BoardInstall all resistors, D1, IC2 and allcapacitors except C2. Install a jumper madefrom an excess resistor lead, the IC socket,terminal block, Q1 - Q4 and IC2. Install C2,the wires for R1, S1, S2 and T1. Connectthe wires to R1, S1 and S2. Solder the leadsfrom a DC wall transformer to the PC boardholes marked +V and -V. Use a transformerwith a voltage rating similar to that of thestepper motor and a current rating a littlemore than twice the motor current rating.Plug IC1 into its socket being careful tohandle it as a static sensitive device andyour control board is complete. The control


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board may be mounted in a suitableenclosure with R1, S1 and S2 accessiblefrom the top or front.

Driver BoardInstall all the resistors, capacitors, diodesand IC5, then two jumpers made fromexcess resistor leads. Next install the ICsockets and terminal block. Insert andsolder power FETs Q2 through Q5 beingvery careful to handle them as staticsensitive devices. Plug IC3 and IC4 whichare also static sensitive devices into theirsockets and your driver board is complete.

InstallationMost stepper motors have a 1/4 inchdiameter shaft. You can mount a flat facedknob on the motor shaft using the knob setscrew to hold it in place. The object to berotated can be attached to the knob using aself-adhesive Velcro fastener. You can keepthe motor from rotating more than 360degrees if this is desirable by using a longscrew as a mechanical stop in one of themotor mounting holes. Another long screwused in place of a knob set screw will stopagainst it. If the knob slips on the motorshaft, file a small flat on the shaft for the set

screw to rest against. If you have access toa machine shop even better mountingschemes can be devised including weatherprotection for outdoor use.

Solder the motor center tap leads to theholes marked +V on the PC board and theremaining leads to the holes marked A, B, Cand D as shown in the schematic. Be surethat the leads from one winding connect toA and B. The leads of the other windingshould connect to C and D. Mount thedriver circuit board near the motor. The

current rating of the motor used is limited bythe 2 ampere current rating of bridgerectifier BR1.

Although stepper motors that run on 9 to 24volts can be used, care must be taken whenusing a 24 volt wall transformer, that thevoltage applied to the control board neverexceeds 30 volts. Many transformers supplymore than their specified voltage when

unloaded or lightly loaded. When using a 24volt transformer, be sure that the motor isconnected and the L1, L2 terminals areinterconnected before applying power.Voltages in excess of 30 volts may damageregulator ICs, capacitors and diodes. Powerto the stepper motor should be maintainedto keep the object pointed in the desireddirection. Stepper motors have a smallamount of holding torque with no powerapplied but wind or other forces couldovercome this torque and cause the objectto move.

A positioner has been run with 500 feet of22 gauge wire connecting the control anddriver boards while using a 16 volt 200milliamp motor. Heavier gauge wire ispreferred for lower voltage drop and shouldbe used for greater distances or largermotors.


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A

B

C

D

FIGURE 1STEPPER MOTOR

+V

+V

GLOLABStepper Motor Camera Positioner

Glolab Corporation134 Van VoorhisWappingers Falls, NY 12590

http://www.glolab.comemail [email protected] (914) 297-9772

c 1999


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IC1

T1

IC2

120VAC VDC

12+C2

1000

C3

.1

+5

L2

L1

Q4

R1 5MEG

R2100K

R30.56K

C1

0.47

TWO WIRE STEPPER MOTOR POSITIONER FIGURE 2

8 4

6

7

2

1

3

D1

R410K

S1

S2

+

-

Q

+V

L2

L1

+5

+




c 1999

R510K

R62K

Q1Q2

Q3 +V


6/7

IC3A

IC3B

IC4A

IC4B

Q5

Q6

Q7

Q8

A

B

C

D

13

11

25

6

10

4

8

13

12

5

6

2

13

4

C4

.001

R94.7K

IC5

D6 C5

100

L1+5

FIGURE 3

9

IC3, IC4PIN 14 = +5PIN 7 = GROUND

TWO WIRE STEPPER MOTOR POSITIONER

R8

100K

R10

100K

D3

M1

R710K

L2

D4 D5BR1

+V

+V

+




c 1999

D2


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TWO WIRE STEPPER MOTOR POSITIONER PARTS LIST

DESCRIPTION SOURCE PART NUMBER

R1 - 5MEG potentiometer Mouser 31VA605R2, R8, R10 - 100K 1/8 watt 5% Digi-keyR3 - .56K 1/8 watt 5% Digi-KeyR4, R5, R7 - 10K 1/8 watt 5% Digi-KeyR6 - 2K 1/8 watt 5%R9 - 4.7K 1/8 watt 5% Digi-Key

C1 - .47 MFD 35 volt tantalum Mouser 581-0.47K35VC2 - 1000 MFD 35 volt electrolytic Mouser 539-SKR35V1000C3 - .1 MFD 50 volt metalized film Digi-KeyC4 - .001 MFD 50 volt metalized film Digi-Key P4513C5 - 100 MFD 16 volt electrolyticD1, D2, D3 - 1N914 silicon diode Mouser 610-1N914D4, D5 - 1N4752 zener diode Mouser 1N4752D6 - 1N4004 rectifier MouserQ1 - MPSA05 NPN transistor MouserQ2, Q3 - MPSA55 PNP transistor MouserQ4, Q5, Q6, Q7, Q8 - IRL530N hexfet Digi-Key IRL530NBR1 - 2 AMP 400 volt bridge rectifier Mouser 583-RC204

IC1 - LMC555 CMOS timer Jameco 126797IC2, IC5 - 78L05 5 volt regulator Jameco 51182IC3 - CD4013 dual D flip flop Jameco 12677IC4 - CD4070 quad exclusive or Jameco 13258M1, M2 - two phase unipolar 24 voltsT1 - DC or AC adapter transformer to match motor Jameco 117321IC socket - 1 eight pin Digi-Key A9308IC sockets - 2 fourteen pin Digi-Key A9314Terminal blocks - 2 two position Digi-Key ED1975S1 - momentary N/O push button switch Mouser 101-0461S2 - double pole double throw toggle switch Circuit SpecialistsHookup wire - 24 gauge 24 inches Digi-Key

Control printed circuit boardDriver printed circuit board

two wire stepper motor positioner

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