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DIY KIT 94.STEPPER.
MOTOR.DRIVER
This circuit illustratesthe cornplex operationsthat can go
on insidemodenrdedicatedintegratedcilcuits.The cilcuit
usesa bi-directionaldigital rotary encoderfrorn Boum to
step a unipolar stepper rnotor, one click on the encoder
steps the stepper motor one step (or half a step as
described belorv.) This discrete motion can of course
then be gearedup or down to suit your particular purpose.
The steppermotor is not supplied in the kit. Six wire
unipolar stepper motors are readily obtainable for a
couple of $US. The kit is not designedfor 4 wire, bipolar
steppers.
In this kit, we are using a preprograrnlned PIC
rnicrocontroller (uC) and a dedicated stepping rnotor
driver lC, UCN5804B to replace what would have
fonnerly been a board full of discretegatessuch as AND,
OR, NOT, etc. followed by a set of power transistors.
The microcontroller
The P1C16C54 microcontroller takes the input from a
rnechanical encoder and converts it to two separate
signals: pulse and direction. As the encoder is turned it
generatestwo square waves which are in quadrature - 90
degrees apart. By doing a bit of rnathematical
manipulation, the microcontroller then works out how far
the encoderhas tumed and in what direction.
Once the direction and magnitude of the rotation has been
worked out in the uC, it is sent out as pulse and direction
signals to pins 7 and 6, respectively of the UCN5804
steppermotor driver IC.
The Driver
The 5804 stepper driver is one of those marvellous
devices that makes life so easy you wonder how you
managed to get along without it. There was a very good
atticle on stepping rnotors and the use of the 5804 in
Electronics Australia Oct & Nov '94. The Links page of
our website (http://www.kitsrus.com) lists several online sources of information about stepper motors.
The driver will operatesix - wire motors at up to 35V and
L25A. The step input is to pin 7 and direction goes to pin
6 ofthe 5804. Pins 9 and 10 on the PIC control one phase
and half step operation, respectively. Pins I - 8 are the
connections to the stepping motor. Five & eight wire
steppers can be adapted to use this kit; see Kit 113
documentationwhich can downloaded from our website.
Half step and single/double phase refer to rnethods of
operating stepping motors. In one phase operation only
one coil athactsthe rotor at a tirne. This is also referred to
as wave drive. Alternately, two phasedrive energisestwo
adjacentphasedin eachrotor detent position giving nuch
better torque and speedcharacteristics.
Half step operationis a cornbinationof one and two phase
drives causing the rotor to take twice as many steps per
revolution. For a more detailed explanation see the
Allegro data sheet on the UCN5804 which can be got
fionr Allegro (rvrvrv.allegronricro.com)or frorn our o\l,n
rvebsite.Kit 113 also has a ntore detaileddiscussion.Tlre
docurnentationfor Kit I l3 rna1,also be doii,nloadedliom
our websiteat http://n'rvrv.kitsrus.com.
Digital Contacting Rotary Encoder
Also called Digital Panel Control, a Bit Switch, Grey
switch or Digital Switch, rotary encodersprovide a pair of
digital Grey-coded signals that allow a uC to detennine
the speed & direction of the rotation of a shaft. (For
exarnple,a computer mouse uses fwo digital encoders to
track the x & y axis lnovements of a ball in it.) The
PICl6Cxx Applications Handbook by Parallax has a
section (Section 4) on the details of these encoders.The
advantageof the encoderis that it permits the direct entry
of digitised analog data into a digital circuit rvithout A/D
conversion.The data sheet(zipped pdf file) of the ECWIJ
Bourne digital contacting encoder used in this kit can be
obtainedfrom outweb page at
http:i/wrvw.kitsrus.com/soft.htmi
The circuit
There is surprisingly little to the circuit. The encoder
input is to pins l7 and 18 of the rnicro and the pins are
pulled high by R4 and R5 until grounded by the encoder.
The supplied encoder is a 24 cycle type which will
actually generate96 pulsesper revolution.
The microcontroller is a PIC 16C54 and this is run using
an RC oscillator as a clock input. The RC in quesiion is
Cl and R3 and the values chosen give a clock speed of
about 3 MHZ. Note that sirnply changing Ri will raise or
lower the clock speedand consequentlyspeeduu or slotv
down the motor. The source code is available for
downloading frorn our website.
Both the uC and the driver 5804 IC's run on 5V and this
is provided by a standard78L05 regulator together with
capacitorsC2 - C4. Interestingly, the driver actually runs
on 5V despite the fact that the motor side can handle up
to 35V.
There is provision for continuous rotation ofthe stepping
motor. Pin 11 of the PIC is pulled to ground by R6.
Connecting this pin to 5V will result in the motor rotating
at its rnaxirnum speed.
It nray seem strangeto pull pins 1 ard2 of the uC up with
Rl and R2, but there are good reasonsfor it. The software
dependson thesepins being high as they are part of port
a which is the encoder input port. They are not connected
directly to the 5V rail for a rather subtle reason:the port
assignmentsare all done in software so that the relevant
pin can be input or output. The problem is that when there
is a bit ofelectrical noise around the port assignrnentscan
be corrupted resulting in, say, pin I trying to pull the
supply rail down to ground. Exit one rnicroconfi'oller.
DIY KIT 94.STEPPBRI\{OTORDRIVER
Constltction and lesting
The voltage regrlalor and chip socketsare installed and
the circuit is pon'ered up. Check for correcl l'ollages at
the pou'er suppll'pins of ihe micro and the dnver'
hrt in all tie resistors and pot't'er it all trp again Check
rhat all the pins that are pulled up are at 5V and all tltc
pulled dorilt pius are al ground potential Note to add the
Linlt required situated betueett the lrvo IC"s.
The cncodel has lluee pins' The ccntcr pin is tlte carth
pil. Use sonre lvire to collllect the 3 pius to the 3 pin
ienninal block ou lhe PCB Il does not tnatter lvhich lvay
around the X & Y terudnals are cotutected.
There are tr,vo SPDT srvitches on the board to select lulf
step and one/nvo phase. Conneclitlg pins 9 and l0 to G'
ground. will give trvo phase drive. Note that corulectitlg
both to +V turns offthe nrotor.
PARTSLIST - Kit 94
. . I. . . . . ' . . . . . . I
7 8 L 0 r5e g u l a t o. .r. . , , . . . . , . . ......Q
1 6 C 5 , 1 - R C I P P. .I.C. . . . . . . . . . ..I.C. .1. . .. . . . ." " " ' " I
u c N 5 8 0 , 1I C
9 . . . . . . ., . . . . . . I C 2 . . . . . . . .. .. .. .. .. .. . . . . . . . I
1 8p i nI C s o c k s. t. . . . . . . . . .
ECWIJ.
BourncRotaryencoder
,'..,'.2
SPDT su'itch,.
3 pole terntinalblock ........
2 pole terminal bIock.... ....
........
6 rrire harness/socket
. . . . . . I. .
Capacilors:
I 5 p Fc e r a m i c ........ . . . . ' . . . . . C. 1. . .. . .. . . . "
l 0 0 n F m o r r o . 2p"i t c h. . . . . . . C 2 C ' +. . .. . ' . '
C 3 . . . . ' . . . .. . . .
l000uF/35V
Resistors57o,carbonfiltn:
Put in the driver IC aud solder up tlle stepping molor
leads to finish the job. lf you are having lrouble
identif ing the leads then get out yolu multiureter and set
il to ohms. There should be livo sels of three leads'
Solder one center lead to pin 2 ofthe 580'{ brouglrt out to
Lhe 6-pin header and the other two leads A & B to pitts I
and 3. the order is not ilnportant. The other ceuter lead
then goes to pin 7 and the remaining leads C & D go to
pins 6 aud 8.
Softrvare
The sonrce code for Kil 94. the dala sheet (pdf forntal)
for lhe UCN5804 driver and the documentation for
(giving more infontlation on nnipolar stepper
Kitll3
nrotor connections & ballast resistors) is availabtc on the
softrvare dou'nload page our rvebsile- http;//l<itsrus'com
Yori should find that turning the encodef once *'ill rotate
the motor twice for tlvo phase drive, assuming a 48 step
motor. Connect the Continuous Rotation pads and the
motor should sPin haPPilv.
As the motor is spinning. trv varying the supplv voltage'
This will make the motor nrn more roughly or smoolhly'
Stepping tnotors are very sensitive to supplv voltage
variatious. Try the same lhing while htnling the encoder"
vou n'ill qtricklv get a feel for stepping motor quirks'
If It Does Not Work
First check that the SPDT svritches are not botlt in the
+V position. That tums off the motor. Second check that
the IC's are in the correct lvaY around Finally the
problems must be the connection of the stepper lnotor to
ih" Ita*ess. A detailed explauation of how to get the
correct comections is given in Kit ll3 documentation
Make sure lhe pins A B C D from the Stepper rnotor are
nratched with the overlaY. The + conunon frotn each
winding goes to pins 2 & 5 of the six-pin haruess' See
the schematic for a detailed colurectioll pattem'
A
B
+ +
C
D
Figure l. Six wire steppermotor. Five & eight wire
rt"pp". motorscan be wired to tlris fonn to be usedwitlt
Kir 94.
PC PANALLEL
PORT
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OPTIOT{AL USE OF
FONCING RESISTOR