WARNING!

Fig.4. PIC QuickStep printed circuit board component layout and full-size copper foil master. Refer to Fig.1 for motor wiring.
CONSTRUCTION
The layout of components on the printed
circuit board is shown in Fig.4. This board
is available from the EPE PCB Service,
code 448. It has been designed so that it can
be literally cut into three sections if some of
the functions are not required. On the left is
the controller, which can drive a dedicated
i.c. if needed. In the centre is the driver, and
on the right the power output stage.
Positions for pins to give access to the
inputs and outputs of each section are provided,
but there is no need to fit these
unless they are likely to be needed. The
prototype has just the supply and output
pins fitted, plus the two for frequency
counter connection.
Dual-in-line (d.i.l.) sockets should be
used for both PICs. All the other components
are soldered directly to the board.
Potentiometer VR1 is a type designed to fit
to the component side of the board with a
built-in mounting bracket, but where this is
not available there is sufficient room to fit a
standard pot to the board with its mounting
bush and nut, and connect it with short
leads.
All the components except IC1 and IC2
should be fitted. Throughly check the accuracy
of your assembly and soldering before
applying power.
OPERATIONAL CHECKS
The first check is to power up with a supply
of 6V or more, and check that the 5V
output from IC3 is present and correct.
After this IC1 can be inserted. Link LK1
should be omitted and switches S1 and S2
should be off. The two outputs, the wire
links to the right, should be high (+5V). If
S5 is pressed, the upper output link should
go low (0V). If S6 is pressed, the upper output
link should alternate between high and
low at a rate adjustable with VR1.
Switches S4 and S3 should have a similar
effect on the lower output link. If this
works, this part of the circuit should be
fully functional, but feel free to try “direction
and step” mode with link LK1 fitted,
and to check out the counter output from
TP1 if desired.
IC2 can be fitted next, with LK2 omitted
and LK3 in place. Incidentally, LK1 and
LK2 should always be fitted or removed as
a pair so that the modes of IC1 and IC2 are
the same, so LK1 should also be omitted at
this point in testing.
If S9 (Wave) is on and S7 and S8 are off,
repeatedly pressing S5 (Forward Single
Step) should result in the l.e.d.s lighting
sequentially, one at a time from left to right.
S4 (Reverse Single Step) should have them
lighting from right to left. Switching off S9
will show the full-step sequence, and
switching on S8 will show the half steps.
Switching on S7 (Powerdown) should
show brief l.e.d. flashes as pushswitches S3
to S6 are pressed.
If LK1 and LK2 are now fitted, S4
should cause the stepping and S5 should set
the direction.
Low voltage d.c. stepper motor.
MOTOR CONNECTIONS
The unit can now be tested with a motor!
If this came with connection data there
should be no problem connecting it up to
this project. If it didn’t, or it was salvaged
from scrap equipment, the connections will
have to be identified.
The “common” leads can be located with
a meter. Where a resistance can be measured
across any two leads, it will be found
that it will be either the value for a coil lead
to a common, or twice that value, i.e. two
coils in series via a common. So, the common(s)
will be the lead(s) having the lower
resistance value compared to two or more
of the others. Fig.1 shows how this comes
about.
Having identified the common(s), connect
them to the positive output of a
Everyday Practical Electronics, June 2004 379