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A stepper motor has four
coils. The direction of rotation (clockwise or
anti-clockwise) depends on the order in which the currents
supplied to the coils are switched on. If you use the
motors type 55SI-25 DAYA, having a connector as shown
below, |
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2 1 3 4
will turn the motor clockwise and |
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1 2 4 3
will turn the motor anti-clockwise |
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The numbers here refer to the numbers
of the sockets on the motor connector. Sockets 5 and 6 are
both connected to the positive of the motor supply. The
motor driver is connected to the parallel port of a
computer.
A program is required to run the
motors. The program simply sends a series of numbers to
the parallel port: 32 16 64 128, to turn a motor clockwise
and 16 32 128 64 to turn a motor anti-clockwise. These
numbers are sent using data lines 4 to 7; data lines 0 to
3 are used to select which motor you want to activate.
The computer runs much too fast for the motors so the
output from the port is stored in a "latch". The latch
inputs are only transferred to the outputs if the "store"
pin is high (at 5v). The store input is connected to data
line 0 or 1 or 2 or 3 of the port so the computer can run
one motor by putting bit 0 = 1(data line 0 at 5v), a
second motor by putting bit 1 = 1 (data line 0 at 5v) etc.
So this method could be used to control up to four motors. |
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The basic idea
is illustrated below |
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The outputs of the latch are
used to switch "Darlington" high gain, high current
transistors (type BD679, BD683 etc). This is necessary
because the motors need currents of about 300mA to run
correctly. |
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Circuit of one coil
driver (four needed for each motor) |
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N.B. Some Darlington
transistors also have a protection diode (not shown in the
diagram). The resistor should be about 4k7. |
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Vero diagrams |
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The data outputs are pins 2 to
9 (pin 2 = bit 0 ..... pin 9 = bit 7) |
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