Stepper
motors are used when rotation by a precise angle is required. A
stepper motor has four coils, say A,B,C and D. Whenever we send a
current through A and B and then change it tot B&C the motor
takes one step. The sequence is like AB, BC, CD, DA .... for one
direction and AB, DA, CD .. in the opposite direction. The coils
current is turned ON or OFF through
software.
We
have used old stepper motor from a 5.25” floppy drive. (the one
that moves the head back and forth over the disk - NOT the one that
spins the disk). It has FIVE wires coming out of it. One of them is
COMMON and the other four are the other ends of the coil. Using a
multimeter you can identify the common. It gives about 75 ohms to all
other leads. The other leads will be A,B,C and D starting from common
in that order. This need to be confirmed by driving the motor.To
drive the motor connect the COMMON to the 5V output, coils to the
outputs ABCD and run the test program called 'stepper'. The outputs
ABCD are collectors of transistors whose base is controlled by the
TTL outputs from the computer.
The outputs A,B,C and D can also be
used individually for driving relay coils etc.
More information on Stepper Motors.