This Stepper Motor Control works in either free-standing or PC controlled mode. In free-standing mode an internal square-wave oscillator based on IC2:B of the 4093 supplies timing pulses to the OSC output. The frequency of these pulses and thus thespeed of the stepper motor is controlled by the trimpot VR1 (100K.) A series 1K resistor controls the maximumfrequency. You may increase the value of this resistor for your own needs.
These pulses are fed into the STEP inputwhich is buffered and inverted by IC2:D. This helps prevent false triggering. Similarly, IC2:C buffers andinverts the DIRection input. A SPDT taking the input to +5VDC or ground controls the direction of rotation.IC3:C and D (4030 or 4070 exclusive OR gates) invert the outputs available at Q and /Q outputs of each of the flipflops(FF) IC4:A and IC4:B. The incoming step-pulses clock the FF, thus toggling the Q & /Q outputs and thisturns the MOSFET’s on and off in sequence. The IRFZ44’s have a low on-resistance and can deliver up to6A each without needing a heatsink. Power to the stepper motor is connected to V+ and GND terminals.There is a separate power supply to the 78L05 to power the IC’s. 8V – 12VDC will be sufficient. R2/C2 form a low-passfilter to filter fast-rise switching transients from the motor.
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