Three-phase stepper motor control circuit

As can be seen from the figure, the input stage of the +DC solid state relay (SSR) is a photoelectric isolator. When the switching output terminal is high level,
it changes to low level after the inverting drive circuit, so that the light-emitting diode has Electric current passes through and emits light, and the light turns on the phototransistor,
producing an output voltage at the collector , which can be used to control external circuits. The output stage of SSR is a high-power transistor, and its output voltage can reach '30-180V. Each phase of the stepper
motor's A, B, and C phases is controlled by a single-flow SSR, which can be controlled by the ports PAO~PA2 of the 8255 respectively .