Circuit shown in Figure 3-12. It has a variable speed and timing control functions. When the switch S placed in the 1 position, press the button SB, the motor starts running, a
fter a period of delay, the motor automatically shut down, adjust the potentiometer RPz, may change the timing of time (5-60min). When S is placed Z position, the word is stepless speed circuit, adjust RPi, continuously changing the motor speed. Mainly through 555 IC A.