Construction and Working
In this website we already published about Speed control of DC motor with timer IC, here this circuit constructed for the basic motive to meet the forward / Reverse operation of DC motor with speed control.
The DC motor is connected to the supply through DPDT ( double pole double through ) switch, by changing the switch position we can get forward and reverse rotation from the DC motor because this switch interchanges power supply polarity applied to the DC motor.
The diode D1 protects the DC motor from the back emf effect hence there is no output load effect rise. The NPN transistor BD 139 drives the output from timer IC, this output pulse duration decides the speed of DC motor, by varying the VR1 resistor we can vary the pulse output of timer.