This is speed motor controller circuit of 12V DC motor. as SCR DC motor speed control circuit using IC-CMOS. You can adjust the speed of rotation of the spindle motor from 5-60 cycles per minute.

The work of circuit, The IC1-(CD4081) is nand gate ic type. It accepts the voltage from the bridge diode BD1. But there is no filter to smooth current.The other in the pin 2.The VR1, C1 and R1 is a phase shift or time delay to slow down,voltage from pin 3 to triggers pin the gate of SCR1 to work. Or conductors to the motor, causing it to rotate. Speed of the motor, can be achieved by adjusting VR1.

The power supply input pin 14 of IC1 is filtered to smooth the current, by through D2 and C2. The D1 prevents the noise from the motor. and D3 is reverse-voltage protection of motors. This can cause circuit damage. If the circuit is used with a motor that consumes more power. Heat sink should be attached to BD1, D1 and SCR1, because heat up. May cause equipment damage.

reference;
http://slidesharezunaibali/to-control-the-speed-of-dc-motor-simple-project