Charalampos Andrianakis writes:
In the need of controlling a 7A 20Volt DC Motor i designed a speed controller with some cheap components. The circuit is a digital circuit and works with Pulse Width Modulation (PWM) which is one of the best ways to control a dc motor. This circuit can drive up to 33A 10V DC motor with a big heat sink placed on the switching mosfet.
Summarily i used in this circuit, the AVR ATtiny13 to control the PWM , a n-mosfet IRF540N for switching the motor and a Rotary Encoder to adjust the PWM Duty Cycle.
DC Motor Speed Controller - [Link]