Figure 1 – Multi-speed DC-Motor control
The number of diodes used in each section of the circuit determines the reduction step of the system. If you use three diodes in each step, for instance, you can control the speed by varying the voltage in steps of 2 V.
The switch is a 1 pole x n throw, where n is the number of speeds (switch positions) you want to the control. Note that, in the íirst position, the motor runs at its maximum speed, as no diode is in the operating part of the circuit.
Use 1N4002 diodes for motors up to 1 A and 1N5402 to motors up to 3 A.
