Motor Speed Controller

This motor controller is obsolete because the motor speed control can be implemented with a PWM (Pulse Width Modulation) circuit. Although those PWM circuits are more complicated to implement, nowadays there are cheap PWM controllers that you can purchase on eBay.

PWM control allows transistor saturation and thus less power dissipation.

My design includes a short circuit protection feedback.

Supplies

Components: Shown in the circuit.

Optional components: Solder.

Tools: Soldering iron, plies, wire stripper.

Optional tools: USB Oscilloscope, Multi-meter.

Step 1: Design the Circuit

The button is a single pole double throw (SPDT). You can also replace a button with a switch. However, buttons are more reliable because of more simpler mechanical designs.

If the circuit output voltage drops the zero then the Q1 transistor will turn OFF, thus turning OFF the Q2 transistor.

Step 2: Simulations

Simulations show that the maximum motor current is 250 mA.