This project uses the principle of pulse width modulation to vary the speed of a hand drill or other small brush-type motor up to 200 watts.  It provides from 0% to 98% of maximum speed.  It also works great as a lamp dimmer.

Components:  resistor, potentiometer, 2 capacitors, 2 diodes, 2 neon bulbs, 2 SCRs, slide switch, outlet, line cord

Principles taught:  pulse width modulation, SCRs