Pulse width modulation (PWM) is a fundamental technique in electronics. It comes as no surprise, therefore, that there are many applications for this digitally-programmed design.A pulse width modulator can form the basis of many fascinating projects. The speed of a DC motor, for example, can be smoothly varied from zero to 100%. Connect a power MOSFET and you can control model trains, drills, lamps and many other devices. This design is particularly interesting because of its digital control input: operation is governed not by an analogue voltage, but rather by five binary inputs which can be connected to a PLC or a microprocessor.