PWM - Pulse Width Modulation

PWM stands for Pulse Width Modulation. Below is an example of 4 square wave pulses.

A pulse has a beginning and an end. The duration or width of the pulse (time from beginning to end) can be measured – in this example each pulse is a 2 millisecond duration.





The pulse is an electrical signal. No signal = zero volts, Signal present= 5 volts. See note #1

The pulse starts with an rising voltage from zero volts – this is the (rising edge) and ends with a falling voltage (falling edge). See note #2

There is a gap between each pulse (no signal, zero volts) this is required so you can determine the end of one pulse and the beginning of the next.

The 4 pulses in the diagram are combined into what is know as a frame, typically a frame length has a duration of 20ms.

Note #1 5 volts is a typical voltage, 3.3 volts is another standard that is used in logic circuits but this could be any voltage

Note #2 PWM signals can be reversed e.g. pulse starts with falling voltage and ends with a rising voltage