►Introduction

Pulse width Modulation or PWM is one of the powerful techniques used in control systems today. They are not only employed in wide range of control application which includes: speed control, power control, measurement and communication. This tutorial will take you through the PWM basics and implementation of PWM on 8051 and AVR microcontrollers.


►Basic Principal of PWM

Pulse-width Modulation is achived with the help of a square wave whose duty cycle is changed to get a varying voltage output as a result of average value of waveform. A mathematical explaination of this is given below.

Consider a square wave shown in the figure above.

T_on is the time for which the output is high and T_off is time for which output is low. Let T_total be time period of the wave such that,



Duty cycle of a square wave is defined as

The output voltage varies with duty cycle as...


So you can see from the final equation the output voltage can be directly varied by varying the T_on value.

If T_on is 0, V_out is also 0.

if T_on is T_total then V_out is V_in or say maximum.

This was all about theory behind PWM. Now lets take a look at the practical implementation of PWM on microcontrollers.



◄ Introduction to PWM  |  8051 PWM Example Code  |  AVR PWM Example Code ►

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