Microb Technology/2006/electronics/PWM

What is PWM ?

Pwm mean Pulse Width Modulation

Its by this way we can control our motor speed without any digital to analogic convertor. The speed of the motor is determined by the average value of this cyclic signal. For a well working PWM signal the frequence should be around 15 Khz. (In fact this works with lowest frequencies but they may be audible and the motor will do some crasy noises).

This signal don't setup the sens of rotation. You have to add an additionnal signal to chose the motor to turn clockwide or counterclockwide.

Have a look at this shematic

And some screenshot of real signal

The signal is a litle bit dirty, but it's a good sample of what you should obtain.

How the motor turn ?

Of course with only a 5v numeric power the motor can' t rotate. Thats why we use an amplificator to convert our 0-5 V signal to a 0 V 24 V power signal. This is the role of the H bridge. We use LMD18200T for that.