varying frequency PWM

[yassin.kraouch]

hI HAVE anyone an idea on how to vary the frequency that i obtain from a microcontroller, by a resistor or something like this ?

 

[FvM]

I assume, that you understand, that changing the PWM frequency mainly involves timer programming and also scaling of output values. You can basically make the PWM frequency (respectively period) depend on a variable value in your application. If you manage it, then it's easy to use e.g. an analog input to control it, and connect a variable resistor or potentiometer as a control.

The said additional calculations needed in set-point scaling may however reduce the performance of your PWM. A very basic method to tune the PWM frequency would be in using an external RC oscillator for the processor and tune it by a resistor. The processor will be rather slow in this case, and all processor frequency based timing and baud rates will be varied as well.

 

[yassin.kraouch]

have you please a schematic that can help me ?? do i use a simple Resistor and capacitor ?

 

[FvM]

For the RC oscillator option, refer to the uP datasheet. Or use a standard 555 oscillator circuit.

 

[yassin.kraouch]

so i can replace the quartz with a standard 555 oscillator ?

 

[FvM]

If it fits the intended frequency range. You can also operate the PWM timer from a separate clock input. But you didn't tell about specific processors or clock frequencies.