PWM by software

jaguar · Joined: 10 Sep 2008 Posts: 3 Location: Oaxaca, Mexico

Hi!

I need to generate three independent PWM signals (by software) with a frequency of 100 Hz or 150 Hz. Each signal with different duty cycle which can be modified using several values saved in PIC's memory.

Any idea about the programming?

I want to use the PIC12F683, thanks for your attention
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Best wishes

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

Tell us the maximum PIC oscillator frequency that you will permit in your
design (4 MHz, 20 MHz, etc.), and tell us the resolution of the PWM that
you require (either in number of bits, or number of steps).

Guest · Posted: Wed Sep 10, 2008 4:15 pm

Configure a timer to operate at some multiple of your desired frequency.

The more duty cycle resolution you want, the higher the multiple.

Then in the timer isr, use a incrementing variable to control duty cycle

So say you wanted to do 100Hz with 100 different possible duty cycles

Configure the timer to interrupt every 0.0001 seconds, and increment a variable, say x, for example in the isr. When x reaches a certain value (determined by duty cycle), set the output to low. When reaches 100, reset the variable to 0, and set the output high. For a duty cycle of 50%, set the output change to happen at x=50. For a duty cycle of 10, set the output change to happen at x=10.

jaguar · Joined: 10 Sep 2008 Posts: 3 Location: Oaxaca, Mexico

jaguar · Joined: 10 Sep 2008 Posts: 3 Location: Oaxaca, Mexico

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

http://www.ccsinfo.com/forum/viewtopic.php?t=35160&start=3