You Are Here: Home » AVR ATmega Projects » 8 Channel PWM using AVR microcontroller

8 Channel PWM using AVR microcontroller




The assembly code given here was written to see what it would take to make an AT90S1200 generate 8 channels of proper PWM. In this case, by proper, I mean with the maximum high frequency content consistent with the needed duty cycle and give clock. Take a look at the scope shots below and notice that when the data value is =$02, there pulse frequency is twice that which occurs when the data value is =$01. The significance of this is that the percent of ripple voltage out of the low pass filter stays much more constant as the data values change than they would with a conventional PWM that merely varies the width of a single pulse (see the auto zero code for the RF Field Strength Probe for an example of code that does this). Take a look at the pictures below to see the effect.

pwm

When running with a 4 MHz clock, this code provides 8 channels of 8 bit resolution with a 60 Hz minimum frequency (which occur at data values of $01 and $FF. By adjusting the interrupt timer reload value, the minimum frequency can be taken to 100 Hz, but at the cost of time available for other tasks. Of course, changing the clock oscillator frequency is another way to increase the minimum frequency.

 

For more detail: 8 Channel PWM using AVR microcontroller

Leave a Comment

You must be logged in to post a comment.

Read previous post:
AVR Programmer with ATMega8-16

About AVR Programmer   This simple AVR Programmer will allow you to painlessly transfer hex programs to most ATMEL AVR...

Close
Scroll to top