Sinusoidal pwm frequency adjustment

[seyyah]

atmel avr pwm sinusoidal look-up table program

I'm producing spwm at different frequencies. I have sin table. At low frequencies i make the duty cycle change slowly at constant period (carrier signal's period). At high frequencies make it change more rapidly. E.g

Sin Table (Assume that letters are sin values)
____
a
b
c
d
e
f
g
h
i
j

In low frequency duty cycle (DC) changes like this at every end of the period:

1- DC=a
2- DC=b
3- DC=c
etc

But as frequency goes up it changes like this

1- DC=a
2- DC=c
3- DC=e

etc. This method works. But i wonder is there a more general or easy way to do this? Especially to achieve more frequency steps. I make the changes for 1Hz. But i would like to achieve 0.1Hz or more without a significant load onto the program or dsp.

 

[RegUser_2]

sinusoidal pwm generator

Use this search string in Google:

"digitally controlled oscillator"

 

[echo47]

spwm lookup table

I don't quite understand your a b c description, but I think you may be looking for a Direct Digital Synthesizer (DDS). It's a simple way of generating precise frequencies by using a phase accumulator, a sine table, a DAC, and a low-pass filter. Search Google for more info. Here's one:
http://www.geocities.com/CapeCanaveral/5611/dds.html

 

[seyyah]

atmel pwm lookup table

I'll use a µcontroller which can produce pwm signals. For spwm, duty cycle will change along a one period of the putput sinus signal. a,b,c's are values which duty cycle will take, along the period of the output sinus signal. For low frequncy duty cycle must change slowly from the first value to the last value. But as frequncy goes up it must change rapidly from first value to the end value. Because of this some values are passed and not assigned to duty cycle register. This is my method. And i wonder what other methods are available for digital and µcontrollers?

 

[artem]

I see what you are trying to. you can manipulate via input freq to your PWM counter or via skipping indices in your sin lookup table .
Just few hours before i was watching Atmel AN for DTMF tone generation . it is worth to have a look there :

AVR314: DTMF Generator (PWM based)
http://www.atmel.com/dyn/resources/prod_documents/DOC1982.PDF
http://www.atmel.com/dyn/resources/prod_documents/AVR314.zip