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Re: [avr-gcc-list] sine wave generator. ~~~

From: Marlin Unruh
Subject: Re: [avr-gcc-list] sine wave generator. ~~~
Date: Fri, 26 Jul 2002 09:31:16 -0600


Sometimes I get lazy and think software is the easiest way to fix things. I have ample PCB real estate so that isn't a valid excuse. I think you are right with the R2R network scheme. I believe that is the direction I will take. The R2R network, it would seem to me, would be the most stable solution considering temperature.

Thank you for sharing your thoughts.  :-)


At 12:04 AM 7/27/2002 +1000, you wrote:
G'Day Marlin,

Doing that would be essentially the same as PWM. You're just adjusting the duty cycle of a waveform, which is then converted into an analogue voltage via a low pass filter.

The easiest way, in my mind, would be the R2R network. But... If you'd like to do the LPF thing, I'd go with PWM. You just have to choose your PWM frequency high enough that its a fair bit higher than your maximum output frequency. Then you have to choose your LPF cutoff such that it will pass your maximum output frequency, but attenuate the PWM frequencies.

Talk to you soon,


On Friday, July 26, 2002, at 10:35 PM, Marlin Unruh wrote:


The R2R ladder network was one thing I was thinking about. Then use a lookup table of values to place on the port connected to the R2R network at a given time duration. This may be the solution.

I was also wandering if I could use the SPI output pin and shift out bit patterns and run them through a RC filter. If you sent out a series of zeros the voltage would go to ground, or a series of ones the voltage would go to VCC. If you keep shifting out 10101010 thru the RC filter the voltage would go to VCC/2, with some ripple. The RC filter would need to be matched to the clock rate on the SPI MOSI pin. This may not take that much overhead for the processor depending on the clock rate of the SPI. I would use the SPI data register empty interrupt to feed the SPI data register.

Does that sound stupid? Although for me it would cause some problem because I need the SPI port to communicate with another micro controller on the same PCB. I will have to think about it.

Thanks again.  :-)


At 07:41 AM 7/26/2002 +0200, you wrote:
How about this:


Always been meaning to try it out :-)

>>> Marlin Unruh <address@hidden> 07/26/02 03:51AM >>>

I am needing to generate a sine wave using an AVR. The sine wave needs
change in frequency between 1500Hz to 5500Hz approx. Is there a mostly

digital solution? I could use an AVR that basically had nothing else to
but read a port as input and generate the sine wave. Using a resistor
capacitor on the PWM output for a wave shaper really wouldn't work
the frequency isn't constant. Right?

I have several ideas,but think I am making it more complex that it
really is.

I hope I'm not abusing this forum with this question!

Any pointers would be appreciated.


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