Re: microcontroller for simple audio project

From: Mark Borgerson (mborgerson_at_comcast.net)
Date: 02/02/05 

Date: Wed, 2 Feb 2005 13:09:46 -0800

In article <1107376351.002612.227710@c13g2000cwb.googlegroups.com>,
ethan.bordeaux@gmail.com says...
> i've thought about this, but am concerned about MIPS and power
> consumption. any idea on the processor overhead to implement this? is
> this something that could be implemented with PWM or a typical uC timer
> allowing for very low overhead? i want as many cycles as possible to
> calculate new outputs, so i'd rather not be stuck shifting bits. an
> onboard parallel DAC seems like the easy choice, but since i'm trying
> to be very cheap, i might not have the luxury of going the easy route!
>
>
Yes, this chore is something that many MCUs with a hardware PWM
capability could handle. Changing the output voltage then becomes a
matter of storing the new value in a register.

The output sample rate is then limited by the timer clock rate and
the number of bits resolution. For a timer with an 8MHz clock and
8 bits output resolution, the PWM period is 256 cycles, or
about 31,250 steps per second. That, and the acceptable
distortion, will limit your maximum output frequency.

If you only need 5KHz output response, you could use a
slower clock speed or more bits of resolution. The PWM
generation will probably not be the limiting factor in
determining your maximum frequency. It will take only
a microsecond or two to adjust the output. You still
have to calculate the next output before the next
output sampling point.

Mark Borgerson

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