[sdiy] A/D converter with good accuracy for a reasonable price?

[dan snazelle]

On May 5, 2011, at 10:12 AM, Eric Brombaugh wrote:

> 
> On May 5, 2011, at 6:32 AM, Karl Ekdahl wrote:
> 
>> I'm trying to find a decent A/D for converting pitch-CV into digital, given this it needs to be fairly accurate and probably at least 14 bits. Seems to me it's hard to find anything that's not like $25 a piece. It only needs to have one converter (i'll use a multiplexer in front of it) and i guess a sample rate would be whatever would be apropriate for a seemingly seamless variation in pitch - a few 100 samples per second?
> 
> You don't specify, but I assume you're talking about a 1V/Oct pitch CV. I've found that a 12-bit converter is fine for this in the digital oscillators I've worked on. However, my systems are typically sampling > 10kHz and using the inherent integration of the NCO to do a bit of smoothing, so the apparent resolution may be greater than the 12-bits might suggest. If you're sampling slowly and not integrating then YMMV. That said, I'd consider using an inexpensive microcontroller with a 12-bit multiplexed ADC and then averaging the readings to get more resolution - you pick up an extra bit for every 4x you average (assuming there's some noise riding on the input signal), so a 12-bit converter oversampled by 16x might get you to the resolution you're looking for.
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How does one go about AVERAGING the readings? I am working with AVRS which have 10bit A2D's and I would be interested in getting better resolution through this process

thanks!