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

[Scott Gravenhorst]

dan snazelle <subjectivity at hotmail.com> wrote:
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>On May 5, 2011, at 10:12 AM, Eric Brombaugh wrote:
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>> On May 5, 2011, at 6:32 AM, Karl Ekdahl wrote:
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>>> 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 

If you are averaging (for example) four ADC readings, you collect them,
add them together and divide by four (or right shift by 2 bits).

-- ScottG
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-- Scott Gravenhorst
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