simple 8 bit ADC?

[John Speth]

I think that non-integrated ADC circuits aren't as simple as their DAC counterparts.  A long time ago I designed and built an 8 channel ADC that read 8 pots and stored the 8 bit value to a latch.  It used an 8 bit DAC808 DAC, an 8 bit counter, and an analog comparator.  

The idea is that, assuming the sample voltage is constant during the entire count, a counter is started counting up from zero.  The counter drives the DAC which drives one side of the comparator.  The other side of the comparator is driven by the voltage to be sampled. When the comparator switches, the counter value can be considered the digital value of the analog value being sampled.  The downside of this design is that it could take up to 256 times the counter clock period to get your answer.  If your clock is sufficiently fast, this might not be a problem.

This is a very simple and classic ADC design.  The trick is how you will interface it to your system.  You need to decide if you'll need to sample/hold the sample voltage, whether the ADC sample will be free-running or externally started and other stuff.  That's where the lions share of my design was in.  

I'd be happy to share the details with anyone interested.

John Speth
Object Engineering, Inc.
johns at oei.com

-----Original Message-----
From:	R.Fahl [SMTP:8brain at spiritone.com]
Sent:	Sunday, December 21, 1997 5:42 PM
To:	synth-diy at mailhost.bpa.nl
Subject:	simple 8 bit ADC?

Does anyone know of a simple 8Bit ADC circuit?  I don't need anything
fancy, prefer something with off the shelf parts.

ROmeo