> For results accuracies better than a few percent a true comparator or > a gate with a stable and symmetric switching point is needed. > I am using a Z8 with an internal comparator but a PIC, AVR or other > processor with comparator would work equally well. Russell, when you say "comparator" I start thinking "something compared to something" but it looks like the Z8 comparator in this case is just comparing the input voltage to some internally generated mid point. Am I understanding this correctly? Years and years ago (I think I was 14) I built R2R D2A on my RCA1802 "Cosmic ELF" and then connected that to one input of a comparator (seems like I remember LM339) and an external signal to the other. The comparison was read by the 1802 and I got about 7 bits accuracy with it after going through about a gillion resistors to find a matched set (great education in what 5% tolerance means). I later connected one output pin through a resistor to a cap to ground and used the top of the cap to feed the comparator instead of the D2A. I just continually turned on the output pin when the comparator returned 0 and turned it off when the comparator returned 1. PWM D2A. I counted the on-time and off-time and calculated the ratio (that was the hard part on the 1802!). I remember being very happy to get better than 8 bits on stable input voltages. This is just a voltage follower right? it provides current gain... so I later hooked up a transistor, audio coupling transformer and a small speaker and used the uProcessor as an audio amplifier. Had to decouple the input but it worked ok (some distortion). A variable resistor acting as a voltage divider between the output pin and the cap provided variable gain. I was also able to record and play back the sound by recording the ratios in RAM, then ignoring the comparator and just modulating the output pin. Had the only talking "Cosmic ELF" on the block! That was the only thing I ever did that would actually fill up my 4k RAM board. The grand dream was to do voice recognition... but that was a bit beyond me at the time. Could never understand FFT or any DSP for that matter. Anyway, sorry for the reminiscing but I was trying to say that I think your continuous conversion idea has merit. James Newton, webmaster http://get.to/techref jamesnewton@geocities.com 1-619-652-0593 phoneÊ James Newton, webmaster http://get.to/techref jamesnewton@geocities.com 1-619-652-0593 phoneÊ