There were a few circuits flying around at about the same time as the AFR. Just wondering if anyone sussed them out....

I believe they were using a 555 timer and a few discrete components....

 

I mirrored the top image so it is in the same orientation as the lower picture. It is a very primitive solution - simple dumb analog filtering, no time compensation, poor signal to noise ratio. I've not bothered because now I have Delta Dash and it seems to show you knock that would never register on a Knocklink. The best would be one of the Texas Instruments DSP chips - they are not horrifically expensive.

http://focus.ti.com/docs/apps/catalo...ctName=spra039

I didn't get as far with the TI stuff to see if you could get it in a non-SMT (DIL) package though.

[Edited by john banks - 4/28/2002 5:54:26 PM]