There are two problems on one shots on the signal edges is that they give in effect a hysterisis on the signal edge position. The second problem is the one shot needs to fire on both positive and negative transitions. The real beauty of quadrature encoding is the 4 counts per wheel slot. (ie 200 slot wheel gives 800 counts per revolution) This is well worth preserving. Once we stopped trying to condition the signals other than using as low a value of sensor pull-up as was reasonable our errors essentially went to zero. The asynchronous algorithm is self correcting on miss-read edges. The only error case left is the double transition (00 -> 11, 01 -> 10, 10 -> 01, 11 -> 00) if you just ignore that case and it is indeed noise then the asyncronous algorithm will act like a you have a low pass filter that corrects in two cycles and as long as the quadrature is not moving fast enough to cross a full count in two cycles there will be no accumulated error in position measurements. Walter Banks ---------- > From: Montaigne, Mike > To: PICLIST@MITVMA.MIT.EDU > Subject: Re: quadrature encoders for telescope automation > Date: Tuesday, January 27, 1998 2:13 PM > > Most errors (I think) are caused by noise spikes and can be eliminated > (this is really a question) by a width gate, ie anything > below a certain width gets discarded. I am getting very occasional > errors now with my optical encoders, ('standard' hardware oneshot off > each 'A' & 'B' transition feeding and gates to detect cw/ccw rotation. > and I am using a input c/r network (.01uf/1K pull-up) which helps. > Mike Montaigne > Atomic Energy of Canada Ltd. > > ---------- > > From: Walter Banks[SMTP:walter@BYTECRAFT.COM] > > Sent: Tuesday, January 27, 1998 1:22 PM > > To: PICLIST@MITVMA.MIT.EDU > > Subject: Re: quadrature encoders for telescope automation > > > Errors can be ignored in mice (They are generally > > caused by dust covered sensors) On the telescope mount > > they need to be formally dealt with.