Post by thread:[EE] Stepper motor as an encoder

> power the windings I'm imagining perfect results already ! Will try your suggestions today and report back Funny how projects develop. Sometimes they go in the Too Hard basket and are abandoned, sometimes pride and curiosity takes over and you just have to keep picking away

> 2. Power one winding, measure back emf on it, and use your current > method for the other winding. At a minimum it increases cogging, > which means individual steps will happen more quickly and thus emit > sharper pulses Adam, works beautifully. I powered one winding with 5V via an 820 ohm resistor and captured the wave from the other winding. This power level is ample to introduce enough detent for even the pedantically slow Your thought about cogging hit the snail on the head. I'd been thinking along those lines myself, but mechanically, forgetting that the very simplest way was right in front of me Here's a comparison http://home.clear.net.nz/pages/joecolquitt/pdg_slow.gif Top trace is unpowered, bottom is powered, on the same scale Additionally, the waveform on the powered coil is a lovely sinusoidal series of positive peaks that can go straight into a comparator. Would rather not try to capture that with the soundcard at this stage but will do at some time or my records. With both coils powered, signals from each are so clean and useable with minimal processing. The noise and bounce has gone and the motor is much less sensitive to vibration Thanks for kicking the day off on a positive note !!!

> > On Nov 8, 2008, at 12:37 AM, Jinx wrote: > > Adam, > > http://home.clear.net.nz/pages/joecolquitt/stepper_as_encoder.gif > > still looking at optimisation but it's pretty solid already > > Thanks again for the suggestion So the BAT46 passes positive going pulses and feeds them to a differentiator* which then feeds them to a variable ( pot based ) threshold comparator. With no rotation A and B output should be zero volts. 47n and 100K are an RC time constant of 4.7 msec. Where does the 150 msec come from ? Did I miss something ? *http://www.ecircuitcenter.com/Circuits/opdfr/opdfr.htm MA WFT Electronics Denver, CO 720 222 1309 " dent the UNIVERSE " All ideas, text, drawings and audio , that are originated by WFT Electronics ( and it's principals ), that are included with this signature text are to be deemed to be released to the public domain as of the date of this communication .

I'm glad it's working! If it's ok with you, I'd like to do a little writeup of it on my website. If not, I'll mention it and put links to your website (I've had people ask me before about using steppers as encoders). -Adam On Sat, Nov 8, 2008 at 2:37 AM, Jinx <spam_OUTjoecolquittTakeThisOuTclear.net.nz> wrote: > Adam, > > http://home.clear.net.nz/pages/joecolquitt/stepper_as_encoder.gif > > still looking at optimisation but it's pretty solid already > > Thanks again for the suggestion > > -