Post by thread:[PIC]: Mouse encoders

Hi, Iam building myself a UV light box timer, everything is working fine so far and now I want to try and use a mouse encoder with a knob on the end so I can dial in the time to count down from. This is where I need some advice, looking at a mouse with a scope I find 3 pins on the photo transistor or whatever it is and 2 pins output a square wave when I spin the encode wheel. Iam ok so far, but how do I detect which direction the wheel is spinning? I thought you get one pulse on both pins for one direction and a pulse only on one pin and not the other for the opposite direction. This doesn't appear to be happening, or at least I can't see it and it's quite tricky spinning by hand and trying to study the waveforms as I have my scope triggering off one of the pins so I can see the phase difference between channels a and b. Oh.. and Iam using a 16f84 to drive the seven seg leds and read the mouse encoder Hope that made sense ! I'd appreciate any help Thanks, russell. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spam_OUTlistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

Hi ! On other optic encoders, it can look like this: one pin is the reference signal. The signal on the other pin is different in phase, if the edge comes before the ref signal, the disc spins in one direction, if the edge comes after the reference signal, the disc spins in the other direction. I think that applies to mouse encoders as well. 73 Attila Muhi - SM4RAN -----Ursprungligt meddelande----- Från: Russell Farnhill <.....r.farnhillKILLspam@spam@STOR-WAVE.CO.UK> Till: PICLISTKILLspamMITVMA.MIT.EDU <.....PICLISTKILLspam.....MITVMA.MIT.EDU> Datum: den 6 mars 2001 15:26 Ämne: [PIC]: Mouse encoders {Quote hidden}>Hi, > >Iam building myself a UV light box timer, everything is working fine so far >and now I want to try and use a mouse encoder with a knob on the end so >I can dial in the time to count down from. This is where I need some advice, >looking at a mouse with a scope I find 3 pins on the photo transistor >or whatever it is and 2 pins output a square wave when I spin the encode >wheel. >Iam ok so far, but how do I detect which direction the wheel is spinning? I >thought you get one pulse on both pins for one direction and a pulse only >on one pin and not the other for the opposite direction. This doesn't appear >to be happening, or at least I can't see it and it's quite tricky spinning >by >hand and trying to study the waveforms as I have my scope triggering off one >of the pins so I can see the phase difference between channels a and b. > >Oh.. and Iam using a 16f84 to drive the seven seg leds and read the mouse >encoder > >Hope that made sense ! > >I'd appreciate any help > >Thanks, > >russell. > >-- >http://www.piclist.com#nomail Going offline? Don't AutoReply us! >email EraseMElistservspam_OUTTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body > > > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

Hi! > by > hand and trying to study the waveforms as I have my scope triggering off one > of the pins so I can see the phase difference between channels a and b. The phase difference between the two cannels is the answer. Regarding the direcetion of the movement first channel A and THEN channel B toggle it's level and in the other direction channel B and THEN channel A toggle it's level. Sorry for my bad english. cu, Doc ... -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email @spam@listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

On Tue, 6 Mar 2001 14:30:34 -0000, you wrote: >Hi, > >Iam building myself a UV light box timer, everything is working fine so far >and now I want to try and use a mouse encoder with a knob on the end so >I can dial in the time to count down from. This is where I need some advice, >looking at a mouse with a scope I find 3 pins on the photo transistor >or whatever it is and 2 pins output a square wave when I spin the encode >wheel. >Iam ok so far, but how do I detect which direction the wheel is spinning? I >thought you get one pulse on both pins for one direction and a pulse only >on one pin and not the other for the opposite direction. This doesn't appear >to be happening, or at least I can't see it and it's quite tricky spinning >by >hand and trying to study the waveforms as I have my scope triggering off one >of the pins so I can see the phase difference between channels a and b. > >Oh.. and Iam using a 16f84 to drive the seven seg leds and read the mouse >encoder These encoders usually have a roughly 90 degree phase shift between the 2 outputs. The simplest way is to wait for (or have an interrupt on) a falling edge on one of the inputs, and when received, sample the other input. The state of the second input represents direction, so you either add or subtract one from the position depending on the state, e.g. <wait for falling edge on input 1> movlw -1 btfsc <input 2> movlw 1 addwf position There are other ways which give more resolution but you probably won't need to for your application. One alternative, which gives the best resolution, is to use a state lookup table, where on every change(rising or falling) in either input (e.g. using RB4-7 int on change), you create a 4 bit value consisting of the new and old states of the 2 inputs, and look up the increment value (-1, +1 or 0 for illegal states) in a table. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email KILLspamlistservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

> Iam ok so far, but how do I detect which direction the wheel is spinning? I > thought you get one pulse on both pins for one direction and a pulse only > on one pin and not the other for the opposite direction. This doesn't appear > to be happening, or at least I can't see it and it's quite tricky spinning > by > hand and trying to study the waveforms as I have my scope triggering off one > of the pins so I can see the phase difference between channels a and b. You usually use two detectors in quadrature (90 degrees out of phase) for this. With both signals you can determine direction and number of steps. ***************************************************************** Olin Lathrop, embedded systems consultant in Devens Massachusetts (978) 772-3129, RemoveMEolinTakeThisOuTembedinc.com, http://www.embedinc.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spamBeGonelistservspamBeGonemitvma.mit.edu with SET PICList DIGEST in the body

>Iam ok so far, but how do I detect which direction the wheel is spinning? I >thought you get one pulse on both pins for one direction and a pulse only >on one pin and not the other for the opposite direction. This doesn't >appear >to be happening, or at least I can't see it and it's quite tricky spinning >by The opto has two light sources/receivers in it. The slots in the opto wheel are set up so that one diode is partially occluded while the next slot is clear as it turns around. If the "second" diode is uncovered while the first is being covered, it's turning one direction. If the opposite happens, it's turning the other direction. Try looking at the output of the pins on a storage scope. Maybe you can see the difference more clearly. I would really suggest searching for this on the internet... I found a GREAT page that showed *exactly* how this works, but since I didn't have a project for it, I kind of skimmed over it. Sorry if this doesn't really help; look for that internet page... it's out there. --Andrew _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email TakeThisOuTlistservEraseMEspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

on 3/6/01 6:30 AM, Russell Farnhill at r.farnhillEraseME.....STOR-WAVE.CO.UK wrote: > Iam ok so far, but how do I detect which direction the wheel is spinning? I > thought you get one pulse on both pins for one direction and a pulse only > on one pin and not the other for the opposite direction. This doesn't appear > to be happening, or at least I can't see it and it's quite tricky spinning > by > hand and trying to study the waveforms as I have my scope triggering off one > of the pins so I can see the phase difference between channels a and b. What you're doing is called quadrature encoding/decoding, and here is a link to help explain it: http://kahuna.sdsu.edu/~kennedy/research/firmware/rotdec/rotdec.html this page talks about creating a state machine out of ABEL code, but you can probably apply the principals to PIC firmware. Let me know what you come up with; I have to do the same thing myself soon. BTW, let me also suggest Bourns rotary encoders. They're probably much handier than trying to use a mouse encoder. http://www.bourns.com/html/encoders.html I've got a handful of the ECW line, and so far I like them. I think Digi-Key sells them. ------------------------------------------------------------ Roderick Mann EraseMErmannlatencyzero.com.sansspam -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics