SPDT debounce doesn't
in [Basics]
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From: Jon Kirwan on 3 Dec 2009 21:47 On Thu, 03 Dec 2009 21:28:30 -0500, "Michael A. Terrell" <mike.terrell(a)earthlink.net> wrote: >Jon Kirwan wrote: >> >> Interesting points. >> >> Speaking of Cherry, I still have one of their really nice keyboards >> that uses reed relays under each and every switch and donut magnets in >> the key plungers. Absolutely rock solid. Damned if I can find >> anything like that being build, today. > > > You didn't look very hard: ><http://www.cherrycorp.com/english/keyboards/Industrial/index.htm> I didn't mean "Cherry Corp." I meant "reed relay and ring magnets for each key." Can you point me to one, there? I'd appreciate it. Thanks, Jon
From: Jon Kirwan on 3 Dec 2009 21:52 On Thu, 03 Dec 2009 17:01:24 -0800, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: ><snip> >Sounds like a combination of bad switches, bad electronics (esd >sensitivity) and bad code. So don't do that. A reasonable physical >shock shouldn't cause a switch closure on a human interface panel. ><snip> What's kind of funny about this discussion (brings a smile to my face) is that I've never once had to discuss any of this with an electronics designer for longer than a few moments. Usually, they want to be sure _I_ am aware and will deal with it. So I'm actually enjoying the new experience you are affording me. Did you read Ganssle's paper cited here in this thread by IanM? There are some modest scope diagrams there. Jon
From: krw on 3 Dec 2009 23:12 On Thu, 03 Dec 2009 18:52:30 -0800, Jon Kirwan <jonk(a)infinitefactors.org> wrote: >On Thu, 03 Dec 2009 17:01:24 -0800, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >><snip> >>Sounds like a combination of bad switches, bad electronics (esd >>sensitivity) and bad code. So don't do that. A reasonable physical >>shock shouldn't cause a switch closure on a human interface panel. >><snip> > >What's kind of funny about this discussion (brings a smile to my face) >is that I've never once had to discuss any of this with an electronics >designer for longer than a few moments. Usually, they want to be sure >_I_ am aware and will deal with it. So I'm actually enjoying the new >experience you are affording me. > >Did you read Ganssle's paper cited here in this thread by IanM? There >are some modest scope diagrams there. With a SPDT (see: subject) switch one can make the "perfect" debouncer. Don't need no steenkin' software. ;-)
From: John Larkin on 3 Dec 2009 23:25 On Thu, 03 Dec 2009 22:12:21 -0600, krw <krw(a)att.bizzzzzzzzzzz> wrote: >On Thu, 03 Dec 2009 18:52:30 -0800, Jon Kirwan ><jonk(a)infinitefactors.org> wrote: > >>On Thu, 03 Dec 2009 17:01:24 -0800, John Larkin >><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>><snip> >>>Sounds like a combination of bad switches, bad electronics (esd >>>sensitivity) and bad code. So don't do that. A reasonable physical >>>shock shouldn't cause a switch closure on a human interface panel. >>><snip> >> >>What's kind of funny about this discussion (brings a smile to my face) >>is that I've never once had to discuss any of this with an electronics >>designer for longer than a few moments. Usually, they want to be sure >>_I_ am aware and will deal with it. So I'm actually enjoying the new >>experience you are affording me. >> >>Did you read Ganssle's paper cited here in this thread by IanM? There >>are some modest scope diagrams there. > >With a SPDT (see: subject) switch one can make the "perfect" >debouncer. Don't need no steenkin' software. ;-) A lot of pushbuttons, especially membranes, are SPST. Non-click-dome membranes often have absurd sliding/bouncing behavior. John
From: John Larkin on 3 Dec 2009 23:43
On Thu, 03 Dec 2009 18:52:30 -0800, Jon Kirwan <jonk(a)infinitefactors.org> wrote: >On Thu, 03 Dec 2009 17:01:24 -0800, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >><snip> >>Sounds like a combination of bad switches, bad electronics (esd >>sensitivity) and bad code. So don't do that. A reasonable physical >>shock shouldn't cause a switch closure on a human interface panel. >><snip> > >What's kind of funny about this discussion (brings a smile to my face) >is that I've never once had to discuss any of this with an electronics >designer for longer than a few moments. Usually, they want to be sure >_I_ am aware and will deal with it. So I'm actually enjoying the new >experience you are affording me. I'm an EE who mostly does my own programming, so I usually don't have to collaborate with anybody to get things to work. > >Did you read Ganssle's paper cited here in this thread by IanM? There >are some modest scope diagrams there. I'd seen that one before. It's not earth-shaking. One way we debounce things in FPGAs is to clock the external state into an N-bit shift register, N=4 maybe, using the local system clock, sometimes divided down. If all SR bits are 1, set an RS flipflop; if all are 0, clear it. That's usually for stuff much faster than contact closures, like count inputs coming in from a customer or an asynchronous system that might have ringing or glitches. John |