Subject:
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Re: touch sensors aren't just switches (was Re: ideas for a RIS 2.0
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Newsgroups:
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lugnet.robotics
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Date:
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Wed, 25 Aug 1999 05:50:03 GMT
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Viewed:
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835 times
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In article <FH02r0.Hn7@lugnet.com>, "Robert Munafo"
<munafo@NOgcctech.SPAMcom> wrote:
> In lugnet.robotics, lego-robotics@crynwr.com (Tilman Sporkert) writes:
> > Many "buttons" in today's electronic devices are designed that way. Check
> > your TV remote control, your key-chain remote control for your garage door
> > opener or car alarm, the buttons on your phone etc. It eliminates the need
> > for a physical switch. All you need is a pair of copper pads under each
> > button. These are just part of the normal circuit board that you need
> > anyway. The rest is a hole in the cover, a piece of plastic ("the button"),
> > a spring, and a small piece of conductive rubber.
>
> I think it also removes the need to eliminate "keybounce", the annoying thing
> that happens with real switches due to dirt on the contact surfaces and tiny
> arcs (sparks) just before initial contact.
You can still get keybounce on rubber buttons. Perhaps there is a special
design that would eliminate keybounce entirely, but in my experience some
degree of debouncing is still required.
I believe the transition is a more gradual one since the resistance slowly
decreases as pressure increases, but there is still some chatter -
especially if you're wiring it into a CMOS gate that's going to make a
hard logical decision. Perhaps a Schmitt trigger or something similar
could clean it up, but I've never tried the hardware solution - debounce
in software is easy enough.
In the case of the RCX, I believe the sensors are wired to the ADC and
there is some significant debouncing in the firmware. Its been a while
since I looked at the code, but I think the debounce time is something
like 300ms.
Dave Baum
--
reply to: dbaum at enteract dot com
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