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 22:03:27 GMT
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Original-From:
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David B. Gustavson <DBG@avoidspamSCIZZL.COM>
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Viewed:
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1010 times
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Any motion between two hard surfaces, including sliding metal on
metal (often called contact wiping), creates intermittent contact
that has to be "debounced".
The only switches that don't bounce are mercury-wetted contacts, such
as one used to find in some reed switches, relays, and some
thermostat mechanisms, and magnetic Hall-effect or
optical-interrupter switches (some of these will have slow
transitions that will "bounce" when ambient noise (physical or
electrical) is added in--electrical hysteresis has to be used to
avoid this).
At 21:47 +0000 990825, Robert Munafo wrote:
> In lugnet.robotics, Ralph Hempel writes:
> > > 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.
> >
> > The actual source of bounce is NOT the arc just before contact. It
> > actually is the bouncing of the contact due to the action of the spring
> > in the contact!
>
> That obviously depends on what type of physical design is used for the switch.
>
> Some switches are not capable of bouncing the way you describe
> because there is
> no impact or acceleration during contact (example: slide switches that move
> leaf springs across traces on a PCB -- many linear and rotary
> multipole-multithrow switches are built that way)
>
> And of course, some switches do. So, if you wish to be complete, you
> should add
> "actual physical vibration" to the other causes ("dirt" and "arcing") that I
> mentioned.
>
> - Robert Munafo http://www.mrob.com/
> LEGO: TC+++(8480) SW++ #+ S-- LS++ Hsp M+ A@ LM++ YB64m IC13
> --
> Did you check the web site first?: http://www.crynwr.com/lego-robotics
--David B. Gustavson, tel:650/961-0305 fax:961-3530
IEEE Computer Society Microprocessor Standards Committee chair
Exec. Director, SCIzzL: Assoc. SCI Local Area Memory Port Users
1946 Fallen Leaf Lane, Los Altos, CA 94024-7206 dbg@SCIzzL.com
For SCIzzL-supported standards info see http://www.SCIzzL.com
--
Did you check the web site first?: http://www.crynwr.com/lego-robotics
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