Subject:
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RE: multiplexed touch sensors [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 18:28:21 GMT
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Viewed:
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820 times
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Kekoa wrote:
> Having revisited this entire sub-thread, it seems people started rambling
> on (constructively, I think) about switch times, debouncing, etc.
>
> Getting back to multiplexed touch sensors, I bet it's possible to get the
> Lego touch sensors to work fine with custom firmware and some sensible and
> reasonably simple debouncing logic to throw away readings during
> transitions. The caveat occurs in the hopefully special case where
> multiple buttons are being pressed and released all at the same time;
> readings might never settle long enough to determine the state of the
> buttons.
The problem with the LEGO touch sensors is that their resistance varies
with the force on the plunger. To get the debouncing algorithm to work,
you need to know how long the switch might be in the indeterminate state.
> If micro-contact switches work, then I would suppose it is because their
> switch time is substantially less than your sensor sampling rate, thereby
> making more complicated debouncing unnecessary.
Typical switch bounce can be 5 to 15 msec! It is good embedded practice
to debounce your switch readings anyways. Does LegOS really sample at
0.1msec? Yikes! Even the 3msec sample rate is very fast.
Micro contacts work not because they transition quickly, but because they
transition cleanly. You should debounce them anyways.
Cheers,
Ralph Hempel - P.Eng
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Check out pbFORTH for LEGO Mindstorms at:
<http://www.hempeldesigngroup.com/lego/pbFORTH>
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Reply to: rhempel at bmts dot com
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