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"Kevin L. Clague" <kevin_clague@yahoo.com> writes:
>
> LEGO purists use LEGO light bricks as resistors.
I don't think that would work very well, as the lights have a
rather low resistance, lower than a pressed touch sensor
(http://www.loria.fr/~stuber/lego/resistance.html).
But as a purist you can use the cybermaster sensors to multiplex three inputs
(http://www.loria.fr/~stuber/lego/cybermaster-touchsensors.html).
Jürgen
--
Jürgen Stuber <stuber@loria.fr>
http://www.loria.fr/~stuber/
> rot 13 "fr"
"se"
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> But as a purist you can use the cybermaster sensors to multiplex three
> inputs (http://www.loria.fr/~stuber/lego/cybermaster-touchsensors.html).
Hi Jürgen,
I have tried this method too, and as you say in your text, it is plagued by the
rubber contacts whose value goes down as more pressure is applied to the switch.
I measured resistance of several touch sensors while applying a very progressive
pressure, using a two stages worm screw down gearing driving a threaded axle
pushing sensor button. At the very beginning of contact, resistance is as high
as 10000 ohms, then go down very rapidly and reach an asymptote at about 500
ohms (exact value varies between touch sensors).
I'll post soon the results.
As the difference between switches resistances is only 2000 ohms, false readings
will happen (and I even doubt that double reading will cure the problem in
several mechanical designs).
But using only yellow and white sensors with 5k difference should be almost safe
- better than nothing !
Philo
www.philohome.com
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Here is a chart showing the variation of contact resistance of several touch
sensors while pressing button very progressively.
- There are huge differences between various sensor
- Lightly pressed touch sensors have contact resistance in the 2 to 5 KOhms range.
- Fully depressed resistance varies (for the samples I measured) between 400 and 560 Ohms
Photographs of the test contraption:
Top view
Touch sensor
close-up
Philo
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