Subject:
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Re: Multiplexing 4 touch sensors on an RCX input port
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Newsgroups:
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lugnet.robotics.rcx
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Date:
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Tue, 9 Sep 2003 19:45:31 GMT
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Viewed:
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4089 times
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In lugnet.robotics.rcx, Mark Bellis wrote:
> You can use four touch sensors per input port on the RCX.
While in theory, this sounds very cool, in pratice, I doubt it will work quite
that well.
The biggest problem will be that the standard touch sensors may not be 100% on
when you press it. This means the sensor itself can provide some resistance,
depending on how hard you press it.
You can test this by hooking up a touch sensor (configured to display raw
values) and softly press it. You'll notice, the harder you press it (to a
point) the more the number changes. (I forget if they go up or down, using the
standard software/firmware). Then, as you release the button (VERY slowly) you
see the numbers change, again.
So, the sensors won't give you a solid on/off reading. I believe the reading
can easily vary 5 or 10 percent.
That means, if you have 4 touch sensors, there are 16 possible combinations, so
each can vary by at most 6.25% (100%/16readings=6.25%) or there is 6% between 1
and 2 or 2 and 3
So, given that each sensor could vary as little as 5%, then at BEST you have
1.25% difference. At worst, the reading differ by -20% (readings overlap 20%)
It doesn't exactly come out like that, but let's just say it won't work very
well.
> Of course you can also put a light sensor in parallel as is done on the soccer
> robots. So now you have 15 sensors on your RCX!!
This, doesn't even work in theory.
While it IS possible to connect a single touch sensor and a single light sensor
to the same port, you can not use a touch sensor multiplexor with a light
sensor.
I can go into detail, but let's just say if your reading is ~50%, does that mean
the light sensor is on gray, OR are you pressing half the touch sensors?
There's no way to tell.
Nice idea, but it won't quite work.
Steve
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Message has 3 Replies:
Message is in Reply To:
 | | Multiplexing 4 touch sensors on an RCX input port
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| You can use four touch sensors per input port on the RCX. The Cybermaster touch sensors have resistors in parallel, and this is how the Cybermaster knows which implement is attached to the tracked robot. It uses its sensor input as a temperature (...) (21 years ago, 5-Sep-03, to lugnet.robotics.rcx)
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