Subject:
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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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Fri, 5 Sep 2003 06:32:18 GMT
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Viewed:
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3848 times
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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 sensor reader in order to read the
resistance value on the input, which is different for each switch.
If you use the same method on the RCX (after enabling the temperature sensor in
the advanced control page) you can use four touch sensors like this:
Put resistors of 82k, 56k, 47k and 39k in series with the four switches.
Cut in half some short 9Volt leads and put 12Volt plugs on them. Then use choc
block (barrier strip) for the resistor assembly, with 1/0.6 bell wire protruding
- shove these wires into the middle of the 12V plug pins. One wire goes to the
RCX port and one to each switch.
Alternatively use Veroboard for a tidier solution, but I haven't got round to it
yet.
You can determine which of the four (and every combination of 2, 3 or 4 of them)
has been triggered by testing for temperature sensor values. This is great for
robots with multiple bumpers.
I picked the resistor values to make all combinations line up on the linear part
of the value vs resistance graph (the linear region is in the middle).
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!!
Happy sensing!
Mark Bellis
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