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> A light sensor connected to port 2 can cause on output from port 1. To see
> this (if you are using lejos), download the View object and hook up a light
> sensor to port 2. On my RCX, the port 1 raw values fluctuate between about
> 1010 and 1019. A similar effect can be observed by viewing port 2 and
> connecting the light sensor to port 3. These are the only combinations show
> this kind of cross talk. If the light sensor is connected to a port that is
> activated (so the red light glows), the cross talk effect is not visible.
> This caused a problem because I was using port 1 to multiplex several touch
> sensors, so S1 was in raw mode. A light sensor was connected to port 2 but
> was not activated. The SensorListener monitoring S1 suffered repeated
> calls to its stateChanged() method before any touch sensor was bumped.
> Which took me some time to figure out. The solution is to discard any raw
> values from S1 that are larger than 1000. (or else active S2 earlier)
> Has anyone else been bitten by this undocument feature?
If you've ever worked with multi-port A/D converters on a micro, and scanned
all of the inputs you've been bitten by this one. It's caused by two things,
parasitic capacitance on the chip itself and leakage between the lines going
to the A/D ports.
Cheers, Ralph
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Message is in Reply To:
 | | Sensor port cross talk
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| A light sensor connected to port 2 can cause on output from port 1. To see this (if you are using lejos), download the View object and hook up a light sensor to port 2. On my RCX, the port 1 raw values fluctuate between about 1010 and 1019. A (...) (22 years ago, 1-Aug-02, to lugnet.robotics.rcx)
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