Subject:
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Re: Question?
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 7 Feb 2002 11:33:11 GMT
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Original-From:
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PeterBalch <PETERBALCH@COMPUSERVE.COMnospam>
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Viewed:
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537 times
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> How do you connect a sensor backwards?
I meant that the sensor can be connected either way round.
> If you look at the schematics (say at
http://philohome.free.fr/sensors/legorot.htm)
busted link!
I've yet to find a working link to _any_ schematic of the light or rotation
sensor
> It might be simpler to look at it in terms of current flows; "dark" is no
current, and "light" is full current, regardless of polarity.
Maybe that is the case.
I was under the impression that some of the sensors had contained active
components that amplified or buffered the signal. In which case which way
round the sensor is can give rise to problems unless the the designers are
quite clever.
In the case of the light sensor, the input seen by the RCX is the same no
matter which way round the sensor is plugged.
If I replace the sensor with a variable resistor (R) then the sensor value
reported by the RCX is approx:
(1-1/(1+10000/R))*160
That implies it's easy. The RCX connector is just the bottom half of a
potential divider.
But the light sensor can't be the equivalent of a resistor across the
terminals.
Firstly the sensor is a photodiode or phototransistor - which only works
one way round. Ok so you put the photodiode inside a bridge rectifier and
it will work fine.
But secondly, someone mentioned that there is an Op-Amp in the sensor. The
signal from the photodiode is buffered. Which brings us back to my original
point that it's hard to make a circuit that's connected to just two wires
and doesn't care which way round those wires are connected.
Peter
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Message has 1 Reply:
 | | Re: Question?
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| Hi Peter, (...) it works for me. (URL) shows another schematics that doesn't show the real rotation sensor circuit, but has the same interface to the RCX. (...) Yes, that's the case. (...) That's what the rectifier bridges are for. (...) With the (...) (23 years ago, 7-Feb-02, to lugnet.robotics)
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