Subject:
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Re: Voltage or resistance
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Newsgroups:
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lugnet.robotics
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Date:
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Sun, 27 Dec 1998 23:55:20 GMT
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Viewed:
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1261 times
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I'm joining this thread a little late, so sorry if any of this has already
been stated...
For "passive" sensors, the RCX measures a voltage level, but since there's
a pullup you may not get what you expect. If memory serves, the RCX ADC
uses a 5.0V reference and a 10K pullup. This means that a 10K resistor
across passive sensor contacts would read about half (512 in raw, 50 in
percent mode).
CdS cells are essentially a light controlled variable resistor, so they
work very nicely.
Supplying a "voltage" to the sensor inputs may give you surprising results
unless you take into account the effects of the pullup resistor (or happen
to have an "ideal" voltage source).
Dave
In article <40cf404b.3686a86e@aol.com>, lego-robotics@crynwr.com wrote:
> After experimenting with various photo sensors, it appears that resistance is
> what is measured. Solar cells produce no change in readings, but CdS photo
> resisters do.
>
> I managed to hook up a BASIC STAMP (a small microcomputer by Parallax) to one
> of the input ports using an LED (using pulse width modulation to vary
> brightness) and a photoresister. The idea is to use the light input to signal
> changes in the STAMP - perhaps touch sensors - the STAMP has 7 inputs left
> over.
>
> The problem is that the readings on the RCX fluxuate too much. I figure that
> with some creative programming, I might can get 3, maybe 4 identifiable
> readings. I'll look for an octocoupler that uses resistance. Maybe that will
> give me a more stable reading.
>
> chris
--
reply to: dbaum at enteract dot com
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Message is in Reply To:
 | | Voltage or resistance
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| After experimenting with various photo sensors, it appears that resistance is what is measured. Solar cells produce no change in readings, but CdS photo resisters do. I managed to hook up a BASIC STAMP (a small microcomputer by Parallax) to one of (...) (26 years ago, 27-Dec-98, to lugnet.robotics)
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