Subject:
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Re: CdS cells
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Fri, 8 Aug 1997 16:54:08 GMT
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Original-From:
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Randy Sargent <rsargent@newtonlabs=spamcake=.com>
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Viewed:
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1726 times
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> David,
>
> I believe you will want to purchase ones that have a dark resistance
> more than say 20K. The sensor is part of a divider circuit that includes
> a 47K resistor. The sensed signal equals (sensor resistance)/(sensor +47K)
> multipled by 255. If your sensor has too low a dark resistance the
> difference between bright light and no light is like 0 and 3.
> That's what I got with the sensors I received from Gleason. They
> have a dark resistance of about 1K. If you really want to differentiate
> between light and dark you need a much larger dark resistance.
>
> Don
It's certainly easiest to start out with a sensor that has a reasonable
resistance range. However, if for whatever reason you have sensors that
tend to be lower in resistance to the ideal, simply add your own resistor
between the signal and +5v, which is also available on the sensor
connector. This new resistor is in parallel with the on-board 47k, so you
can do the math (Rparallel = 1/(1/R1 + 1/R2)) to lower the resistance of
the divider leg opposite your sensor.
It's more work to wire up, but sometimes might be less work than finding
the ideal sensor.
-- Randy
----------------------------------------------------------------
Randy Sargent Newton Research Labs
Senior Design Engineer Robotic Systems and Software
rsargent@newtonlabs.com http://www.newtonlabs.com/
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