Subject:
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Re: Radio Shack CDS cells in parallel
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Newsgroups:
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lugnet.robotics.rcx
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Date:
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Tue, 8 Feb 2000 22:43:38 GMT
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Viewed:
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1656 times
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In lugnet.robotics.rcx, Mike Burger writes:
> When I first checked out the Radio Shack CDS [snip]
> very large metal cased one that
> had a horrible super low resistance range, perhaps defective.
I built a sensor out of one of those and it works fine, so yours is probably
defective. I superglued mine to the top of a 2x2 brick with the studs
removed. You can see my high tech design at http://www.ben.com/LEGO/rcx/
> I tried this idea and it worked. You can put several of the small
> higher resistance CDS cells in parallel to partially adjust their
> resistance and response range.
You could also just connect a suitable fixed resistor in parallel to adjust the
resistance range down (or in series to adjust it up). Given R1 and R2: in
series, Rtotal = R1 + R2; in parallel, 1/R1 + 1/R2 = 1/Rtotal.
If you want a larger "viewing angle" then multiple CdS sensors might be the way
to go.
The most clever design I've seen uses two CdS sensors as a voltage divider
(buffered by an op amp) as a "comparative light sensor". I've breadboarded one
of those but not built it into a brick yet. Maybe I should learn how to do
surface mount. :-)
--Ben
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Message has 1 Reply:
 | | Re: Radio Shack CDS cells in parallel
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| (...) ----- True, but the RS CDS cells are cheap and using them in parallel or series also changes the response range, since all the resistances change with light levels. This would be most dramatic in the series connected case at the low resistance (...) (25 years ago, 9-Feb-00, to lugnet.robotics.rcx)
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Message is in Reply To:
| | Radio Shack CDS cells in parallel
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| When I first checked out the Radio Shack CDS cell five packs, the cells were all alike, about 1/4 inch and flat on two sides. But when I went back, I found some packs that had different cells. They had three of the usual small ones and a 1/2 inch (...) (25 years ago, 8-Feb-00, to lugnet.robotics.rcx)
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