You didn't say what data rate you were trying to receive. LDR's have really=
=20
poor frequency characteristics, don't expect much better than 5 to 20 Hz,=20
especially with a 500k series resistor.

When I first read you message, I thought you were just trying to detect=20
ambient light levels, but not sure.

Phototransistors are good for low data rates, up to 10Khz or a tad higher=20
if you are using them in small signal mode. Otherwise, look at a photodiode=
=20
for big bandwidth and a very large dynamic range.

Smile, it can always be worse:>:

Art

At 02:05 PM 4/18/04, you wrote:
>I am in need for a low cost light detector that has a use settable
>trigger point for the light/dark threshold. My first thought has been to
>just set up a voltage divider in the following way.
>
>         +5V
>           |
>          | |
>          | | 500K
>          | |
>           |
>           |
>           |--------- PIC ADC
>           |
>           |
>          | |
>          | | LDR
>          | |
>           |
>           |
>          ---
>
>The LDR has >500K resistance in darkness and 3K-20K at 10 Lux.
>
>One could use a PIC output pin to feed the divider instead of the +5V
>and just activate this when a measurement is needed.
>
>Is there any drawbacks with such a scenario? Is there a better way to do
>this in a low cost way?
>
>/Ake
>
>  ---
>Ake Hedman (YAP - Yet Another Programmer)
>eurosource, Brattbergav=E4gen 17, 820 50 LOS, Sweden
>Phone: 46 657 413430 Cellular: 46 730 533146
>Company home: http://www.eurosource.se      Kryddor/Te/Kaffe:
>http://www.brattberg.com
>Personal homepage: http://www.eurosource.se/akhe
>
>--
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>ways.  See http://www.piclist.com/#archives for details.

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