You're right about photocells not operating on resistance unless he's using
Cadmium Sulfide cells, Olin (Heaven forbid)! ;-)


----- Original Message -----
From: "Olin Lathrop" <olin_piclist@EMBEDINC.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Wednesday, April 16, 2003 7:48 AM
Subject: Re: [PIC]: How to connect photocell to pic a-d


> > I am somewhat new to pics and would appreciate some help with using a
> > photocell on a pic A-D port. The range of light on the photocell will
> > not cover the full resistance range of the photocell (whichever one I
> > use),
>
> Photocells convert light to electrical energy, and don't operate on
> varying resistance.  Your best bet for measuring light intensity is to
> measure the photocell's short circuit current.  This can be done with an
> opamp and feedback resistor.
>
>
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