>
> Technical Geniuses,
>
> I'm considering a first project! I'm wanting to sample a CdS cell(s) using a
> 16C84, but I'm not quite sure as to what A/D converter I would use. I'm at
> Maxim's site, and they offer samples...hehe, could anyone recommend a
> particular A/D Converter?
> Thank you guys again for your vast ammount of knowledge!

Well unless you need something really high speed you don't need an A/D
converter to do the job. Here's two really quick ways of doing it.

1) I'm using this one for my outside light controller. Put the CDS in a simple
555 timer circuit set for one shot mode with a PIC line for the trigger and
another for the output of the 555. The PIC code triggers the 555 and
measures how long the output remains high.

2) Another way to do it is to roll your own version of the Parallax BasicStamp
POT command which measures variable resistance. The basic idea is to charge a
capacitor to full charge, then to measure the amount of time it takes to
gradually discharge the same cap through a variable resistance. The trick
that I missed when trying this method is for the PIC to actively discharge the
cap by switching the sensing line between output low and input causing the
cap to discharge bit by bit. I haven't implemented this method yet but the
next time I need to measure a varaible resistance, I plan to try it.

Hope these ideas help. The 555 is simple, cheap, and can be done with $3 of
Radio Shack parts.

BAJ
>
> Tim H.
>