Make sure you use AC to measure the resistance.  The probes will corrode
very quickly otherwise.  Maybe a pushbutton to calibrate the device for wet
and dry states?  How about making the probes on flying leads so that you
could connect several plant pots in series?

Regards

Mike Rigby-Jones

> -----Original Message-----
> From: Benjamin Petersen [SMTP:benjamin@MARK-INFO.COM]
> Sent: Monday, May 10, 1999 9:47 AM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      "Plant out of water project"
>
> I have an (old) idea for a new pic project.
> I would like to attatch this device to a plant and make it beep when the
> plant needs water.
>
> I was thinking about using :
> 1 3v litium batt
> 1 PIC12c508
> 1 Pizo-beeper
> 2 metal pins pluged into the plants pot (or what ever you call it)
>
> I would like to make some kind of A/D converter, and as far as i can
> recall
> it can be done with a cap and a res.
> And something with pulsing an output and reading an input.I was thinking
> that the water alarm should NOT beep during the night, messured either by
> an
> internal clock or by a photosenser. Dryness alarm should be dynamic.
>
> When this project is done it will ofcause be public.
>
> Regards
> Benjamin Petersen