I would use a opamp configured as a comperator to measure the resistance
between two electrodes in the Plant pot. By using this approach you will
have a 0 or 5 v signal to the 12c508, and you can add a pot to adjust the
sencivity of the moist sensor.

Regrads Henrik Holmgaard

> -----Original Message-----
> From: Benjamin Petersen [SMTP:benjamin@MARK-INFO.COM]
> Sent: 10. maj 1999 09:47
> 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