Problems I encountered when I built one of these:

1.  Soil resistance changes over time.  I would plug my two probes into the
wet soil, then an hour later it would start beeping.  I made a little
circuit to plot this on my datalogger, and noticed a dramatic change in soil
resistance.  Of course I was measuring with an AC signal to prevent
corrosion.

2. You can buy other people's attempts at doing this, that also don't work,
at dimestores for $4.00.  See Consumer reports, early this year.

3.  I made a real nice cricket chirp, and made a resistance measurer using
AN512 style RC timer measurement.   Can't find the code anymore, so I
must've erased it in disgust.






-----Original Message-----
From: Michael Rigby-Jones <mrjones@NORTELNETWORKS.COM>
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: Monday, May 10, 1999 4:52 AM
Subject: Re: "Plant out of water project"


>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