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Subject: Re: Water sensor
X-Newsreader: Forte Agent 1.91/32.564
NNTP-Posting-Date: Tue, 14 Jan 2003 15:52:46 GMT
Organization: Insight Broadband
Date: Tue, 14 Jan 2003 15:52:46 GMT
On Tue, 14 Jan 2003 13:44:28 GMT, robert wrote in message
>Bruce Murphy wrote:
>> Marc_F_Hult writes:
>> > My first suggestion would be to test parallel gold-plated pins on cloth
>> > in a voltage-divider circuit with the water from your AC units. A voltage
>> > divider made from a resistor+ parallel probe input to an LM339 comparator
>> > circuit can be used to drive a relay through a transistor or provide
>> > TTL-level signal.
>> Okay, this seems to be the way to go with experiments. I was thinking
>> of a small patch of fabric between the probes with a few wicking
>> threads to improve coverage area, but I'm going to need some
>> experimentation to work out what the time-effectiveness-sensitivity
>> tradeoffs are.
>i made one like this just recently and have achieved good wet/not wet
>result logic from a very weakly pulled-up CMOS gate, with the parallel
>wires forming a switch to ground. (idea from Terry Pinnel's water circuit
>the sensor is several rows of plain copper wire with every other wire
>going to one of two sides. the patch of fabric in my case is three layers
>of paper towel the i moisted slightly and ironed dry onto the grid.
>it is not AC excitation but in my application the water will mean a disaster
>is occuring and the sensor is viewed as sacrificial. (under the dishwasher,
>refrigerator and so forth).
>i put a microcontroller (PIC, there's my CMOS input) between the sensor
>and an RF xmitter module from Laipac, which sends periodic wet/not wet
>messages to the "base station" which monitors 4 such sensors on one
>frequency. each sensor has its own period of transmitting, all around
>60 seconds. the micro sleeps in between xmissions so batteries will last
>a long time. and when the base station loses contact with a sensor it
>alerts me to the fact, most likely a dead battery.
>each sensor has its own squeaker for local audible alert.
Sounds neat. Plain ol' CMOS 4xxx devices would also work. It shouldn't be too
hard to adapt a PIC/AVR program to AC excitation which is quite necessary for
long-term use of typical sensors used for soil moisture measurements (e.g
Watermark www.irrometer.com). I have the recommended specs for this
application if anyone is interested.
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