Path: utzoo!censor!geac!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!usc!elroy.jpl.nasa.gov!ncar!asuvax!mcdphx!citek.mcdphx.mot.com!hbg6
From: hbg6@citek.mcdphx.mot.com
Newsgroups: comp.robotics
Subject: Re:dirt cheap immersion sensor?
Message-ID: <14143@mcdphx.phx.mcd.mot.com>
Date: 28 Nov 90 20:43:22 GMT
Sender: news@mcdphx.phx.mcd.mot.com
Reply-To: hbg6@citek.mcdphx.mot.com
Organization: Motorola Microcomputer Division, Tempe, Az.
Lines: 32
Summary:
Expires:
References:<1990Nov24.211134.28944@uunet!unhd>
Sender:
Followup-To:
Distribution:comp

In article <1990Nov24.211134.28944@uunet!unhd> rg@unhd.UUCP (Roger Gonzalez ) writes:
> ....
>I need a cheap, fast, and small sensor to detect when its been submerged
>in (fresh) water.  I assume that this sort of thing exists for turning
>on automatic bilge pumps.  We need one for our EAVE vehicle, but I was
>also considering an automatic waterbowl filler for my cats...
> ....

Dig out the National Semiconductor "Special Purpose Linear Devices" data
book and look up the LM1830 (page 5-123 in my copy). The 1830 is a one
chip fluid detector. The fluid to be detected must be a little conductive
to work. I've used them with city water, rain water and aquarium water
with no problem. In a nut shell, the device uses two probes; one is 
connected to the circuit ground and the other to the chip. There is a TTL
level output indicating 'fluid detected'. Two capacitors are all that is
needed to make the chip work. Even the most novice hardware type should be
able to get it working.

I have another solution that uses a float, 3 Lbs. of salt, a mouse, a hungry
cat, 9 feet of twine and a lit candle but I'll save it for sci.rube.goldberg.
:-)

Later,
John

.....................................................................
reply to 'from' address; hbg6@citek.mcdphx.mot.com
NOT the 'sender' line address!
Someday my sysadm will decide this is a 'real' problem. :-)
.....................................................................
All opinions expressed are mine and not Motorolas, their loss.
.....................................................................