Water Alarm - my adaptation of Tony van Roon's fluid-level sensor

 

Tony's schematic and notes are here:
http://www.sentex.ca/~mec1995/circ/sensor3.htm
https://web.archive.org/web/20161112101748/http://www.sentex.ca/~mec1995/circ/sensor3.htm

 

Version 1

This is the first version I built, in 2003.  Click on the thumbnails for full-sized pictures:

 

Version 2

Ambient noise spikes (like lightning) were causing the alarm to "chirp" occasionally, so I modified the circuit slightly, by adding a "test point," so that I could easily adjust R2 to reduce the sensitivity, by adding another resistor in parallel, without opening the box.

 

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