This is a big brother of the earlier piezo version, which can be used as an alarm when filling overhead tanks or as a water tap flow indication. Unlike the piezo version, this alarm can give out fairly loud tone and can even be amplified further up. Tone can also be varied to suit individual needs.
The circuit is shown in Schematic . You would have noticed in the earlier circuit that the trigger terminal (2) is connected to the threshold terminal (6) to make it an astable oscillator. Now the trick here is that these terminals are coupled through water.
There is not much of a change from the earlier circuit. Remove the jumper connecting Pin 2 and Pin 6 and connect two wires from each terminal and use them as probes. These wires can be any hook up wires or wires used for the domestic wiring. Scrap the ends of the wires a little and use them as probes. Pure water is non-conducting but domestic water and water supplied from the wells conducts a little bit and that is enough for this alarm to operate. You may have to occasionally clean these ends, when you notice scaling.
Parts are same as the above circuit. Only you need long wires.This alarm can be modified to check out if the overhead tank is empty. This is more important as the tanks have inevitable tendency to get empty at a wrong time just as the guests arrive and the power also goes out just about the time. This can be used to forewarn impending low level. Such an alarm can be used to check if the sump level is low, or if the water level in the cooler has gone down. The circuit can be adopted to give an alarm when the water level goes low by manipulating wiring at 6 (Threshold) and 2 (Trigger) pins or by the pin connections at 4 (reset) and 1 (ground).
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