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Simple Water Alarm Indicator Circuit using 555

2015-01-12 23:28  
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Here is a water alarmindicator circuit. An On/Off switch is provided and remember to use a non-reactive metal for the probe contacts. Gold or silver plated contacts from an old relay may be used, however a cheap alternative is to wire alternate copper strips from a piece of veroboard. Theindicator circuituses a 555 timer wired as an astable oscillator and powered by the emitter current of the BC109C. Under dry conditions, the transistor will have no bias current and be fully off. As the probes get wet, a small current flows between base and emitter and the transistor switches on. A larger current flows in the collector circuit enabling the 555 osillator to sound. Here is a schematic water alarmindicator circuit:

Simple Water Alarm Indicator Circuit using 555 400x272 Simple Water Alarm Indicator Circuit using 555

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