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A water activated alarm circuit

2016-02-21 13:39  
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This article describes a water-activated alarm circuit theory. For your better understanding in the diagram, we recommend that you look at the text. The circuit uses a 555 timer connected as a non-steady state emitter current of the oscillator and  BC109C . In dry conditions, the transistor will be no bias current and fully off. As a probe wet, a small current betw1een base and emitter of the transistor switch. A larger current flows in the collector circuit of the oscillator 555 sounds. An on / off switch is provided and remember to use a metal detector contacts without reactance. Gold or silver-plated contacts and old relay may be used, but a cheap alternative is to replace copper wire from a Vero board. These eventually ends, but only a few basic circuit oxidation current flows, the higher the impedance caused by the oxidation is not important. No base resistor is necessary for the transistors in the emitter follower, the current limiting impedance of the transmitter (oscillator circuit). Understanding of the text, you can plug a high efficiency.
 

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