Water Activated Sensor Alarm Using 555 PCB

Posted on Feb 7, 2014

The circuit comprises a 555 IC as the core. This is designed to work as an astable multivibrator. When we connect a positive 9 volt to pin no. 8, the circuit will produce a sound through speaker. But here the connection to pin 8 goes through the transistor BC 109c or BC 548. In this condition, the base of the NPN transistor haven`t any positive vo

Water Activated Sensor Alarm Using 555 PCB
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ltage. But when the resistance between the "contacts" is lower due to water, the transistor get it base voltage and the circuit will produce a sound. We can connect the the 555 output pin no. 3 to loudspeaker through a 100uF electrolytic capacitor. The resistors, R1 and R2 are used for IC biasing. We can change the tone of the sound coming from the speaker by changing the value of capacitor C1.

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