Water sensor is a little unit which is used to give an audible alarm when a hose of the washing machine has burst or when it starts to rain, so that you can save the washing machine from being rain drenched, or it can give an alarm to call you to the bathroom when the bathwater is needed to turn on.
Undoubtedly you can think of some more utilization of water sensor.
You can power the circuit from a 9 V PP3 battery. Since the current consumption is very low, chances are it will last for a year at least. After a year the battery loses its ability of self-discharge.
Therefore, after a year the unreliable battery must be replaced. The water detector unit is made up of a sensor, an R-S bi-stable, an oscillator and a sensor stage which works as the alarm buzzer.
How the Water Sensor Fabricated
The sensor is made of a waste-piece of wiring board which is of 40x20 mm in size. One needs to connect all odds and all even tracks together with the wire link in such a way so that 1 connects to 3 to 5, on the other hand 2 connects to 4 to 6.
You need to protect the tracks with tin to prevent them from corrosion. The resistance between two sets of tracks stays high when the board remains dry. However, when the board is wet, a sharp decline in resistance is observed.
How the Circuit Works
The sensors which remain in series with resistor R2 and the two together form a voltage divider which is dependent on humidity.
The voltage divider resets the R-S bi-stable when input 1 of N2 drops down. At that point oscillator N3 is switched on and the buzzer is being energized by the driver N4.
The bi-stable is automatically set when the power goes up via the R1 and C1 series combination.
One can also modify this water sensor circuit as a lie-detector. In that case the sensor is needed to be replaced by two lengths of wire.
This particular wire’s ends are being stripped. The stripped wires are bare and it is then placed in the hands of the person who will be interrogated for lie-detection. If the person lies, his hands will go moist by sweat.
Due to the dampness of his hands the buzzer will make a noise. The sensitivity of the circuit is being calculated by the value of R2.
However, some experiments are still required in this regard. The switch S1 helps to disable the oscillator and the buzzer.