Water Sensor Circuit

Summary

This water sensor circuit is very sensitive to trigger and activate the audio visual alarm when wetness is sensed at its probes. This project is useful at homes to detect the water supply in the situations when the timing of water supply is not fixed. This circuit uses the 555 timer along with some sensor element which can detect moisture.
In this water sensor circuit based project, 555 timer works in astable mode. It is driven by the emitter current which is coming from BC548 transistor as this transistor has high gain. In astable mode IC 555 functions as an oscillator. So for 555 to work in full oscillator mode a high current is required so as to trigger it. As the probes sense the moisture on it, the transistor gets switched ON and small current starts flowing between the base and the emitter. When no moisture is detected i.e. in dry state it remains OFF.

Description

Initially as the supply is switched ON, the voltage at output pin of 555 timer is 0V. At this stage transistor will not conduct as the emitter current is LOW. Pin8 i.e. Vcc of 555 timer is connected to the collector of the transistor. As the transistor is switched OFF there will be no supply to 555 timer. As the water is sensed at the probes, transistor gets into its saturation region and starts conducting. As a result 555 gets supply for its operation. Its operation starts very soon as it is in astable mode. Sound is produced because of output pulses at pin3 which drives the loud speaker.
 
An ON/OFF state switch is used to control the conduction. The probes should be made up of non reactive metal so that there will be no inductance or capacitance present. An alternative can also be there i.e. use of alternate copper wires. No base resistor is required in this circuit because the transistor is in switch mode. The impedance at the emitter or the oscillator circuit acts as current limit. 

Circuit Diagram

Components
Resistor Image
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 Resistor

Resistor is a passive component used to control current in a circuit. Its resistance is given by the ratio of voltage applied across its terminals to the current passing through it. Thus a particular value of resistor, for fixed voltage, limits the current through it. They are omnipresent in electronic circuits.

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Capacitor image
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 Capacitor

 

 

Capacitor is a passive component used to store charge. The charge (q) stored in a capacitor is the product of its capacitance (C) value and the voltage (V) applied to it. Capacitors offer infinite reactance to zero frequency so they are used for blocking DC components or bypassing the AC signals. The capacitor undergoes through a recursive cycl...

LEDs | Light Emitting Diode
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 LED
 
Light emitting diodes (LEDs) are semiconductor light sources. The light emitted...
BC548 | Transistor BC548
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 Transistor BC548

BC548 is general purpose silicon, NPN, bipolar junction transistor. It is used for amplification and switching purposes. The current gain may vary between 110 and 800. The maximum DC current gain is 800.

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Speaker Image
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 Speaker
A loudspeaker (or "speaker") is a transducer that converts electrical energy into acoustical energy. When an electric signal is applied to the input pin of speaker, it generates sound waves. The other pin is connected to ground. A speaker is commonly used to produce sound in response to a sensor output. For example, in an...
555 Timer | IC 555 | NE555
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 555 Timer IC

555 is a very commonly used IC for generating accurate timing pulses. It is an 8pin timer IC and has mainly two modes of operation: monostable and astable. In monostable mode time delay of the pulses can be precisely controlled by an external resistor and a capacitor whereas in astable mode the frequency & duty cycle are controlled by two external resistors and a...

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