Water Sensor Circuit
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.
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.
