4. Rain Alarm Click here for Circuit Diagram.
circuit gives out an alarm when its sensor is wetted
A 555 astable multivibrator is used here
which gives a tone of about 1kHz upon detecting water.
The sensor when wetted by water completes the circuit
and makes the 555 oscillate at about 1kHz.
sensor is also shown in the circuit diagram.
has to placed making an angle of about 30 - 45 degrees
to the ground. This makes the rain water to flow through
it to the ground and prevents the alarm from going on
due to the stored water on the sensor.
used to make the sensor has to be aluminium and not
copper. This is because copper forms a blue oxide on
its layer on prolonged exposure to moisture and has
to be cleaned regularly.
The aluminium foils may be secured to the wooden / plastic
board via epoxy adhesive or small screws.
The contact X and Y from the sensor may be obtained
by small crocodile clips or you may use screws.