7/31/2019 Esk 4 Rain Alarm
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RAIN ALARM
This is a simple circuit that can be used to detect rain. It
will give a loud beep when the first
drop of rail falls on the sensor. So it useful to detect rain
where sun drying is carried out.
Op-Amp IC 741 is designed as a voltage comparator. Its inverting
input pin2 receives halfsupply voltage (4.5V) through the potential
divider R1 and R2. Its non-inverting input pin 3 is
connected to touch pads and variable resistor VR1. Output of the
comparator becomes high only
when its pin3 gets a higher voltage than pin2. Normally pin 3 is
low because it is not getting
current from the positive supply. So output remains low. This
inhibits transistor T1 and buzzer
remains off. When the contacts of the touch pad gets water,
current passes through the contacts
to the pin 3 of the comparator. This higher voltage at pin 3
causes the output to go high. LED
lights and transistor conducts. Buzzer then starts beeping to
indicate rain.
Sensor
Sensor can be a short piece Strip board (line type). Solder two
thin wires to the adjacent tracks
of the touch pad and solder wires to points A and B.
Test
Connect battery. Buzzer remains silent. Place a drop of water in
the touch pad. Buzzer starts
beeping and LED lights. Adjust VR1 to regulate current to pin 3
of IC if needed.
SENSOR
A
B
VR1
10K
R1 10K
R2 10K
3
24
7
6
IC1
741
R3 100R
LED
RED
BUZZER
T1
BC 547
9V BATT
+
ESK 4-A
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