This document describes the design and purpose of an electronic rain detector circuit to automatically shut off a sprinkler system when raining. The circuit uses a 4011 integrated circuit with NAND gates to sense when a sponge connected to the circuit becomes wet from rain. When the sponge is wet, the circuit cuts power to an LED, representing the sprinkler system being shut off. The goal is to conserve water by preventing sprinklers from operating unnecessarily during rain storms.

1. Electronic Rain Detector SystemToConserve Water
Submitted By:
Praveen Rajarathinam
S.R. Public Sr. Sec. School
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2. Table of Contents
ABSTRACT ...................................................................................................... 3
OBJECTIVE...................................................................................................... 4
INTRODUCTION ............................................................................................. 4
TERMS AND CONCEPTS .................................................................................. 7
MATERIALS AND EQUIPMENT ........................................................................ 7
EXPERIMENTAL PROCEDURE .......................................................................... 7
REFERENCES................................................................................................... 9
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3. ABSTRACT
"Waste not, want not" is a common saying. These four words sum up an important
principle: if you "waste" an importantresource, you might find you don't have enough
of it when you "want" it.
One of the most important resources we have isclean water. In many parts of the
world, including the major parts of India, water shortage pose seriousproblems. In
this science project, we have built an electronic circuit that can
1) Detect when it is raining and
2) Shut offpower, such as to the sprinkler system.
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4. OBJECTIVE
To build a circuit that detects rain and can shut power off to a sprinkler system when
it is raining.
INTRODUCTION
Benefits of Water Consumption
One benefit is energy conservation. Water-pumping, delivery, and wastewater-
treatment facilities consume a significantamount of energy. In some regions of the
world over 15 percent of total electricity consumption isdevoted to water
management. Saving water conserves this energy for other uses. Another benefit is
habitatconservation. Overuse of fresh water can lower the levels of lakes and rivers,
causing significant environmental problems.Minimizing human water use helps
preserve freshwater habitats for local wildlife and migrating waterfowl, as well
asreduces the need to build new dams and other water-diversion infrastructures.
There are few things as wasteful as a water sprinkler system running during a rain
storm. The goal of this environmentalengineering science project is to build an
electronic circuit that can detect when it is raining and that can shut off thepower to
an automatic sprinkler system.
The circuit containsan electronic part called a 4011 integrated circuit (IC). The 4011
IC has four NAND gates (the word NAND is derivedfrom "not and," reflecting the fact
that the "NAND" output is the reverse of the "and" output). A NAND gate is able to
turn things on or off, depending on the kind of input it receives. The NAND gate has
two inputs, labelled 1 and 2 in Figure 1, below. The input is "on" when it is at 9 volts
(V) and "off" when itis connected to ground.
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5. Figure 1.A Rain Detector Circuit.
When the sponge is wet, no current flows from input 3 to ground, so the circuitshuts
off power. When the sponge is dry, the circuit allows current to flow through the LED
to ground (the LED is asubstitute for the sprinkler; when it is on or off, the sprinkler
would be on or off). The circuit "senses" rain becausethere is an electrical
connection between the wires when the sponge is wet. When this electrical
connection is made(when the sponge is wet) the voltages at inputs 1 and 2 become
high (9 V, "on") and output goes to 0 ("off"). To turnoff a sprinkler system, the power
that controls the sprinklers would be connected through the circuit.
Here is how the output is controlled by the two inputs. When inputs 1 and 2 are both
at 9 V (that is, 1 and 2 are both"on"), the output from input 3 is "off." For all other
combinations of the states of inputs 1 and 2 (off/off, on/off, off/on) theoutput from
input 3 is "on" (9 V). You can put this relationship in a truth table, as shown below.
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6. This science project involves making the circuit shown in Figure 1 and demonstrating
that it shuts off power to the lightemittingdiode (LED) when the sponge is wet. The
LED represents the sprinkler system. In an automatic sprinkler system, the water is
turned on andoff by a solenoid. When the solenoid is powered by a voltage, a part
(called a diaphragm) moves so that the water canflow. When the power is turned off,
the part falls back to its original location and the water flow is blocked.If the circuit
were to be usedoutside, the wet sponge would keep the power off until it was
allowed to dry out. It is important to note that the circuitallows electricity to flow only
when two conditions are met: the power switch is "on" (as it would be when the
sprinklersystem is turned on) and the water detector does not sense water. In the
circuit, turning the power on just meansmoving the power switch to the "on" position.
For a sprinkler system, the power would most likely be turned on by atimer. When
the water sensor is wet in a sprinkler system, the electricity is not allowed to flow,
even when the power isturned on.
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7. TERMS AND CONCEPTS
4011 integrated circuit
NAND gate
Ground, in circuitry
Truth table
Light-emitting diode (LED)
Solenoid
MATERIALS AND EQUIPMENT
4011 integrated circuit
R1 and R2: Resistors,100K-ohm (2)
R3: Resistor, 10M-ohm
R4: Resistor, 470-ohm
LED, red
Wire of various lengths to make circuit connections
Breadboard
Battery, 9-V
Sponge, rectangular, type you'd use in your kitchen
Scissors
EXPERIMENTAL PROCEDURE
1. Attach the 9-V battery, following the directions that came with the sensor board.
2. Push the power and display switches off.
3. The circuit you will use is shown on page 52 of the workbook.
a. The circuit is modified to make it a water detector.
b. Instead of using a touch sensor to control the circuit, you will use a sponge
that turns the circuit off whenit is wet.
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8. 4. Insert the 4011 IC across the slot in the breadboard, with pin 1 at F5.
a. See the diagram on page 16 of the Sensors Lab workbook for how to position
the IC across the slot.
5. Insert R1 into F1. The free end will be part of the water sensor.
6. Insert R2 into G1. The free end will be part of the water sensor.
7. Insert R3 across G4 and L7.
8. Insert R4 across H3 and N3.
9. Insert LED across N4 (anode) and L4 (cathode). The anode is the longer lead on
the LED.
10. Connect L1 to ground with a white wire.
11. Connect F7 to +9V with a white wire.
12. Connect F4 to +9V with a white wire.
13. Connect J1 to K1 with a white wire.
14. Connect K2 to L2 with a white wire.
15. Connect G10 to H10 with a white wire.
16. Connect K10 to L10 with a white wire.
17. Connect H9 to K9 with a white wire.
18. Connect L9 to ground with a white wire.
19. Connect the unused pins of the 4011 (pins 5, 6, 8, 9, 12 and 13) to ground.
20. Push the power switch on.
21. The LED should light up. If it does not light up, check your wiring carefully.
22. Cut the sponge into two parts (square shapes).
23. Soak one piece of sponge in tap water. Keep the other piece dry.
24. Touch the wet sponge to the two free leads from resistors R1 and R2.
25. Touch the dry sponge to the two free leads from resistors R1 and R2.
26. Turning on the power to your circuit is equivalent to the sprinklersystem's timer
starting the sprinkler. The LED shows whether or not electricity is flowing. When the
LED is on,the sprinkler would be on.
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9. REFERENCES
WEBSITES
www.google.co.in
All about circuits - Basic nand gate function.
www.sciencebuddies.org
Wikipedia – www.wikipedia.org
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