Smart Irrigation System Science project

1. What is this project?

Have you ever forgotten to water a plant? In this project, you will build a Smart Irrigation System that waters a plant by itself whenever the soil gets too dry.

You do not need to write any code. The soil moisture sensor module has a small built-in “decision maker” that checks whether the soil is wet or dry. It tells a relay (an electrically controlled switch) to turn a water pump ON or OFF.

How it works

1. Soil moisture sensorchecks the soil
2. Relayswitches the pump
3. Water pumpmoves the water
4. Plantgets watered

• Dry soil: the sensor signals the relay, the pump turns ON, and water reaches the plant.
• Wet soil: the sensor signals the relay, the pump turns OFF.

2. What you need

3. Meet the soil moisture sensor

The sensor has two parts.

A. The probe. This is the fork-shaped part that goes into the soil. Wet soil carries electricity better than dry soil, and the probe uses this to measure moisture.

B. The module. This small circuit board reads the probe and makes the decision. It has these pins and parts:

We use only DO. It sends a simple ON/OFF-style signal that the relay understands.

4. Meet the relay

A relay lets a small signal control a larger device, like our pump. Think of it as a light switch that flips by itself when it receives a signal.

Control side (the signal)

Switch side (the pump): COM, NO and NC

Relay resting (OFF):        Relay activated (ON):

COM ── X ── NO              COM ────── NO
COM ────── NC               COM ── X ── NC

5. Why do we need a relay?

A sensor can only send a very tiny signal. It cannot supply enough power to run a pump. The relay bridges the gap: the small signal from the sensor flips the switch, and the switch lets the full power flow to the pump.

6. Wiring diagram

7. Step-by-step assembly

1. Prepare the plant. Fill a small pot with soil. Push only the probe into the soil. Keep the electronic module out of the soil and away from water.
2. Connect the probe to the module using the cable that comes with the sensor.
3. Wire the sensor. Connect VCC to 5V (+) and GND to 5V (−). Leave DO for the next step.
4. Wire the relay. Connect VCC to 5V (+) and GND to 5V (−). Then connect the sensor’s DO to the relay’s IN.
5. Prepare the pump. Place the pump in the water container. Attach the tube to the pump outlet and place the other end near the plant. Make sure the tube is not bent or blocked.
6. Wire the pump through the relay.
   • 5V (+) to COM
   • NO to Pump (+)
   • Pump (−) to 5V (−)
7. Switch on the power and test.

8. Testing and setting up

Test 1: Does the pump work when the soil is dry?

Power the system with the probe in dry soil or in the air. The pump should turn ON.

Test 2: Does the pump stop when the soil is wet?

Slowly add water to the soil, or dip the probe into a glass of water. The pump should turn OFF.

Setting the sensitivity

The small screw on the blue potentiometer decides how dry the soil should be before the pump starts.

1. Put the probe in soil that is as moist as you want it to be.
2. Slowly turn the screw with a small screwdriver.
3. Stop at the point where the sensor’s output LED changes. That is your “wet enough” level.
4. Test again with dry and wet soil, and fine-tune if needed.

Every sensor and soil type is slightly different, so always set this using your own sensor instead of copying someone else’s setting.

9. Troubleshooting

10. Safety rules

11. What you will learn

• Agriculture: how soil moisture affects plants
• Electronics: sensors, switches and relays
• Circuits: control signals and power circuits
• Water saving: giving water only when needed
• Automation: turning a manual job into an automatic one

12. Conclusion

In this project, you built an automatic watering system using only a sensor, a relay and a pump. The sensor checks the soil, the relay acts as the switch, and the pump waters the plant when needed.

Sense, Decide, Act. This is the same idea used in real farms, greenhouses and smart homes around the world.