Build an automatic plant watering system

Measure how wet the soil is, and switch a small pump on through a relay to water a plant in short bursts, with limits that cap how much it can water.

Time2 weekends

Parts₹837–882

Free. Make an account and you come straight back to start it.

Before you start

Tools: Laptop with the Arduino IDE, USB phone charger or power bank, A potted plant, and a jar or bottle for the water tank, A measuring jug or a cup marked in ml, A plastic box or tub with a lid, for the electronics, Electrical tape, A tray, or the sink, for testing, Multimeter with a continuity (beep) setting (borrow one if you can), Small flat screwdriver, for the relay's screw terminals
Skills: A first Arduino project. No soldering. Steps 1–4 use code (or Get the code); step 5 is installing it at the plant.
Safety: Low voltage only: USB for the Uno, 4 AA cells for the pump. Water and electronics don't mix: keep the Uno, relay and batteries in a box above and away from the water. The relay could switch mains, but never connect mains to it.
Prices: Checked 2026-10, with a clone Uno, a USB cable, 4 AA cells and 1 m of tube; the top figure adds a second metre of tube and a relay module with an optocoupler; an original Uno adds about ₹1,950

Step 1 of 5

Soil readings, calibrated

The capacitive sensor reads the soil, and your sketch turns it into 0–100 % using your own dry and wet readings.

Task 01 of 08

Look at the sensor. The long flat part goes into the soil. Above the white line are the chip and the connector, which must never get wet.

Check: You can point to the line.

You need

9600 baud

Expect to see

Soil reading and moisture percent, about twice a second: not seen yetraw 412 moisture 41 %

Get the codeThe full sketch comes with the build.