ESP32 S3 UNO - Automatic Irrigation System

Hardware Preparation

Or you can buy the following kits:

Buy Note: Many soil moisture sensors available in the market are unreliable, regardless of their version. We strongly recommend buying the sensor with TLC555I Chip from the DIYables brand using the link provided above. We tested it, and it worked reliably.

Overview of soil moisture sensor and Pump

This project combines two parts. If one of them is new to you, read its own tutorial first. You will learn the pinout, how it works and how to program it.

• ESP32 S3 Uno - Soil Moisture Sensor tutorial
• ESP32 S3 Uno - Controls Pump tutorial

In short, the soil moisture sensor gives an analog voltage. A higher value means drier soil. The pump needs 12V, which the board cannot give, so a relay works as a switch between the 12V adapter and the pump. The ESP32 S3 Uno only tells the relay when to switch.

ESP32 S3 Uno Pinout

The image below shows the pinout diagram of the ESP32 S3 Uno form board. Use it to find the A0 and D2 headers and their GPIO numbers when you wire the circuit.

Wiring Diagram

The sensor goes to A0 and the relay input goes to D2. The pump runs from its own 12V power adapter through the relay.

This image is created using Fritzing. Click to enlarge image

Connect the pump, the 12V power adapter and the DC power jack to the relay's COM and NO screw terminals. Never power the pump from the ESP32 S3 Uno.

ESP32 S3 Uno Code

The sketch reads the soil moisture sensor on A0 (GPIO2) every half second. If the value is above the threshold, the soil is dry, so it turns the relay and the pump on. Otherwise it turns them off and prints the state with the raw value to the Serial Monitor.

In setup(), the code calls analogSetAttenuation(ADC_11db). By default, the ESP32 S3 Uno ADC can only measure a small voltage. With 11 dB attenuation, the analog pin can read the full range, from 0V up to about 3.3V. Without this line, the readings hit 4095 too early and the sensor values look wrong.

The threshold of 2120 is the old 0 to 1023 value of 530 scaled up for the 12-bit ADC (0 to 4095). It is only a starting point. Your sensor, your soil and the 3.3V supply all change the real value, so calibrate it as shown in the steps below.

Detailed Instructions

Follow these steps in order:

1. New to the ESP32 S3 Uno? Follow ESP32 S3 Uno - Getting Started first.
2. Wire it up as shown in the diagram.
3. Connect the board to your computer with a USB Type-C cable.
4. Open Arduino IDE, choose the ESP32S3 Dev Module board and the correct COM port.
5. Find your threshold. Measure the value where the soil changes from wet to dry, as shown in ESP32 S3 Uno - Calibrates Soil Moisture Sensor.
6. Update the code. Put your value in the THRESHOLD line.
7. Open the Serial Monitor in Arduino IDE and set it to 9600 baud.
8. Upload the code by clicking the Upload button.
9. Check the output. Put the sensor in dry soil, then in wet soil, and watch the Serial Monitor.

1. Tip: Test with a cup of water before you put the pump in your garden. Push only the sensor's marked area into the soil and keep its electronics dry.

Code Explanation

Every line of the sketch has a comment that tells you what it does. Read the comments in the code above to follow the logic step by step.

Video Tutorial

Watch the video below to see this ESP32 S3 Uno project step by step.

FAQ

Why is the threshold 2120 and not 530 like on the UNO R4?

The ESP32 S3 Uno has a 12-bit ADC, so analogRead() returns 0 to 4095. The UNO R4 sketch used 0 to 1023. The value 530 times 4 is about 2120. Because the sensor also runs at 3.3V here, always calibrate and use your own value.

Why does the code call analogSetAttenuation(ADC_11db)?

It sets the ESP32 S3 Uno ADC input range to about 0 to 3.3V, so the full soil moisture signal maps to 0 to 4095. Without it the range is smaller and readings saturate early. The UNO R4 does not need this line, as it is ESP32-only. Keep the sensor output at 3.3V or less.

Can I power the soil moisture sensor from 5V?

No. With 5V, the AOUT pin can give more than 3.3V, and the ESP32 S3 Uno pins are not 5V tolerant. The capacitive sensor works well at 3.3V, so connect its VCC to the 3.3V pin.

Can I power the relay module from the 3.3V pin of the ESP32 S3 Uno?

Most relay modules have a 5V coil, so power their VCC from the 5V pin. The IN pin can still take the 3.3V signal from the ESP32 S3 Uno on most modules. If your relay does not click, use a 3V relay module or a module with a transistor driver.

What if my garden needs more sensors or pumps than the Uno headers give?

The ESP32 S3 Uno has two extra rows of holes with more GPIOs. GPIO15 and GPIO16 are I/O, PWM and analog. GPIO45 and GPIO35 to GPIO42 are I/O and PWM. GPIO47 and GPIO48 are output only, with PWM. Solder pin headers to use them and write the GPIO number in code. For more soil moisture sensors, use GPIO15 or GPIO16. For more relays, GPIO35 to GPIO42 are a good choice. Be careful with two things. First, GPIO47 and GPIO48 may run at 1.8V instead of 3.3V on some modules (especially ones with "V" in the name, like R8V or R16V), so 3.3V devices can be damaged or act strangely. Second, GPIO0, GPIO3 (D6), GPIO45 and GPIO46 (D9) are boot strapping pins, and a wrong connection can stop the board from booting or uploading code. Use the other extra pins first.

Why does the pump turn on and off very fast near the threshold?

When the value is close to the threshold, small changes make the relay switch often. You can use two thresholds, one to start and one to stop the pump, or add a minimum watering time in the code.

Troubleshooting

Learn More

• ESP32 S3 UNO - Soil Moisture Sensor