ESP32 - Ultrasonic Sensor - Relay

This tutorial instructs you how to use ESP32 and Ultrasonic sensor to control the relay. In detail:

The ESP32 automatically turns relay on when an object is close to the ultrasonic sensor.
The ESP32 automatically turns relay off when an object is far from the ultrasonic sensor.

We can extend this tutorial to use the ultrasonic sensor to control a led strip, siren, light bulb, or motor... by connnecting them to the relay.

Hardware Used In This Tutorial

1	×	ESP-WROOM-32 Dev Module
1	×	USB Cable Type-A to Type-C (for USB-A PC)
1	×	USB Cable Type-C to Type-C (for USB-C PC)
1	×	Ultrasonic Sensor
1	×	Relay
1	×	Optionally, Solenoid Lock
1	×	Optionally, 12V Active Buzzer
1	×	Optionally, 12V Cooling Fan
1	×	Optionally, 12V Warning Light Bright Waterproof
1	×	12V Power Adapter
1	×	Breadboard
1	×	Jumper Wires
1	×	Optionally, DC Power Jack
1	×	Recommended: Screw Terminal Expansion Board for ESP32
1	×	Recommended: Breakout Expansion Board for ESP32
1	×	Recommended: Power Splitter for ESP32

Or you can buy the following kits:

1	×	DIYables ESP32 Starter Kit (ESP32 included)
1	×	DIYables Sensor Kit (30 sensors/displays)
1	×	DIYables Sensor Kit (18 sensors/displays)

Disclosure: Some of the links in this section are Amazon affiliate links, meaning we may earn a commission at no additional cost to you if you make a purchase through them. Additionally, some links direct you to products from our own brand, DIYables .

Introduction to Relay and Ultrasonic Sensor

We have specific tutorials about relay and ultrasonic sensor. Each tutorial contains detailed information and step-by-step instructions about hardware pinout, working principle, wiring connection to ESP32, ESP32 code... Learn more about them at the following links:

Wiring Diagram

This image is created using Fritzing. Click to enlarge image

If you're unfamiliar with how to supply power to the ESP32 and other components, you can find guidance in the following tutorial: The best way to Power ESP32 and sensors/displays.

ESP32 Code

/* * This ESP32 code is created by esp32io.com * * This ESP32 code is released in the public domain * * For more detail (instruction and wiring diagram), visit https://esp32io.com/tutorials/esp32-ultrasonic-sensor-relay */ #define TRIG_PIN 23 // ESP32 pin GPIO23 connected to Ultrasonic Sensor's TRIG pin #define ECHO_PIN 22 // ESP32 pin GPIO22 connected to Ultrasonic Sensor's ECHO pin #define RELAY_PIN 26 // ESP32 pin GPIO26 connected to Relay's pin #define DISTANCE_THRESHOLD 50 // centimeters // variables will change: float duration_us, distance_cm; void setup() { Serial.begin (9600); // initialize serial port pinMode(TRIG_PIN, OUTPUT); // set ESP32 pin to output mode pinMode(ECHO_PIN, INPUT); // set ESP32 pin to input mode pinMode(RELAY_PIN, OUTPUT); // set ESP32 pin to output mode } void loop() { // generate 10-microsecond pulse to TRIG pin digitalWrite(TRIG_PIN, HIGH); delayMicroseconds(10); digitalWrite(TRIG_PIN, LOW); // measure duration of pulse from ECHO pin duration_us = pulseIn(ECHO_PIN, HIGH); // calculate the distance distance_cm = 0.017 * duration_us; if (distance_cm < DISTANCE_THRESHOLD) digitalWrite(RELAY_PIN, HIGH); // turn on Relay else digitalWrite(RELAY_PIN, LOW); // turn off Relay // print the value to Serial Monitor Serial.print("distance: "); Serial.print(distance_cm); Serial.println(" cm"); delay(500); }

Quick Instructions

If this is the first time you use ESP32, see how to setup environment for ESP32 on Arduino IDE.
Do the wiring as above image.
Connect the ESP32 board to your PC via a micro USB cable
Open Arduino IDE on your PC.
Select the right ESP32 board (e.g. ESP32 Dev Module) and COM port.
Copy the above code and paste it to Arduino IDE.
Compile and upload code to ESP32 board by clicking Upload button on Arduino IDE

Move your hand in front of sensor
See the change of relay's state

Line-by-line Code Explanation

The above ESP32 code contains line-by-line explanation. Please read the comments in the code!

Video Tutorial

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