ESP8266 - Ultrasonic Sensor - Relay

This tutorial instructs you how to use ESP8266 and ultrasonic sensor to control relay. In detail:

By connecting a relay to a light bulb, LED strip, motor or actuator, we can use ESP8266 and an ultrasonic sensor to control the light bulb, LED strip, motor or actuator.

Hardware Preparation

1×ESP8266 NodeMCU
1×Micro USB Cable
1×Ultrasonic Sensor
1×Warning Light Bright Waterproof
1×12V Power Adapter
1×DC Power Jack
1×Jumper Wires
1×(Optional) 5V Power Adapter for ESP8266
1×(Optional) ESP8266 Screw Terminal Adapter

Or you can buy the following sensor kits:

1×DIYables Sensor Kit (30 sensors/displays)
1×DIYables Sensor Kit (18 sensors/displays)
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Overview of Relay and Ultrasonic Sensor

If you are not familiar with relay and ultrasonic sensor (pinout, how it works, how to program ...), the following tutorials will help you:

Wiring Diagram

The wiring diagram between ESP8266 NodeMCU and Ultrasonic Sensor Relay

This image is created using Fritzing. Click to enlarge image

See more in ESP8266's pinout and how to supply power to the ESP8266 and other components.

ESP8266 Code

/* * This ESP8266 NodeMCU code was developed by * * This ESP8266 NodeMCU code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * */ #define TRIG_PIN D1 // The ESP8266 pin D1 connected to Ultrasonic Sensor's TRIG pin #define ECHO_PIN D2 // The ESP8266 pin D2 connected to Ultrasonic Sensor's ECHO pin #define RELAY_PIN D7 // The ESP8266 pin D7 connected to Relay's pin #define DISTANCE_THRESHOLD 50 // centimeters float duration_us, distance_cm; void setup() { Serial.begin (9600); // Initialize the Serial to communicate with the Serial Monitor. pinMode(TRIG_PIN, OUTPUT); // Configure the ESP8266 pin to the output mode pinMode(ECHO_PIN, INPUT); // Configure the ESP8266 pin to the input mode pinMode(RELAY_PIN, OUTPUT); // Configure the ESP8266 pin to the output mode } void loop() { // Produce a 10-microsecond pulse to the TRIG pin. digitalWrite(TRIG_PIN, HIGH); delayMicroseconds(10); digitalWrite(TRIG_PIN, LOW); // Measure the pulse duration from the 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); }

Detailed Instructions

To get started with ESP8266 on Arduino IDE, follow these steps:

  • Check out the how to setup environment for ESP8266 on Arduino IDE tutorial if this is your first time using ESP8266.
  • Wire the components as shown in the diagram.
  • Connect the ESP8266 board to your computer using a USB cable.
  • Open Arduino IDE on your computer.
  • Choose the correct ESP8266 board, such as (e.g. NodeMCU 1.0 (ESP-12E Module)), and its respective COM port.
  • Plug the USB cable into the ESP8266 and the PC.
  • Launch the Arduino IDE, choose the correct board and port.
  • Copy the code and open it in the Arduino IDE.
  • Click the Upload button in the Arduino IDE to send the code to the ESP8266.
Arduino IDE Upload Code
  • Place your hand in front of the sensor and observe how the relay's state is altered.

Code Explanation

Check out the line-by-line explanation contained in the comments of the source code!


The code shown above is intended for educational purposes. The ultrasonic sensor is highly susceptible to noise. If you plan to use it in a practical setting, you should apply noise filtering to the ultrasonic sensor. For more information on how to filter noise from ultrasonic sensor distance measurements, please see this tutorial.

Video Tutorial


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