Arduino Nano - Ultrasonic Sensor - Relay

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

By linking a relay to a light bulb, LED strip, motor or actuator, we can use Arduino Nano and an ultrasonic sensor to manage the light bulb, LED strip, motor or actuator.

Hardware Preparation

1×Arduino Nano
1×USB A to Mini-B USB cable
1×Ultrasonic Sensor
1×Warning Light Bright Waterproof
1×12V Power Adapter
1×DC Power Jack
1×Jumper Wires
1×(Optional) 9V Power Adapter for Arduino Nano
1×(Recommended) Screw Terminal Adapter for Arduino Nano

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 unfamiliar with relay and ultrasonic sensor (including pinout, operation, and programming), the following tutorials can help:

Wiring Diagram

The wiring diagram between Arduino Nano and Ultrasonic Sensor Relay

This image is created using Fritzing. Click to enlarge image

Arduino Nano Code

/* * This Arduino Nano code was developed by * * This Arduino Nano code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * */ #define TRIG_PIN 4 // The Arduino Nano pin connected to TRIG pin of ultrasonic sensor #define ECHO_PIN 3 // The Arduino Nano pin connected to ECHO pin of ultrasonic sensor #define RELAY_PIN 2 // The Arduino Nano pin connected to relay #define DISTANCE_THRESHOLD 50 // in centimeters float duration_us, distance_cm; void setup() { Serial.begin (9600); // Initialize the Serial to communicate with the Serial Monitor. pinMode(TRIG_PIN, OUTPUT); // set arduino pin to output mode pinMode(ECHO_PIN, INPUT); // set arduino pin to input mode pinMode(RELAY_PIN, OUTPUT); // set arduino pin to 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

  • Plug the USB cable into the Arduino Nano and the PC.
  • Launch the Arduino IDE, choose the correct board and port.
  • Open the code in the Arduino IDE.
  • Click the Upload button on the Arduino IDE to compile and upload the code to the Arduino Nano.
Arduino IDE Upload Code
  • Move your hand in the vicinity of the sensor and observe the alteration in the state of the relay.

Code Explanation

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


The code above is intended for educational purposes. The ultrasonic sensor is very susceptible to interference. If you plan to use it in a practical setting, noise filtering should be applied to the ultrasonic sensor. For more information on how to filter noise from distance measurements of the ultrasonic sensor, please refer to this tutorial.

Video Tutorial


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