Arduino Nano - Ultrasonic Sensor - Relay

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

Arduino Nano activates the relay when the object is near the ultrasonic sensor
Arduino Nano deactivates the relay when the object is distant from the ultrasonic sensor

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	×	Official Arduino Nano
1	×	Alternatively, DIYables Nano V3.0 Development Board
1	×	USB A to Mini-B USB cable
1	×	Ultrasonic Sensor
1	×	Relay
1	×	Warning Light Bright Waterproof
1	×	12V Power Adapter
1	×	DC Power Jack
1	×	Jumper Wires
1	×	Breadboard
1	×	Recommended: Screw Terminal Expansion Board for Arduino Nano
1	×	Recommended: Breakout Expansion Board for Arduino Nano
1	×	Recommended: Power Splitter for Arduino Nano

Or you can buy the following kits:

DIYables Sensor Kit (18 sensors/displays)

Disclosure: Some of the links provided in this section are Amazon affiliate links. We may receive a commission for any purchases made through these links at no additional cost to you.
Additionally, some of these links are for products from our own brand, DIYables .

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

This image is created using Fritzing. Click to enlarge image

The diagram below shows the same connections without a breadboard:

The wiring diagram between Arduino Nano and Ultrasonic Sensor Relay (No Breadboard)

This image is created using Fritzing. Click to enlarge image

Pushing jumper wires into the headers is quick, but the wires can slip out. In this case, use a Screw Terminal Expansion Board for Arduino Nano. The Arduino Nano plugs into it, and each pin gets a screw terminal. The wiring stays the same. Only the wires now go to the screw terminals, as shown below.

The wiring diagram between Arduino Nano and Ultrasonic Sensor Relay Screw Terminal

This image is created using Fritzing. Click to enlarge image

See The best way to supply power to the Arduino Nano and other components.

Arduino Nano Code

/* * This Arduino Nano code was developed by newbiely.com * * This Arduino Nano code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * https://newbiely.com/tutorials/arduino-nano/arduino-nano-ultrasonic-sensor-relay */ #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.

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!

※ NOTE THAT:

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.

Relay vs MOSFET Module

A relay is not the only way to switch a device. If your device runs on DC power, such as a 12V solenoid lock, a 12V pump or a 12V fan, a MOSFET module can do the same job.

	Relay	MOSFET Module
What it can do	turn the device on or off	turn the device on or off, and set its power (PWM)
Noise when switching	a click every time	no sound
How fast it switches	slow, a few milliseconds	very fast
Life	the contacts wear out after many switches	nothing moves, so it lasts long
Type of power	AC or DC	DC only
Device power supply	any voltage the relay is rated for	about 6V or more
Isolation from the Arduino	yes, between coil and contacts	yes, by the PC817 optocoupler
Good for	AC devices, or a simple ON/OFF	DC devices, or dimming and speed control

Both the relay and the MOSFET module turn on when the Arduino Nano pin is HIGH. So for a simple ON/OFF, the code above stays the same. Only the wiring changes. For AC mains devices, always use the relay.

To learn the MOSFET module pinout, wiring, PWM code and safety tips, see the Arduino Nano - MOSFET Module tutorial.

Video Tutorial

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