Arduino - Ultrasonic Sensor - Relay

We are going to learn how to:

If the object is close to ultrasonic sensor, turn relay on
If the object is far from ultrasonic sensor, turn relay off

By connecting relay to light bulb, led strip, motor or actuator... We can use the ultrasonic sensor to control light bulb, led strip, motor or actuator...

Hardware Required

1	×	Arduino UNO or Genuino UNO
1	×	USB 2.0 cable type A/B
1	×	Ultrasonic Sensor
1	×	Relay
1	×	Jumper Wires
1	×	(Optional) Solenoid Lock
1	×	(Optional) 12V Power Adapter
1	×	(Optional) DC Power Jack
1	×	(Optional) 9V Power Adapter for Arduino
1	×	(Recommended) Screw Terminal Block Shield for Arduino Uno

Or you can buy the following sensor kit:

DIYables Sensor Kit 30 types, 69 units

Please note: These are Amazon affiliate links. If you buy the components through these links, We will get a commission at no extra cost to you. We appreciate it.

About Relay and Ultrasonic Sensor

If you do not know about relay and ultrasonic sensor (pinout, how it works, how to program ...), learn about them in the following tutorials:

Wiring Diagram

This image is created using Fritzing. Click to enlarge image

Arduino Code

/* * Created by ArduinoGetStarted.com * * This example code is in the public domain * * Tutorial page: https://arduinogetstarted.com/tutorials/arduino-ultrasonic-sensor-relay */ // constants won't change const int TRIG_PIN = 7; // Arduino pin connected to Ultrasonic Sensor's TRIG pin const int ECHO_PIN = 6; // Arduino pin connected to Ultrasonic Sensor's ECHO pin const int RELAY_PIN = A5; // Arduino pin connected to Relay's pin const int 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 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() { // 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 Steps

Connect Arduino to PC via USB cable
Open Arduino IDE, select the right board and port
Copy the above code and open with Arduino IDE
Click Upload button on Arduino IDE to upload code to Arduino

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

Code Explanation

Read the line-by-line explanation in comment lines of source code!

※ NOTE THAT:

The above code is for the learning purpose. The ultrasonic sensor is very sensitive to noise. If you want to use the ultrasonic sensor in practice, you should filter noise for the ultrasonic sensor. See how to filter noise for ultrasonic sensor

Video Tutorial

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Ultrasonic Sensor and Relay on Commercial Products

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