Arduino - Ultrasonic Sensor - Relay

We are going to learn how to:

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×Warning Light Bright Waterproof
1×12V Power Adapter
n×Jumper Wires
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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

Arduino Ultrasonic Sensor Relay Wiring Diagram

Image is developed 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 = 3; // 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
  • Arduino IDE Upload Code
  • 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!

Video Tutorial

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