Arduino - Ultrasonic Sensor

Hardware Required

1×Arduino UNO or Genuino UNO
1×USB 2.0 cable type A/B
1×Ultrasonic Sensor
4×Jumper Wires
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About Ultrasonic Sensor

Ultrasonic sensor HC-SR04 is used to measure the distance to an object by using ultrasonic waves.


The ultrasonic sensor HC-SR04 includes four pins:

  • VCC pin needs to be connected to VCC (5V)
  • GND pin needs to be connected to GND (0V)
  • TRIG pin this pin receives the control signal (pulse) from Arduino.
  • ECHO pin this pin sends a signal (pulse) to Arduino. Arduino measures the duration of pulse to calculate distance.
  • Ultrasonic Sensor Pinout

How It Works

This section is the in-depth knowledge. DON'T worry if you don't understand. Ignore this section if it overloads you, and come back in another day. Keep reading the next sections.
  1. Micro-controller: generates a 10-microsecond pulse on the TRIG pin.
  2. The ultrasonic sensor automatically emits the ultrasonic waves.
  3. The ultrasonic wave is reflected after hitting an obstacle.
  4. The ultrasonic sensor:
    • Detects the reflected ultrasonic wave.
    • Measures the travel time of the ultrasonic wave.
  5. Ultrasonic sensor: generates a pulse to the ECHO pin. The duration of the pulse is equal to the travel time of the ultrasonic wave.
  6. Micro-controller measures the pulse duration in the ECHO pin, and then calculate the distance between sensor and obstacle.

How to Get Distance From Ultrasonic Sensor

To get distance from the ultrasonic sensor, we only need to do two steps (1 and 6 on How It Works part)

  • Generates a 10-microsecond pulse on TRIG pin
  • Measures the pulse duration in ECHO pin, and then calculate the distance between sensor and obstacle

Distance Calculation

We have:

  • The travel time of the ultrasonic wave (µs): travel_time = pulse_duration
  • The speed of the ultrasonic wave: speed = SPEED_OF_SOUND = 340 m/s = 0.034 cm/µs


  • The travel distance of the ultrasonic wave (cm): travel_distance = speed × travel_time = 0.034 × pulse_duration
  • The distance between sensor and obstacle (cm): distance = travel_distance / 2 = 0.034 × pulse_duration / 2 = 0.017 × pulse_duration

Arduino - Ultrasonic Sensor

Arduino's pins can generate a 10-microsecond pulse and measure the pulse duration. Therefore, we can get the distance from the ultrasonic sensor by using two Arduino's pins:

  • One pin is connected to TRIG PIN to generate 10µs pulse to TRIG pin of the sensor
  • Another pin is connected to ECHO PIN measure pulse from the sensor

Wiring Diagram

Arduino Ultrasonic Sensor Wiring Diagram

Image is developed using Fritzing. Click to enlarge image

How To Program For Ultrasonic Sensor

digitalWrite(9, HIGH); delayMicroseconds(10); digitalWrite(9, LOW);
  • Measures the pulse duration (µs) in Arduino's pin by using pulseIn() function. For example, pin 8:
duration_us = pulseIn(8, HIGH);
  • Calculate distance (cm):
distance_cm = 0.017 * duration_us;

Arduino Code

/* * Created by ArduinoGetStarted, * * Arduino - Ultrasonic Sensor HC-SR04 * * Wiring: Ultrasonic Sensor -> Arduino: * - VCC -> 5VDC * - TRIG -> Pin 9 * - ECHO -> Pin 8 * - GND -> GND * * Tutorial is available here: */ int trigPin = 9; // TRIG pin int echoPin = 8; // ECHO pin float duration_us, distance_cm; void setup() { // begin serial port Serial.begin (9600); // configure the trigger pin to output mode pinMode(trigPin, OUTPUT); // configure the echo pin to input mode pinMode(echoPin, INPUT); } void loop() { // generate 10-microsecond pulse to TRIG pin digitalWrite(trigPin, HIGH); delayMicroseconds(10); digitalWrite(trigPin, LOW); // measure duration of pulse from ECHO pin duration_us = pulseIn(echoPin, HIGH); // calculate the distance distance_cm = 0.017 * duration_us; // print the value to Serial Monitor Serial.print("distance: "); Serial.print(distance_cm); Serial.println(" cm"); delay(500); }

Quick Steps

  • Copy the above code and open with Arduino IDE
  • Click Upload button on Arduino IDE to upload code to Arduino
  • Arduino IDE - How to Upload Code
  • Open Serial Monitor
  • Move your hand in front of ultrasonic sensor
  • See the distance from the sensor to your hand on Serial Monitor
  • COM6
    distance: 29.4 cm distance: 27.6 cm distance: 26.9 cm distance: 17.4 cm distance: 16.9 cm distance: 14.3 cm distance: 15.6 cm distance: 13.1 cm
    Autoscroll Show timestamp
    Clear output
    9600 baud  

Code Explanation

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

Video Tutorial

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Challenge Yourself

Use ultrasonic sensor to do one of the following projects:

  • Collision avoidance for RC car.
  • Detecting the fullness of dustbin.
  • Monitoring level of the dustbin.
  • Automatically open/close the dustbin. Hint: Refer to Arduino - Servo Motor.

Additional Knowledge

Some manufacturers provide the ultrasonic sensor that has 3 pins. TRIG signal and ECHO signal are in the same pin. In this case, we need to use only one Arduino's pin for both purposes: generating a pulse to the sensor and measuring pulse from the sensor.

Alternative Ultrasonic Sensors

The above code also works with the following ultrasonic sensor:

Ultrasonic Sensor on Commercial Products

  • Otto DIY Robot Builder Kit

Ultrasonic Sensor Applications

  • Collision Avoidance
  • Fullness Detection
  • Level Measurement
  • Proximity Detection

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