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Arduino - Ultrasonic Sensor
In this tutorial, we are going to learn:
- How to ultrasonic sensor works
- How to use ultrasonic sensor HC-SR04 to measure the distance to an object
- How to filter noise from distance measurements of 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.
Pinout
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.
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.
- Micro-controller: generates a 10-microsecond pulse on the TRIG pin.
- The ultrasonic sensor automatically emits the ultrasonic waves.
- The ultrasonic wave is reflected after hitting an obstacle.
- The ultrasonic sensor:
- Detects the reflected ultrasonic wave.
- Measures the travel time of the ultrasonic wave.
- Ultrasonic sensor: generates a pulse to the ECHO pin. The duration of the pulse is equal to the travel time of the ultrasonic wave.
- 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
So:
- 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
Image is developed using Fritzing. Click to enlarge image
How To Program For Ultrasonic Sensor
- Generate a 10-microsecond pulse in Arduino's pin by using digitalWrite() and delayMicroseconds() functions. For example, pin 9:
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, https://arduinogetstarted.com
*
* Arduino - Ultrasonic Sensor HC-SR04
*
* Wiring: Ultrasonic Sensor -> Arduino:
* - VCC -> 5VDC
* - TRIG -> Pin 9
* - ECHO -> Pin 8
* - GND -> GND
*
* Tutorial is available here: https://arduinogetstarted.com/tutorials/arduino-ultrasonic-sensor
*/
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
- 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
Clear output
9600 baud
Newline
Code Explanation
Read the line-by-line explanation in comment lines of code!
How to Filter Noise from Distance Measurements of Ultrasonic Sensor
The measurement result from ultrasonic sensor contains noise. In some application, the noised result causes the unwanted operation. We can remove noise by using the following algorithm:
- Taking multiple measurements and store in an array
- Sorting the array in ascending order
- Filtering noise
- The some smallest samples are considered as noise → ignore it
- The some biggest samples are considered as noise → ignore it
- ⇒ get average of the middle samples
The below example code takes 20 measurements
- The five smallest samples are considered as noise → ignore it
- The five biggest samples are considered as noise → ignore it
- ⇒ get average of the 10 middle samples (from 5th to 14th)
/*
* Created by ArduinoGetStarted.com
*
* This example code is in the public domain
*
* Tutorial page: https://arduinogetstarted.com/tutorials/arduino-ultrasonic-sensor
*/
#define TRIG_PIN 9 // TRIG pin
#define ECHO_PIN 8 // ECHO pin
float filterArray[20]; // array to store data samples from sensor
float distance; // store the distance from sensor
void setup() {
// begin serial port
Serial.begin (9600);
// configure the trigger and echo pins to output mode
pinMode(TRIG_PIN, OUTPUT);
pinMode(ECHO_PIN, INPUT);
}
void loop() {
// 1. TAKING MULTIPLE MEASUREMENTS AND STORE IN AN ARRAY
for (int sample = 0; sample < 20; sample++) {
filterArray[sample] = ultrasonicMeasure();
delay(30); // to avoid untrasonic interfering
}
// 2. SORTING THE ARRAY IN ASCENDING ORDER
for (int i = 0; i < 19; i++) {
for (int j = i + 1; j < 20; j++) {
if (filterArray[i] > filterArray[j]) {
float swap = filterArray[i];
filterArray[i] = filterArray[j];
filterArray[j] = swap;
}
}
}
// 3. FILTERING NOISE
// + the five smallest samples are considered as noise -> ignore it
// + the five biggest samples are considered as noise -> ignore it
// ----------------------------------------------------------------
// => get average of the 10 middle samples (from 5th to 14th)
double sum = 0;
for (int sample = 5; sample < 15; sample++) {
sum += filterArray[sample];
}
distance = sum / 10;
// print the value to Serial Monitor
Serial.print("distance: ");
Serial.print(distance);
Serial.println(" cm");
}
float ultrasonicMeasure() {
// generate 10-microsecond pulse to TRIG pin
digitalWrite(TRIG_PIN, HIGH);
delayMicroseconds(10);
digitalWrite(TRIG_PIN, LOW);
// measure duration of pulse from ECHO pin
float duration_us = pulseIn(ECHO_PIN, HIGH);
// calculate the distance
float distance_cm = 0.017 * duration_us;
return distance_cm;
}
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
Function References
The Best Arduino Starter Kit
See Also
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