Arduino Ultrasonic Sensor
The sensor sends out an ultrasonic sound wave from the TRIG pin. When the sound wave hits an object, it reflects back and is detected by the ECHO pin.
The Arduino measures the time it takes for the signal to return and uses that to calculate the distance.
Distance (cm) = (Time in microseconds × 0.034) / 2The speed of sound is 0.034 cm/µs. We divide by 2 because the sound travels to the object and back.
Required Components
| Component | Quantity | Purpose |
|---|---|---|
| Arduino Uno / Nano / Mega | 1 | Main microcontroller |
| HC-SR04 Ultrasonic Sensor | 1 | Measures distance |
| Jumper Wires | 4 | Connections |
| Breadboard (optional) | 1 | Easy wiring |
| USB Cable | 1 | Power & programming |
Pin Connections
Connect the HC-SR04 sensor to the Arduino as shown below:
| HC-SR04 Pin | Arduino Pin |
|---|---|
| VCC | 5V |
| GND | GND |
| TRIG | Digital Pin 9 |
| ECHO | Digital Pin 10 |
Note: The ECHO pin outputs 5V, which is safe for Arduino Uno/Nano/Mega.
Arduino Code
Upload the following code to your Arduino:
#define TRIG_PIN 9
#define ECHO_PIN 10
void setup() {
Serial.begin(9600);
pinMode(TRIG_PIN, OUTPUT);
pinMode(ECHO_PIN, INPUT);
}
void loop() {
long duration;
float distance;
// Clear trigger
digitalWrite(TRIG_PIN, LOW);
delayMicroseconds(2);
// Trigger ultrasonic burst
digitalWrite(TRIG_PIN, HIGH);
delayMicroseconds(10);
digitalWrite(TRIG_PIN, LOW);
// Measure echo time
duration = pulseIn(ECHO_PIN, HIGH);
// Convert time to distance
distance = (duration * 0.034) / 2;
// Output result
Serial.print("Distance: ");
Serial.print(distance);
Serial.println(" cm");
delay(500);
}
Code Explanation
- pulseIn() measures the duration of the ECHO signal.
- The sensor sends a 40 kHz ultrasonic burst using the TRIG pin.
- Arduino calculates the distance based on the speed of sound.
- Distance is printed in centimeters to the Serial Monitor.
Testing the Sensor
- Upload the code to your Arduino
- Open the Serial Monitor
- Set the baud rate to 9600
- Move your hand in front of the sensor
- Watch the distance update live
You should see something like:
Distance: 15.4 cmTroubleshooting
| Issue | Cause | Solution |
|---|---|---|
| Always reads 0 cm | Incorrect pin wiring | Check TRIG and ECHO |
| Values jump around | Object surface curved or too small | Use a flat object |
| No Serial output | Wrong baud rate | Set Serial Monitor to 9600 |
| Sensor not working | No power | Ensure 5V and GND connected properly |
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