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HC-SR04 Ultrasonic Distance Meter

A project that measures the distance to the object in front of an HC-SR04 ultrasonic sensor in centimetres and writes it to the Serial Monitor about 10 times a second. The sensor measures how long the echo of its sound wave takes to come back; the code turns that time into centimetres by dividing it by 58. No extra library needed.

What you need

• 1 × Arduino Uno R3
• 1 × HC-SR04 Ultrasonic Distance Sensor
• 4 × Jumper Wire - Male/Female

Wiring steps

1. 1

   Power the sensor

   

   Plug a red jumper wire into the 5V pin on the Arduino's POWER header. Connect its other end to the HC-SR04's Vcc pin.

2. 2

   Connect the trigger (Trig) line

   

   Plug a green jumper wire into the Arduino's digital pin 2. Connect its other end to the HC-SR04's Trig pin. The Arduino starts a measurement by sending a 10-microsecond pulse on this pin (HC_TRIG 2).

3. 3

   Connect the echo (Echo) line

   

   Plug a blue jumper wire into the Arduino's digital pin 3. Connect its other end to the HC-SR04's Echo pin. The sensor holds this pin HIGH until the sound wave has gone and come back; the code measures that time with pulseIn (HC_ECHO 3).

4. 4

   Ground (GND) connection

   

   Plug a black jumper wire into the GND pin on the Arduino's POWER header. Connect its other end to the HC-SR04's Gnd pin. That completes all four of the sensor's connections.

Arduino sketch

#define HC_TRIG 2   
#define HC_ECHO 3   

unsigned long duration; 
uint16_t distance;    

void setup() {
  Serial.begin(9600);             
  pinMode(HC_TRIG, OUTPUT);        
  pinMode(HC_ECHO, INPUT);         
  digitalWrite(HC_TRIG, LOW);      
}

void loop() {
  digitalWrite(HC_TRIG, LOW);      
  delayMicroseconds(2);            
  digitalWrite(HC_TRIG, HIGH);     
  delayMicroseconds(10);           
  digitalWrite(HC_TRIG, LOW);      

  // Timeout set to 30,000 uS (approx. 5 meters)
  duration = pulseIn(HC_ECHO, HIGH, 30000);   
  
  if (duration == 0) {
    Serial.println("Distance: Out of Range!");
  } else {
    distance = duration / 58;           
    Serial.print("Distance = ");       
    Serial.print(distance);
    Serial.println(" cm");
  }
  
  delay(100);
}

What the Serial Monitor shows

Distance = 12 cm
Distance = 13 cm

If a wire is loose

Distance: Out of Range!