HC-SR04 Ultrasonic Distance Sensor

Wiring

HC-SR04 Pin	Arduino Pin
VCC	5V
GND	GND
TRIG	D9
ECHO	D10

Code

const int trig = 9, echo = 10;
void setup() { Serial.begin(9600); pinMode(trig, OUTPUT); pinMode(echo, INPUT); }
void loop() {
  digitalWrite(trig, LOW); delayMicroseconds(2);
  digitalWrite(trig, HIGH); delayMicroseconds(10);
  digitalWrite(trig, LOW);
  long duration = pulseIn(echo, HIGH);
  float distance = duration * 0.034 / 2; // cm
  Serial.print(distance); Serial.println(" cm");
  delay(500);
}

Specifications

• Range: 2–400 cm
• Accuracy: ±3 mm
• Angle: ~15° beam width

Troubleshooting

• Always reads 0 — check TRIG/ECHO pins, sensor needs 5V, not 3.3V
• Wrong readings — object outside the 15° beam or too close (under 2 cm)
• ESP32 note — HC-SR04 needs 5V power but ECHO outputs 5V. Use voltage divider on ECHO pin