HC-SR04 Ultrasonic Distance Sensor - Pinout, Calculation & 3D STL Bracket

Module Overview & How It Works

The HC-SR04 is a popular, cost-effective ultrasonic ranging module providing non-contact measurement from 2 cm to 400 cm with a precision down to 3 mm. The module includes an ultrasonic transmitter transducer, a receiver transducer, and a control circuit.

To measure distance, the microcontroller sends a short 10μs high pulse to the Trig pin. The sensor automatically transmits an 8-cycle sonic burst at 40 kHz. When the reflected sound waves bounce back off an obstacle, the Echo pin goes HIGH for a duration proportional to the round-trip distance traveled by sound.

Technical Specifications

Pinout Table & Voltage Divider for 3.3V MCUs (ESP32)

Arduino Sample Code (Distance in cm & inches)

const int trigPin = 9;
const int echoPin = 10;

void setup() {
  Serial.begin(115200);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
}

void loop() {
  // Clear trigger
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);

  // Send 10 microsecond pulse
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // Read Echo duration
  long duration = pulseIn(echoPin, HIGH);

  // Calculate distance: sound speed is ~0.0343 cm/microsecond
  float distanceCm = duration * 0.0343 / 2.0;

  Serial.print("Distance: ");
  Serial.print(distanceCm);
  Serial.println(" cm");

  delay(200); // 5Hz sampling rate
}

3D Printing & Enclosure Recommendations

Mounting the HC-SR04 firmly is critical to prevent acoustic echo false-triggers caused by mechanical wobble:

• Transducer Hole Diameter: The two metal transducer barrels have a standard diameter of 16.0mm. Our 3D model features a 16.3mm opening for a clean friction fit without fracturing the solder joints.
• Servo Mount Compatibility: The base includes mounting bosses designed to screw directly into SG90 or MG90S micro servo horns for obstacle-avoiding radar swiveling.