How to Use HC-SR04 Ultrasonic Sensor: Examples, Pinouts, and Specs

The HC-SR04 is an ultrasonic distance sensor that uses sonar to measure the distance to an object. It emits a high-frequency sound wave and measures the time it takes for the echo to return, allowing it to calculate the distance based on the speed of sound. This sensor is widely used in robotics, automation, and obstacle detection systems due to its accuracy, affordability, and ease of use.

• Obstacle detection in robotics
• Distance measurement in automation systems
• Liquid level sensing
• Parking assistance systems
• Proximity detection in security systems

The HC-SR04 sensor is designed for precise distance measurement and operates within a specific range of environmental conditions. Below are its key technical details:

The HC-SR04 has four pins, as described in the table below:

The HC-SR04 sensor is simple to use and can be integrated into a variety of circuits. Below are the steps to use it effectively:

1. Connect the VCC pin to the 5V output of your microcontroller or power supply.
2. Connect the GND pin to the ground of your circuit.
3. Connect the Trig pin to a digital output pin of your microcontroller.
4. Connect the Echo pin to a digital input pin of your microcontroller.

1. Send a 10 µs HIGH pulse to the Trig pin to trigger the sensor.
2. The sensor will emit an ultrasonic burst and set the Echo pin HIGH.
3. Measure the duration of the HIGH signal on the Echo pin. This duration is proportional to the distance.
4. Use the formula below to calculate the distance: [ \text{Distance (cm)} = \frac{\text{Time (µs)} \times 0.034}{2} ]
   • The factor 0.034 represents the speed of sound in cm/µs.
   • Divide by 2 because the sound wave travels to the object and back.

Below is an example Arduino sketch to measure distance using the HC-SR04:

// Define pins for the HC-SR04 sensor
const int trigPin = 9; // Trigger pin connected to digital pin 9
const int echoPin = 10; // Echo pin connected to digital pin 10

void setup() {
  // Initialize serial communication for debugging
  Serial.begin(9600);
  
  // Set pin modes
  pinMode(trigPin, OUTPUT); // Trig pin as output
  pinMode(echoPin, INPUT);  // Echo pin as input
}

void loop() {
  // Send a 10 µs HIGH pulse to the Trig pin
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // Measure the duration of the HIGH signal on the Echo pin
  long duration = pulseIn(echoPin, HIGH);

  // Calculate the distance in cm
  float distance = (duration * 0.034) / 2;

  // Print the distance to the Serial Monitor
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  // Wait before the next measurement
  delay(500);
}

• Ensure the sensor is powered with a stable 5V DC supply for accurate readings.
• Avoid placing the sensor in environments with excessive noise or vibrations, as this can interfere with measurements.
• The sensor's measuring angle is 15°, so ensure there are no obstructions within this cone for accurate results.
• Use a capacitor (e.g., 10 µF) across the VCC and GND pins to filter out power supply noise.

1. No Output or Incorrect Readings

   • Ensure all connections are secure and correct.
   • Verify that the sensor is powered with 5V DC.
   • Check the trigger pulse duration (should be 10 µs).

2. Fluctuating Distance Measurements

   • Ensure there are no moving objects or noise sources near the sensor.
   • Add a capacitor across the power supply pins to stabilize the voltage.

3. Echo Pin Always LOW

   • Verify that the object is within the sensor's range (2 cm to 400 cm).
   • Check for obstructions blocking the ultrasonic waves.

4. Distance Readings Are Too High

   • Ensure the sensor is not tilted or misaligned.
   • Verify the formula used for distance calculation.

Q: Can the HC-SR04 measure distances below 2 cm?
A: No, the sensor's minimum range is 2 cm. Objects closer than this may not be detected accurately.

Q: Can I use the HC-SR04 with a 3.3V microcontroller?
A: The HC-SR04 requires 5V for operation. However, you can use a level shifter to safely interface the Echo pin with a 3.3V microcontroller.

Q: What is the maximum sampling rate of the HC-SR04?
A: The sensor requires approximately 60 ms for each measurement, allowing a maximum sampling rate of about 16 Hz.

Q: Can the HC-SR04 detect transparent objects?
A: The sensor may struggle to detect transparent or very small objects, as they may not reflect enough ultrasonic waves.

By following this documentation, you can effectively integrate the HC-SR04 ultrasonic sensor into your projects for accurate distance measurement.