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

The HC-SR04 is an ultrasonic distance sensor that measures distance by emitting ultrasonic waves and calculating the time it takes for the echo to return. It is widely used in robotics, automation, and IoT applications for obstacle detection, distance measurement, and proximity sensing. Its affordability, ease of use, and accuracy make it a popular choice for hobbyists and professionals alike.

• Obstacle detection in robotics
• Distance measurement in automation systems
• Proximity sensing in IoT devices
• Liquid level measurement in tanks
• Parking assistance systems

The HC-SR04 sensor operates by emitting ultrasonic waves at 40 kHz and measuring the time it takes for the echo to return after hitting an object. Below are its key technical details:

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

1. Power the Sensor: Connect the VCC pin to a 5V power supply and the GND pin to ground.
2. Trigger the Sensor: Send a 10 µs HIGH pulse to the Trig pin to initiate a measurement.
3. Read the Echo: Measure the duration of the HIGH pulse on the Echo pin. This duration is proportional to the distance of the object.
4. Calculate Distance: Use the formula below to calculate the distance: [ \text{Distance (cm)} = \frac{\text{Pulse Duration (µs)}}{58} ] Alternatively, for distance in inches: [ \text{Distance (in)} = \frac{\text{Pulse Duration (µs)}}{148} ]

• Ensure the sensor is mounted securely and aligned properly for accurate measurements.
• Avoid placing the sensor near ultrasonic noise sources, as they may interfere with readings.
• The sensor has a minimum range of 2 cm; objects closer than this may not be detected accurately.
• Use a resistor divider or level shifter if interfacing with a 3.3V microcontroller.

Below is an example of how to use the HC-SR04 with an Arduino UNO:

// Define pins for the HC-SR04 sensor
const int trigPin = 9;  // Trig 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 for Trig and Echo
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, 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 pulse on the Echo pin
  long duration = pulseIn(echoPin, HIGH);

  // Calculate the distance in centimeters
  float distance = duration / 58.0;

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

  // Wait for a short period before the next measurement
  delay(500);
}

• The pulseIn() function measures the duration of the HIGH pulse on the Echo pin.
• The calculated distance is printed to the Serial Monitor for debugging or display purposes.
• Adjust the delay() value in the loop() function to control the measurement frequency.

1. No Output or Incorrect Readings:

   • Cause: Incorrect wiring or loose connections.
   • Solution: Double-check all connections and ensure the sensor is powered correctly.

2. Unstable or Fluctuating Measurements:

   • Cause: Electrical noise or interference.
   • Solution: Use decoupling capacitors near the sensor's power pins and avoid noisy environments.

3. Sensor Not Detecting Objects:

   • Cause: Object is outside the sensor's range or too small to reflect ultrasonic waves.
   • Solution: Ensure the object is within the 2 cm to 400 cm range and has a sufficient surface area.

4. Echo Pin Always HIGH or LOW:

   • Cause: Faulty sensor or incorrect trigger signal.
   • Solution: Verify the trigger signal timing and replace the sensor if necessary.

Q1: Can the HC-SR04 measure distances through transparent materials like glass?
A1: No, the HC-SR04 relies on ultrasonic waves, which do not pass through transparent materials like glass effectively.

Q2: Can I use the HC-SR04 with a 3.3V microcontroller?
A2: Yes, but you need a level shifter or resistor divider to safely interface the Echo pin with the microcontroller.

Q3: What is the maximum measurement frequency of the HC-SR04?
A3: The sensor requires a minimum delay of 60 ms between measurements, allowing for a maximum frequency of approximately 16 Hz.

Q4: How can I improve measurement accuracy?
A4: Use a stable power supply, avoid ultrasonic interference, and ensure the sensor is mounted securely and aligned properly.