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HC-SR04 Ultrasonic Sensor Example with Pi4J

This project demonstrates how to use the HC-SR04 ultrasonic sensor with a Raspberry Pi via the Pi4J library to measure distances in centimeters. The application continuously measures and displays the distance from the sensor to an object every second.

Requirements

  • Raspberry Pi (any model with GPIO support)
  • HC-SR04 Ultrasonic Sensor
  • Pi4J library (version compatible with your Pi and Java setup)
  • Java 11 or later

Wiring

  1. TRIG (trigger) pin on the HC-SR04 sensor is connected to GPIO 23 on the Raspberry Pi.
  2. ECHO (echo) pin on the HC-SR04 sensor is connected to GPIO 24 on the Raspberry Pi.
  3. VCC pin on the HC-SR04 sensor is connected to the 5V power pin on the Raspberry Pi.
  4. GND pin on the HC-SR04 sensor is connected to a ground (GND) pin on the Raspberry Pi.

Note: Some Raspberry Pi models use 3.3V GPIO pins, so if needed, use a voltage divider to lower the ECHO signal voltage.

Compile and Run

  1. Build the project: 
    mvn clean install
  2. Navigate to the distribution directory: 
    cd target/distribution
  3. Run the application with optional GPIO parameters: 
    sudo ./runHCSR04.sh <TRIG_PIN> <ECHO_PIN>

Example Usage

  • Using Default GPIO Pins (TRIG=23, ECHO=24): 
    sudo ./runHCSR04.sh
  • Specifying GPIO Pins (e.g., TRIG=20, ECHO=21): 
    sudo ./runHCSR04.sh 20 21
  • Getting Help Information: 
    sudo ./runHCSR04.sh -h

Code Overview

HCSR04 Class

The HCSR04 class configures the GPIO pins to interact with the sensor and provides a measureDistance method to calculate and return the distance to an object based on the duration of the ECHO pulse.

Key points:

  • Trigger Signal: A 10-microsecond pulse on the TRIG pin starts the measurement.
  • Echo Measurement: The class measures the duration of the ECHO pulse to calculate the distance.
  • Distance Calculation: Uses the speed of sound to convert pulse duration into centimeters.

HCSR04_App Class

The HCSR04_App class is a simple application that initializes the Pi4J context and the HCSR04 sensor instance. It enters a loop to repeatedly measure and print the distance to the console every second.

Example Output

When running the application, you should see output similar to the following:

Starting HC-SR04 distance measurement application...
Distance: 25.30 cm
Distance: 24.95 cm
Distance: 24.80 cm
...

If the object is out of range or no reading is detected, the output will indicate an invalid reading:

Out of range or invalid reading.