Procedure

Hardware Setup

To interface the HC-SR04 Ultrasonic Sensor with the Raspberry Pi, follow the wiring instructions carefully:

• Connect the Vcc pin of the Ultrasonic Sensor to the 5V PWR pin of the Raspberry Pi.
• Connect the Trig pin of the Ultrasonic Sensor to GPIO 18 of the Raspberry Pi.
• Connect the GND pin of the Ultrasonic Sensor to a Ground (GND) pin on the Raspberry Pi.
• Connect the Echo pin of the Ultrasonic Sensor to a 1KΩ Resistor.
• Connect the 1KΩ Resistor pin, which is connected with GPIO 24, to Ground (GND).
• Connect the 2KΩ Resistor pin, which is connected with the 1KΩ Resistor, to Ground (GND).

Software Setup

To control the Ultrasonic Sensor using Python 3 on Raspberry Pi OS, follow these steps:

1. Import Required Libraries

• Import the RPi.GPIO module to interact with Raspberry Pi GPIO pins.
• Import the time module for timing operations.

2. Set GPIO Mode

• Use GPIO.setmode(GPIO.BCM) to refer to GPIO numbers instead of physical pin numbers.

3. Define Sensor Pins

• Assign GPIO 18 to the Trigger pin.
• Assign GPIO 24 to the Echo pin.

4. Configure GPIO Pins

• Set the Trig pin as an output.
• Set the Echo pin as an input.

5. Trigger the Sensor and Measure Response Time

• Set the Trigg pin HIGH for 10 microseconds to send an ultrasonic burst at 40 KHz.
• Set the Trig pin LOW and measure the time taken for the sound wave to return.

6. Calculate Distance

• Compute distance using the time difference between sending and receiving the pulse.

• The formula used is:

  [ \text{Distance} = \left( \text{Pulse Duration} \times 34300 \right) / 2 ]

  where 34300 cm/s is the speed of sound in air, and the result is divided by 2 to account for the round trip.

7. Display Output

• If the measured distance is within 2 cm and 400 cm, print the calculated value with 0.5 cm calibration.
• Otherwise, display "Out of Range".

Python Code Implementation

import RPi.GPIO as GPIO  # Import GPIO library
          import time  # Import time library
          
          # GPIO pin configuration
          GPIO.setmode(GPIO.BCM)  # Use Broadcom (GPIO) pin numbering
          TRIG = 18  # Assign GPIO 18 to Trigger
          ECHO = 24  # Assign GPIO 24 to Echo
          
          # Set up GPIO pin modes
          GPIO.setup(TRIG, GPIO.OUT)  # Set Trigger as output
          GPIO.setup(ECHO, GPIO.IN)  # Set Echo as input
          
          try:
              while True:
                  GPIO.output(TRIG, False)  # Ensure Trigger is LOW
                  print("Sensor is stabilizing...")
                  time.sleep(2)  # Allow sensor to settle
          
                  # Send ultrasonic pulse
                  GPIO.output(TRIG, True)
                  time.sleep(0.00001)  # 10 microseconds pulse
                  GPIO.output(TRIG, False)
          
                  # Measure the time of flight
                  while GPIO.input(ECHO) == 0:
                      pulse_start = time.time()  # Record start time
          
                  while GPIO.input(ECHO) == 1:
                      pulse_end = time.time()  # Record end time
          
                  # Calculate distance
                  pulse_duration = pulse_end - pulse_start
                  distance = (pulse_duration * 34300) / 2  # Convert to cm
                  distance = round(distance, 2)  # Round to 2 decimal places
          
                  # Display results
                  if 2 <= distance <= 400:
                      print(f"Distance: {distance - 0.5} cm")  # Apply 0.5 cm correction
                  else:
                      print("Out of Range")
          
                  time.sleep(1)  # Delay before next measurement
          
          except KeyboardInterrupt:
              print("Measurement stopped by user")
              GPIO.cleanup()  # Reset GPIO settings