HC-SR04 Ultrasonic Sensor

The HC-SR04 measures distance using ultrasonic pulses. Range: 2 cm – 4 m, accuracy: ±3 mm.

Wiring (Raspberry Pi)

HC-SR04	Raspberry Pi
VCC	Pin 2 (5V)
GND	Pin 6 (GND)
TRIG	GPIO23 (Pin 16)
ECHO	GPIO24 via voltage divider (Pin 18)

WARNING

ECHO outputs 5V. Use a voltage divider (1kΩ + 2kΩ) to bring it down to 3.3V before connecting to the Pi GPIO.

Python Code

import RPi.GPIO as GPIO
import time

TRIG = 23
ECHO = 24

GPIO.setmode(GPIO.BCM)
GPIO.setup(TRIG, GPIO.OUT)
GPIO.setup(ECHO, GPIO.IN)

def get_distance():
    GPIO.output(TRIG, True)
    time.sleep(0.00001)
    GPIO.output(TRIG, False)

    while GPIO.input(ECHO) == 0:
        pulse_start = time.time()
    while GPIO.input(ECHO) == 1:
        pulse_end = time.time()

    duration = pulse_end - pulse_start
    distance = duration * 17150  # cm
    return round(distance, 2)

try:
    while True:
        print(f"Distance: {get_distance()} cm")
        time.sleep(0.5)
finally:
    GPIO.cleanup()