How to Set Up and Use an HC-SR04 Distance Sensor with Raspberry Pi

 The HC-SR04 Ultrasonic Distance Sensor is a great way to measure distance using your Raspberry Pi. In this guide, I’ll show you how to wire the sensor, set up a voltage divider, and write a Python script to calculate distance readings.

The Raspberry Pi’s GPIO pins work at 3.3V logic, but the HC-SR04’s ECHO pin outputs 5V. To safely connect it, we need a voltage divider that reduces 5V to 3.3V.

For this, we’ll use:

• 1kΩ resistor (R1)
• 2kΩ resistor (R2)

This creates the correct voltage drop, protecting your Pi.

Wiring the HC-SR04 to Raspberry Pi

Here’s the wiring setup:

• VCC → Pin 2 (5V)
• Trig → Pin 7 (GPIO 4)
• Echo → R1 (1kΩ resistor)
• R2 (2kΩ resistor) → from R1 to Ground
• Wire between R1 & R2 → Pin 11 (GPIO 17)
• GND → Pin 6 (Ground)

Steps to Build the Circuit:

1. Connect Pin 6 (GND) to the breadboard ground rail
2. Connect Pin 2 (5V) to the VCC of the HC-SR04
3. Connect Pin 7 to the Trig pin
4. Place a 1kΩ resistor from Echo pin to breadboard
5. Connect a 2kΩ resistor from the same row to ground rail
6. Connect a jumper from between R1 & R2 to Pin 11 on the Pi

Writing the Python Script

We’ll now create a Python script to read distance values.

Step 1: Create a folder and file

mkdir ~/distance_sensor
cd ~/distance_sensor
nano distance_sensor.py

Step 2: Add the following code

#!/usr/bin/python
import RPi.GPIO as GPIO
import time

try:
    # Use board pin numbering
    GPIO.setmode(GPIO.BOARD)

    PIN_TRIGGER = 7
    PIN_ECHO = 11

    GPIO.setup(PIN_TRIGGER, GPIO.OUT)
    GPIO.setup(PIN_ECHO, GPIO.IN)

    # Ensure trigger is low
    GPIO.output(PIN_TRIGGER, GPIO.LOW)
    print("Waiting for sensor to settle")
    time.sleep(2)

    print("Calculating distance...")

    # Trigger pulse
    GPIO.output(PIN_TRIGGER, GPIO.HIGH)
    time.sleep(0.00001)
    GPIO.output(PIN_TRIGGER, GPIO.LOW)

    # Measure echo response
    while GPIO.input(PIN_ECHO) == 0:
        pulse_start_time = time.time()

    while GPIO.input(PIN_ECHO) == 1:
        pulse_end_time = time.time()

    pulse_duration = pulse_end_time - pulse_start_time
    distance = round(pulse_duration * 17150, 2)

    print("Distance:", distance, "cm")

finally:
    GPIO.cleanup()

Step 3: Save and exit

Press CTRL+X, then Y, and hit ENTER.

Running the Code

Run the script with:

python ~/distance_sensor/distance_sensor.py

If everything is wired correctly, you’ll see something like:

Waiting for sensor to settle
Calculating distance...
Distance: 29.69 cm

Your reading will vary depending on the object in front of the sensor.

How It Works

• The Trig pin sends a short ultrasonic pulse.
• The Echo pin measures the time it takes for the pulse to bounce back.
• Using the speed of sound (343 m/s), we calculate distance with:

Distance = (Pulse Duration × Speed of Sound) / 2

(The divide by 2 accounts for the pulse traveling to the object and back.)

You’ve now successfully:

• Wired the HC-SR04 to your Raspberry Pi
• Built a safe voltage divider for the Echo pin
• Written a Python script to measure distance

This setup is the foundation for robotics, obstacle detection, and smart automation projects with Raspberry Pi.