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Lesson 23: Ultrasonic Sensor Module (HC-SR04)

In this lesson, you’ll learn how to connect an ultrasonic distance sensor to a Raspberry Pi and write a Python script for reading distance measurements. We’ll guide you through the process of wiring the sensor’s trigger pin to GPIO 17 and the echo pin to GPIO 27. The provided Python code will assist you in measuring distances and displaying them in centimeters.

Required Components

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name	ITEMS IN THIS KIT	LINK
Universal Maker Sensor Kit	94	Universal Maker Sensor Kit

You can also buy them separately from the links below.

Component Introduction	Purchase Link
Raspberry Pi 5	BUY
Ultrasonic Sensor Module (HC-SR04)	BUY
Breadboard	BUY

Wiring

../_images/Lesson_23_ultrasonic_sensor_Pi_bb.png

Code

#!/usr/bin/env python3
from gpiozero import DistanceSensor
from time import sleep

# Initialize the DistanceSensor using GPIO Zero library
# Trigger pin is connected to GPIO 17, Echo pin to GPIO 27
sensor = DistanceSensor(echo=27, trigger=17)

try:
    # Main loop to continuously measure and report distance
    while True:
        dis = sensor.distance * 100  # Measure distance and convert from meters to centimeters
        print('Distance: {:.2f} cm'.format(dis))  # Print the distance with two decimal precision
        sleep(0.3)  # Wait for 0.3 seconds before the next measurement

except KeyboardInterrupt:
    # Handle KeyboardInterrupt (Ctrl+C) to gracefully exit the loop
    pass

Code Analysis

Importing Libraries

The script begins by importing DistanceSensor from the gpiozero library for the ultrasonic sensor, and sleep from the time module for timing control.
```
from gpiozero import DistanceSensor
from time import sleep
```
Initializing the Distance Sensor

A DistanceSensor object named sensor is created with echo and trigger pins connected to GPIO 27 and GPIO 17, respectively. These pins are used to send and receive the ultrasonic signals for distance measurement.
```
sensor = DistanceSensor(echo=27, trigger=17)
```
Implementing the Continuous Monitoring Loop
- A try block with an infinite loop (while True:) is used to continuously measure the distance.
- Within the loop, sensor.distance gives the measured distance in meters, which is then converted to centimeters and stored in dis.
- The distance is printed with two decimal points of precision using the format method.
- sleep(0.3) adds a 0.3-second delay between each measurement to control the frequency of readings and reduce CPU load.
```
try:
    while True:
        dis = sensor.distance * 100
        print('Distance: {:.2f} cm'.format(dis))
        sleep(0.3)
```
Handling KeyboardInterrupt for Graceful Exit

The except block is used to catch a KeyboardInterrupt (typically Ctrl+C). When this occurs, the script exits the loop gracefully without any additional actions.
```
except KeyboardInterrupt:
    pass
```