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Lesson 12: PIR Motion Module (HC-SR501)

In this lesson, you will learn how to set up and use a motion sensor with the Raspberry Pi. We’ll walk you through connecting a digital motion sensor to GPIO pin 17. You’ll write a Python script to continually check the sensor’s state, printing a message when motion is detected and another when the area is clear. This hands-on tutorial is focused on practical skills in electronic circuitry and Python programming, making it perfect for beginners who want to explore real-world applications of the Raspberry Pi in monitoring and automation projects.

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
PIR Motion Module (HC-SR501)	-
Breadboard	BUY

Wiring

Code

from gpiozero import DigitalInputDevice
from time import sleep

# Initialize the motion sensor as a digital input device on GPIO pin 17
motion_sensor = DigitalInputDevice(17)

# Continuously monitor the state of the motion sensor
while True:
    if motion_sensor.is_active:
        print("Somebody here!")
    else:
        print("Monitoring...")

    # Wait for 0.5 seconds before the next sensor check
    sleep(0.5)

Code Analysis

1. Importing Libraries

   The script starts by importing the DigitalInputDevice class from the gpiozero library for interfacing with the motion sensor, and the sleep function from the time module to introduce delays.

   from gpiozero import DigitalInputDevice
   from time import sleep
   

2. Initializing the Motion Sensor

   A DigitalInputDevice object named motion_sensor is created, connected to GPIO pin 17. This assumes that the motion sensor is connected to this GPIO pin on the Raspberry Pi.

   motion_sensor = DigitalInputDevice(17)
   

3. Implementing Continuous Monitoring Loop

   • The script employs a while True: loop for continuous monitoring.

   • Inside the loop, an if statement checks the is_active property of the motion_sensor.

   • If is_active is True, it suggests that motion is detected, and “Somebody here!” is printed.

   • If is_active is False, suggesting no motion is detected, “Monitoring…” is printed.

   • The sleep(0.5) function is used to pause the loop for 0.5 seconds between each sensor check, reducing the processing demand and controlling the frequency of sensor polling.

   
   

   while True:
       if motion_sensor.is_active:
           print("Somebody here!")
       else:
           print("Monitoring...")
       sleep(0.5)