MotionSensor (PIR) in Raspberry Pi - Mini Project: Build & Apply

MotionSensor (PIR) with Raspberry Pi

📖 Scenario: You have a Raspberry Pi connected to a PIR motion sensor. The sensor detects movement in a room and sends a signal to the Pi. You want to write a simple program to read the sensor's signal and print a message when motion is detected.

🎯 Goal: Build a Python program that reads input from a PIR motion sensor connected to the Raspberry Pi's GPIO pin and prints "Motion detected!" when movement is sensed.

📋 What You'll Learn

Use the RPi.GPIO library to interact with GPIO pins.

Set up the GPIO pin connected to the PIR sensor as input.

Detect when the PIR sensor output goes HIGH (motion detected).

Print "Motion detected!" each time motion is detected.

💡 Why This Matters

🌍 Real World

Motion sensors are used in home security systems, automatic lighting, and energy-saving applications to detect presence and movement.

💼 Career

Understanding how to read sensor input and control GPIO pins is essential for embedded systems, IoT development, and hardware interfacing jobs.

1

Set up GPIO and PIR sensor pin

Import the RPi.GPIO library as GPIO and set the GPIO mode to GPIO.BCM. Create a variable called pir_pin and set it to 4, which is the GPIO pin number connected to the PIR sensor.

Raspberry Pi

# Import RPi.GPIO and set GPIO mode
# Your code here

Hint

Use import RPi.GPIO as GPIO to import the library. Use GPIO.setmode(GPIO.BCM) to set pin numbering. Assign 4 to pir_pin.

2

Configure PIR pin as input

Use GPIO.setup to set the pir_pin as an input pin.

Raspberry Pi

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
pir_pin = 4
# Set pir_pin as input
# Your code here

Hint

Use GPIO.setup(pir_pin, GPIO.IN) to configure the pin as input.

3

Detect motion with a loop

Write a while True loop that reads the PIR sensor state using GPIO.input(pir_pin). If the input is GPIO.HIGH, print "Motion detected!".

Raspberry Pi

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
pir_pin = 4
GPIO.setup(pir_pin, GPIO.IN)

# Start infinite loop to detect motion
# Your code here

Hint

Use while True: to create an endless loop. Inside, check if GPIO.input(pir_pin) equals GPIO.HIGH. If yes, print the message.

4

Clean up GPIO on exit and run program

Add a try-except block around the loop to catch KeyboardInterrupt. Inside except, call GPIO.cleanup() to reset GPIO pins. Run the program and observe the output when motion is detected.

Raspberry Pi

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
pir_pin = 4
GPIO.setup(pir_pin, GPIO.IN)

# Add try-except to handle keyboard interrupt and cleanup GPIO
# Your code here

Hint

Use try: before the loop and except KeyboardInterrupt: after. Inside except, call GPIO.cleanup().

Practice

1.

What does a PIR MotionSensor detect when connected to a Raspberry Pi?

easy

A. Temperature changes in the room

B. Sound levels around the sensor

C. Movement by sensing infrared changes

D. Light intensity variations

Solution

1. Step 1: Understand PIR sensor function

   A PIR sensor detects motion by sensing changes in infrared radiation emitted by objects.

2. Step 2: Compare options with sensor purpose

   Only Movement by sensing infrared changes matches the PIR sensor's function of detecting movement via infrared changes.

3. Final Answer:

   Movement by sensing infrared changes -> Option C

4. Quick Check:

   PIR sensor = Movement detection [OK]

Hint: PIR sensors detect motion, not temperature or sound [OK]

Common Mistakes:

• Confusing PIR with temperature sensors
• Thinking PIR detects sound or light
• Assuming PIR measures humidity

2.

Which of the following is the correct way to set up a GPIO pin as input for a PIR sensor in Python using RPi.GPIO?

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
# What goes here?

easy

A. GPIO.setup(17, GPIO.IN)

B. GPIO.setup(17, GPIO.OUT)

C. GPIO.input(17)

D. GPIO.output(17, GPIO.HIGH)

Solution

1. Step 1: Identify pin mode for PIR sensor input

   PIR sensor output should be read as input on the Raspberry Pi GPIO pin.

2. Step 2: Match correct GPIO setup syntax

   GPIO.setup(pin_number, GPIO.IN) sets the pin as input, which is needed to read sensor data.

3. Final Answer:

   GPIO.setup(17, GPIO.IN) -> Option A

4. Quick Check:

   GPIO input setup = GPIO.setup(pin, GPIO.IN) [OK]

Hint: Use GPIO.IN to read sensor signals, not GPIO.OUT [OK]

Common Mistakes:

• Using GPIO.OUT instead of GPIO.IN
• Calling GPIO.input() instead of GPIO.setup() to configure pin
• Trying to write output to sensor pin

3.

What will be the output of this Python code snippet when the PIR sensor detects motion?

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
PIR_PIN = 4
GPIO.setup(PIR_PIN, GPIO.IN)

if GPIO.input(PIR_PIN):
    print("Motion Detected")
else:
    print("No Motion")

medium

A. Motion Detected

B. No Motion

C. SyntaxError

D. GPIO pin not set

Solution

1. Step 1: Understand GPIO.input behavior

   GPIO.input(PIR_PIN) returns True (1) if motion is detected, False (0) otherwise.

2. Step 2: Analyze if condition with PIR sensor detecting motion

   If motion is detected, GPIO.input returns True, so the code prints "Motion Detected".

3. Final Answer:

   Motion Detected -> Option A

4. Quick Check:

   GPIO.input True = Motion Detected [OK]

Hint: GPIO.input True means motion detected, prints accordingly [OK]

Common Mistakes:

• Assuming GPIO.input returns string
• Confusing True/False logic in if statement
• Not setting up GPIO pin before reading

4.

Identify the error in this PIR sensor code snippet and choose the fix:

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
PIR_PIN = 18
GPIO.setup(PIR_PIN, GPIO.IN)

try:
    while True:
        if GPIO.input(PIR_PIN):
            print("Motion!")
        time.sleep(1)
except KeyboardInterrupt:
    print("Exit")

medium

A. Use GPIO.input() outside the loop

B. Change GPIO.setup to GPIO.OUT

C. Remove time.sleep(1)

D. Add GPIO.cleanup() in except block

Solution

1. Step 1: Check for GPIO cleanup after program ends

   GPIO pins should be cleaned up to reset their state when the program exits.

2. Step 2: Add GPIO.cleanup() in the except block

   Adding GPIO.cleanup() ensures pins are properly reset on KeyboardInterrupt.

3. Final Answer:

   Add GPIO.cleanup() in except block -> Option D

4. Quick Check:

   Always cleanup GPIO pins on exit [OK]

Hint: Always call GPIO.cleanup() when program ends [OK]

Common Mistakes:

• Forgetting GPIO.cleanup() causes warnings on rerun
• Setting input pin as output
• Removing sleep causes high CPU usage

5.

You want to count how many times motion is detected in 10 seconds using a PIR sensor on GPIO pin 23. Which code snippet correctly implements this?

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
PIR_PIN = 23
GPIO.setup(PIR_PIN, GPIO.IN)

count = 0
start_time = time.time()
while time.time() - start_time < 10:
    if GPIO.input(PIR_PIN):
        count += 1
        time.sleep(0.5)  # debounce delay
print(count)
GPIO.cleanup()

hard

A. Does not count because GPIO pin is not set as output

B. Counts motion detections with debounce, prints count after 10 seconds

C. Counts continuously without delay, causing multiple counts per motion

D. Infinite loop without exit condition

Solution

1. Step 1: Analyze loop timing and counting logic

   The loop runs for 10 seconds, checking PIR input and incrementing count on detection.

2. Step 2: Understand debounce with time.sleep(0.5)

   The 0.5 second sleep prevents counting the same motion multiple times quickly.

3. Step 3: Confirm GPIO cleanup and print

   After loop ends, count is printed and GPIO.cleanup() resets pins properly.

4. Final Answer:

   Counts motion detections with debounce, prints count after 10 seconds -> Option B

5. Quick Check:

   Debounce delay + timed loop = correct count [OK]

Hint: Use sleep to debounce and time.time() for timed loops [OK]

Common Mistakes:

• Missing debounce causes inflated counts
• Setting pin as output instead of input
• No exit condition causes infinite loop