MotionSensor (PIR) in Raspberry Pi - Step-by-Step Execution

Concept Flow - MotionSensor (PIR)

Start Program

↓

Setup GPIO Pin

↓

Wait for Motion

↓

Motion Detected?

No→Keep Waiting

Yes↓

Print "Motion Detected!"

↓

Repeat Waiting

The program sets up the sensor pin, waits for motion, prints a message when motion is detected, then continues waiting.

Execution Sample

Raspberry Pi

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
GPIO.setup(17, GPIO.IN)

while True:
    if GPIO.input(17):
        print("Motion Detected!")
        time.sleep(1)

This code waits for motion on GPIO pin 17 and prints a message when motion is detected.

Execution Table

Step	GPIO.input(17)	Condition (Motion Detected?)	Action	Output
1	False	No	Wait
2	False	No	Wait
3	True	Yes	Print message	Motion Detected!
4	False	No	Wait
5	True	Yes	Print message	Motion Detected!

💡 Program runs indefinitely, continuously checking for motion.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5
GPIO.input(17)	N/A	False	False	True	False	True

Key Moments - 2 Insights

Why does the program keep printing "Motion Detected!" multiple times?

Because the loop continuously checks the sensor state and prints whenever motion is detected (see execution_table steps 3 and 5). To avoid repeated prints, you would add a delay or state check.

What happens if GPIO.input(17) is False?

The program does nothing and keeps waiting (see execution_table steps 1, 2, and 4). It only acts when the sensor detects motion.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of GPIO.input(17) at step 3?

A False

B True

C None

D Error

💡 Hint

Check the 'GPIO.input(17)' column at step 3 in the execution_table.

At which step does the program print "Motion Detected!" for the first time?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'Output' column in the execution_table to find when the message first appears.

If GPIO.input(17) never becomes True, what will the program do?

A Keep waiting without printing

B Print "Motion Detected!" once

C Print "Motion Detected!" repeatedly

D Crash with error

💡 Hint

Refer to execution_table steps where GPIO.input(17) is False and see the action taken.

Concept Snapshot

MotionSensor (PIR) on Raspberry Pi:
- Setup GPIO pin as input
- Loop: read sensor state
- If motion detected (input True), print message
- Repeat indefinitely
- Use delays or state flags to avoid repeated prints

Full Transcript

This program uses a PIR motion sensor connected to GPIO pin 17 on a Raspberry Pi. It sets up the pin as input and enters an infinite loop. Each loop iteration reads the sensor state. If motion is detected (GPIO.input(17) returns True), it prints "Motion Detected!". Otherwise, it waits silently. The program keeps checking continuously, printing the message each time motion is detected. Beginners often wonder why the message prints multiple times; this happens because the loop runs fast and prints every time the sensor is active. To prevent this, you can add a delay or track previous state. The execution table shows the sensor state and program actions step by step.