First GPIO program (LED blink) in Raspberry Pi - Step-by-Step Execution

Concept Flow - First GPIO program (LED blink)

Start Program

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Setup GPIO Pin as Output

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Turn LED ON

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Wait (delay)

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Turn LED OFF

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Wait (delay)

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Repeat Loop

The program sets up a pin to control an LED, then repeatedly turns it on and off with pauses in between.

Execution Sample

Raspberry Pi

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
GPIO.setup(18, GPIO.OUT)

while True:
    GPIO.output(18, GPIO.HIGH)
    time.sleep(1)
    GPIO.output(18, GPIO.LOW)
    time.sleep(1)

This code makes an LED connected to pin 18 blink on and off every second.

Execution Table

Step	Action	Pin 18 State	Delay (seconds)	Loop Iteration
1	Setup pin 18 as output	LOW (default)	0	0
2	Turn LED ON (HIGH)	HIGH	0	1
3	Wait 1 second	HIGH	1	1
4	Turn LED OFF (LOW)	LOW	0	1
5	Wait 1 second	LOW	1	1
6	Repeat loop back to turn LED ON	LOW	0	2
7	Turn LED ON (HIGH)	HIGH	0	2
8	Wait 1 second	HIGH	1	2
9	Turn LED OFF (LOW)	LOW	0	2
10	Wait 1 second	LOW	1	2
...	Loop continues indefinitely	Alternates HIGH/LOW	1 each delay	3,4,5,...

💡 Program runs forever until manually stopped (no automatic exit).

Variable Tracker

Variable	Start	After Step 2	After Step 4	After Step 6	After Step 9	Final
Pin 18 State	LOW (default)	HIGH	LOW	LOW	LOW	Alternates HIGH/LOW
Loop Iteration	0	1	1	2	2	Increases by 1 each cycle

Key Moments - 3 Insights

Why does the LED blink instead of staying on?

Because the program turns the LED ON, waits 1 second, then turns it OFF and waits 1 second repeatedly, as shown in steps 2-5 in the execution table.

What happens if we remove the time.sleep() calls?

The LED would appear to stay ON or OFF because the program would switch states too fast to see blinking, as the delays control visible timing (see steps 3 and 5).

Why does the program never stop on its own?

Because the while True loop runs forever, repeating the ON/OFF cycle endlessly, as noted in the exit_note and steps 6-10.

Visual Quiz - 3 Questions

Look at the execution table, what is the state of pin 18 at step 4?

A LOW

B Undefined

C HIGH

D Flashing

💡 Hint

Check the 'Pin 18 State' column at step 4 in the execution_table.

At which step does the program wait for 1 second after turning the LED ON?

A Step 5

B Step 3

C Step 2

D Step 4

💡 Hint

Look for 'Wait 1 second' after 'Turn LED ON' in the execution_table.

If the delay after turning LED OFF is removed, how would the blinking change?

A LED would stay ON

B LED would stay OFF

C LED would blink faster

D No change

💡 Hint

Refer to key_moments about the role of time.sleep() delays controlling blink speed.

Concept Snapshot

First GPIO program (LED blink):
- Import GPIO and time modules
- Set GPIO mode (BCM)
- Setup pin 18 as output
- Loop: turn LED ON, wait 1s, turn OFF, wait 1s
- Repeat forever to blink LED
- Use delays to make blinking visible

Full Transcript

This program controls an LED connected to Raspberry Pi pin 18. It first sets the pin as an output. Then, inside an endless loop, it turns the LED on by setting the pin HIGH, waits one second, turns the LED off by setting the pin LOW, and waits another second. This cycle repeats forever, causing the LED to blink on and off every second. The delays are important to make the blinking visible to our eyes. Without delays, the LED would switch states too fast to notice. The program runs continuously until stopped manually.