Single LED control in Raspberry Pi - Step-by-Step Execution

Concept Flow - Single LED control

Start Program

↓

Setup GPIO Pin as Output

↓

Turn LED ON

↓

Wait for a moment

↓

Turn LED OFF

↓

Cleanup GPIO

↓

End Program

The program sets up the GPIO pin, turns the LED on, waits, turns it off, cleans up, then ends.

Execution Sample

Raspberry Pi

import RPi.GPIO as GPIO
import time

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

GPIO.output(18, GPIO.HIGH)  # LED ON

time.sleep(1)  # wait 1 second

GPIO.output(18, GPIO.LOW)   # LED OFF

GPIO.cleanup()

This code turns an LED connected to pin 18 on for 1 second, then turns it off and cleans up.

Execution Table

Step	Action	Pin 18 State	Output/Effect
1	Set GPIO mode to BCM	N/A	GPIO library ready to use BCM numbering
2	Setup pin 18 as output	N/A	Pin 18 ready to control LED
3	Set pin 18 HIGH	HIGH	LED turns ON
4	Wait 1 second	HIGH	LED stays ON for 1 second
5	Set pin 18 LOW	LOW	LED turns OFF
6	Cleanup GPIO	N/A	GPIO pins reset to default
7	Program ends	N/A	LED remains OFF, program stops

💡 Program ends after cleaning up GPIO, LED is OFF

Variable Tracker

Variable	Start	After Step 3	After Step 5	Final
Pin 18 State	N/A	HIGH	LOW	LOW

Key Moments - 3 Insights

Why do we need to call GPIO.cleanup() at the end?

GPIO.cleanup() resets the pins so they don't stay in output mode, preventing unexpected behavior. See step 6 in execution_table.

What happens if we skip the time.sleep(1) line?

The LED would turn ON and immediately OFF, so you might not see it light up. This is shown between steps 3 and 5.

Why do we use GPIO.setmode(GPIO.BCM)?

It tells the program to use the Broadcom pin numbering, matching the physical pin 18. This is step 1 in execution_table.

Visual Quiz - 3 Questions

Look at the execution table, what is the state of pin 18 after step 3?

A LOW

B N/A

C HIGH

D Undefined

💡 Hint

Check the 'Pin 18 State' column at step 3 in the execution_table.

At which step does the LED turn OFF?

A Step 4

B Step 5

C Step 3

D Step 6

💡 Hint

Look for when 'Pin 18 State' changes to LOW in the execution_table.

If we remove GPIO.cleanup(), what would likely happen?

A GPIO pins remain set, possibly causing issues later

B Program will not run

C LED stays ON forever

D LED blinks automatically

💡 Hint

Refer to key_moments about why cleanup is important.

Concept Snapshot

Single LED control on Raspberry Pi:
- Use GPIO.setmode(GPIO.BCM) to select pin numbering
- Setup pin as output with GPIO.setup(pin, GPIO.OUT)
- Turn LED ON with GPIO.output(pin, GPIO.HIGH)
- Use time.sleep() to keep LED ON
- Turn LED OFF with GPIO.output(pin, GPIO.LOW)
- Always call GPIO.cleanup() at the end

Full Transcript

This program controls a single LED connected to Raspberry Pi pin 18. First, it sets the GPIO mode to BCM to use Broadcom pin numbers. Then it sets pin 18 as an output pin. The program turns the LED ON by setting pin 18 HIGH, waits for one second so the LED stays lit, then turns the LED OFF by setting pin 18 LOW. Finally, it calls GPIO.cleanup() to reset the pins to their default state. This prevents pins from staying in output mode and avoids unexpected behavior. The program then ends with the LED off.