Multiple LED patterns in Raspberry Pi - Step-by-Step Execution

Concept Flow - Multiple LED patterns

Start Program

↓

Initialize LEDs

↓

Select Pattern

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Pattern 1: Blink All

↓

Turn LEDs ON

↓

Wait

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Turn LEDs OFF

↓

Wait

Back to Select Pattern↓

Pattern 2: Chase

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Turn ON LED 1

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Turn OFF LED 1

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Turn ON LED 2

Back to Select Pattern↓

Pattern 3: Alternate

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Turn ON even LEDs

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Wait

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Turn ON odd LEDs

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Wait

↩Back to Select Pattern

The program initializes LEDs, then repeatedly selects and runs different LED patterns in a loop.

Execution Sample

Raspberry Pi

import time
import RPi.GPIO as GPIO

GPIO.setmode(GPIO.BCM)
leds = [17, 27, 22]
for led in leds:
    GPIO.setup(led, GPIO.OUT)

# Pattern 1: Blink all LEDs
for _ in range(2):
    for led in leds:
        GPIO.output(led, True)
    time.sleep(0.5)
    for led in leds:
        GPIO.output(led, False)
    time.sleep(0.5)

This code sets up three LEDs and blinks them all on and off twice.

Execution Table

Step	Action	LED States (17,27,22)	Wait (seconds)	Output/Note
1	Setup GPIO mode BCM	OFF, OFF, OFF	0	GPIO initialized
2	Setup LED pins as output	OFF, OFF, OFF	0	Pins 17,27,22 ready
3	Turn ON all LEDs	ON, ON, ON	0	All LEDs lit
4	Wait	ON, ON, ON	0.5	Pause for 0.5 seconds
5	Turn OFF all LEDs	OFF, OFF, OFF	0	All LEDs off
6	Wait	OFF, OFF, OFF	0.5	Pause for 0.5 seconds
7	Turn ON all LEDs	ON, ON, ON	0	All LEDs lit again
8	Wait	ON, ON, ON	0.5	Pause for 0.5 seconds
9	Turn OFF all LEDs	OFF, OFF, OFF	0	All LEDs off again
10	Wait	OFF, OFF, OFF	0.5	Pause for 0.5 seconds
11	End of blink loop	OFF, OFF, OFF	0	Pattern 1 complete

💡 Blink loop runs twice, then program can continue to next pattern or stop.

Variable Tracker

Variable	Start	After Step 3	After Step 5	After Step 7	After Step 9	Final
LED 17 state	OFF	ON	OFF	ON	OFF	OFF
LED 27 state	OFF	ON	OFF	ON	OFF	OFF
LED 22 state	OFF	ON	OFF	ON	OFF	OFF

Key Moments - 3 Insights

Why do all LEDs turn off after being turned on?

Because the code explicitly sets each LED to OFF after the wait (see steps 5 and 9 in execution_table), turning them off to create the blinking effect.

Why is there a wait after turning LEDs on or off?

The wait (time.sleep) pauses the program so the LEDs stay in their current state long enough to be visible (see steps 4, 6, 8, 10). Without it, changes would be too fast to see.

How does the loop control how many times LEDs blink?

The for loop runs twice (see execution_sample code), so the on-off sequence repeats two times, shown by steps 3-6 and 7-10.

Visual Quiz - 3 Questions

Look at the execution_table, what is the LED 27 state at Step 5?

A ON

B Blinking

C OFF

D Undefined

💡 Hint

Check the 'LED States' column at Step 5 in the execution_table.

At which step does the program wait for the first time?

A Step 3

B Step 4

C Step 5

D Step 6

💡 Hint

Look for the first 'Wait' action in the execution_table.

If the wait time is removed, what happens to the LED blinking pattern?

A Blinking happens too fast to see

B LEDs stay OFF permanently

C LEDs stay ON permanently

D Program crashes

💡 Hint

Refer to key_moments about why wait is needed after turning LEDs on/off.

Concept Snapshot

Multiple LED patterns on Raspberry Pi:
- Initialize GPIO pins as outputs
- Use loops to create patterns (blink, chase, alternate)
- Turn LEDs ON/OFF with GPIO.output(pin, True/False)
- Use time.sleep() to pause and make patterns visible
- Repeat patterns in loops for continuous effect

Full Transcript

This example shows how to control multiple LEDs connected to a Raspberry Pi. First, the program sets up the GPIO pins for output. Then it runs a simple blink pattern where all LEDs turn on together, wait half a second, then turn off, and wait again. This on-off cycle repeats twice. The execution table traces each step, showing LED states and wait times. Variables track each LED's state after each step. Key moments explain why waits are needed and how loops control repetition. The quiz tests understanding of LED states at specific steps and the role of wait. The snapshot summarizes how to create multiple LED patterns using GPIO control and timing.