Introduction to Python and Microcontrollers

Flowing Light

Control a 10-LED bar graph to create a flowing light animation — LEDs light up one at a time from left to right, then right to left, repeating in a loop.

New Concepts

• Lists

Lists

Python lists hold a sequence of values, for example l = [1, 2, 3] is a list holding the values 1, 2, and 3. Values in a list can be access by index, so l[0] accesses the first item in the list, 1 using the example from above.

See Python documentation for more info on lists.

Component List

Component Knowledge

LED Bar Graph

A LED bar graph integrates 10 individual LEDs into a single compact component. Each LED has its own pair of pins at the bottom — one anode and one cathode — just like a standalone LED.

Circuit

Wiring Diagram

Disconnect all power before building the circuit. Reconnect once verified.

If the LED bar does not light up, try rotating it 180°. The label orientation is not standardized across all units.

Schematic Diagram

Each LED anode connects to its GPIO pin. Each cathode connects to GND through a 220Ω resistor.

Code

File: `01_first_examples/code/FlowingLight.py

import time
from machine import Pin

pins = [21, 47, 48, 38, 39, 40, 41, 42, 2, 1]

def showled():
    length = len(pins)
    # Left to right
    for i in range(0, length):
        led = Pin(pins[i], Pin.OUT)
        led.value(1)
        time.sleep_ms(100)
        led.value(0)
    # Right to left
    for i in range(0, length):
        led = Pin(pins[(length - i - 1)], Pin.OUT)
        led.value(1)
        time.sleep_ms(100)
        led.value(0)

while True:
    showled()

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How to Run

Online

1. Open Thonny → 01_first_examples/code/.
2. Double-click FlowingLight.py.
3. Click Run current script — LEDs sweep left to right, then right to left.

Code Explanation

Pin list

pins = [21, 47, 48, 38, 39, 40, 41, 42, 2, 1]

Stores the 10 GPIO pin numbers in order from left to right. Using a list makes it easy to iterate over all LEDs.

Left-to-right sweep

for i in range(0, length):
    led = Pin(pins[i], Pin.OUT)
    led.value(1)
    time.sleep_ms(100)
    led.value(0)

Turns each LED on for 100ms then off, moving forward through the list.

Right-to-left sweep

for i in range(0, length):
    led = Pin(pins[(length - i - 1)], Pin.OUT)
    led.value(1)
    time.sleep_ms(100)
    led.value(0)

Iterates forward through i but accesses the list in reverse using length - i - 1.

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Key Concepts

• Lists: store multiple GPIO pin numbers for easy iteration
• len(list): returns the number of items in a list
• range(start, end): generates a sequence of integers for the for loop
• Reverse indexing: pins[length - i - 1] accesses list items in reverse order without reversing the list itself

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Reference

for i in range(start, end, step=1)

Iterates from start up to (but not including) end, incrementing by step each time.

range(0, 5)      # → 0, 1, 2, 3, 4
range(0, 10, 2)  # → 0, 2, 4, 6, 8

Back to Module

Adapted from Python_Tutorial.pdf Project 3.1

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