What you'll learn

Controlling ten outputs from a list of pins
Lighting one LED at a time by comparing an index
Building a back-and-forth sequence from two ranges
Using one resistor per LED

Difficulty: Beginner
Time: About 20 minutes
Board: Raspberry Pi Pico
Parts: 12

How it works

Ten Pico pins, GP16 to GP22 and GP26 to GP28, each go through a 220 ohm resistor to one segment of the LED bar. The other ends of the segments go to ground.

The program lights exactly one bar at a time, for a tenth of a second each. The light runs from the first bar to the tenth, then back down the other way. After each full sweep it prints sweep.

Parts list

12 parts, plus the jumper wires. They retail for about $5.30; on Mokxi they're free.

1 × Raspberry Pi PicoIn Fight Stick Kit.
1 × LED bar graph, 10 segmentsIn Spaceship Panel Kit.
10 × Resistor, 220 ΩIn Starter Kit, Claw Machine Kit, Halloween Prop Kit.

Kits that can build it

This starter kit has every part in the circuit. Each kit's page lists what else it can build.

Freenove Ultimate Starter Kit for Raspberry Pi Pico

Wiring table

Every connection, pin by pin, read from the circuit itself. Each row joins the pin on the left to the pin on the right, by a jumper wire or a breadboard strip.

Part and pin	Connects to
Resistor, 220 Ω (1) pin 1	Raspberry Pi Pico pin GP28
Resistor, 220 Ω (2) pin 1	Raspberry Pi Pico pin GP27
Resistor, 220 Ω (3) pin 1	Raspberry Pi Pico pin GP26
Resistor, 220 Ω (4) pin 1	Raspberry Pi Pico pin GP22
Resistor, 220 Ω (5) pin 1	Raspberry Pi Pico pin GP21
Resistor, 220 Ω (6) pin 1	Raspberry Pi Pico pin GP20
Resistor, 220 Ω (7) pin 1	Raspberry Pi Pico pin GP19
Resistor, 220 Ω (8) pin 1	Raspberry Pi Pico pin GP18
Resistor, 220 Ω (9) pin 1	Raspberry Pi Pico pin GP17
Resistor, 220 Ω (10) pin 1	Raspberry Pi Pico pin GP16
Resistor, 220 Ω (1) pin 2	LED bar graph, 10 segments pin A1
Resistor, 220 Ω (2) pin 2	LED bar graph, 10 segments pin A2
Resistor, 220 Ω (3) pin 2	LED bar graph, 10 segments pin A3
Resistor, 220 Ω (4) pin 2	LED bar graph, 10 segments pin A4
Resistor, 220 Ω (5) pin 2	LED bar graph, 10 segments pin A5
Resistor, 220 Ω (6) pin 2	LED bar graph, 10 segments pin A6
Resistor, 220 Ω (7) pin 2	LED bar graph, 10 segments pin A7
Resistor, 220 Ω (8) pin 2	LED bar graph, 10 segments pin A8
Resistor, 220 Ω (9) pin 2	LED bar graph, 10 segments pin A9
Resistor, 220 Ω (10) pin 2	LED bar graph, 10 segments pin A10
LED bar graph, 10 segments pin C10	Ground
LED bar graph, 10 segments pin C9	Ground
LED bar graph, 10 segments pin C8	Ground
LED bar graph, 10 segments pin C7	Ground
LED bar graph, 10 segments pin C6	Ground
LED bar graph, 10 segments pin C5	Ground
LED bar graph, 10 segments pin C4	Ground
LED bar graph, 10 segments pin C3	Ground
LED bar graph, 10 segments pin C2	Ground
LED bar graph, 10 segments pin C1	Ground

The code

The MicroPython code exactly as the editor opens it. Change a line there and press Run: the board runs it on the official MicroPython firmware, with nothing to compile.

main.py · Raspberry Pi Pico

# Flowing light: one bar of the LED bar graph lit at a time, along the
# bar and back, a tenth of a second each.
from machine import Pin
import time

pins = [16, 17, 18, 19, 20, 21, 22, 26, 27, 28]
leds = [Pin(n, Pin.OUT, value=0) for n in pins]

def light(i):
    for n, led in enumerate(leds):
        led.value(n == i)

while True:
    for i in list(range(10)) + list(range(8, 0, -1)):
        light(i)
        time.sleep_ms(100)
    print("sweep")

Code walkthrough

The key functions of the sketch, and what each one does.

`light` main.py

Goes through every LED in leds and sets it on only if its position matches i. So calling light(3) lights bar 3 and turns every other bar off.

def light(i):
    for n, led in enumerate(leds):
        led.value(n == i)

Troubleshooting

The usual mistakes with this circuit, and the fix for each.

The light jumps instead of flowing This project
Check the pins list matches your wiring. The pins skip from GP22 to GP26.
No bar lights This project
Check each segment's resistor and that the cathode pins go to ground.
Segments are dim, uneven, or the chip is damaged. LED bar graph
Every segment is its own LED and needs its own current-limiting resistor, about 220 to 330 ohms at 5 V. One shared resistor makes brightness change with how many are lit.
The bar lights in reverse order or a segment never lights. LED bar graph
Check pin 1 and the orientation. Anode and cathode sides are on opposite rows. Some bars are numbered the other way around, so test with one segment at a time.
The LED is dim, burns out, or the pin reads wrong because the resistor value is off. Resistor
Read the color bands again. A 220 ohm to 330 ohm resistor suits a typical LED on 5 V. 10k is a common pull-up or pull-down value. Check with a multimeter if unsure.
A pull-up or pull-down resistor is missing, so the input floats and reads random values. Resistor
Tie the input to 5 V or ground through about 10k. Or use INPUT_PULLUP and wire the switch to ground.
The Pico does not show up as a drive, or the program will not load. Raspberry Pi Pico
Hold the BOOTSEL button while you plug in USB. A drive named RPI-RP2 appears. Then copy the UF2 file onto it.
A 5 V signal or sensor is wired to a GPIO pin. Raspberry Pi Pico
Pico GPIO pins are 3.3 V only and are not 5 V tolerant. Use a level shifter or a voltage divider for any 5 V output going into the board.