4. Embedded programming¶

Group assignment:¶

• Compare the performance and development workflows for other architectures.

To see our group assignment click here

Individual assignments:¶

• Browse through the data sheet for your microcontroller

• Program a microcontroller development board to interact and communicate

Programming the XIAO RP2040 with MicroPython¶

Hardware Used¶

Setting Up the Environment¶

1. Installing the MicroPython Firmware¶

Before programming the board, you need to flash the MicroPython firmware onto it.

1. Download the .uf2 firmware from: https://micropython.org/download/RPI_PICO/
2. Hold down the BOOT button on the XIAO RP2040
3. Plug the USB cable into your PC (while still holding BOOT)
4. Release the BOOT button
5. A drive named RPI-RP2 appears in Windows Explorer
6. Copy and paste the .uf2 file into that drive
7. The board restarts automatically with MicroPython installed

2. Installing and Configuring Thonny¶

Thonny is the recommended IDE for MicroPython. It is easy to use and includes a built-in serial terminal.

1. Download Thonny from: https://thonny.org (Windows .exe version)
2. Run the installer (default settings)
3. Open Thonny
4. Click on "Python 3 local" in the bottom-right corner → select "MicroPython (Raspberry Pi Pico)"

1. Select the correct COM port from the list (e.g. COM7)
2. Click OK

MicroPython v1.27.0 on 2025-12-09; Raspberry Pi Pico with RP2040
Type "help()" for more information.
>>>

3. Issue Encountered: COM7 Error¶

During the first connection attempt, the following error appeared:

Unable to connect to COM7: Cannot configure port, something went wrong.
PermissionError(13, 'A device attached to the system is not functioning correctly.')

Possible causes and solutions:

• Another program was already using the COM port → close all other software
• The firmware had not been flashed yet → flash the .uf2 file first
• Wrong port selected → check the Device Manager in Windows
• Unplug and replug the board to force detection

4. Installing the HC-SR04 Library¶

The HC-SR04 ultrasonic sensor requires an external MicroPython library.

1. Download hcsr04.py from GitHub: https://github.com/rsc1975/micropython-hcsr04
2. In Thonny: File Open select hcsr04.py from your PC
3. File → Save a copy Raspberry Pi Pico
4. Keep the filename hcsr04.py and confirm

Project 1 : Simple LED Blink¶

Goal¶

Make the built-in RGB LED on the XIAO RP2040 blink without any external component.

About the Built-in LED¶

MicroPython Code¶

from machine import Pin
from time import sleep

# Built-in green LED (16=Red, 17=Green, 25=Blue)
led = Pin(17, Pin.OUT)

while True:
    led.value(0)   # Turn ON (inverted logic)
    sleep(1)
    led.value(1)   # Turn OFF
    sleep(1)

Result¶

Project 2 : Presence Detection with Ultrasonic Sensor¶

Goal¶

Automatically turn on the board's built-in LED when the HC-SR04 ultrasonic sensor detects a presence closer than 30 cm.

Wiring Diagram¶

MicroPython Code¶

from machine import Pin
from time import sleep
from hcsr04 import HCSR04

# Ultrasonic sensor
sensor = HCSR04(trigger_pin=4, echo_pin=5)

# Built-in green LED (inverted logic)
led = Pin(17, Pin.OUT)
led.value(1)  # OFF at startup

DISTANCE_THRESHOLD = 30  # in cm

while True:
    try:
        distance = sensor.distance_cm()
        print("Distance:", distance, "cm")

        if distance < DISTANCE_THRESHOLD:
            led.value(0)   # Turn ON the LED
            print("⚡ Presence detected!")
        else:
            led.value(1)   # Turn OFF the LED

    except Exception as e:
        print("Error:", e)

    sleep(0.3)

Result¶

Uploading the Program to the Board (main.py)¶

To have the program run automatically without Thonny or a PC, save it as main.py directly on the board.

Steps in Thonny¶

1. File → Save as...
2. Choose "Raspberry Pi Pico" (not "This computer")
3. Name the file exactly: main.py
4. Click OK

Why main.py ?¶

This is a core MicroPython convention. At startup, the board automatically looks for files in this order:

1. boot.py   → system configuration (optional)
2. main.py   → main program (auto-start)

Standalone Test¶

1. Unplug the USB cable from your PC
2. Plug the board into any USB power source (phone charger, power bank...)
3. The program starts automatically within a few seconds ✅

Validation Checklist¶

• MicroPython .uf2 firmware flashed onto the board
• Thonny installed and configured on the correct COM port
• MicroPython v1.27.0 connection established in Thonny
• hcsr04.py library copied onto the board
• Project 1: LED blinking works
• Project 2: Ultrasonic detection + LED works
• Program saved as main.py on the board
• Standalone startup (without PC) validated

Conclusion¶

This session covered the fundamental steps of embedded programming with MicroPython on the XIAO RP2040 under Windows. Both projects provide a solid foundation for going further in digital fabrication.

Conclusion¶

References & Prompt Used¶

Technical References¶

Hardware¶

Firmware & Language¶

IDE¶

Ultrasonic Sensor Library¶

Website Documentation¶

| Resource | Link | | MkDocs Material Admonitions | https://squidfunk.github.io/mkdocs-material/reference/admonitions/ |

Prompt Used to Generate This Documentation¶

Full Prompt¶

https://wiki.seeedstudio.com/XIAO-RP2040/

I want to program this board using Python.
I want us to build two projects:

Project 1: Simple LED blink
Project 2: LED + ultrasonic sensor
  → Scenario: when the ultrasonic sensor detects a presence,
    the onboard indicator LED should turn on.

Help me prepare the necessary tools (IDE, libraries).
I am on Windows.

---

Document this entire session from start to finish using MkDocs syntax.
Also provide an English version.
Give the references I should add to my documentation.
Organize the prompt that produced this result so that anyone
who wants to reproduce it can use the same prompt.

How to Adapt This Prompt to Your Project¶

If you want to reproduce this work with a different board or sensors, here are the elements to change in the prompt:

Tools Used During This Session¶

Board        : Seeed Studio XIAO RP2040
Firmware     : MicroPython v1.27.0
IDE          : Thonny (Windows)
Library      : hcsr04.py (micropython-hcsr04)
Documentation: MkDocs + Material Theme
AI Assistant : Claude (Anthropic) — claude.ai

• Extra credit: use different languages &/or development environments