micro:bit Microphone Over USB Serial

1Introduction

I saw a micro:bit demo at the school I work and picked one up for myself. Turns out it’s a neat little device for collecting sensor data — and you don’t need a browser, an IDE, or any Microsoft-flavored tooling to work with it, which I first was afraid of. I’ve been using Arduinos, since their inception. After Qualcomm acquired Arduino, they are not that fun anymore — not that BBC (the owner of micro:bit) is flawless.

This guide shows how to read microphone data from the micro:bit over USB serial and visualize it as a live bar in the terminal. You can generalize this into reading any sort of data over USB serial from the device.

2Prerequisites

pipx install uflash
pipx install pyserial

uflash handles flashing MicroPython scripts onto the device (this is where the no-browser achievement is acquired). pyserial handles reading from the serial interface.

3Step 1: Mount the micro:bit

The micro:bit shows up as a USB mass storage device (after connected). Mount it with your user (usually UID=1000) owning the mount point:

doas mount -ouid=1000 /dev/sda ~/mnt/strg01

The device path may vary — /dev/sda is what it showed up as here. Check dmesg och lsblk after plugging it in if you’re unsure. I use ~/mnt/strg01 as my mount point, but you can use whatever.

4Step 2: Write the Firmware

This is the script that runs on the micro:bit itself. It reads the microphone level and prints it over serial every 50 ms. Quite lean, if I do say so myself — and that is good on such a small device. Turns out, it’s easy to get the 405 :( memory error quite easy.

mic_sender.py

from microbit import microphone, sleep

while True:
 print(microphone.sound_level())
 sleep(50)

5Step 3: Write the Listener

This runs on your computer and reads from the serial port, drawing a live colored bar in the terminal.

mic_listener.py

#!/usr/bin/env python3

import serial
import sys
import glob

BAR_WIDTH = 40
MAX_VAL = 255


def find_microbit():
 candidates = glob.glob("/dev/ttyACM*") + glob.glob("/dev/ttyUSB*")
 if candidates:
 return candidates[0]
 return None


def draw_bar(value):
 filled = int((value / MAX_VAL) * BAR_WIDTH)
 bar = "█" * filled + "░" * (BAR_WIDTH - filled)

 if value < 80:
 colour = "\033[92m"
 elif value < 160:
 colour = "\033[93m"
 else:
 colour = "\033[91m"
 reset = "\033[0m"
 print(f"\r{colour}[{bar}]{reset} {value:>3}", end="", flush=True)


def main():
 port = sys.argv[1] if len(sys.argv) > 1 else find_microbit()
 if not port:
 print("Could not find micro:bit. Plug it in or pass port as argument:")
 print("  python3 mic_listener.py /dev/ttyACM0")
 sys.exit(1)

 print(f"Connecting to {port} at 115200 baud... (Ctrl+C to stop)\n")

 with serial.Serial(port, baudrate=115200, timeout=1) as ser:
 try:
 while True:
 line = ser.readline().decode("utf-8", errors="ignore").strip()
 if line.isdigit():
 draw_bar(int(line))
 except KeyboardInterrupt:
 print("\nStopped.")


if __name__ == "__main__":
 main()

The bar is green below 80, yellow below 160, and red above that. Values range from 0–255 (8bit resolution).

6Step 4: Flash the Firmware

uflash mic_sender.py ~/mnt/strg01

Replace ~/mnt/strg01 with wherever you mounted the device. The flashing process can take a few seconds.

7Step 5: Unmount

umount ~/mnt/strg01

8Step 6: Run the Listener

python mic_listener.py

Or if you’ve made it executable:

chmod +x mic_listener.py
./mic_listener.py

The script will auto-detect the micro:bit on /dev/ttyACM* or /dev/ttyUSB*. If you have other devices on those interfaces, pass the port explicitly:

./mic_listener.py /dev/ttyACM0

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