{BOM} - {JOURNAL} - {PCB} - {FIRMWARE} - {CAD}

mp3-player

A minimalist open source pocket sized¹ mp3 player

(¹ if your pocket is big enough to fit a 115mmx50mmx20mm brick)

Why did I even build this?

I bring my phone every time, everywhere I go. My main excuse is that I need it for music, but that's not usually what ends up happening... So I built this to have a dedicated music player that I could bring with me when I don't need a phone! (mainly high school or going for a walk)
I also wanted to learn how to design a more complex & integrated pcb!

If you find this cool, you should read the journal I kept while designing this!

Overview

Specs:

• mcu: rp2350b
• bluetooth module: fsc-BT1114QI
• dac: PCM5102A
• power: 505050 battery + BQ24075 power path ic
• pcb: 4 layer (signal, ground, power, signal) 115mmx50mm
• case: 3d printed

Features:

• full size sdcard slot
• 2.8 inch high definition color display (480x640, around 286 dpi)
• custom themes
• 3.5mm headphone jack
• bluetooth le + classic support
• modern and clean ui

Hardware

pcb & cad screenshots

The brain is a 4 layer hand routed pcb, designed to be compact & cheap to manufacture (jlcpcb 4 layers basic tolerances).
I first planned to use a nrf chip for the audio but finally moved to a feasycom module to support classic A2DP bluetooth audio (basically everything that is not recent/high end) because I realized my headphones were not le compatible (but now my new ones are!).
Full size sdcard support is because I wanted to be able to use my mac's sdcard reader to easily transfer new music + not lose super small micro sd cards.
I also originally wanted to make the case in transparent resin, but I ended up choosing 3d printing for multiple reasons:

• way cheaper
• faster to iterate on
• petg is way more shock resistant than resin
• faster to get a finished project

explore the board & schematics in your browser

Firmware

warning: this is a wip and some parts of the firmware have been ai generated to get a poc working quickly, but I plan to rewrite it very soon.

The firmware is written in c and uses the pico sdk. I also wrote a desktop simulator that allows you to test ui changes without reflashing all the time/having the device.

Building to run on device:

If you just need an already built uf2, you can just grab it from the releases page or directly from the actions tab (action runs on every commit inside src/firmware)

(You need cmake, a pico sdk, an arm-none-eabi toolchain, pico-extras installed)

• clone this repo
• export these env vars:
  • PICO_SDK_PATH -> path to pico-sdk
  • PICO_TOOLCHAIN_PATH -> path to an arm-none-eabi toolchain (Applications/ArmGNUToolchain/15.2.rel1/arm-none-eabi/bin on my laptop)
  • PICO_EXTRAS_PATH -> path to pico-extras
• go to src/firmware/ & run ./build_pico.sh --clean
• flash the uf2 via usb (hold BOOTSEL while plugging in the device, then drag the uf2 to the mounted drive)

Building to run on desktop:

(this allows you to run/test the same ui on your computer without flashing the device!)
(you need sdl2 installed)

• go to src/firmware/ & run ./run_emulator.sh --clean

License

Firmware is MIT, hardware is CERN-OHL-S, and the 3d files + docs are CC-BY-SA.
See LICENSE for details.