PicoDAC

PicoDAC

USB-C to 3.5mm HiFi mini DAC

Fully custom PCB and 3D printed case.

Design

Preview Images

Note that a specially cut transparent acrylic sheet will be used as the top lid of the main PCB case which will be superglued to part of the case that is non-detachable.

The main PCB case also requires this 2.5X8 screw that will be used to attach the detachable part with the non-detachable part.

As for the case of the board - 2, since it really is just two directly connected USB-C plugs, the top and bottom part of the case will be glued together after seating the board-2 PCB inside it properly (after testing it).

All the design files are available in the CAD folder.
Exported STEP files for 3d-printing are available in /CAD/exports.

Also note that the files:
1_PicoDAC_Case_DetachablePart.step
2_PicoDAC_Case_Main.step
3_board2_top_case.step
4_board2_bottom_case.step
need to be printed as separate bodies.
All these files are also available in .stl format inside the CAD/exports/stl_files directory.

Motivation

I recently bought a cheap USB-C to 3.5mm DAC and it was working perfectly fine until it broke.

I use my phone in bed a lot (yes i know this is a bad habit) vertically with the bottom of my phone resting on my chest. Since the USB-C port is at the bottom of my phone, anything connected to it has to do the heavy lifting of keeping the phone upright.

Naturally, the red part I've highlighted in the image slowly got bent and broke :(

To fix this issue, learn more about audio electronics, engineer a cool device and also make a higher-quality DAC in the process, I've started this project.

Hardware

Main hardware components are:

• 1x CS43131-CNZR (A high-performance, 32-bit resolution, stereo audio DAC that supports up to 384-kHz sampling frequency with integrated low-noise ground-centered headphone amplifiers.): LCSC part
• XIAO RP2350 instead of the 2040 as it has integrated fractional dividers (also see: this git issue)
• 9x SK6812 RGB LEDs for music level visualization

View complete BOM

PCB Preview:

The complete schematics look like:

Main Board:

Board 2:

Note that the PCB and schematic files can be opened using KiCAD. They are located in the /hardware/PicoDAC directory and /hardware/usbc_m2m directory inside this repository.

Steps for viewing the PCB schematics and layout:

• Open KiCAD
• Click File (top left) >> Open Project
• Navigate to the the repository's saved destination,
• For Main board:
  • Open /hardware/PicoDAC directory
  • Select the file PicoDAC.kicad_pro
• For Board 2:
  • Open /hardware/usbc_m2m directory
  • Select the file usbc_m2m.kicad_pro

Firmware

Checkout the firmware directory for the firmware README.md file and current status. It contains building, flashing instructions and also some special notes that might help with the process.

Ordering Parts, PCB/PCBA

I will be using JLCPCB along with their PCB Assembly service to get this PCB built assembled as it is the cheapest and best option available in my region.

Other than that, the only extra part is the XIAO RP2350 MCU which is available on robu.in.

Note that the following PCB, PCBA costs are for 5 PCBs out of which 2 are assembled (this is the MOQ for JLCPCB) and also I have used basic components instead of extended wherever possible to reduce costs.

BOM

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The DXF file for the acrylic lid is available as Main_Case_Lid_DoNotPrint.dxf
Robu.in does not allow laser cutout service orders in the same cart as normal products, hence the two different 0.51$ shipping costs.

Please checkout the /hardware/Ordering/ directory to get the gerber, bom and cpl files for both boards, to upload on JLC website.

JLC Cart for main board

References

• All datasheets in BOM.csv
• https://datasheets.raspberrypi.com/rp2350/rp2350-datasheet.pdf
• https://github.com/raspberrypi/pico-sdk/issues/1924
• https://electronics.stackexchange.com/questions/336836/understanding-audio-jack-connection
• https://electronics.stackexchange.com/questions/95575/how-does-the-phone-detect-if-3-5-mm-jack-circuit-is-closed
• https://www.lcsc.com/product-detail/C33196.html
• https://www.lcsc.com/product-detail/C2867798.html (english version: https://www.ti.com/lit/ds/symlink/sn74axc4t245.pdf)
• https://www.totalphase.com/blog/2024/07/what-are-i2c-pull-up-resistors-calculate-their-values/
• https://forum.arduino.cc/t/why-use-a-47k-resistor-between-3-3v-and-sda-and-scl-port-of-esp3266/850553
• https://files.seeedstudio.com/wiki/XIAO-RP2350/res/Seeed-Studio-XIAO-RP2350-v1.0.pdf
• https://www.alldatasheet.com/datasheet-pdf/pdf/1265214/TI/TPS7A201825PDQNR.html
• https://wiki.seeedstudio.com/xiao_rp2350_arduino/
• https://forum.kicad.info/t/how-to-create-teardrops-in-pcb-editor/61920/
• https://electronics.stackexchange.com/questions/686845/pcb-design-question-power-plane-or-fat-traces-for-high-current
• https://www.eevblog.com/forum/eda/should-plane-be-used-to-connect-power-or-just-thicker-tracks/

😼💖