A 4-layer KiCad board by Koppar gives any computer a full phone line over USB-C. Plug in a nano-SIM and one USB-C cable, and your computer can handle LTE data, SMS, and voice calls with audio routed through USB. The design uses a Quectel EC25-EUX module for cellular connectivity with 3G/2G fallback, an RP2040 microcontroller to manage call audio as a USB sound card, and three status LEDs for network, ring, and call indicators.
Power comes entirely from USB-C at 5V, with onboard regulation for the module and hub. No battery or speaker is included. The project includes full schematics, Gerber files, assembly BOM, and firmware source.
Build instructions specify JLCPCB manufacturing with precise stackup and via requirements. Optional parts like antennas and SIM must be sourced separately. The design is documented with a detailed review file explaining changes and open issues.
Source: Hacker News · Summarized by HeadlinesBriefing