A maker details building a pocket texting device by combining a sub-$20 4G hotspot running Linux with a Clicks iPhone keyboard and a SHARP memory display. The project required a custom adapter PCB, kernel driver patches for the display, and multiple enclosure iterations.
Indexed summary. This entry is an agent-written synopsis of an article first published at bkovac.github.io. Read the original for the full text.
The author assembled what they call the "Clicks Communicator" from three items that happened to land on the same desk: a cheap 4G modem (the MF800) that can be reflashed to run mainline Linux via the OpenStick project, a Clicks Keyboard designed for the iPhone, and an Adafruit SHARP memory display selected for its high contrast.
The hardware challenges were substantial. The keyboard connects over USB but the modem needs to act as USB host, which it does not support natively, requiring a custom adapter PCB built around the TUSB320 mode-switch chip, a 5V booster, level shifters, and an FPC connector for the display. The MF800's Qualcomm SoC mishandles the display's SPI chip-select line, so the author patched the driver to toggle CS manually via libgpiod.
Key points
The MF800 ships with Android but has accessible EDL pads for reflashing; OpenStick community tooling makes Linux installation straightforward.
A custom two-layer PCB handles USB host/device switching, power conversion, and display signal level translation.
The display driver used is ardangelo's sharp-drm-driver compiled against a mainline 6.12.1 kernel; the author extended it with selectable dithering algorithms (Atkinson for video, Floyd-Steinberg for stills).
Cutting the MF800 PCB to fit the keyboard did not sever any critical traces; the modem continued to work.
Sleep and a power button remain unsolved; the device is not yet practical for all-day use.
Why it matters
This write-up is a detailed, honest account of a real hardware project, including every false start and workaround. It is a useful reference for anyone interested in the OpenStick ecosystem, custom display drivers on ARM SBCs, or adapter PCB design for repurposing commodity modems.