A hacker has turned a $20 4G wireless hotspot into a texting device by stripping its display, building a custom PCB, and making it work with iPhones. The project, shared as a “Show HN” post on Hacker News, documents every step of the build.
The build combines three things found on a desk: a cheap 4G modem, a Clicks keyboard, and a custom circuit board. The result is a small device that sends text messages through a cellular connection.
The Cheap 4G Modem
The heart of the project is a 4G modem sold on AliExpress for under $20 shipped. It comes with WiFi, Bluetooth, a display, a battery, and a SIM slot. The hacker ditched the display, which was powered by a GC9107 chip, because it looked bad.
The modem runs Android out of the box, but the hacker accessed the underlying hardware through adb, a debugging tool built into Android. From there, the device can be reflashed using edl, a low-level interface. Pins on the PCB allow a short to trigger edl directly.
The Clicks Keyboard
The keyboard is the input device. It connects through USB, and the hacker describes it as pleasant to use, though pricey and requiring cutting.
The protocol between the keyboard and the iPhone follows MFi rules, which stand for Made For iPhone. That means the keyboard acts as a regular USB keyboard with an extra Apple-specific endpoint that the iPhone authorizes before letting the keys pass through.
The keyboard itself is powered by a CH32V203 or similar chip. The hacker found no reason to flash custom code onto it yet, but wants a configuration utility in the future.
Building the Custom Board
The PCB handles USB host mode power, USB host-device switching, display power, and display signal level conversion. The hacker ordered the board assembled and made compromises to fit everything on one side, using the other side for solder points.
The design files live on GitHub. The PCB includes:
- A USB host controller
- Power regulation for the display
- Level shifting for the display signals
- Solder points for PCB-to-PCB connections
Cutting the PCB
To fit the modem inside a Clicks case, the hacker trimmed the board horizontally rather than mounting it vertically. The right cut removed the battery connection line, which had to be patched later.
The device booted normally after the cut, and the hacker concluded no crucial traces ran through the area.
Debugging the USB Connection
The USB test was the hardest part. The hacker wired the power supplies first, since those could be tested as an isolated unit, and then moved on to the data lines.
The first attempt failed. Probing the pads showed correct voltages, but the laptop’s dmesg log showed the device tried to enumerate, meaning something was happening.
The problem was speed. The device tried to use high-speed USB, which surprised the hacker. The fix was simple: twist the wires tighter. That worked.
Connecting to the Display
The display signals were tested using gpio commands. The hacker extracted the running device tree from the Android system and confirmed which pins carried the display SPI lines.
Power supplies and grounds were tested by disabling them in the device tree and rebooting. The hacker also reused the pads from the old display rather than the labeled pads next to the unpopulated micro SD connector.
Final Assembly
The assembled device combines the trimmed modem PCB, the custom USB host board, and the Clicks keyboard. The result is a small, battery-powered texting device that connects to an iPhone via USB.
The project shows how far a cheap modem can go with some careful hacking. The hacker documented every step, from sourcing parts to debugging the USB connection.
Commentary
This is a delightful piece of engineering. The hacker took a $20 hotspot, stripped its display, and turned it into a useful device. The documentation is thorough, and the project is open on GitHub.
The project’s popularity on Hacker News reflects the appeal of practical electronics. It is a reminder that even cheap consumer devices carry real value when opened up.
“It’s a display. You send commands. It displays.”
That line sums up the whole project. It is a simple idea, executed with care. The hacker’s honesty about the mistakes — the wrong pads, the tight wires, the patched battery line — makes the story more relatable.
The battery patch remains to be completed, and the configuration utility for the keyboard is still planned. But the core hack is done, and it works.
The device is a reminder that a little patience and a multimeter can accomplish a lot. It is the kind of project that inspires others to open their own gadgets and see what is inside.
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