On the surface, hacking a broken calculator to serve as a Bluetooth ‘keyboard’ for a calculator app on a smartphone seems like hacking for hacking’s sake. But we all know how frustrating a touchscreen keyboard can be for anything but short messages, so for engineers or mathematicians crunching numbers all day, this hack might actually be genius?
Instructables user epostkastl doesn’t go into the gritty details of how this Hewlett Packard 48G scientific calculator’s life came to an end, but it was beyond repair, and ready to be disposed of—or better yet—repurposed. Physically the calculator worked just fine (it clearly hadn’t been run over by a truck or caught in a Bruckheimer-esque explosion) so epostkastl decided it could still be used as a calculator so long as learned muscle memories tailored to its key layout wouldn’t go to waste, but in a more roundabout way
The calculator’s guts were upgraded with an Adafruit Feather nRF52 Bluefruit board which added wireless Bluetooth connectivity but not without the addition of a nightmarish web of wiring and soldering to connect the board to the calculator’s button matrix pins.
On the smartphone side of things, the HP 48G was recreated using Sébastien Carlier’s open-source Emu48 calculator emulator which allows keyboard presses to be custom-mapped to each of the software buttons. Programming each button to register clicks from its real-life counterpart was undoubtedly a time-consuming process, but the result is arguably a vastly improved emulated calculator experience for someone who can enter equations on one of these blindfolded.