Muxcard is a working, programmable computer built into the footprint and roughly the thickness of a credit card. Its developer, who goes by krauseler on GitHub, published the hardware and firmware specification as open source and has a working prototype in hand.
"After months of iteration, sleepless nights, frustrating setbacks and a borderline unhealthy obsession over shaving off every single mil of thickness, I can finally hold the very first functioning prototype of a fully working computer the size of an actual credit card," writes krauseler.
Smartcards with displays are not new, but earlier "card-sized" devices were thick as heck. Muxcard targets about 1mm total (close to the 0.76mm ISO 7816 smartcard spec), so will live happily in a regular wallet. The device runs on an ESP32-C3 microcontroller, has a 1.54-inch, flexible 200×200-pixel E-Paper display; an RC522 chip provides read/write NFC, a LIS2DW12 accelerometer for motion and wake detection, and an ultra-thin rechargeable LiPo cell for power.
As you can see, this one is a literal 'ugly' prototype, but it serves as a proof of concept to find out what the real challenges are beyond component hieght. Although the first handmade one feels like it would break just by breathing wrong, it gave me good insight into theory in CAD vs real physical stackability because of unplanned things like connections, bending buffer, bonding material, real world tolerances and so on. But in a technicaly perspective, it works very well!
Suggested uses include a minimalist wallet for QR codes, tickets, boarding passes and so on (the E-Paper display holds an image without power), 2FA/TOTP generator, smart-home control, pentesting, and general Flipper Zero-type fun. How about a tiny game console?
