This is/was the start of a clamshell - style calculator. A 49-key keypad, about 10cm x 6cm. Thanks to the Calculator origins, the artwork has suggested calculator functions for the keys.
The connector is PMOD-compatible, with and extra pin used to send interrupts back to the microcontroller. Schematics and PCB are in KICAD files at the Github.
There are other mini keyboards around: fully functional, bluetooth connection, and cost less than what I'm charged for SMD switches [let alone diodes, board, controller chip, case, keycaps etc]. But maybe the design can be used as a stating point for YOUR design...
Evaluation, Demonstration Kits, Boards and Modules / Evaluation Kits, Boards and ModulesKeyboard Encoder
1N4148 SMD Diode
Discrete Semiconductors / Diodes and Rectifiers
EVQ-PQHB55 SMD Switch
Switches and Relays / Switches