A side project for the Portable Dumb Terminal, this silicone membrane keyboard is a custom keyboard, much like the buttons in a TV remote control. It was designed in Fusion360 and manufactured for ~$1/piece in quantity 1000.
The keyboard presents 69 keys to the user and is interfaced with a custom Eagle library for ‘carbon pill’ buttons. Reading the keyboard is as like any keypad scanning firmware, with the exception that diodes are not used in this implementation – instead, a custom scanning protocol was used to prevent key ghosting.
The keyboards were manufacured with a process that is like – but not identical to – injection molding. Imagine putting a sheet of silicone inside a waffle iron. Legends were then printed onto the keycaps using a pad printing process. Because the legend printing is seperate from the forming of the silicone, many different legend styles can be created without manufacturing a new mold, DVORAK, QWERTZ, and AZERTY, for example.
More information can be found in the Portable Dumb Terminal repository.