Hardware
The key is based on an Atmel Attiny85 microcontroller. It is very inexpensive (~1€) and can be easily found. Some basic components must be added to allow the chip to communicate via USB.
- 1 Atmel Attiny85 chip
- 1 USB male connector
- 2 Zener Diods 3V6
- 2 1kΩhm resistors (only one is necessary if you don't want the use a LED)
- 1 2.2kΩhm resistor
- 2 68Ωhm resistors
- 1 push button
- 1 standard LED (optional)
- 1 board for soldering (e. g. a prototype board)
Refer to the following drawing to build the key.
The following images can be used as an exemple of how to solder the components. Pay attention to the fact that because of a lack of 68Ωhm resistors, two resistors have been connected in series instead.
Use the 3D files to print an enclosure for the key to complete the building. The case and the lid can be printed out of PLA/ABS. If you're looking for a better protection, you can add a sheath which should be printed out of a flexible filament like TPU.
