Features

• Up to 8 DS1990 keys stored in EEPROM.
• A button for quick access to keys from the 4th to the 8th.
• Any battery with a voltage of 8-30V is suitable for programming (for example, CR-9V).
• A bridge rectifier to prevent wrong battery polarity.
• Works with most popular intercoms.
• No special programmer or computer is needed for programming.

The device is designed just for fun and as a souvenir.

Project Overview (English subtitles): https://youtu.be/5b73LqXjfCg

Summary

Battery-free emulator of the well-known iButton key based on ATtiny13. The frame of the key is the same size as the original one, and the microcontroller's EEPROM memory allows to store up to 8 key codes.

The key itself runs on parasitic power, but programming requires an external 5-30 volt power source, for example, a CR-9V (PP3) battery.