Replace a the IC of an RF Control (Intertechno) by an Attiny212 to customize and add functions. In my case, control a Sonoff Slampher RF Socket.
See code comments on how to use. Developed using Arduino IDE and flashing by UPDI, therefore one pin only as input usable which limits the options. Since I'm currently not able to use high voltage programming and it would be required to set the fuse and program the Attiny even when the UPDI pin is used as output.