“TinyRemoteXL is a 12-button IR remote control based on an ATtiny13A powered by a CR2032 or LIR2032 coin cell battery.
The basic hardware is similar to the 5-button TinyRemote. The main difference is that the ATtiny13 has to query 12 buttons here. There are various options for using a larger number of buttons with just a few pins. However, most of them do not meet the following conditions:
there are only four pins available for twelve buttons,
a keystroke must trigger an asynchronous interrupt to wake the ATtiny from deep sleep mode,
the circuit must not consume any electricity as long as no button is pressed.”