USB keyboard based on ATmega32U4 Pro Micro board with IR Receiver
It appears as Keyboard HID device and sends multimedia keys (e.g. VolumeUp, VolumeDown)
It works in parallel with existing keyboard.
To learn new IR codes, open any text editor and rapidly toggle CAPS-LOCK led on-off 10 times.
Next follow the instructions printed in the text editor.
Note: On MAC you need software (e.g. https://pqrs.org/osx/karabiner/) to sync CAPS-LOCK led between all keyboards connected to computer
Schematic:
Connect a Vishay TSOP38238, 38kHz IR Receiver to D4, VCC and GND pins of the ATmega32U4 Pro Micro board.
Boards you can use:
MIT license