Gonkyo is small cli tool that allows you to control you onkyo amp or receiver via RI interface and raspberry pi gpio.
Its written in pure golang using cobra and go-rpio library.
This project was inspired by onkyo-rpi project, but i wanted something statically compiled without extra dependencies.
You can check onkyo-ri protocol description here, but it goes something like this:
There is also generic signal command that you can use to send any message to your amp.
I have onkyo A-9150 stereo amp so i've created subcommands for that specific amp, but you can easily extend code to accommodate your use case.
The connection to the RI interface is a simple 3.5 mm mono headphone jack. Connect the tip of the jack to a GPIO output pin (default gpio: 25, physical: 37) and the ground of the jack to a ground pin on your raspberry pi.