To the internal to establish communication between pilot and co-pilot I have a few second-hand " Ruscool intercom boards’ on the head can tap.

According to the seller never used and right out of the box ...

Per station you have one intercomkaart necessary, i.e. one for the Capt and one for the F/O. You can expand with a third card, for example, the instructor or observer.

These cards are made at the company Ruscool out of New Zealand.

Later these’ intercom boards’ built-in ‘avionics pedestal’

The previous intercomproject I stopped due to serious issues with the microphones.