I used the hardware UART (i think) - I just connected pin 0 and 1 of the Uno to the TX and RX on the MAX card, connected it to the DB9 connector of the pioneer and checked if the volume changed to a fixed value every 5:th second.
I used the hardware UART (i think) - I just connected pin 0 and 1 of the Uno to the TX and RX on the MAX card, connected it to the DB9 connector of the pioneer and checked if the volume changed to a fixed value every 5:th second.