MP3 Trigger Board Wiring

[theguitarman]

Hello,

I am currently wiring up my MP3 Trigger Board, and powering it via the barrel plug. In this setup, there USB/EXT switch on the board provides an on/off switch.

I am trying to communicate to the MP3 Trigger Board via serial commands from an Arduino Mega. The Mega is also powered by barrel plug, so these two board should, in theory, share a common ground and power source. To connect from an output pin of the Mega to the Rx pin of the MP3 Trigger Board, what wires do I need to connect? Do I need to connect the ground to the common ground? Do I need to provide 5V from the Mega to the MP3 trigger board? Does the switch need to be in the Ext position to receive commands via serial?

Thanks!

[theguitarman]

Any help? Thanks!