Digital Inputs

You can add a digital button channel via the Head Tracker by cheating a little bit and use the analog input pins. Although this isn't going to be of too much use as your radio usually has plenty of switches :) Maybe you want an extra button on your headset for some reason.

Wire your switch from the 3.3V pad on the Arduino Nano through your switch and into A6 or A7. (As of V2.1 you can use A4-A6). You will need a pull down resistor to keep the signal at zero when the switch is off. On the Analog page of the GUI leave the settings as default. Gain=310, Offset=0.

You can also make this work with a 3 position switch and two 10K resistors. Wire like shown below for a 3 position switch. When in the center it makes a voltage divider inputting 1.65v into the analog pin. Switching the toggle up or down will drive the pin to zero or 3.3v.