Please excuse the rookie question but I want to be sure I don't damage the Arduino....
I'm using a bi-color (red/green) LED with a common ANODE for the gear indicators. The anode is connected to the 5v pin with a resistor and each cathode (one for green, one for red) are connected to digital pins (38 & 39).
If using an Arduino sketch, I reverse logic to ground the terminal high to keep the respective LED in the off state and low to make it glow (i.e. "digitalWrite(38, HIGH);" turns it off and "digitalWrite(38, LOW);" makes it go on).
Does the Sim Vim programing require using only common cathode LEDs or will it ground the pin automatically when necessary? If not, can it be user modified to reverse the polarity when X-Plane signals the indicators?