I'm curious if my cable choices are limited by this design. The MCT62H has a maximum forward LED current of 20 or 30mA, and it works perfectly well on the breadboard with a momentary switch. 28AWG wire is only about 0.065?/ft, which is insignificant over these runs, but I was thinking it might be a better idea to use data-oriented cable, which I believe are often around 110-120?/ft (or /m?). Anyway, I'm planning on using an XLR interface so I don't have to worry about a flexible cable getting damaged.
The question is will any sort of cabling over that length dissipate too much current to turn on the LED in the optocoupler.