Add support for Infinium X1 Optical Fader.

[jmamma]

Infinium (Behringer) X1 Optical Fader: Same fader as in the Octatrack.

45mm travel length.

The fader has a single (female) connector with 3 pins. The connector pins have 2mm spacing (slightly narrower than Arduino connecter)

Red = GND Centre = TX Black = 3.3V

TX transmits serial at MIDI Baud 31250. Each byte received is a value between 0-127.

When stationary the fader will transmit its current position every ~ 500ms When the fader is moving the new position is transmitted immediately on change.

https://github.com/jmamma/MIDICtrl20_MegaCommand/files/3031779/infinium.x1.pdf

[jmamma]

The expansion ports on the MC board, do not have 5v or 3v3 rails. Instead I opted to include Vcc and GND and then try and cram as many IO pins as possible.

The drawback of Vcc is that you'll need to use an external power supply (not the USB). Also, physical access to the USB port is blocked if you use the right hand connector.

--

I've just realised that we can use the extra IO pins as a reliable 5V voltage source (setting them to high). They're rated at 40mA each. For comparison, the 3v3 pin is only rated at 50ma.

To get 3v3 from 5V we can use a small regulator "https://www.adafruit.com/product/2166"