Kinkennon MIDI Resources
USB-MIDI
A fundamental function of a VPO console is to convert all control functions to MIDI signals. Keys, pedals, pistons, stops, expression pedals, as well as other controls, send and/or receive information as MIDI data. The PC monitors the status of the console and sends data to control stops, displays, and other functions.
MIDI is commonly transmitted over the original 5-pin MIDI cables, USB, and Ethernet. At this time MIDI over USB predominates though not always for VPOs. Both USB and Ethernet offer huge speed increases over the 5-pin cable. Ethernet is particularly flexible for routing multiple sources and destinations over extended distances.
USB-MIDI is easier to implement as it is a native communication method for PCs. My advice would be to use USB-MIDI wherever possible to extend the useful life of the VPO.
Encoders
An encoder is a device which receives data from a VPO console and converts it to MIDI to be forwarded to a PC which hosts the Virtual Pipe Organ software. Typical inputs to an encoder would include voltages from a manual's key switches (usually 51), the switches in stops and pistons, and the analog voltage from a potentiometer which would vary from 0v to 3.3v, or to 5v for earlier encoders.
On the encoder a Microcontroller Unit (MCU) senses the changing voltages and converts them to MIDI messages. It is necessary to check every input, potentially many hundreds, every few milliseconds to run fast enough to eliminate potential sound delays. Additionally, the MCU needs to be a mainstream device to insure an active user community, a lower price, and readily available programming tools. Modern MCUs run at 3.3v or less with some still at the 5v level. The above requirements are good reason for the popularity of Arduino devices for DIY encoder builds. An Arduino variant, the Teensy 4.1 is currently one of the fastest MCUs available (at 600 Mhz) and offers lots of output pins, an onboard ethernet PHY, and a low cost. This is the MCU used in our examples, but our code is easily modified for similar Arduino hardware.