Pipe organs built before the 1970's that were of the non-mechanical (Tracker) types included a switching mechanism that controlled which stops would play when the stop controls would be activated. Before we go into the specifics we need to make a distinction between "Rank" and "Stop." A Rank is a physical set of organ pipes that make up a particular voice. A stop is a control that brings a Rank into play. However there can also be a many to one relationship here. With the use of a relay a rank can appear as multiple stops as shown below:
Here we have a physical set of 97 pipes that play at 16, 8, 4 and 2 foot pitches. This could be four stops on a single keyboard or as in the case with a lot of instruments, four on the upper, four on the lower and two on the pedal -- out of a single rank of pipes. So it is deceiving to speak of "stops" when speaking about the size of an instrument. This Casavant has five ranks, but twenty-five stops. The technique described above is called "Unification." A Relay is needed to make this happen.
This relay also is responsible for implementing "couplers" (which are used to join keyboards and allow keyboards to also play at super and sub octaves). This can allow the keyboards to be joined together so that entirety of the instrument can appear on one keyboard for increased volume. It's generally not a good idea to combine couplers and unification on a single instrument, because it is redundant. The Casavant has only two couplers. One to join the upper keyboard to the lower and one to join the lower keyboard to the pedals.
The issue with these older relays is that they use contacts and leather pouches with over time get worn out and fail to function properly or at all. The picture below is an example of part of a relay showing the pouch and contacts. When one of this gets worn out, the leather develops holes, preventing the pouch from inflating and allowing it to function and/or contacts can get pitted which prevents the electrical function to work:
With the new system, everything happens inside a computer and there are just control chips that make the relay function.
At the time of this writing (December 13) the design is complete and parts are starting to arrive as seen in the picture below:
The two larger objects in the top left are control computers. One will go in the console (where the keyboards exist) and one will go into the pipe enclosure. They will connect either through a physical network connector or Wi-Fi. The other packages (the bags) contain the chips that will read the keyboards and play the pipes.
A while back I performed a study to measure latency of using a Wi-Fi connection and the data bears it out as a possibility. This would also allow multiple consoles to control the pipes.
At present work is occurring to create the circuit boards and writing the control programs that run on the console and pipe enclosure computers.
