A Brief History of Electronics in Pipe Organs
The pipe organ is a complicated musical instrument which has advanced over many years through improvements in technology. The pipe organ dates back to the 3rd century B.C. and continues to please the world today. In its simplest form, a pipe organ has pipes, a chamber that stores wind (with pressure generated mechanically), and wind-access to pipes controlled by a keyboard. 
Changes in technology have changed the method of controlling the generation and delivery of wind to each pipe that produces sounds. Beginning in the 17th century, pipe organs began to use mechanical or ‘tracker’ action so that they could be made larger with more variety of sounds from different types of pipes. But they proved costly to maintain and lacked flexibility so that only the larger and wealthier institutions could afford them. Hence, in the 1840’s pipe-organ builders attempted to use pneumatic action to overcome the mechanical limitations. In the 1860’s they graduated to tubular-pneumatic technology and, with the increasing availability of electricity, to electro-pneumatic action. Electro-pneumatic action uses an electric current controlled by the keys to open valves under the individual pipes. The high voltages and currents of early electro-pneumatic systems caused key contacts to arc and burn as well as rapidly depleting batteries that were then the only source of direct current. In 1900, a reduction in voltage and current due to improved magnetic technology, combined with the use of small, high-current, rotary generators, became widespread. Electro-pneumatic action allowed a greater distance between keys and pipes  resulting in larger organs with improved controllability. However, as the organ increased in functionality to include all manner of coupling between keys, the amount of wiring involved with electro-pneumatic action became excessive .
To facilitate coupling while overcoming the inconvenience in wiring, electro-pneumatic action was superseded in the mid 1920’s by a variety of electromagnets and relays. Pipe organ relays, Coupler relays, Chimes relays, Unit organ relays and electronic organ relays all attempted to reduce the quantity of contacts under each key. Contacts under the keys would be wired to a multi-contact key relay with contacts that fanned out to 61-contact relays for each coupler. Their wires would eventually go to magnets on the pipe chests to perform Pipe organ keying and coupling functions. It all resulted in masses of wiring. One of the early attempts to reduce some of this switching used two diodes and a resistor to replace all contacts but one under the keys and controlled signals for coupling.  This system is commonly referred to as the organ diode-coupler.
The invention of transistors in 1948 brought about the solid-state organ relay/solid-state switching era in organ design . Transistors could control a large current by means of a small current which eliminated the arcing of key contacts. They also allowed the size of the relay to be greatly reduced as each relay contact was replaced by a transistor. The amount of wiring, however, was not greatly reduced.
The development of integrated circuits, and subsequently microprocessors, has led to the implementation of combination action (combo action) as well as organ multiplex functions in small units containing modular circuit boards which are flexible and customizable to the needs of organists and organ builders. Multiplexing converts parallel information from key switches, stop switches, pistons, etc., into a high-speed serial data stream which can be manipulated by a micro-processor system for coupling and other functions before being converted back to parallel information to drive the pipe magnets. In such systems, all the coupling is done within a computer program through the use of numbers - no moving parts whatever between the key switches and the pipe magnets. Hence, a minimum of wiring. In fact, even the key switches can be done with electronic optical devices requiring only a light-interrupting shutter under each key. The whole organ can be specified on a programmable "chip" while the hardware is basically the same for any organ. It is incredibly flexible and can be changed in a moment to suit changing requirements in the organ specification.
Continuing in the tradition of using technology to improve the pipe organ, Classic Organ Works is bringing MIDI into the pipe organ. Our Pipe organ MIDI system is implemented in our industry-leading Console Control Computer and Pipe Control Computer boards. Now, our innovative line of MIDI products brings the organ into your home for practice purposes. Like those before us who contributed to the modern organ, Classic Organ Works research and development uses technology to improve functionality, flexibility, and reliability for your musical enjoyment.