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In addition to the standard hardware of any pipe organ -- blower, reservoirs, windchests, pipes, etc. -- there is the added electronic hardware that replaces the old electropneumatic control system.

Originally, the chest magnets were activated by current from a series of contacts on the keyboard, switched through a series of air-actuated gang switch relays in the console, and connected via bundles of many hundreds of  wires to more relays in the chambers.

Shown at right is one of the main chamber relays. The top section has a magnet for each note in each manual division, operating a series of contacts going to the appropriate windchest magnets.

Below that are gang switches with 61 or more poles. The vertical wooden pieces have a leather bellows attached under them that inflates when activated and presses movable contacts onto the bus bars below them. These are for the sub and super couplers as well as for the intermanual ones.

The combination action was handled by a cleverly-designed electropneumatic memory system. The two cabinets at right were connected to the console via a series of large cables.

Each  drawknob and tilting tablet had a whole row of two-position switches, one for each piston, mounted on a wooden slat.

These slats slid horizontally when the drawknob was pulled (which turned on a magnet that inflated the leather bellows in the left of the picture, pulling the slat to the left).

For normal operation, whenever a piston was pushed, the drawknobs assigned to that piston would be turned on or off (pulled or pushed in) depending on the position of the little memory switch, which rotates on it axis making one of two contacts close.

However, if the set piston was being held while the piston was pushed, then that piston's aluminum bar (seen at right) would be pulled down by another pneumatic bellows, and depending on whether the drawknob was currently on or off (and therefore whether the horizontal slat was shifted so that one end of the switch or the other was under the bar), it would rotate the little switch seen in the closeup at right the proper way, thus memorizing the new state of the drawknob or tablet.

Here are a few of the boards that replace all that.
From left to right on the Artisan Instruments control unit are:

Main CPU and Communication
A/D and LCD Controller
Output Controller
Input Controller

All of the boards are powered by a 5VDC supply and plug into a common motherboard.
One of the design features of the Artisan Instruments system is the concept of distributed processing.

Rather than have one microprocessor try to do everything, there are a number of them, each with a dedicated task.

 The CPU board provides overall control of everything in the console -- it collects the current state of the various inputs, then sends state change message packets to the chamber computer via the communications link.

It also processes the combination action, changing drawknobs and tilting tablets as necessary, and updates the display LEDs and LCD.

The MIDI I/O Board (with the two connectors at right) sends MIDI data showing each note played or stop changed. It also receives MIDI input and sends the data to the chambers just as if an organist had played the keys directly on the console. In fact, you can play along with the MIDI (for example, this can be useful for practicing pedal technique without having to concentrate on the manuals).

The A/D - LCD Board to its right receives a 0-5V signal from each of the expression shoe potentiometers and converts them to the appropriate digital data. It also drives the LCD status display (four lines of 20 characters each).

The Output Control Board and Input Control Board (the two at right with the modular cables) interface between the Input Boards and Output Driver Boards and the CPU bus, doing the scanning and conversion work so that the main CPU doesn't have to process that information.

These boards are actually identical except for the programming code in the EEPROM, just as the Console and Chamber CPU cards are. This is a great feature -- it means that boards can be switched position (by either changing or reprogramming the EEPROM) to test them if you suspect a hardware problem,

Inputs switch 5V logic levels to ground through Input Boards shown at left. These are connected via six-wire modular cable to the Input Control Boards, Each Input Board has 64 inputs and up to four boards (256 bits) can be connected to each of the four ports on the Input Control Board.

Here are three of the seven input boards. They are all mounted on a vertical panel near the back of the console for easy access. All wires are tied with flat teflon lacing tape, and pass through holes drilled in wooden supports before connecting to the screw-down PCB terminals.

The Output Control Board drives the four Output Driver Boards that control the drawknob and tilting tablet magnets, LEDs, and other console outputs. These are the same boards used as the chest magnet drivers in the chambers, Again, this interchangeability is a nice feature if service is ever required.

Power for the control magnets, LCD backlight and LEDs comes from a 55 amp switching power supply.

All 14V power uses heavy gauge color-coded wire and power neutral connection bars for low resistance.

Although there is very little power used most of the time, a large registration change (such as general cancel) may draw a surge of over 50 amps if all of the drawknobs are pulled at the time (only the magnets of controls that need to change get energized).

The control system is mounted in the large brown box seen at left.

For safety, there is a 15A main disconnect circuit breaker in the box under it to cut off the incoming AC line power to all console components for servicing.

To its right is the 5V power supply for the control system, while the 14V supply is mounted horizontally to its left.

In addition to the Artisan Instruments control system, other console hardware includes the original Moller keyboards (rewired) and original Moller pedalboard (rewired with removable connector added).

In the chambers, Peterson provided the new chimes, shade controllers, and Dyna-Trem units to replace the Moller tremolos.

New Peterson solenoid-operated drawknobs and tilting tablets with reed-switch contacts replaced the Moller electropneumatic ones.

(photo courtesy Peterson)

A four line by 20 character backlit LCD display (seen during console rebuilding at right) provides status information.

We can program it to show whatever we want, and can modify it at any time in just a few minutes should our needs change.

The added pistons to the rught change the memory level.  The new LEDs below it are some of the added status indicators.

Although the current Choir and Swell shade positions as well as the Crescendo shoe position are shown in the LCD display, I added a homebrew LED bar graph above the LCD to provide a more easily-read indicator for the organist.
The choir and swell shoes each show zero to four green bars depending on position, while the 32 crescendo levels are approximated by ten bars, progressing from green through yellow to red for those (hopefully) rare occasions when full crescendo is musically justifiable.

The new pistons for the transpose, mapping and  memory level functions, also the  expression shoe potentiometers with their rack-and-pinion mechanisms, came from Klann Organ Supply





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This page was last updated on 11/10/08.
All content copyright 2006 Brian F. Bailey, W4OLF