EMOTION ORGAN
ORGAN MODIFICATION - PHYSICAL INPUTS
Jan-Feb 2005


I am currently investigating different options for organ modification with focus on the physical inputs.



(click on image for larger sketch of physical inputs)

The keyboard is my main concern right now as it requires the most work.

Following a lead from Per Platou I started to hunt down "readymade" solutions, called "retrofits":

01. MOOG PIANO BAR (midi)
Fits over the keyboard of 88 key pianos. Uses infrared sensors so that nothing actually touches the keys. The piaono bar has beautiful LED displays showing which notes are being played.

I contacted Moog to ask if they custom-built their piano bar and if they could give me more technical info. Negative response :(

0.2 KS-61 MIDI CONTROLLER
Optical sensors mounted on a wooden bar and installed under the keyboard. I emailed Allen Moe of Moe Piano & Organ Co. for advise. He wrote:

I have only put switches under the keys one time and it was rather difficult and required some structural modification to the organ to make it work. They were also not touch sensitive. The main thing that I do to pump organs involves the other aspect of MIDI, playback. I install machinery inside the organ case that physically plays the organ from a MIDI recording. Gulbransen makes a product that goes under the keys and comes in 61 note sizes. I have seen this device and I believe it could be installed under the keys of a reed organ without any "major" structural changes. The only problem is the range of your keyboard. This system is intended for use on church organs whose keyboard goes from C to C. It might be worth looking into this device and inquiring about having it programmed for the F to F range.

Here is a link to a retail seller of the system:
http://www.midi9.com/products.htm

If you want this installed, or a system doing only note on-off I can do it for you but would need the organ here
which may not be feasible. Let me know if I can be of any further help.

Unfortunately he lives in Minnesota!

03. TFT RECORD STRIP (midi)
The TFT sensor strip, which PianoDisc calls Touch Film Technology, consists of four pieces of piezo polymer film. Each piece is screen-printed with conductive carbon ink on both sides, resulting in a pattern of 22 sensor "fingers." The four films--only 28µ thick and about 1.5 inches wide--mount within a long flat piece of extruded aluminum having a slight convex upward curve where the sensor fingers meet the piano keys. The sensor strip has relatively no effect on how the piano feels to a player.

The with are sandwiched between the aluminum strip and four printed circuit boards (PCBs). Corresponding electrode pads on the PCBs press directly on the carbon ink sensor surfaces to achieve electrical contact. The PCBs also contain eight analog-to-digital converters, each scanning 11 of the sensor fingers. The system scans each sensor at a rate of 961 times per second.

The sensor strip sits under the keys near the movement's fulcrum, where the total range of key motion is only about 10mm. Each keys rests on a sensor, preloading it. The sensor strip fingers are carefully positioned to avoid picking up motion from nearby keys.

When the pianist strikes a key, its movement slightly stretches the piezo film sensor over the convex cross-sectional curve in the aluminum strip. This action develops a voltage in the sensor, whose magnitude varies with the force (acceleration) of the key stroke. The velocity and duration of each note played are meticulously decoded and translated into MIDI data.

After the sensor voltage rises above a predetermined threshold, the CPU will start collecting data for that key. The threshold is set high enough to avoid triggering by ambient noise, and low enough to capture subtle keyboard movements by the pianist. The system has sufficient sensitivity to distinguish between accidental brushing of the keys and softly-struck notes.

The CPU keeps a running check on sensor voltages beyond the threshold, noting whether they are increasing or decreasing, and accumulating a rough integral of the voltage waveform. When a sensor's voltage reaches a plateau or starts to decrease, the key has hit the bottom of its stroke and the hammer has struck the string. At this point the CPU infers the MIDI velocity based on the maximum sensor voltage, assigning a value between 0 and 127. For example, a value of 10 would represent a soft note, while a value of 110 would represent a loud one. Meanwhile, the CPU continues to follow the sensor output, checking for the time that the pianist releases the key. The sensor develops a negative voltage at release.

The PianoDisc system includes a switch sensor to determine and record whether the damper pedal is on or off. During playback, a separate solenoid mimics pedal action by raising all the piano's dampers. This permits the strings to continue to resonate after the release of a key.

I have contacted the company to find out about prices and overseas sales, and am waiting for a response ......