[sdiy] organ pedals, was:Synth Keybards and Number of Keys

[Ingo Debus]

Am 02.03.2007 um 02:30 schrieb John Luciani:

> I am building a couple of two octave pedal boards that use slotted
> optical switches
> (PCBs arrive tomorrow!). I am thinking of doing some keyboards that  
> use slotted
> optos in an analog mode.

Are you using the slotted optical switches just for switching or also  
for displacement sensing?
I was thinking about adding a displacement sensor to one of my  
pedalboards, so the thing could double as an expression pedal. This  
pedalboard (a very old one) already has a common switch for all keys,  
probably used to trigger an envelope. That switch moves nicely when  
any key is pressed down, so I thought I could just attach a small  
magnet there and measure the field with an analog hall sensor. Of  
course this would only sense the displacement of one key at a time,  
but I don't think that this is a drawback. The individual key  
switches are still there.

One option I'd like to have when a synth parameter is controlled with  
key displacement: the setting should keep its value even after the  
foot is removed from the key. I was thinking about two modes: when  
the key is pressed first (mode 1) only values greater than the  
current value are output. Once the key is pressed all the way down it  
switches to mode 2: then only values smaller than the current value  
are output. If it's completely released it switches back to mode 1.  
This way a value could be held as long as the key isn't pressed all  
the way down. Pressing it all the way down then releasing it would  
set the value back to 0. A LED for each key indicating which mode it  
is in is probably a good thing.
Any better ideas?

Ingo