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

[John Luciani]

On 3/2/07, Ingo Debus <debus at cityweb.de> wrote:
>
> 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 am using them as switches. If you build a vane that varies the amount of light
that goes through the slot as the displacement changes you could
determine the displacement with an A/D. Make sure you get slotted
optos that are analog not digital.

Check out patents 5,001,339 and 5,231,283. There are probably other
patents on optical sensing you could take a look at.

> 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.
>

That should work. Attaching a vane that passes through the slot of
the opto would also work.

> 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?

Since adding those modes to the uC software is easy there is nothing
to be lost by
giving it a try. I am not sure about the LEDs for each key. Are you going to be
watching all of those LEDs while you are playing?

(* jcl *)

-- 
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