[sdiy] Keyboard Control

[Ray Wilson]

You should be fine with more keys Mike. once you adjust the constant current
source it will always puts out 83.3 mA so that you get an 83.3 mV drop per
each resistor in the resistor ladder. With more keys it will actually be
driving less load (due to the higher resistance of the whole ladder).

I have heard of others doing this with magnetic reed switches with good
results. I'm going to check out the link you provided. I may try this route
since I have another piano style keyboard that came out of an organ. The
switches on the keys are terrible but the action is nice.

Cheers

Ray

-----Original Message-----
From: Michael Boracci [mailto:mboracci at nfpcomputer.com]
Sent: Monday, October 20, 2003 7:31 AM
To: Ray Wilson; harrybissell; Thomas Holley
Cc: synth-diy at dropmix.xs4all.nl
Subject: RE: [sdiy] Keyboard Control


Ray,
I would like to ask you about adapting your single bus design to 72 keys, or
49 keys. Would the current source have different values based on the total
ladder resistance? Sounds like simple Ohms law, but I am not sure.

I am building mine with magnetic switches. I saw this design at the Allen
organ store. It is easy to make two or even three busses that way. Meder
Electronics makes the reed switches. I was given some samples to try out.


http://www.meder.com/


I would also think that using two switches at different points in the
mechanical arc would allow one to develop an inverted ramp output to affect
a velocity type CV.



MB

-----Original Message-----
From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of Ray Wilson
Sent: Saturday, October 18, 2003 7:59 PM
To: harrybissell; Thomas Holley
Cc: synth-diy at dropmix.xs4all.nl
Subject: RE: [sdiy] Keyboard Control


Hi Guys

Just a note on this. I feed the current from the top end of the keyboard and
I still get low note priority because when more than one key is pressed you
are essentially bypassing all of the intervening resistors and since the
current is constant (in the design I use) you get the voltage that is
dropped across the low side of the resistor ladder.

Ray



-----Original Message-----
From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of harrybissell
Sent: Saturday, October 18, 2003 3:03 PM
To: Thomas Holley
Cc: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] Keyboard Control


Yes, you are right. By taking the output from the low side you will
also get low note priority (which I for one, insist on :^)

H^) harry

Thomas Holley wrote:

> Thanks Harry,
>  I have the keyboard controller arranged so that the current source is to
> one end (HI) of a resistor ladder and the other end (LO) referenced to
> ground. The keyboard is from an old broken ensonique with little spring
> contacts on each key. I have it so when the key is pressed the contact
> grounds that point in the resistor ladder. The reference voltage for the
> controller is taken from the top of the resistor ladder where the current
> source connects (copied from an old ARP patent). With this arrangement I
> think the current source should then go on the low (left) key side to give
> the highest voltage reference to the high (right) keys. Is this right or
do
> I have it turned around?
>
> Thomas
> ----- Original Message -----
> From: "harrybissell" <harrybissell at prodigy.net>
> To: "Thomas Holley" <thomasholley at adelphia.net>
> Cc: <synth-diy at dropmix.xs4all.nl>
> Sent: Saturday, October 18, 2003 1:57 PM
> Subject: Re: [sdiy] Keyboard Control
>
> > Hi Thomas
> >
> > Higher pitches (to the right side of the keyboard) get higher
> > voltages...
> > so the current source should go on the highest note side...
> >
> > H^) harry
> >
> > Thomas Holley wrote:
> >
> > >     I have a rather fundamental question. In a keyboard controller
> > > resistor ladder, does the high voltage side go to high pitch key or
> > > the low pitch key. I have been tinkering with an old keyboard and
> > > soldered up a 100 ohm resistor between each key for a nice ladder when
> > > it finally dawned on me that I had not a clue which side to put the
> > > current source on and which one to ground. Thanks for your help Thomas
> >
> >




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