[sdiy] Keyboard Circuit - Seperate Keyboard and Gate buses?

[Ray Wilson]

Here are some ideas for you. One bus and still CV, Gate and Triggers.

http://www.musicfromouterspace.com/analogsynth/keybrdcontroller.html

Ray

----- Original Message ----- 
From: "Richard Wentk" <richard at skydancer.com>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Friday, February 24, 2006 3:23 PM
Subject: Re: [sdiy] Keyboard Circuit - Seperate Keyboard and Gate buses?


> At 21:48 24/02/2006, Chris Manders wrote:
>>Hi folks
>>
>>I am planning on building a simple keyboard circuit
>>for my Synth.
>>
>>Looking at some synth schematics, I notice that a
>>large amount of them make use of two seperate bus bars
>>- One for the CV (using a resistor ladder) and one for
>>the gate. Indeed the (later?) ARP Odyssey used three -
>>One further to generate an additional trigger pulse.
>>
>>For the ones that use two, why should they choose
>>this? Surely (and I what I have in mind) is that if
>>any voltage is present on the CV input line as a key
>>touches the resistor ladder, then that would be
>>sufficient to generate the 'gate'? Surely just one bus
>>would suffice?
>
> Potentially you could have the lowest note = 0V, which would cause a 
> problem for any amp+clamp gate circuit.
>
> Also there's often quite a bit of bounce on keyswitches, and it's easier 
> to deal with this with two circuits.
>
> But that aside there's no reason a single line design wouldn't work. It's 
> just not traditional. If you wanted to get tricky about this you could 
> something like checking for an open circuit, maybe by having a nominal 
> pull-down to - say - -12V with a big resistor+diode for a tiny current. 
> When a key was pressed a much larger current from the resistor ladder 
> would swamp this, giving you enough information to split the data into 
> gate+CV from that one input.
>
> This would be more complicated to design, and you'd have to put more 
> current through the ladder than you'd normally use. But it might possibly 
> easier to put together mechanically.
>
> Richard