[sdiy] EDP gnat keyboard

[Dan Snazelle]

ALSO///when i first looked at the schematics for the GNAT i was excited because it seemed they had found a simple  way to convert square waves to saw...but the more i look at it, the more it seems that you might need to have the cv from pin 10 of the 4046 feeding into the 3900, so it is not a simple matter.

what does the signal from pin 10 actually do?

thanks so much






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> From: tim102 at tstinchcombe.freeserve.co.uk
> To: subjectivity at hotmail.com; synth-diy at dropmix.xs4all.nl
> Subject: RE: [sdiy] EDP gnat keyboard
> Date: Sun, 4 Jan 2009 17:20:47 +0000
> 
> Hi Dan,
> 	I can answer directly (though re-ordered):
> 
>> is it simply a button underneath a key "button" or is it a 
>> resistor chain like in a regular keyboard?  
>> (ic10,1c25,1c33///those are 4051's right?)
> 
> There are no mechanical contacts (at least for the ordinary Gnat and the
> 'Special'), it is all done with capacitive touch plates, so the note
> annotations at the bottom of sheet 2 are simply large areas in the etched
> PCB, in the form of a keyboard pattern. (And, minor point, the chips are
> 4052s by the way.)
> 
>> I was wondering...on the keyboard multiplexer...
>> do the 4051's connect directly to the keyboard? 
>> and if so...what IS the method of keyboards giving a gate signal?
> 
> Each plate/note is scanned sequentially (via all the switches), and routed
> to a flip-flop (IC28, sheet 3), whose output is triggered by the change in
> capacitance if the 'key' is being touched - the test instructions document
> has a fairly easily understood description of how it works, para 17, sheet
> 3:
> 
> www.timstinchcombe.co.uk/synth/gnat/Gnat_Test_Instructions.pdf
>  
>> and thanks to TIM for  drawing those schematics! 
> 
> My pleasure! They get about a hit a day on my website, which I think is
> probably quite a high level of interest in it, considering it is such a
> small, obscure synth. I am also in infrequent touch with someone who is
> trying to put a PCB together, but I haven't heard anything from him in
> several months now...
> 
> Tim
> __________________________________________________________
> Tim Stinchcombe 
> 
> Cheltenham, Glos, UK
> email: tim102 at tstinchcombe.freeserve.co.uk
> www.timstinchcombe.co.uk
> 
> 
> 
>