[sdiy] Keyboards good for scrap / repurposing?

[Roman Sowa]

That's exactly how keyboard scanning is done in old organ consoles you 
all are talking about now. Not in every one, but usually in Ahlborn, one 
of the major european organ makers. The HC138 decoder is already mounted 
on the PCB with rubber contacts.

I heard from many organ repairmen that rubber contacts fail first, 
especially in Fatar keyboards. They literally fall apart. Probably not 
an issue for casual mono synth player, but those kind of organs are 
heavy banged every day with 10 fingers.

Don't bother looking for old broken toy synths, they all have keys made 
so one octave is made of 2 pieces of plastic, one white with 8 keys and 
the other one black with 5 keys. And the piece of plastic that holds it 
together is also back support and return spring. This is also the case 
in entry level Yamaha digital pianos.

Roman

W dniu 2018-02-19 o 01:29, rsdio at audiobanshee.com pisze:
> Steve,
> 
> Since you are writing your own firmware, you might be interested in one simple way to reduce the number of GPIO pins needed. Since the Columns in a matrix of switches are only ever active one at a time, you can use a CMOS 3-to-8 decoder chip. That requires only 3 GPIO pins, but generates 8 Column strobes. The 4-to-16 variations of the chips come in both active high and active low variations (I seem to recall that the 3-to-8 do not). You can just hard-wire the Enable pin so that one Column is always active (unless that screws up some part of your circuit that is shared), and then your firmware can increment a binary variable that is directly written to the GPIO port as 3 or 4 bits, as appropriate.
>