[sdiy] Keyboards good for scrap / repurposing?

Mikko Helin maohelin at gmail.com
Mon Feb 19 12:05:34 CET 2018

You could make optical scanner for any keyboard like an acoustic piano.


19.2.2018 10.59 "Roman Sowa" <modular at go2.pl> kirjoitti:

> 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.
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