[sdiy] Matrix keyboard idea

Colin Fraser colinf at ntlworld.com
Mon Mar 19 14:28:38 CET 2001

> -----Original Message-----
> From: owner-synth-diy at node12b53.a2000.nl
> [mailto:owner-synth-diy at node12b53.a2000.nl]On Behalf Of Ullrich Peter
> Sent: 19 March 2001 08:40
> To: 'steve jones'; synth-diy at node12b53.a2000.nl
> Subject: AW: [sdiy] Matrix keyboard idea
> >On Scott Rider's page:
> >http://www.mcs.com/~syzygy/webdoc/mpx61.html
> >
> >he describes his design (from 1985) for providing MIDI in
> for any MATRIX
> >keyboard. Has anyone worked on this idea since then?
> I made a MIDI-interface like this one but with special matrix
> circuits from Mitel instead
> of the many analog switches. I use MT8816 analog matrix switches.
> I use a 89S8252 microcontroller and 4 of these matrix chips
> playced on a Euro-card.
> The midi interface is a little pcb that can be mounted on the
> backpanel of the keyboard.

I made a similar matrix spoofing interface some years ago based on a 6502,
but redesigned it recently using an AVR 90s2313.

I used 74HC374 latches with diodes added to the outputs to act as open
This greatly reduces the chip count needed - I just used a latch for every 8
keys, and wire-ored the outputs together.
The column select lines from the scanner just enable the outputs on each

I put a photo of the board installed in my Polysix at
I'll put the code and single sided PCB foil up before long.

It may be possible to do away with the latches altogether.
By raising an interrupt when a scanning pulse appears that detects which
column is being scanned then outputs the row bits as needed on a cpu port,
you could do the whole thing in half a dozen chips.
There are timing issues with this approach I would need to check out first -
I wouldn't want the CPU to ever miss a scan pulse.

Colin f

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