[sdiy] Matrix keyboard idea

Colin Fraser colinf at ntlworld.com
Mon Mar 19 19:11:29 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 13:34
> To: synth-diy at node12b53.a2000.nl
> Subject: AW: [sdiy] Matrix keyboard idea
> Bojan Burkeljc made a simple PIC-interface that I want to
> biuld into my Polysix.
> This is the simplest circuit I have ever seen for this purpose:
> http://pages.hotbot.com/edu/syncon/p6retro.html

Has anyone else tried this circuit ?
It looks to have some problems to me (no disrespect to the designer, if it
works it's a very sleek design)

The 16F84 doesn't have a UART, so it must be using software midi reception.
The keyboard scanning pulses on the polysix are only about 1 ms long -
shorter than a burst of 2 or more midi messages.
While the PIC is receiving midi data, it is unlikely to be able to respond
to a scanning pulse and output the correct data on the port.
This would suggest that sometimes the scanning processor may get the wrong
data, or see sudden erroneous changes in the state of keys.
Or that sometimes the software UART may miss bytes.

The designer may have found ways round these problems or may not have used
the keyboard in circumstances where they would show up.
I would want to test the device under heavy midi bandwidth conditions for
reliable keyboard output before I used it in anger.

Colin f

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