[sdiy] Matrix keyboard idea

[The Old Crow]

On Mon, 19 Mar 2001, Colin Fraser wrote:

> > 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.

  I've disassembled his code.  While I still would choose a UARTed PIC
such as a 16F628 to do this, his code exhaustively checks for active key
scan states, including repeated checks as part of the inter-bit delay in
the software serial receiver.  Not too shabby.
 
Crow

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