[sdiy] Polyphonic keyboard scanner

David G. Dixon dixon at interchange.ubc.ca
Fri Jul 31 19:33:26 CEST 2009

I'm building a (slightly unconventional) monophonic scanner, and it already
takes up 4" x 6" of board space.  I think this would be the main reason for
me to learn programming.

> No scorn or derision here - sounds like an interesting exercise in
> creative anachronism. I imagine that a basic 64-key scanner would need a
> 6-bit counter with the top 3 bits coupled to a 3->8 decoder for a column
> driver. A switch matrix with diodes at each crossing so that multiple
> keys could be down without creating phantom closures. That feeds into an
> 8->1 mux driven from the low 3 bits of the counter to detect closures in
> each row.
> At that point you've detected all the key closures but you still have to
> prioritize them and convert them to CVs. That requires some sort of
> memory stack for the priorities as well as an accurate DAC and
> potentially some sort of lookup-table ROM for the CV conversion.
> When all is said and done you've probably got at least 15 - 20 sq in of
> PCB space, along with $5 - $10 worth of logic ICs. Contrast that with
> the $2 you'd pay for a low-end MCU that could do the job and you've got
> to ask yourself if you're doing it to scan a keyboard, or for the 'stone
> knives & bearskins' experience. Both are perfectly valid in a hobby
> context (witness the all-transistor clock projects that are floating
> around).

More information about the Synth-diy mailing list