William Chops Westfield wrote:
>
> Hmm.  How tiny can you make a SW touchtone decoder if you only want to
> decode four "buttons" (ie one row or one column of the matrix...)
>
> BillW

The smallest versions I could create had these specs:

Single frequency decoder that resolves both quadrants: 7 cycles/sample

Dual tone decoder sampling one of the dual tones (e.g. simultaneously
sample one row and one column) : 27 cycles/sample

DTMF decoder that simultaneously decodes all 8 tones: 84 cycles/sample

Each of these cases includes the over head for the appropriate phase
accumulators too.

Now for 4 buttons in a 2 X 2 matrix, 4 frequencies must be resolved.
My guess is that about 40 to 50 cycles/sample would be needed.

Scott
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