On Wed, 2 Dec 1998, Michael Hagberg wrote:

> Connect a 4 x 4 keyboard using only one pin.
>
> There was an article in 'Electronic Design' May 1998 issue that connected a
> 4 x 4 key matrix to a single I/O pin. By using resistors between the columns
> and rows and connecting them to a  cap. The cap is then discharged (by
> making the I/O and output and driving it low), then change the I/O to an
> input and measure the length of time it takes to charge the cap.

I haven't seen this article but I'd like to say that solutions involving R
chains longer than 8 keys are seldomly used in practice, for noise and
repeatability reasons. The solution that I had suggested in another
message could be used with 16 keys per chain because it uses an extra IO
pin for calibration. These considerations apply equally well when a spare
8-bit ADC is used to read the chain.

hope this helps,

Peter