Hi-
Hey this is great!  Can you push multiple keys?  That should be possible, but we
would need a 16 bit A/D.
David H

Dave Dilatush wrote:

> David Harris wrote...
>
> >CHALLENGE: can you scan a keyboard, and run an LCD display with only 8 pins/bits
> >= 1 port -- without extra active hardware?
>
> How about operating a keypad with nothing more than a single PIC A/D
> input pin?
>
> The diagram below shows how this can be done, by connecting the
> row/column lines of the keypad to resistors so that each key (the X's in
> the diagram below) results in a different resistance value.  This
> resistance is connected, along with a load resistor (the 22K shown
> below), in a voltage divider between Vcc and ground; each key gives a
> different voltage, thus a different A/D reading.
>
> I didn't dream this up on my own, BTW, so I can't take "challenge"
> credit for it; I saw it about a year ago in the Design Ideas column in
> one of the electronics rags (either EDN or Electronic Design, I forget
> which).  It should work, even if it is a little unusual...
>
>      X-------X-------X-------X----------+--Vcc
>      |       |       |       |          |
>      |       |       |       |          |
>      X-------X-------X-------X---4.7K---+
>      |       |       |       |          |
>      |       |       |       |          |
>      X-------X-------X-------X---10K----+
>      |       |       |       |          |
>      |       |       |       |          |
>      X-------X-------X-------X---15K----+
>      |       |       |       |
>      |     1.2K    2.4K    3.6K
>      |       |       |       |
>      +-------+-------+-------+--> To PIC A/D Input
>                              |
>                             22K
>                              |
>                             GND
>
> Hope this helps...
>
> Dave
>
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