David Harris wrote...

>CHALLENGE: can you scan a keyboard, and run an LCD display with only 8 =
pins/bits
>=3D 1 port -- without extra active hardware?

How about operating a keypad with nothing more than a single PIC A/D
input pin? =20

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    =20
     |       |       |       |          |        =20
     |       |       |       |          |        =20
     X-------X-------X-------X---4.7K---+         =20
     |       |       |       |          |        =20
     |       |       |       |          |        =20
     X-------X-------X-------X---10K----+         =20
     |       |       |       |          |        =20
     |       |       |       |          |        =20
     X-------X-------X-------X---15K----+       =20
     |       |       |       |                   =20
     |     1.2K    2.4K    3.6K                  =20
     |       |       |       |                   =20
     +-------+-------+-------+--> To PIC A/D Input =20
                             |                   =20
                            22K                  =20
                             |                   =20
                            GND                  =20
                                              =20
Hope this helps...

Dave

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