> Hi guys,
>
> I'm working on a little project and have just one i/o pin left in the
> pict.  Two things about it, first, is that I feel that really must
> find something for that pin to do as not to go to waste =) and,
> second, I would really like to include a keyboard/keypad in this
> project.  I once saw a "16-button analog keypad" circuit which used 1
> pic i/o pin configured as analog input, (obviously) 16 momentary
> switches and some resistors.  The theory behind it was that for each
> key pressed, a different voltage would be present to the analog input
> and the pic could tell what key was from that voltage.
>
> The only problem is that I tried all sorts of google search phrases
> and can't find anything other than the usual 16 button keypad
> interfaces and PC/AT keyboard interfaces.
>
> Anyone here has a link or details about how this is implemented?  I
> would be specially helpfull if you had a diagram WITH the resitor
> values in it =) but I can try to come up with those values on my own
> if you have a schematic (or a good explanation of how everthing is
> connected).

> Hi guys,
>
> I'm working on a little project and have just one i/o pin left in the
> pict.  Two things about it, first, is that I feel that really must find
> something for that pin to do as not to go to waste =) and, second, I would
> really like to include a keyboard/keypad in this project.  I once saw a
> "16-button analog keypad" circuit which used 1 pic i/o pin configured as
> analog input, (obviously) 16 momentary switches and some resistors.  The
> theory behind it was that for each key pressed, a different voltage would
> be present to the analog input and the pic could tell what key was from
> that voltage.
>
> The only problem is that I tried all sorts of google search phrases and
> can't find anything other than the usual 16 button keypad interfaces and
> PC/AT keyboard interfaces.
>
> Anyone here has a link or details about how this is implemented?  I would
> be specially helpfull if you had a diagram WITH the resitor values in it
> =) but I can try to come up with those values on my own if you have a
> schematic (or a good explanation of how everthing is connected).
>

> On 7/1/05, Mario Mendes Jr. <EraseMEmariospam_OUTTakeThisOuTmmendes.com> wrote:
> > Hi guys,
> >
> > I'm working on a little project and have just one i/o pin left in the
> > pict.  Two things about it, first, is that I feel that really must find
> > something for that pin to do as not to go to waste =) and, second, I would
> > really like to include a keyboard/keypad in this project.  I once saw a
> > "16-button analog keypad" circuit which used 1 pic i/o pin configured as
> > analog input, (obviously) 16 momentary switches and some resistors.  The
> > theory behind it was that for each key pressed, a different voltage would
> > be present to the analog input and the pic could tell what key was from
> > that voltage.
> >
> > The only problem is that I tried all sorts of google search phrases and
> > can't find anything other than the usual 16 button keypad interfaces and
> > PC/AT keyboard interfaces.
> >
> > Anyone here has a link or details about how this is implemented?  I would
> > be specially helpfull if you had a diagram WITH the resitor values in it
> > =) but I can try to come up with those values on my own if you have a
> > schematic (or a good explanation of how everthing is connected).
> >
>
>  Thre are many way of doing this, and I've guess you have already got
> the answers:
> 1. use the ADC and a rezistive network divizor switched by buttons
> 2. use the comparator (internal or external) with the internal voltage
> reference which has the required resolution
> 3. use an RC network with a fixed C and a keypad switched resistor
> network and measure a time variation
> 4. use a paralel to serial converter and share the clock pin required
> with other function
>
> best regards,
> Vasile
>