At 20.04 2005.04.12 -0700, you wrote:
>The "analog trick" is interesting. Where only one switch at a time is
>closed, I've used a resistor network to make a voltage divider with
>several taps. I then use SPDT switches to tap off the voltage divider to
>the A/D input on the PIC. The signal is "looped through" the NC contacts
>of the other switches so we end up with a sort of priority encoding. This
>prevents an invalid input if more than one switch is pressed. Instead,
>just the switch "closest" to the PIC is recognized.
>
>I've used a similar technique to "encode" 15 momentary switches on a pair
>of wires that are across the room somewhere. Multiple sets of boxes can be
>put across the same pair of wires to put several switch sets in a room.
>
>As a previous poster mentioned, I also like to TRY to leave RB6 and RB7
>free for the ICD-2 for debugging. Of course, you can connect switches or
>other I/O to these pins as long as they don't interfere with the ICD. My
>luck (or lack of luck) has been that the part of code that needs the most
>debugging is, of course, the stuff on RB6 and RB7.
>
>Finally, on scanning matrix keyboards, I've generally set the column lines
>high, then put them low one at a time and watch the row lines. If the user
>presses enough keys simultaneously, you end up with two columns shorted
>together, shorting a high output to a low output on the PIC. Not real
>good... I should probably add some current limit resistors in series with
>these lines, but that's more parts!

Or e.g. a 1N4148 diode for each key and the problem is completely solved.

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist