Greg Brault wrote:

> again, i fooled around with dualling each i/o pin as input and output.
> i also ran into probs thinking about what would happen if the same
> player hit their switch again, while the pin was set as output.  at
> least with my couple designs i tried to come up with, i couldn't get > > one t
hat wouldn't short something out

Greg,

You could put a 270 ohm resistor in series with each contestant switch
to limit current in case a PIC I/O pin was incorrectly high while the
program was running.  With a similar value resistor for the current
limiting for the LED, the 2 volts of drop across the LED will still give
you a low input into the PIC when the switch is pressed.

But why? If the program never makes an output high there is no problem.
You are either grounding an input or grounding a low output pin.

If the program tells a pin to go high and the switch burns out an
output  you need to throw the OTP part away, fix the program and program
another chip anyway.

Yea, for development purposes you would want to stick a scope or at
least a meter on any pin before you ground it or limit current.

Also you might look at the Motorola MC14490 Motorola Hex Contact Boune
Eliminator CMOS chip in their data book for information on switch bounce
and dealing with it.

For reference:

Connect momentary N/O switches to ground the I/O pins and LED cathodes
when pressed.

Your program sets all 10 pins as inputs then continuously scans them
looking for a low input.  You'd probably need 100k pull-ups on the I/O
pins.

When a switch is pressed, it lights the corresponding LED through the
switch.

(The LED anode is connected to power(+5v) and the switch grounds the LED
cathode through a resistor and the PIC input at the same time)

The PIC sees that input is low and then jumps to a routine to make that
input an output and then make it low until reset.  The LED for the first
contestant will stay on after the switch is released and no other LED
can light.

Again, the problem is swiches bouncing (causing square waves) when
closing or opening and a contestant pushing a switch when the PIC is
scanning at the other end of the 10 switches.

I'll bet the above would work just fine.

Build one and test it.  Good luck.

Don