Protecting IO pins generically

Archiver

Hi all,

I want to make a generic PCB that could be programmed to do many different
jobs (a kind of Activity Board) but more simple and smaller. I want to give
external access to 5 IO pins, but I have a problem: I can either specify the
voltage and current limits of the pins, and hope for the best, or I find a
way of protecting them.

I thought of optocouplers, but they restrict the circuit and the way that
each pin can be configured as input or output. Are there good resistor
values for general purpose protection?

All the best,

Mike

Archiver

Mike:
270 ohm series resistors would limit each pin current to ~18 ma if shorted.
The Stamp2 spec is 20 ma source/25 ma sink. Then, the only other way to
kill the stamp is to apply an external overvoltage (like 12 volts or more)
to the pins.

Ray McArthur

> I thought of optocouplers, but they restrict the circuit and the way that
> each pin can be configured as input or output. Are there good resistor
> values for general purpose protection?