Protecting AVR pins (interfacing to another board)

Projects General Guidance
1

Here's the setup... AVR and LCD on a Printed Circuit board, interfaced to another PC board via ribbon cables. While the whole system is "closed", and not "user serviceable" such that a user ever needs to handle that ribbon cable, I'm not sure if I need protection on the AVR pins.

The other board is running +5, -5, +18, -18. Granted, the +18/-18 and -5V shouldn't reach the AVR pins but what about protection from static electricity, or a blown +5V regulator... then all bets are off on how much voltage the AVR pins will see.

So I guess I'm asking how do you make the AVR more robust. I've read zener diodes and small resistors on each pin, but I'm not sure if that's enough.

Should there be buffers on all inputs and output lines on the (2) boards I described above?

Looking for ideas... how would you tackle this issue? Thanks.

2

Why don't you read through the product description page for the Ruggeduino 'clone' board for the methods one can use to make a board as 'bullet proof' as practical. Many of the ideas are easily applied in your own projects.

http://ruggedcircuits.com/html/ruggeduino.html

Lefty

3

Thanks Lefty. That ruggeduino gave me some ideas.

Also found more options for protecting MCU inputs on this site.
http://www.kevinmfodor.com/home/My-Blog/microcontrollerinputprotectiontechniques