> I'm just trying to make my projects as idiot-proof as possible :-)

Nathan,

It can take more than just a resistor, particularly for inputs.
Current limiting is fine but you need also to look at voltage
limiting

Diodes (Zener, Schottky, TVS, etc) need to be used in some
environments to soak up charge

For example, a circuit with an electromechanical device, eg
relay, solenoid, or capacitor shorting, can impose a spike
when de-energising that is below Vss-0.6V. This can cause
an input pin in the vicinity to latch up and fry. So it needs at
least a Schottky diode (which has a lower Vf than the PIC's
internal diodes) to conduct that spike. In this case, anode to
Vss, cathode to pin. I learned that after losing several analogue
pins and smoked a couple of PICs big time

That's just one example. Noise and voltages come in many
permutations. I've one board which needs much filtering
because it sits right next to a spark plug, another is close to
a 5W radio transmitter

Mostly circuits don't need general over-protection, mostly,
but there are times when you need to consider a specific
circumstance

eg Google for input pin protection

Joe
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