Cheap protection...

[Mike Blakey]

>The main "problem" I can see with that circuit is that a voltage
>higher than 5V appears at the uC due to the forward voltage of the
>1N4148.
>
Hi bernd,
The voltage at your uC will be fine, about .6 < 5v.
This is OK for most uP input.

>It could be worthwhile setting up a "dirty rail" at about 4V (based
>on the 5V regulated) to absorb the over-voltage currents from all
>inputs.

I've used this circuit on many applications, and for the simple "learning" projects 
it works great.
I've also used the same design on more elaborate projects for taking signals from 
switch inputs etc.
The cost is VERY low and you can easily prove/prototype a design a design without 
spending a fortune in components and time.
Try without the "dirty rail" and if you do get problems, eliminate the noise at 
source, if possible!.
Keep your first circuits simple, and by the time you're ready to tackle a major ECU,
 you will have enough practical knowledge and confidence.

>
>That would also protect the regulated 5V from strange pulses.

PS. Thanks for re-drawing the circuit, I hope it will be of use to others too.
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