Cheap protection...

[Bernd Felsche]

Mike Blakey writes:

>Why bother with isolation? DC coupled will be fine.
> Use a voltage divider and do the de-bounce/filtering in software.
> A simple signal diode from input to Vcc will protect your uP as
> the Vcc is low impedance.

<snip art>

Cool. Hadn't thought of clamping in that direction.

Thanks.

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.

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.

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

-- 
Real Name: Bernd Felsche
    Email: nospam.bernie at perth.DIALix.com.au
     http://www.perth.dialix.com.au/~bernie - Private HP
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