A series resistor of 1k between your key jack and the Nano's A1 should offer plenty of ESD protection.
The Nano's internal pullup to 5v is a minimum of 30k, so when you ground it at the key jack the Nano will see a maximum of 5v * 1k/(1k+30k) = 0.16 volts.
If the series resistor were 10k, Nano sees a maximum of 1.25 volts. ?Should still work assuming I read the datasheet correctly but is getting kind of scary.
If you really want to use diodes, the Bat54s dual shottky's are ideal. ?Tie A1 to the middle node of the Bat54s, and GND and 5v to the outside ends such?
that the diodes are normally reverse biased. ?That plus the series 10k and this thing should take direct hits from lightning bolts.
For a high impedance node such as this where we can get by with a high value series resistor, I'd go with just the series resistor.
Jerry, KE7ER
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On Thu, Jun 15, 2017 at 08:23 am, Allard PE1NWL wrote:
Extra protection wouldn't do any harm. A zener diode might work, perhaps
there are better methods, haven't thought about this yet.
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