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I am building a custom doorbell system that will support multiple doorbell buttons and annunciators. I am using an Adafruit Feather and a couple of FeatherWings for each unit. The project can be viewed here: https://hackaday.io/project/176143-iot-doorbell-system.

One unit will be the "master" and the doorbell buttons will be connected to it. My concern is possible transients on these relatively long lines resulting in either spurious "rings" or damage to the GPIO pins.

Would shielded, twisted pair (aka CAT-5), be a good solution here?

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  • \$\begingroup\$ By itself, any type of shielded cable is not a solution. The cable is the problem; that's for sure but, it's how you deal with what it throws at you that is the solution. \$\endgroup\$
    – Andy aka
    Commented Dec 15, 2020 at 14:38

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If you build this for your home and you live in a EMC quiet place, then you might not need input protection. Else you might want to protect your inputs e.g. with TVS transzorber diodes. Twisting and shielding the cable is also your friend.

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    \$\begingroup\$ TVS' will work for large spikes. Assuming this is for general GPIO I'd also recommend having a 100 ohm resistor in series with these lines (placed close to the micro) maybe a 0.01uF cap to be extra safe. \$\endgroup\$
    – Stiddily
    Commented Dec 15, 2020 at 16:41
  • \$\begingroup\$ 1K resistors will work fine if you use, say, 100k pullup. \$\endgroup\$
    – user57037
    Commented Dec 15, 2020 at 20:55
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As @Stefan Wyss already mentioned a TVS diode ist a goog idea. Another one is to add a opto-isolator module ( also called opto-coupler). See here:opto-coupler

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