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Forum Index : Microcontroller and PC projects : EMI / EMP question

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BrianP
Senior Member

Joined: 30/03/2017
Location: Australia
Posts: 292

Posted: 11:09pm 28 Apr 2017

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Me again. Now that the keypad function is working I am back to working on the door controller for the local public hall (as mentioned in a previous thread). The original plan was to use as much of the existing infrastructure as possible, in particular the external Wiegand protocol keypad. This proved too difficult as the keypad controller pre-processes all keypresses into a composite word terminated by the hash key.

This meant we didn't have control of the individual key entries, & because the existing cable is a 7-wire I have reverted to using the the inbuilt keypad function.

Now the question as indicated in the thread title - if we use the existing 7-wire cable, unshielded & approx 5 metres in length, to what degree might we need to protect the Maximite inputs from rogue electrical interference, in particular nearby lightning events. Fortunately we don't have many of these, but... (hi Grogster!).

Would some series resistance on the pins provide some reasonable protection, & if so (question probably for Geoff) what would be the maximum resistance value permissable without compromising the keypad function. I'm thinking series resistors with schottky clamp diode protection to 3.3v + & - rails.

I know it's not possible to cater for all events, but any protection is better than none - we can but try...

All thoughts welcome.

Regards

Brian P.

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