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Doubt about port protection from mistaken connections

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blapcb

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I have a number of RJ45 connectors on a project, that are used either for serial communication or SPI. I cannot change the pinout. If the wrong device is plugged in to the wrong socket on the board, some bad connections can happen, and I am wondering how to protect against those conditions such as:

1. A Tx pin (-6v) on the board socket that might get connected to Ground pin of a device that is plugged in.

2. A pin on the board socket that supplies Vcc/3.3v to an external connected device, might get connected to Tx (-12v) of another external device (that is connected by mistake).

I can add protection elements either on the board or on the (cable of) the connected device, but can't change the pinouts.

Any solutions greatly appreciated

Thanks
 

embeddedlover

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until and unless u connect ground and supply i don't think there will be any problem
If ur circuit draws high current then there is a chance that ur Tx pin when connected to supply may cause some damage

If at a pin u want to allow only certain level of voltage try to use zener to ground.
The zener rating must be your required vale.

If u want to eliminate reverse voltage try to use SR504 for reverse protection.
 

blapcb

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dharanidhar said:
until and unless u connect ground and supply i don't think there will be any problem
If ur circuit draws high current then there is a chance that ur Tx pin when connected to supply may cause some damage

Actually, there is no direct ground to ground connection, but the ground on the main board would connect to an interrupt (output) pin on a device being connected. So it would look like this:

Ground on connected device <--> Tx (-6v) from main board
Interrupt port on a chip on connected device <--> Ground on main board

So is that enough to constitute a ground connection and make a problem? Or does it have to be actual ground to actual ground.
 

embeddedlover

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I don't think it would be enough and it is not preferable too.
U r trying to ground indirectly which may not work.
 

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