Right, firstly, i am fully aware this question is very much in the "how long is a piece of string" type vein, but bare with me!!
I have a controller, and i'm going to break the UART lines (TX & RX) out to the main connector, to allow easy expansion, logging, and maybe even programming of the device in situ.
In order to protect those lines, i am going to add some series resistance, and clamp them to the rails with suitable diodes. Here, the more resistance i can add, the "safer" those lines will be.
So, how much series R can i add?
It's going to depend upon my chosen baud rate, how much capacitance is present on the external and internal lines and also on the interface device (almost certainly an FTDI usb-uart bridge of some flavour or other)
Now it's easy enough to stick some numbers into a sim, and take a look at the signal distortion due to additional resistance, but i really need some ball park numbers to start with.
So, what have other people found to work to satisfy this type of requirement?
(i need to protect against continuous accidental connection to ground (0v), and power supply (~30vdc, perhaps as high as 40vdc), and against short ESD type pulses)
I'm actually wondering if i shold perhaps hide these lines behind some sort of galvanic isolation to be completely safe? (although that galvanic isolator obviously also needs to be protected, but a simple optocoupler with led/transistor should be fairly robust??)
Comments, Opinions and Experiences welcomed