Implement 24V overcurrent protection on all pins of an arduino?

[flienky]

Hello team!

I am a beginner here. We want to implement a shield for arduino that can accept 24V on all DIO pins and AI pins so that kids learning robotics can safely use this board without fearing of any damage.

How can this protection be achieved? One requirement is that the functionality of arduino shall remain as is, which means that each Pin must be able to be configured as Input or Output on 5V logic levels, also we don't want to split half of the arduino DIO as inputs and half of them as outputs, each pin must work like the original Arduino.

Does anyone have any idea how can this be achieved? It is fine to have this overvoltage mechanism to be able to clamp voltages on maximum of one pin at a time (if that makes the design easier -with some kind of clamp diode?-), so that 24V applied to one DIO pin is fine but 24V applied to two or more will kill the board, this is acceptable.

Also, I am looking at a possibility of overcurrent protection, so that if an DIO is configured as Digital Output, and a kid shorts this pin to GND, then the overcurrent limit will kick off and stop the board from damage. Is that easy to implement?
Thanks!

[ledtester]

Have a look at this page for some ideas:

https://www.rugged-circuits.com/10-ways-to-destroy-an-arduino

[Terry Bites]

 Transient absorbers are not continously rated and may die if the over voltage is sustained for a long period. Avoid or add series input resistor to be safe!
Schemes that use a series resistor and chip's internal diodes risk destruction of the ic in your application. Don't! That works on a PCB (kinda) but not connected to the outside world.

A simple zener clamp will work well for lower speed data inputs. Cheap and effective.
I dont know what yor logic supply volts are so shoose the nearest value zener and a current limiting resistor.
Use 5V1 zeners for 5V systems.
Gives reverse voltage protection too.
So mad money then, say $.05 per input.

[PGPG]

If it should work bidirectionally when working 0..5V and be robust for 24V the only that comes to my mind are something disconnecting pin when overvoltage detected. Something like in semiconuctor relays (two MOSFETs in serie (sources together)). I think on uC side there should be 5V protection (may be diodes with one Zener as diodes have smaller capacitance than Zener) and on the other side the overvoltage detector disconnecting both MOSFETs. There is no problem to design something working that way. The problem is to make it enough fast. I think 5V protection will have to withstand the short pulses until the MOSFETs will be disconnected. A resistor in serie will help 5V protection to limit voltage at this side at no too high value. If 24V is available you should also consider someone connecting it with + to GND and - to pin.

[xvr]

Overvoltage protector - https://www.analog.com/en/products/adg5462f.html (but relatively expensive)
Or ADG467 (but it required some adjusting in power supplies)
ESD protection should be added separately