Arduino - protecting I/O's against short.

[gmc]

I've built a simple circuit using my Arduino  Nano to test old school 2114 static RAM chips from retro computers.

It works well but now I'm worried about short circuit protection on the I/O pins.  Not sure if the 2114 can get damaged enough for the pins to be shorted to Vcc or GND but if this does happen will it kill the Arduino?

Do I need to put some resistors (220R?) in series for the I/O pins? I've read through a few posts where the Arduino might/might-not have this protection built in, but still not sure.

I've attached a image of my schematic. 2114 is just hooked up to the I/O pins.

[Lindley]

Hi,

If you search the web you will find various articles and even ready made boards with added i/o pins and power rail  protection.
 
However to say you can buy the clone Nano boards for under £4 in the Uk or under £2 from China, is it worth worrying about such potential damage ?  just replace the Nano. 

[Ian.M]

OTOH, the resistors are far cheaper than the time and trouble to swap out a damaged Arduino.  I'd also recommend a polyfuse in the Vcc supply to the RAM, (with 100nF decoupling between Vcc and Ground on the RAM side of it), to handle shorts due to badly blown or wrongly inserted RAM chips.

[Siwastaja]

There is no protection in Arduino boards AFAIK.

56R-100R is enough to give you almost 100% protection against short circuit, while still allowing good current to drive LEDs, MOSFET gates, or capacitive lines. 56R to 100R (in series with approx 20 ohms from the IO itself) also happens to be a good series termination to prevent ringing, yet not slow signals too much.

You need some 120R to get below maximum rating of 40mA under full 5V short circuit if you want to stay within specs.

[phil from seattle]

OTOH, the resistors are far cheaper than the time and trouble to swap out a damaged Arduino.

This.   It doesn't take much and you can get resistor arrays to simplify assembly and reduce board space.

I'd also recommend a polyfuse in the Vcc supply to the RAM, (with 100nF decoupling between Vcc and Ground on the RAM side of it), to handle shorts due to badly blown or wrongly inserted RAM chips.

Resettable fuse?  good idea, again.

[gmc]

Thanks for the replies all.

I agree, need some protection and swapping out a damaged Uno everytime would be wasteful.

I"ll add in some resistors inline.

Good thinking on the polyfuse.  Its easy to insert the chip the wrong way around.

[newbrain]

A literal trip down the memory lane...
the first microprocessor board I built used a 3D arrangement of 2114 (and someone thinks that 3D memory is a recent thing  ).

For a grand total of 4KB, 8 chips in two stacks of 4 each, all pins soldered in parallel except for the Chip Selects sticking out horizontally with wires to the (perf-)board (don't judge, I was just a kid!).

Those chips run really hot (even before the stacking...).