Rfid dooropener safety considerations?

hi,

I have made a prototype for an rfid dooropener and I'm ready to do a proper build. Serial numbers of tags should go in eeprom and I have a way to add/remove the id's should there be new ones or if one gets lost. So it is a bit flexible and it will survive a power cycle.

I will have 5v, gnd and serial rx + tx going into a box outside that can be broken. If someone starts connecting these 4 -however unlikely that is- what can they break? I don't expect anyone to be able to enter as the Arduino is checking for a 12 character id being received over serial but I'd hate it if my little friend would be broken by a short-circuit.

Thanks for your ideas on this! Jhh

Is the 5V coming via the Arduino regulator? A short circuit wouldn't be good (although the regulator has a thermal cutout in theory).

It might be a good idea to put an old-fashioned fuse in the 5V line and resistors in RX/TX to limit the current to 20mA.

Ok - I now realize a was a bit brief in my info - the 5v and gnd come from the Arduino. The rfid receiver is a simple RDM6300 and it's powered from the Arduino and sends the tag id back over serial.

I can follow the software side but the electronics is a copy and paste job I have to admit - suggestions are welcome but they'd have to be a bit explicit :+)

Jhh