Hi, I am currently thinking about making an embedded point-of-sale system, with a fixed price, i.e. no computer, just a microcontroller that subtracts a specific amount from the card being used as payment. The money would be stored on the card itself i.e. no centralized database. Currently, I do not have a preference regarding the type of card to use i.e. whether to use an rfid card, a contact smartcard or a magnetic card. The magnetic card seems the cheapest, but most examples seem to favor the contactless card. Therefore, I have two questions I was hoping you could help me with: · Which media offers the best security against duplication (as the money is on the card itself, I would prefer if the card was hard to copy)? Do some cards have, for example a unique, read-only-identifier, that would prevent any copying (assuming the microcontroller is pre-programmed with those unique ids) · Do you know of any example source code that would talk with the card reader, read the amount on the card, subtract a fixed amount and rewrite the new total on the card? For security purposes, some encryption in the driver would be helpful. For the embedded controller, I was considering the arduino, because it seems to be the most popular option (I am a newbie, I will have to learn whatever the microcontroller is). Please let me know if you have any suggestions. Thanks.