We produce Mifare EV1 RFID tags and need to convert the UID to a seven-digit code printed on a wristband. Does anyone have a formula to convert the UID to a seven-digit code using numbers and letters?

Similarly, any group of four bits translates into a hexadecimal digit: 0011 becomes a 3, and 1010 becomes 10, which is usually represented in hexadecimal as a capital A.