Hi it is the Beaver here, I too have tried to use mt seeeduino XIAO )SAMD21) with a RF card reader, MF522,a 128x32 OLED, and D! as output. it sort of works but I an not a coder and sruggling to get the LED to remain on whilt the RFID card is present. and to only turn off 1 second after the card is removed. I plan to have a switch circuit ( using a relay to a contactor with appropriate circutry) to only supply powe if user is regestered as a user.