Today I’ve been playing with a commercial RFID reader and an Arduino UNO. I like the idea of this combo in principle, because I can connect a 12V power supply to the Arduino and power the reader directly from the VIN pin, eliminating the need for two power supplies or a step-down converter.<\/p>\n\n\n\n
I tried several different libraries for Arduino, and wasn’t having the best of luck — I settled on Daniel Smith’s code from Pagemac back in 2012. <\/p>\n\n\n\n
http:\/\/www.pagemac.com\/projects\/rfid\/arduino_wiegand<\/p>\n\n\n\n
Then I made a change that caused buffer overflows and Arduino resets. Once that was fixed, it started reading cards consistently. But it was reading them at twice the actual tag length. A 34-bit card was detected at 68 bits. I changed the pin mode from INPUT to INPUT_PULLUP on both data pins, and bang, I was getting 34-bit tag reads.<\/p>\n\n\n\n
Unfortunately, the code I had only interpretation for 35 and 26-bit formats, so some minor rearrangement of boundaries and bitshifting was required. It’s easy to tell when bitshifting is required, because the result you get is a multiplier or a factor of the result you expect. In my case, the facility code was coming up at 1\/8 of the value of the actual facility code, and the card code was coming up as 2x the actual card code (actual codes were validated by the Proxmark3 RDV4).<\/p>\n\n\n\n
After the bitshifting was done, it was able to read my card properly. Now I just need to set up interpreters for all the known card variants that I need to test against.<\/p>\n\n\n\n
BIG thanks to Kevin for his help in narrowing down the issues I was fighting with.<\/p>\n","protected":false},"excerpt":{"rendered":"
Today I’ve been playing with a commercial RFID reader and an Arduino UNO. I like the idea of this combo in principle, because I can connect a 12V power supply … <\/p>\n