I just received my RC522 RFID reader and made this simple Arduino access control system that uses the reader, a buzzer for the alarm and a relay shield for the security system.

Therefore, an effort was made to design a tool for “identification of impedance changes in metals using an Arduino Uno-based RFID RC522” which is relatively inexpensive and easy to carry.

OK, year-old pop culture references aside [Kyle] dropped us a line to show us his tutorial on using interrupts with your Arduino. Given the single core nature of your average Arduino’s AVR you ...