A real-time clock (often abbreviated as "RTC" for real-time clock) is a component for measuring physical time in which internally generated time data is output via a data bus. A clock crystal (32.768 kHz) serves as the clock source. This can be integrated into the module or connected externally. An internal memory is used to store seconds, minutes, hours, etc. A significant advantage of RTCs, which they not only offer when used in PC or microcontroller systems, is their self-sufficient mode of operation: Time measurement continues for a certain period of time even without an externally supplied operating voltage. This is achieved by a current accumulator that continues to supply the RTC module even when the voltage is deactivated. We offer various shields, modules and complete sets related to NFC.