Unlike most computers, the Pi lacks a Real-Time Clock (RTC). This means the Pi doesn't know what time it is when powered on. While your Pi is connected to a network it will be able to set it's clock correctly using NTP (Network Time Protocol) server. Without a network connection your Pi has no way of knowing what time it is. This could be a problem if you are performing some time sensitive or data logging operations.
This can be solved using a RTC module. This RTC module plug on top of your Pi's GPIO pins and contains a extremely accurate DS3231 clock chip and a backup-battery that tell the Pi what time it is even if the supply is removed. When the Pi reboot, it can set it's own internal clock using the time held in by the RTC.
- Small size
- Works in 3.3V and 5V
- Two Time-of-Day alarms
- Accuracy ±2ppm from 0°C to +40°C
- Digital temp sensor output: ±3°C Accuracy
- Fast (400KHz) I2C interface
- Accurate calendar up to year 2100
- Battery backup included
- Supported by Raspberry Pi and Arduino