It is really difficult when the date and time of the RasPi are not synced with the local time zone while logging the data. It is much more difficult once you set up your logging device or sensor node in a remote place that doesn't have uninterrupted power supply. You might have noticed that whenever the RasPi boots up, the clock shows the incorrect time. Check it yourself by entering the date command in the command-line interface of the RasPi. Also, in the previous chapter, you might have noticed that the time logged in the .csv log file is not showing the refreshed date. No, the RasPi doesn't time-travel when it's sleeping! It's just because it doesn't have a dedicated button cell to power its real-time clock (RTC). To make the RasPi cheaper, the designers removed a lot of functionalities that normal desktops or laptops have.

A desktop computer has an inbuilt button cell to power the internal RTC. To achieve this with the RasPi, you can interface...