NTP/RTC로 정확한 시간 얻기

A reading like "24.3 C" is half a story. To make sense of logged data, every sample needs a timestamp telling you exactly when it happened. ⏰

Your Arduino forgets the date the moment power drops. It only counts milliseconds since boot, so it has no idea what real-world wall-clock time it is.

You can fetch the time from the internet with NTP, or keep it locally with a battery-backed RTC chip. Each fits a different situation.

NTP (Network Time Protocol) asks a time server online for the current moment. It is accurate and free, but it needs an active WiFi connection to work.

On an ESP32 one line of setup points your board at a public time server and your timezone offset. Then the board syncs automatically.

Once synced, you pull the current time into a struct and read its fields. This gives you year, month, day, hour, and minute to label data.

An RTC module like the DS3231 keeps ticking on a tiny coin battery, even with the Arduino fully off. No network needed at all.

Most RTC modules talk over I2C, so you connect just four wires: power, ground, SDA, and SCL. That keeps your build wonderfully simple.

With the RTClib library you grab the current moment as a DateTime object, then read its fields just like the NTP version.

Pick NTP when your device is always online and you want zero extra parts. Pick an RTC for offline or battery nodes that still need the right time.

Many strong designs use both: an RTC keeps time offline, and NTP gently corrects its small drift whenever WiFi is available. 🌐

Which time source still works with no internet connection?

Arduino has no real clock, so add time with NTP online or an RTC offline. Now every reading you log can carry an accurate timestamp. ✅