For connected devices, one of the easiest and most flexible ways to obtain accurate time is through the internet using the Network Time Protocol (NTP). This method is widely used in IoT devices, servers and embedded systems with network connectivity.
NTP allows devices to synchronize their internal clocks with highly accurate time servers distributed around the world.
What Is NTP?
NTP (Network Time Protocol) is a protocol designed to synchronize clocks over a network.
- Uses UDP communication (port 123)
- Connects to public or private time servers
- Compensates for network delays
It is one of the oldest and most reliable internet protocols still in use today.
How NTP Works
An NTP client (your device) communicates with one or more time servers.
- Device sends a request timestamp
- Server responds with its current time
- Client calculates delay and offset
- Local clock is adjusted accordingly
This process is repeated periodically to maintain accuracy.
Accuracy of NTP
- Typical accuracy: a few milliseconds
- Depends on network latency
- More than sufficient for most embedded applications
While not as precise as GPS, NTP is highly practical and easy to use.
Hardware Requirements
To use NTP, the device must have network connectivity:
- WiFi (e.g. ESP8266)
- Ethernet (e.g. W5500 modules)
No additional timekeeping hardware is strictly required.
Using NTP with Microcontrollers
ESP32 / ESP8266
- Built-in WiFi support
- Direct NTP client functions available
Arduino with Ethernet
- Requires Ethernet module
- Uses UDP communication
Most platforms have libraries that simplify NTP integration.
Time Zones and Daylight Saving Time
NTP provides time in UTC (Coordinated Universal Time).
- Time zone must be handled in software
- Daylight saving time adjustments required
This is an important consideration in application design.
Advantages of NTP
- Very easy to implement
- No additional hardware required
- Global availability
- Good accuracy for most applications
Limitations
- Requires internet connection
- Dependent on network stability
- Not suitable for isolated systems
Combining NTP with RTC
In many designs, NTP is combined with an RTC:
- NTP sets the correct time
- RTC maintains time when offline
This hybrid approach provides both convenience and reliability.
Typical Applications
- Smart home devices
- IoT systems
- Web-connected clocks
- Logging and monitoring systems
Public NTP Servers
There are many public NTP servers available:
- pool.ntp.org (global pool)
- Regional or national time servers
Using the global pool is the easiest option for most projects.
Best Practices
- Synchronize periodically (e.g. every few hours)
- Use multiple servers for redundancy
- Combine with RTC for offline operation
Conclusion
NTP is one of the simplest and most flexible ways to obtain accurate time in connected systems. It requires minimal hardware and provides sufficient accuracy for most applications.
For reliable designs, combining NTP with an RTC ensures that time is maintained even when the network is unavailable.