ESP32 - Time and External RTC

date

Jul 15, 2024

type

Post

AI summary

The ESP32 microcontroller has an internal Real-Time Clock (RTC) with limitations in maintaining time during power loss. To overcome this, an external RTC module, such as DS1307, DS3231, or PCF8563, can be integrated with the ESP32. This requires wiring the module to the ESP32, using I2C or other interfaces, and optionally connecting a backup battery. Example code is provided for setting up the external RTC and synchronizing with NTP servers for accurate timekeeping in IoT applications.

slug

esp32-external-rtc

status

Published

Limitations of Internal RTC

The ESP32 microcontroller includes an internal Real-Time Clock (RTC) that relies on a built-in crystal oscillator for timekeeping. This internal RTC is crucial for maintaining accurate time during normal operations and when the device is in deep sleep or briefly powered off. However, complete power loss results in the internal RTC resetting, causing a loss of timekeeping data. This limitation necessitates the use of an external RTC module for applications requiring persistent timekeeping across power cycles.

External RTC on ESP32

External RTCs, powered by backup sources like batteries, offer higher accuracy and retain time data during power loss events. Integrating an external RTC with the ESP32 involves connecting it via I2C or other interfaces, enabling the ESP32 to synchronize time effectively during startup or after power loss. Periodical synchronization with NTP (Network Time Protocol) servers further enhances accuracy by providing precise time information over the internet, ensuring reliable timekeeping in IoT applications.

Hardware Options

Choose an external RTC module compatible with ESP32, such as DS1307, DS3231, or PCF8563. These modules are renowned for accuracy and low power consumption. The DS1307, in particular, is widely used and supported in various RTC libraries.

You could find cost effective options on Aliexpress, while Amazon sellers would charge a lot more for the exact same product.

Wiring to ESP32

Identify I2C Pins:

Locate the SDA (data) and SCL (clock) pins on your ESP32.

Connect these pins to the corresponding SDA and SCL pins on the RTC module.

Power Connections:

Provide VCC (3.3V or 5V) and GND connections between the ESP32 and the RTC module.

Optionally, connect a backup battery to the RTC module to retain time during power loss.

Multiple Devices on the Same I2C Bus:

If you have multiple devices connected to the same I2C bus, don’t worry. Each device typically has a unique address that the ESP32 can recognize.

The ESP32 will automatically select the correct I2C device, in this case, the RTC module, for communication.

For more details, refer to the article by Random Nerd: Multiple I2C devices (same bus, different addresses).

Example Code (Using DS1307)

Syncing with NTP (Network Time Protocol)

To synchronize ESP32 time with an NTP server, use the following code snippet:

Conclusion

By following these steps, you can integrate an external RTC module, such as the DS1307, with your ESP32, ensuring accurate timekeeping and resilience against power interruptions. Synchronizing with an NTP server further enhances time accuracy, making your ESP32 projects reliable for time-sensitive applications.

About Me

Hi, I'm Qiwei Mao, a geotechnical engineer based in Atlanta GA, with a passion for IoT systems. I'm exploring low-power microcontrollers and LoRa communication systems to enable both hobbyist remote monitoring solutions and industrial-grade monitoring or control systems.