This is a great battery-backed real time clock (RTC) that allows your microcontroller project to keep track of time even if it is reprogrammed, or if the power is lost. Perfect for datalogging, clock-building, time stamping, timers and alarms, etc. Equipped with PCF8523 RTC - it can run from 3.3V or 5V power & logic!

We've had a breakout board version of this RTC for a while, but we want to make it even easier for folks to use, so now it comes with STEMMA QT connectors for plug-and-play simplicity.

Works great with an Arduino using our RTC library or with a Raspberry Pi (or similar single board linux computer)

  • PCB & header are included
  • Plugs into any breadboard, or you can use wires
  • Two mounting holes
  • Will keep time for 5 years or more
There are two versions of this board - the STEMMA QT version shown below (the black PCB), and the original header-only version shown above (the blue PCB). Code works the same on both!

To make life easier so you can focus on your important work, we've taken the sensor and put it onto a breakout PCB along with support circuitry to let you use it with 3.3V (Feather/Raspberry Pi) or 5V (Arduino/ Metro328) logic levels. Additionally, since it speaks I2C you can easily connect it up with two wires (plus power and ground!).  We've even included SparkFun qwiic compatible STEMMA QT connectors for the I2C bus so you don't even need to solder! QT Cable is not included, but we have a variety in the shop. Just wire up to your favorite micro and you can use our CircuitPython/Python or Arduino drivers to easily interface with the PCF8523.

The PCF8523 is simple and inexpensive but not a high precision device. It may lose or gain up to 2 seconds a day. For a high-precision, temperature compensated alternative, please check out the DS3231 precision RTC. If you need a DS1307 for compatibility reasons, check out our DS1307 RTC breakout

This guide was first published on Oct 29, 2017. It was last updated on Oct 29, 2017.

This page (Overview) was last updated on Nov 28, 2021.

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