Adafruit PCF8523 Real Time Clock Assembled Breakout Board


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!

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

Note: This product does not come with a CR1220 coin cell battery. We recommend you purchase a coin cell battery to use with this product.

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

Technical Details

Check out our detailed guide for code, libraries, schematics, Fritzing object and more!

Revision History:

  • As of March 25, 2022, this board now may come with a PCB version that has HVSON or SOIC-8 chip package depending on what chip is available in the market. Both are identical functionality!
  • As of Aug 30, 2017 we have updated the design to have an RC filter on the power supply to reduce accidental resetting if power drops too fast!


  • Mounting holes are 2.2mm (0.086in) diameter, 25mm (0.98in) apart
  • This board/chip uses I2C 7-bit address 0x68

Product Dimensions: 25.5mm x 21.7mm x 4.8mm / 1.0" x 0.9" x 0.2"

Product Weight: 1.2g / 0.0oz

    RoHS 2 2011 65 EU CompliantRoHS 2 2015 863 EU Compliant

    Collections: Adafruit

    Type: Breakout Boards > Clocks