The Adafruit PCF8523 Real-Time Clock Breakout keeps track of time even when your microcontroller loses power, with battery backup, 3.3V/5V compatibility and support for Arduino, CircuitPython and Raspberry Pi. CR1220 battery not included. 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 Adafruit's RTC library, with CircuitPython or with a Raspberry Pi (or similar single board Linux computer) Please 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. Features * Battery-backed real time clock (RTC) with PCF8523 chip * Maintains time during power loss or microcontroller reprogramming * Compatible with 3.3V or 5V power and logic * Works with Arduino, CircuitPython, Raspberry Pi and Linux single board computers * Ideal for datalogging, clocks, time stamping, timers and alarms * PCB and header included * Breadboard compatible or connect via wires * Two mounting holes for secure installation * Provides timekeeping for 5+ years with coin cell battery * Accuracy: may lose or gain up to 2 seconds per day * Coin cell battery (CR1220) sold separately Specifications * Mounting holes are 2.2mm (0.086in) diameter, 25mm (0.98in) apart * This board/chip uses I2C 7-bit address 0x68 * Dimensions: 25.5mm x 21.7mm x 4.8mm * Weight: 1.2g 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! Resources * Detailed guide Package Contents * 1x Adafruit PCF8523 Real Time Clock Assembled Breakout Board CR1220 battery not included. https://elecena.pl/product/22713192/adafruit-pcf8523-real-time-clock-assembled-breakout-board 2023-03-06 https://elecena.pl/product/22713192/adafruit-pcf8523-real-time-clock-assembled-breakout-board 2023-12-27 https://elecena.pl/product/22713192/adafruit-pcf8523-real-time-clock-assembled-breakout-board 2024-09-19 https://elecena.pl/product/22713192/adafruit-pcf8523-real-time-clock-assembled-breakout-board 2024-11-29 https://elecena.pl/product/22713192/adafruit-pcf8523-real-time-clock-assembled-breakout-board 2024-11-30 https://elecena.pl/product/22713192/adafruit-pcf8523-real-time-clock-assembled-breakout-board 2025-04-09 https://elecena.pl/product/22713192/adafruit-pcf8523-real-time-clock-assembled-breakout-board 2025-11-28 https://elecena.pl/product/22713192/adafruit-pcf8523-real-time-clock-assembled-breakout-board 2025-11-29