# Adafruit PCF8523 Real Time Clock ## Overview ![](https://cdn-learn.adafruit.com/assets/assets/000/103/706/medium800/adafruit_products_PCF8523_top.jpg?1628024661) 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](https://www.adafruit.com/product/3295), 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. Info: ![](https://cdn-learn.adafruit.com/assets/assets/000/110/791/medium800/adafruit_products_PCF_HVSON_top_view.jpg?1649872379 This is the HVSON chip package version.) Works great with an [Arduino using our RTC library](https://github.com/adafruit/RTClib) or with a [Raspberry Pi (or similar single board linux computer)](../../../../adding-a-real-time-clock-to-raspberry-pi) - PCB & header are included - Plugs into any breadboard, or you can use wires - Two mounting holes - Will keep time for 5 years or more ![](https://cdn-learn.adafruit.com/assets/assets/000/047/717/medium800/circuitpython_3295-04.jpg?1509301556 This is the SOIC-8 chip package version.) Info: 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](https://www.sparkfun.com/qwiic) compatible** [STEMMA QT](https://learn.adafruit.com/introducing-adafruit-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](https://www.adafruit.com/?q=stemma+qt+cable&sort=BestMatch). Just wire up to your favorite micro and you can use our CircuitPython/Python or [Arduino drivers](https://github.com/adafruit/Adafruit_DPS310) to easily interface with the PCF8523. ![](https://cdn-learn.adafruit.com/assets/assets/000/103/705/medium800/adafruit_products_PCF8523_STEMMA_side.jpg?1628024649) 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](https://www.adafruit.com/products/3013). If you need a DS1307 for compatibility reasons, check out our [DS1307 RTC breakout](http://www.adafruit.com/products/3296) ![](https://cdn-learn.adafruit.com/assets/assets/000/103/707/medium800/adafruit_products_PCF8523_back.jpg?1628024676) - [Next Page](https://learn.adafruit.com/adafruit-pcf8523-real-time-clock/pinouts.md) ## Featured Products ### Adafruit PCF8523 Real Time Clock Breakout Board [Adafruit PCF8523 Real Time Clock Breakout Board](https://www.adafruit.com/product/5189) 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 data-logging, clock-building, time stamping, timers, and alarms, etc. Equipped... In Stock [Buy Now](https://www.adafruit.com/product/5189) [Related Guides to the Product](https://learn.adafruit.com/products/5189/guides) ### Adafruit PCF8523 Real Time Clock Assembled Breakout Board [Adafruit PCF8523 Real Time Clock Assembled Breakout Board](https://www.adafruit.com/product/3295) 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... Out of Stock [Buy Now](https://www.adafruit.com/product/3295) [Related Guides to the Product](https://learn.adafruit.com/products/3295/guides) ### Adafruit PiRTC - PCF8523 Real Time Clock for Raspberry Pi [Adafruit PiRTC - PCF8523 Real Time Clock for Raspberry Pi](https://www.adafruit.com/product/3386) This is a great battery-backed real time clock (RTC) that allows your Raspberry Pi project to keep track of time if the power is lost. Perfect for data-logging, clock-building, time-stamping, timers and alarms, etc. Equipped with  **PCF8523**  RTC, it works great with the... In Stock [Buy Now](https://www.adafruit.com/product/3386) [Related Guides to the Product](https://learn.adafruit.com/products/3386/guides) ### CR1220 12mm Diameter - 3V Lithium Coin Cell Battery [CR1220 12mm Diameter - 3V Lithium Coin Cell Battery](https://www.adafruit.com/product/380) These are the highest quality & capacity batteries, the same as shipped with the iCufflinks, iNecklace, Datalogging and GPS Shields, GPS HAT, etc. One battery per order (you'll want one battery per cufflink or pendant.) Brand may vary but all battery brands are verified... In Stock [Buy Now](https://www.adafruit.com/product/380) [Related Guides to the Product](https://learn.adafruit.com/products/380/guides) ## Related Guides - [MacroPad 2FA TOTP Authentication Friend](https://learn.adafruit.com/macropad-2fa-totp-authentication-friend.md) - [Adding a Real Time Clock to Raspberry Pi](https://learn.adafruit.com/adding-a-real-time-clock-to-raspberry-pi.md) - [Blahaj Alarm and Lamp](https://learn.adafruit.com/blahaj-alarm.md) - [I2C Addresses and Troublesome Chips](https://learn.adafruit.com/i2c-addresses.md) - [Plotting Offline Data - JSONL to CSV files, filters and graphs](https://learn.adafruit.com/plotting-offline-data-jsonl-to-csv-files-filters-and-graphs.md) - [NeoTrellis M4 Arpeggiator Synth](https://learn.adafruit.com/neotrellis-arpeggiator-synth.md) - [Adafruit TMC2209 Stepper Motor Driver Breakout Board](https://learn.adafruit.com/adafruit-tmc2209-stepper-motor-driver-breakout-board.md) - [CircuitPython NeoPixel Library Using SPI](https://learn.adafruit.com/circuitpython-neopixels-using-spi.md) - [Split Ortho Keyboard with TCA8418 Matrix Expanders](https://learn.adafruit.com/split-ortho-keyboard.md) - [Kombucha Thermostat with CircuitPython and Feather ](https://learn.adafruit.com/kombucha-thermostat-with-circuitpython-and-feather.md) - [Daily UV Index PyPortal Display](https://learn.adafruit.com/pyportal-uv-index.md) - [Adafruit ATtiny Breakouts with seesaw](https://learn.adafruit.com/adafruit-attiny817-seesaw.md) - [Owl IR TV Remote](https://learn.adafruit.com/owl-ir-tv-remote.md) - [Adafruit Feather RP2040 RFM95](https://learn.adafruit.com/feather-rp2040-rfm95.md) - [TSL2561 Luminosity Sensor](https://learn.adafruit.com/tsl2561.md)