Adafruit DS3231 Precision RTC - STEMMA QT

This Real Time Clock (RTC) is the most precise you can get in a small, low-power package. Most RTCs use an external 32kHz timing crystal that is used to keep time with low current draw. And that's all well and good, but those crystals have slight drift, particularly when the temperature changes (the temperature changes the oscillation frequency very very very slightly but it does add up!) This RTC is in a beefy package because the crystal is inside the chip! And right next to the integrated crystal is a temperature sensor. That sensor compensates for the frequency changes by adding or removing clock ticks so that the timekeeping stays on schedule.

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

This is the finest RTC you can get in a compact, breadboard-friendly breakout. With a coin cell plugged into the back, you can get years of precision timekeeping, even when main power is lost. Great for data-logging and clocks, or anything where you need to really know the time. A CR1220 coin cell (not included) is required to use the battery-backup capabilities!

To make life easier so you can focus on your important work, Adafruit has 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!).  It even comes with SparkFun qwiic compatible STEMMA QT connectors for the I2C bus so you don't even need to solder!

Comes as a fully assembled and tested breakout plus a small piece of header. You can solder header in to plug it into a breadboard, or solder wires directly.