DS3231 Real Time Clock Module, I2C, with EEPROM

Keeping accurate time across power cycles is a genuine problem for most microcontroller projects, since a bare microcontroller has no built-in sense of real-world date or time and loses any software-tracked time the moment power is lost. The DS3231 solves this with a dedicated, temperature-compensated crystal oscillator chip that keeps its own accurate time independently, communicating that time to the host microcontroller over a simple I2C bus running at up to 400kHz.

Accuracy is the DS3231's standout feature compared to cheaper RTC chips: temperature compensation keeps drift to around 2ppm across the 0 to 40C range, working out to roughly one minute of accumulated error per year - a meaningful step up from basic RTC chips that can drift considerably more without that compensation. An integrated temperature sensor, accurate to within plus-or-minus 3C, is also exposed and readable over the same I2C bus, a useful bonus for projects that already need basic ambient temperature data.

Beyond pure timekeeping, the module includes a 32Kbit (AT24C32) EEPROM for storing project configuration data or logs that need to survive power loss alongside the time data itself, two independently programmable calendar alarms for triggering events at specific times or dates, and a programmable square-wave output useful for clocking other circuits. Leap-year compensation is built in and valid all the way until the year 2100, meaning calendar logic doesn't need to be separately handled in firmware.

Operating voltage spans 3.3V to 5.5V, working directly with both common microcontroller logic families. Builders working on a data logger needing accurate timestamps, a scheduling or alarm-clock project, or any application needing reliable real-world time that survives power loss will find the DS3231 a well-proven, accurate RTC solution, genuinely a step above basic RTC chips when timekeeping precision actually matters.