DS3231 Real-Time Clock Module (I2C, AT24C32 EEPROM)

A precise, breadboard-friendly real-time clock

The DS3231 module is described as an extremely precise I2C real-time clock, and the key to that precision is its built-in temperature-compensated crystal oscillator, which continuously adjusts for temperature-driven drift in a way that a plain crystal oscillator cannot. Rated accuracy is 2ppm across the 0C to 40C range, which works out to an error of around 1 minute over roughly a month, a meaningful step up from the cheaper DS1307-based RTC modules commonly seen in beginner Arduino kits.

Alongside the DS3231 clock chip itself, the module carries an AT24C32 EEPROM with 32Kb of non-volatile memory, giving a project extra storage for logging data, configuration values or anything else that needs to persist without relying on the microcontroller's own limited flash.

Backup power and connections

Automatic backup power switching means the module seamlessly moves to a backup battery, typically a CR2032 coin cell fitted into the onboard holder, whenever main power is removed, so the clock keeps accurate time even while the rest of the project is powered down or being reprogrammed. It generates real time clock output for seconds, minutes, hours, day, date, month and year, includes two independently programmable calendar alarm functions, and offers a programmable square-wave output useful for timing other parts of a circuit.

Communication is via I2C at up to 400KHz, and the module includes an internal temperature sensor accurate to plus or minus 3C. Operating voltage runs from 3.3V to 5.5V, and the board measures 38mm by 22mm by 14mm and weighs 8g, designed to be breadboard-friendly for easy prototyping.

Who it suits

Anyone building a data logger, a clock or timer project, or any application needing accurate, drift-resistant timekeeping that survives power loss will benefit from the DS3231's temperature compensation and backup battery switching compared to a basic RTC chip.

Questions buyers ask

How accurate is the clock?

Rated at 2ppm, roughly a minute of drift per month between 0C and 40C.

Does it keep time when main power is off?

Yes, it automatically switches to backup battery power.