DS1302 Real Time Clock Module

Before I2C-based RTC chips became the default choice, the DS1302 was the standard real-time clock module for Arduino projects, and its 3-wire serial interface (rather than a shared I2C bus) is exactly what distinguishes it - it uses dedicated CLK, DAT, and RST lines rather than sharing an address space with other I2C devices, which can actually be an advantage on a board where the I2C bus is already crowded or unavailable. A dual power supply design keeps timekeeping running on backup power even while the main circuit is off.

With 31 bytes of dedicated clock/calendar registers plus 31 bytes of general-purpose battery-backed RAM, it stores not just the time but a small amount of additional data that survives a power cycle - useful for saving simple state information alongside the timestamp. Leap-year compensation through the year 2100 and TTL-compatible 5V logic keep it straightforward to interface with standard Arduino-class boards.

Common uses are legacy or budget-conscious clock and data-logging projects where the widely available DS1302 libraries and tutorials outweigh the DS3231's better accuracy, projects with a crowded I2C bus wanting a separate dedicated clock interface, and educational projects specifically teaching 3-wire serial protocols.