DS3231 RTC Clock with Arduino

Build a real-time clock that survives a power cut and stays accurate to ±2 ppm — about a minute a year.

Difficulty: Through-hole. Estimated build time: about 50 minutes. Estimated parts cost: about US$11.00. 4-part bill of materials with live supplier pricing. Most microcontrollers can keep time, but the moment you lose power the clock resets.