This tiny real-time clock (RTC) module with an onboard ±20-ppm oscillator is a drop-in replacement for the DS1302 in a DIP-8 package. The maximum error is about 10.5 minutes per year. The module is perfect for prototyping f.i. on a breadboard: only three I/O pins are required, and it is supported by open-source Arduino libraries. Add a rechargeable battery or a super capacitor to let it run continuously.