Arduino: real timekeeping and alarms with the DS3231 RTC
Give your Arduino a real clock with the DS3231 RTC module. Set the time, read it back, and fire alarms that survive power loss, drift, and reboot.
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#ds3231
3 tutorials
Arduino: build a digital clock with DS3231 + OLED
Build a desk clock that never drifts: a DS3231 RTC keeps time, a 0.96 inch SSD1306 OLED shows it big. Two I2C devices on the same two wires, plus a button to set it.
Arduino: datalogger with RTC + SD card for timestamped sensor files
Log sensor readings to an SD card with real timestamps from a DS3231 RTC. CSV files your spreadsheet opens directly, and a clock that survives power cuts.