RTC - Real-time Clock

[last updated: 2022-07-31]
programming code
wall clock/timer project
sprinkler system project
See Links below:
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• PCF8523 Real-time Clock (Adafruit PID: 3295)
  • it can run from 3.3V or 5V power & logic
  • CR1220 3v coin cell battery saves current time even if main power is disconnected
    It appears that the RTC will operate even if the CR1220 is not installed, however I did get some mixed results when first trying it, with some errors of: "RTC is NOT running!"
  • Not a high precision device. It may lose or gain up to 2 seconds a day.
  • Communicates with MCU via I2C, with fixed (not changeable) address 0x68.
  • Has a SQW square-wave output that must be enabled via software
  • There are internal 10K pull-ups to Vcc on the PCF8523 on SDA and SCL lines.
  • Uses JeeLab's RTC library, available on GitHub or in the Arduino Library Manager as RTClib.
    Use "RTClib by Adafruit"
    IDE --> Tools --> Manage Libraries
    type RTClib in search bar
    find RTClib by Adafruit
    click Install
  • In Arduino IDE, Open up Examples->RTClib->pcf8523
    Set Serial monitor to 57600 baud

    
    Set the RTC's time:

    • There are different ways and places you can do this:
      • To set the RTC time to a specific time, put a line like this in your Arduino code:
        // year, month, day-of-month, hour, min, sec
        rtc.adjust(DateTime(2022, 1, 1, 13, 0, 0));
      • Use this line to set the RTC time to the time that your computer was at when you last compiled the Arduino program
        rtc.adjust(DateTime(F(__DATE__), F(__TIME__)));

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• DSS3231 Precision RTC Breakout (Adafruit PID: 3013)
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• Reference Links:
  (link to:) Adafruit tutorial

  (link to:) PCF8523 Mfr page

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