How to Use DS3231 RTC: Examples, Pinouts, and Specs

The DS3231 is a highly accurate, low-cost real-time clock (RTC) module with an integrated temperature-compensated crystal oscillator (TCXO) and crystal. It maintains seconds, minutes, hours, day, date, month, and year information, with automatic adjustment for leap years and months with fewer than 31 days. The module communicates with a microcontroller via I2C protocol.

• Timekeeping in embedded systems
• Data logging with time stamps
• Clocks and watches
• Alarm systems
• IoT devices requiring accurate timekeeping

• Time Accuracy: ±2ppm from 0°C to +40°C
• Battery Backup: Maintains timekeeping when main power is off
• Voltage: 2.3V to 5.5V
• Current: 200μA at 3.3V (active), 1μA (timekeeping)
• Operating Temperature: -40°C to +85°C
• Memory: 236 bytes of battery-backed SRAM

1. Connect VCC to a 2.3V to 5.5V power supply.
2. Connect GND to the ground of the power supply.
3. Connect SDA and SCL to the I2C data and clock lines of the microcontroller.
4. Optionally, connect SQW to an interrupt pin on the microcontroller if square wave or alarm interrupt functionality is needed.
5. Optionally, connect 32K to an input pin if a 32kHz clock signal is required.
6. If a reset feature is needed, connect RST to a digital output pin; otherwise, it can be left unconnected or pulled high.

• Ensure pull-up resistors are connected to the SDA and SCL lines, as they are required for proper I2C communication.
• If the module will be used in a battery-backed configuration, ensure a suitable coin cell battery is installed.
• Avoid exposing the module to extreme temperatures to maintain time accuracy.

#include <Wire.h>
#include <RTClib.h>

RTC_DS3231 rtc;

void setup() {
  Serial.begin(9600);
  
  // Check if the RTC is connected correctly
  if (!rtc.begin()) {
    Serial.println("Couldn't find RTC");
    while (1);
  }

  // Check if the RTC lost power and if so, set the time
  if (rtc.lostPower()) {
    Serial.println("RTC lost power, let's set the time!");
    // The following line sets the RTC to the date & time this sketch was compiled
    rtc.adjust(DateTime(F(__DATE__), F(__TIME__)));
  }
}

void loop() {
  DateTime now = rtc.now();
  
  // Print the current date and time
  Serial.print(now.year(), DEC);
  Serial.print('/');
  Serial.print(now.month(), DEC);
  Serial.print('/');
  Serial.print(now.day(), DEC);
  Serial.print(" ");
  Serial.print(now.hour(), DEC);
  Serial.print(':');
  Serial.print(now.minute(), DEC);
  Serial.print(':');
  Serial.print(now.second(), DEC);
  Serial.println();
  
  delay(1000);
}

• Time not accurate: Ensure the battery is installed correctly and has charge.
• I2C communication failure: Check pull-up resistors on SDA and SCL lines.
• Module not recognized: Verify wiring, ensure correct voltage supply, and check for soldering issues.

• If the time drifts significantly, replace the battery to maintain accurate timekeeping during power outages.
• Use the Wire library's setClock() function to adjust I2C clock speed if communication issues arise.
• Ensure the Arduino library for the DS3231 is correctly installed and up to date.

• Q: Can the DS3231 be used without an external battery?
  • A: Yes, but timekeeping will reset if power is lost.
• Q: What is the purpose of the 32K pin?
  • A: It outputs a 32kHz square wave that can be used to drive timers or as a clock reference.
• Q: How do I set an alarm?
  • A: Use the RTC library's alarm functions to configure and enable alarms.