How to Use Adafruit PCF8523 RTC: Examples, Pinouts, and Specs

The Adafruit PCF8523 RTC is a Real Time Clock (RTC) module that offers precise timekeeping capabilities. It is designed to maintain accurate time with the help of a built-in crystal oscillator and can continue to keep time with a backup battery even when the main power supply is disconnected. This component is ideal for a variety of applications, including data loggers, alarm systems, and other time-sensitive projects.

Common applications and use cases:

• Clocks and watches
• Data logging with time stamps
• Time-based automation (e.g., turning lights on/off)
• Scheduling events in embedded systems

• Voltage Supply: 1.8V to 5.5V
• Current Consumption: 55 μA (typical)
• Time Accuracy: ±2ppm from 0°C to +40°C
• Battery Backup: Yes (CR1220 coin cell)
• Interface: I2C
• I2C Address: 0x68 (7-bit)

1. Power Connections: Connect the VCC pin to a 1.8V to 5.5V power supply and the GND pin to the ground.
2. I2C Connections: Connect the SDA and SCL pins to the I2C data and clock lines, respectively.
3. Backup Battery: Insert a CR1220 coin cell into the battery holder to enable timekeeping during power loss.
4. Arduino Connection: For use with an Arduino UNO, connect SDA to A4, SCL to A5, VCC to 5V, and GND to ground.

• Ensure that the power supply voltage is within the specified range to avoid damaging the RTC.
• The I2C bus requires pull-up resistors; most Arduino boards have these built-in, but if you're using a different microcontroller, you may need to add them.
• When placing the backup battery, ensure the correct polarity to prevent damage to the RTC.
• For accurate timekeeping, avoid placing the RTC module near heat sources or components that generate significant heat.

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

RTC_PCF8523 rtc;

void setup() {
  Wire.begin();
  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 has lost power and if so, set the time
  if (!rtc.initialized() || rtc.lostPower()) {
    Serial.println("RTC is NOT initialized, let's set the time!");
    // This 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();

  // Wait for a second
  delay(1000);
}

• Time not accurate: Ensure the backup battery is installed correctly and has charge.
• I2C communication failure: Check the wiring, ensure pull-up resistors are in place, and verify that no other device on the I2C bus has the same address.
• No response from the RTC: Make sure the RTC module is properly powered and that the correct I2C address is being used in the code.

• If the time is not accurate, replace the backup battery with a new one.
• Use an I2C scanner sketch to check if the RTC is detected on the I2C bus.
• Ensure that the Arduino libraries for the RTC are correctly installed and included in your sketch.

Q: Can the PCF8523 RTC module be used with a 3.3V system? A: Yes, the module can operate from 1.8V to 5.5V, making it suitable for both 3.3V and 5V systems.

Q: How long will the backup battery last? A: The battery life depends on the quality of the battery and the environmental conditions but typically lasts for a few years.

Q: Is it necessary to use an external crystal with the PCF8523 RTC? A: No, the PCF8523 has an integrated crystal oscillator that provides accurate timekeeping.