Programming the PCF8523 RTC Using Raspberry Pi and Python

1. Introduction

The PCF8523 is a low-power real-time clock (RTC) module from NXP. It is often used in embedded systems to maintain accurate timekeeping, even when the host system is powered off. This report details the setup and programming of the PCF8523 RTC using a Raspberry Pi and Python, leveraging the I²C interface.

2. System Requirements

2.1 Hardware

• Raspberry Pi (any model with GPIO and I²C support; e.g., Raspberry Pi 4 Model B)

• PCF8523 RTC Module (often available as a breakout board)

• CR1220 coin cell battery (for backup timekeeping)

• Jumper wires

2.2 Software

• Raspberry Pi OS (Bookworm, Bullseye, or earlier)

• Python 3.x

• I2C Tools (i2c-tools package)

• Adafruit CircuitPython PCF8523 library

• Adafruit Blinka (CircuitPython compatibility layer for Raspberry Pi)

3. Hardware Setup

3.1 Wiring

Ensure that the RTC module is powered with 3.3V (not 5V) to avoid damage.

4. Enabling I²C on Raspberry Pi

1. Open terminal and enter:

   sudo raspi-config

2. Navigate to Interfacing Options > I2C and enable it.

3. Reboot the Raspberry Pi:

   sudo reboot

4. After reboot, install the I²C tools:

   sudo apt update sudo apt install -y i2c-tools

5. Detect the RTC:

   i2cdetect -y 1

   You should see the address 0x68 or 0xA2 depending on the breakout board.

5. Installing Python Libraries

1. Install pip if not already installed:

   sudo apt install -y python3-pip

2. Install Adafruit Blinka and the PCF8523 library:

   pip3 install adafruit-blinka

   pip3 install adafruit-circuitpython-pcf8523

6. Python Example Code

6.1 Setting the Time

To set the time, uncomment the rtc.datetime = now line and modify the datetime accordingly. After running the script once, you can comment it out to avoid overwriting the time on every run.

6.2 DateTime Format

The rtc.datetime property returns a time.struct_time object.

7. Advanced Usage

7.1 Battery Backup

The PCF8523 supports battery backup via a CR1220 coin cell. Ensure it's installed correctly to maintain time when the Pi is off.

7.2 Alarm and Timer Features

The PCF8523 supports alarms and countdown timers. However, these are not implemented in the Adafruit library at the time of writing. For advanced features, consider writing raw I²C commands using smbus2 or expanding the Adafruit driver.

8. Conclusion

The PCF8523 RTC is a reliable module for maintaining time on a Raspberry Pi system. With the help of Adafruit’s CircuitPython library and Blinka, integrating and using the RTC is straightforward. This setup is useful in projects requiring timestamping, data logging, or time-based automation.

9. External References

• Adafruit PCF8523 Library: https://github.com/adafruit/Adafruit_CircuitPython_PCF8523

• Adafruit Blinka (CircuitPython on Raspberry Pi): https://learn.adafruit.com/circuitpython-on-raspberrypi-linux

• Raspberry Pi I²C Documentation: https://www.raspberrypi.com/documentation/computers/raspberry-pi.html#i2c

• PCF8523 Datasheet: https://www.nxp.com/docs/en/data-sheet/PCF8523.pdf

• I2C Tools for Linux: https://wiki.debian.org/I2CTools