adafruit-circuitpython-pcf8523

Introduction to Adafruit's PCF8523 Real Time Clock (RTC) Library

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This is a great battery-backed real time clock (RTC) that allows your microcontroller project to keep track of time even if it is reprogrammed, or if the power is lost. Perfect for datalogging, clock-building, time stamping, timers and alarms, etc. Equipped with PCF8523 RTC - it can run from 3.3V or 5V power & logic!

The PCF8523 is simple and inexpensive but not a high precision device. It may lose or gain up to two seconds a day. For a high-precision, temperature compensated alternative, please check out the DS3231 precision RTC. <https://www.adafruit.com/products/3013>_ If you need a DS1307 for compatibility reasons, check out our DS1307 RTC breakout <https://www.adafruit.com/products/3296>_.

.. image:: _static/3295-00.jpg :alt: PCF8523 Breakout Board

Dependencies

This driver depends on the Register <https://github.com/adafruit/Adafruit_CircuitPython_Register>_ and Bus Device <https://github.com/adafruit/Adafruit_CircuitPython_BusDevice>_ libraries. Please ensure they are also available on the CircuitPython filesystem. This is easily achieved by downloading a library and driver bundle <https://github.com/adafruit/Adafruit_CircuitPython_Bundle>_.

Installing from PyPI

On supported GNU/Linux systems like the Raspberry Pi, you can install the driver locally from PyPI <https://pypi.org/project/adafruit-circuitpython-pcf8523/>_. To install for current user:

.. code-block:: shell

pip3 install adafruit-circuitpython-pcf8523

To install system-wide (this may be required in some cases):

.. code-block:: shell

sudo pip3 install adafruit-circuitpython-pcf8523

To install in a virtual environment in your current project:

.. code-block:: shell

mkdir project-name && cd project-name
python3 -m venv .venv
source .venv/bin/activate
pip3 install adafruit-circuitpython-pcf8523

Usage Notes

Basics

Of course, you must import the library to use it:

.. code:: python3

import time
from adafruit_pcf8523.pcf8523 import PCF8523

All the Adafruit RTC libraries take an instantiated and active I2C object (from the board library) as an argument to their constructor. The way to create an I2C object depends on the board you are using. For boards with labeled SCL and SDA pins, you can:

.. code:: python3

import board

Now, to initialize the I2C bus:

.. code:: python3

i2c = board.I2C()

Once you have created the I2C interface object, you can use it to instantiate the RTC object:

.. code:: python3

rtc = PCF8523(i2c)

Date and time

To set the time, you need to set datetimeto atime.struct_time` object:

.. code:: python3

rtc.datetime = time.struct_time((2017,1,9,15,6,0,0,9,-1))

After the RTC is set, you retrieve the time by reading the datetime attribute and access the standard attributes of a struct_time such as tm_year, tm_hour and tm_min.

.. code:: python3

t = rtc.datetime
print(t)
print(t.tm_hour, t.tm_min)

Alarm

To set the time, you need to set alarm to a tuple with a time.struct_time object and string representing the frequency such as "hourly":

.. code:: python3

rtc.alarm = (time.struct_time((2017,1,9,15,6,0,0,9,-1)), "daily")

After the RTC is set, you retrieve the alarm status by reading the alarm_status attribute. Once True, set it back to False to reset.

.. code:: python3

if rtc.alarm_status:
    print("wake up!")
    rtc.alarm_status = False

Documentation

API documentation for this library can be found on Read the Docs <https://docs.circuitpython.org/projects/pcf8523/en/latest/>_.

For information on building library documentation, please check out this guide <https://learn.adafruit.com/creating-and-sharing-a-circuitpython-library/sharing-our-docs-on-readthedocs#sphinx-5-1>_.

Contributing

Contributions are welcome! Please read our Code of Conduct <https://github.com/adafruit/Adafruit_CircuitPython_PCF8523/blob/main/CODE_OF_CONDUCT.md>_ before contributing to help this project stay welcoming.