Introduction to Adafruit's PCF8523 Real Time Clock (RTC) Library
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. If you need a DS1307 for compatibility reasons, check out our DS1307 RTC breakout.
This driver depends on the Register and Bus Device libraries. Please ensure they are also available on the CircuitPython filesystem. This is easily achieved by downloading a library and driver bundle.
Installing from PyPI
On supported GNU/Linux systems like the Raspberry Pi, you can install the driver locally from PyPI. To install for current user:
pip3 install adafruit-circuitpython-pcf8523
To install system-wide (this may be required in some cases):
sudo pip3 install adafruit-circuitpython-pcf8523
To install in a virtual environment in your current project:
mkdir project-name && cd project-name python3 -m venv .env source .env/bin/activate pip3 install adafruit-circuitpython-pcf8523
Of course, you must import the library to use it:
import busio import adafruit_pcf8523 import time
All the Adafruit RTC libraries take an instantiated and active I2C object (from the busio 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:
from board import *
You can also use pins defined by the onboard microcontroller through the microcontroller.pin module.
Now, to initialize the I2C bus:
i2c_bus = busio.I2C(SCL, SDA)
Once you have created the I2C interface object, you can use it to instantiate the RTC object:
rtc = adafruit_pcf8523.PCF8523(i2c_bus)
Date and time
To set the time, you need to set datetime` to a time.struct_time object:
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
t = rtc.datetime print(t) print(t.tm_hour, t.tm_min)
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":
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.
if rtc.alarm_status: print("wake up!") rtc.alarm_status = False
Contributions are welcome! Please read our Code of Conduct before contributing to help this project stay welcoming.
Zip release files
To build this library locally you'll need to install the circuitpython-build-tools package.
python3 -m venv .env source .env/bin/activate pip install circuitpython-build-tools
Once installed, make sure you are in the virtual environment:
Then run the build:
circuitpython-build-bundles --filename_prefix adafruit-circuitpython-pcf8523 --library_location .
Sphinx is used to build the documentation based on rST files and comments in the code. First, install dependencies (feel free to reuse the virtual environment from above):
python3 -m venv .env source .env/bin/activate pip install Sphinx sphinx-rtd-theme
Now, once you have the virtual environment activated:
cd docs sphinx-build -E -W -b html . _build/html
This will output the documentation to
docs/_build/html. Open the index.html in your browser to
view them. It will also (due to -W) error out on any warning like Travis will. This is a good way to
locally verify it will pass.