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.
Dependencies¶
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
Usage Notes¶
Basics¶
Of course, you must import the library to use it:
import time
import adafruit_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:
import board
Now, to initialize the I2C bus:
i2c = board.I2C()
Once you have created the I2C interface object, you can use it to instantiate the RTC object:
rtc = adafruit_pcf8523.PCF8523(i2c)
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 tm_year,
tm_hour and tm_min.
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”:
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
Contributing¶
Contributions are welcome! Please read our Code of Conduct before contributing to help this project stay welcoming.
Documentation¶
For information on building library documentation, please check out this guide.