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.
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
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 *
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
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
attribute and access the standard attributes of a struct_time such as
t = rtc.datetime print(t) print(t.tm_hour, t.tm_min)
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