adafruit-circuitpython-ds3231 2.1.2

CircuitPython library for DS3231 precision real-time clock.

Introduction
============

.. image:: https://readthedocs.org/projects/adafruit-micropython-ds3231/badge/?version=latest
:target: https://circuitpython.readthedocs.io/projects/ds3231/en/latest/
:alt: Documentation Status

.. image :: https://img.shields.io/discord/327254708534116352.svg
:target: https://discord.gg/nBQh6qu
:alt: Discord

.. image:: https://travis-ci.org/adafruit/Adafruit_CircuitPython_DS3231.svg?branch=master
:target: https://travis-ci.org/adafruit/Adafruit_CircuitPython_DS3231
:alt: Build Status

The datasheet for the DS3231 explains that this part is an
"Extremely Accurate I²C-Integrated RTC/TCXO/Crystal". And,
hey, it does exactly what it says on the tin! This Real Time
Clock (RTC) is the most precise you can get in a small, low
power package.

Most RTCs use an external 32kHz timing crystal that is used
to keep time with low current draw. And that's all well and
good, but those crystals have slight drift, particularly when
the temperature changes (the temperature changes the oscillation
frequency very very very slightly but it does add up!) This
RTC is in a beefy package because the crystal is inside the
chip! And right next to the integrated crystal is a temperature
sensor. That sensor compensates for the frequency changes by
adding or removing clock ticks so that the timekeeping stays
on schedule.

This is the finest RTC you can get, and now we have it in a
compact, breadboard-friendly breakout. With a coin cell
plugged into the back, you can get years of precision
timekeeping, even when main power is lost. Great for
datalogging and clocks, or anything where you need to
really know the time.

.. image:: ../docs/_static/3013-01.jpg
:alt: DS3231 Product Image

Dependencies
=============
This driver depends on:

* `Adafruit CircuitPython <https://github.com/adafruit/circuitpython>`_
* `Bus Device <https://github.com/adafruit/Adafruit_CircuitPython_BusDevice>`_
* `Register <https://github.com/adafruit/Adafruit_CircuitPython_Register>`_

Please ensure all dependencies are available on the CircuitPython filesystem.
This is easily achieved by downloading
`the Adafruit library and driver bundle <https://github.com/adafruit/Adafruit_CircuitPython_Bundle>`_.

Usage Notes
===========

Basics
------

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

.. code:: python

import busio
import adafruit_ds3231
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:

.. code:: python

from board import *

You can also use pins defined by the onboard ``microcontroller`` through the
``microcontroller.pin`` module.

Now, to initialize the I2C bus:

.. code:: python

myI2C = busio.I2C(SCL, SDA)

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

.. code:: python

rtc = adafruit_ds3231.DS3231(myI2C)

Date and time
-------------

To set the time, you need to set ``datetime`` to a ``time.struct_time`` object:

.. code:: python

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:: python

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

Alarm
-----

To set the time, you need to set ``alarm1`` or ``alarm2`` to a tuple with a
``time.struct_time`` object and string representing the frequency such as "hourly":

.. code:: python

rtc.alarm1 = (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 corresponding
``alarm1_status`` or ``alarm2_status`` attributes. Once True, set it back to False
to reset.

.. code:: python

if rtc.alarm1_status:
print("wake up!")
rtc.alarm1_status = False

Contributing
============

Contributions are welcome! Please read our `Code of Conduct
<https://github.com/adafruit/Adafruit_CircuitPython_DS3231/blob/master/CODE_OF_CONDUCT.md>`_
before contributing to help this project stay welcoming.

Building locally
================

To build this library locally you'll need to install the
`circuitpython-build-tools <https://github.com/adafruit/circuitpython-build-tools>`_ package.

.. code-block:: shell

python3 -m venv .env
source .env/bin/activate
pip install circuitpython-build-tools

Once installed, make sure you are in the virtual environment:

.. code-block:: shell

source .env/bin/activate

Then run the build:

.. code-block:: shell

circuitpython-build-bundles --filename_prefix adafruit-circuitpython-ds3231 --library_location .

Sphinx documentation
-----------------------

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):

.. code-block:: shell

python3 -m venv .env
source .env/bin/activate
pip install Sphinx sphinx-rtd-theme

Now, once you have the virtual environment activated:

.. code-block:: shell

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.