Merge pull request #1 from deshipu/master

Initial commit

Author: tannewt

LICENSE

@@ -1,6 +1,6 @@
 The MIT License (MIT)
 
-Copyright (c) 2017 Radomir Dopieralski for Adafruit Industries
+Copyright (c) 2017 Radomir Dopieralski, written for Adafruit Industries
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

README.rst

@@ -1,32 +1,61 @@
-
 Introduction
 ============
 
 .. image:: https://readthedocs.org/projects/adafruit-circuitpython-si7021/badge/?version=latest
     :target: https://circuitpython.readthedocs.io/projects/si7021/en/latest/
     :alt: Documentation Status
 
-.. image :: https://badges.gitter.im/adafruit/circuitpython.svg
+.. image:: https://badges.gitter.im/adafruit/circuitpython.svg
     :target: https://gitter.im/adafruit/circuitpython?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge
     :alt: Gitter
 
-TODO
-
 Dependencies
 =============
-This driver depends on:
 
-* `Adafruit CircuitPython <https://github.com/adafruit/circuitpython>`_
-* `Bus Device <https://github.com/adafruit/Adafruit_CircuitPython_BusDevice>`_
+This driver depends on the `Bus Device
+<https://github.com/adafruit/Adafruit_CircuitPython_BusDevice>`_ library.
+Please ensure is is also available on the CircuitPython filesystem.  This is
+easily achieved by downloading `a library and driver bundle
+<https://github.com/adafruit/Adafruit_CircuitPython_Bundle>`_.
 
-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 Example
-=============
+Usage Notes
+===========
+
+Of course, you must import the library to use it:
+
+.. code:: python
+
+    import adafruit_si7021
+
+This driver takes an instantiated and active I2C object (from the `nativeio` or
+the `bitbangio` library) as an argument to its 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 bitbangio import I2C
+    #from nativeio import I2C
+    from board import SCL, SDA
+
+    i2c = I2C(SCL, SDA)
+
+Once you have created the I2C interface object, you can use it to instantiate
+the sensor object:
+
+.. code:: python
+
+    sensor = adafruit_si7021.SI7021(i2c)
+
+
+And then you can start measuring the temperature and humidity:
+
+.. code:: python
+
+    print(sensor.temperature)
+    print(sensor.relative_humidity)
 
-TODO
 
 Contributing
 ============
@@ -35,6 +64,7 @@ Contributions are welcome! Please read our `Code of Conduct
 <https://github.com/adafruit/Adafruit_CircuitPython_si7021/blob/master/CODE_OF_CONDUCT.md>`_
 before contributing to help this project stay welcoming.
 
+
 API Reference
 =============
 

adafruit_si7021.py

@@ -1,6 +1,6 @@
 # The MIT License (MIT)
 #
-# Copyright (c) 2017 Radomir Dopieralski for Adafruit Industries
+# Copyright (c) 2017 Radomir Dopieralski for Adafruit Industries.
 #
 # Permission is hereby granted, free of charge, to any person obtaining a copy
 # of this software and associated documentation files (the "Software"), to deal
@@ -19,11 +19,133 @@
 # LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 # THE SOFTWARE.
+
 """
-`adafruit_si7021`
-====================================================
+``adafruit_si7021``
+===================
 
-TODO(description)
+This is a CircuitPython driver for the SI7021 temperature and humidity sensor.
 
-* Author(s): Radomir Dopieralski
 """
+
+
+from micropython import const
+import ustruct
+import sys
+
+from adafruit_bus_device.i2c_device import I2CDevice
+
+
+HUMIDITY = const(0xf5)
+TEMPERATURE = const(0xf3)
+_RESET = const(0xfe)
+_READ_USER1 = const(0xe7)
+_USER1_VAL = const(0x3a)
+
+
+def _crc(data):
+    crc = 0
+    for byte in data:
+        crc ^= byte
+        for i in range(8):
+            if crc & 0x80:
+                crc <<= 1
+                crc ^= 0x131
+            else:
+                crc <<= 1
+    return crc
+
+
+class SI7021:
+    """
+    A driver for the SI7021 temperature and humidity sensor.
+    """
+
+    def __init__(self, i2c, address=0x40):
+        self.i2c_device = I2CDevice(i2c, address)
+        self.init()
+        self._measurement = 0
+
+    def init(self):
+        self.reset()
+        # Make sure the USER1 settings are correct.
+        while True:
+            # While restarting, the sensor doesn't respond to reads or writes.
+            try:
+                data = bytearray([_READ_USER1])
+                with self.i2c_device as i2c:
+                    i2c.writeto(data, stop=False)
+                    i2c.readfrom_into(data)
+                value = data[0]
+            except OSError as e:
+                if e.args[0] not in ('I2C bus error', 19): # errno 19 ENODEV
+                    raise
+            else:
+                break
+        if value != _USER1_VAL:
+            raise RuntimeError("bad USER1 register (%x!=%x)" % (
+                value, _USER1_VAL))
+
+    def _command(self, command):
+        with self.i2c_device as i2c:
+            i2c.writeto(ustruct.pack('B', command))
+
+    def _data(self):
+        data = bytearray(3)
+        data[0] = 0xff
+        while True:
+            # While busy, the sensor doesn't respond to reads.
+            try:
+                with self.i2c_device as i2c:
+                    i2c.readfrom_into(data)
+            except OSError as e:
+                if e.args[0] not in ('I2C bus error', 19): # errno 19 ENODEV
+                    raise
+            else:
+                if data[0] != 0xff: # Check if read succeeded.
+                    break
+        value, checksum = ustruct.unpack('>HB', data)
+        if checksum != _crc(data[:2]):
+            raise ValueError("CRC mismatch")
+        return value
+
+    def reset(self):
+        self._command(_RESET)
+
+    @property
+    def relative_humidity(self):
+        """The measured relative humidity in percents."""
+        self.start_measurement(HUMIDITY)
+        value = self._data()
+        self._measurement = 0
+        return value * 125 / 65536 - 6
+
+    @property
+    def temperature(self):
+        """The measured temperature in degrees Celcius."""
+        self.start_measurement(TEMPERATURE)
+        value = self._data()
+        self._measurement = 0
+        return value * 175.72 / 65536 - 46.85
+
+    def start_measurement(self, what):
+        """
+        Starts a measurement.
+
+        Starts a measurement of either ``HUMIDITY`` or ``TEMPERATURE``
+        depending on the ``what`` argument. Returns immediately, and the
+        result of the measurement can be retrieved with the
+        ``temperature`` and ``relative_humidity`` properties. This way it
+        will take much less time.
+
+        This can be useful if you want to start the measurement, but don't
+        want the call to block until the measurement is ready -- for instance,
+        when you are doing other things at the same time.
+        """
+        if what not in (HUMIDITY, TEMPERATURE):
+            raise ValueError()
+        if not self._measurement:
+            self._command(what)
+        elif self._measurement != what:
+            raise RuntimeError("other measurement in progress")
+        self._measurement = what

api.rst

@@ -1,5 +1,3 @@
 
-.. If you created a package, create one automodule per module in the package.
-
 .. automodule:: adafruit_si7021
    :members:

conf.py

@@ -28,7 +28,7 @@
 # General information about the project.
 project = u'Adafruit SI7021 Library'
 copyright = u'2017 Radomir Dopieralski'
-author = u'Scott Shawcroft'
+author = u'Radomir Dopieralski'
 
 # The version info for the project you're documenting, acts as replacement for
 # |version| and |release|, also used in various other places throughout the
@@ -118,7 +118,7 @@
 #  author, documentclass [howto, manual, or own class]).
 latex_documents = [
     (master_doc, 'AdafruitSI7021Library.tex', u'Adafruit SI7021 Library Documentation',
-     u'Phiilip Moyer', 'manual'),
+     u'Radomir Dopieralski', 'manual'),
 ]
 
 # -- Options for manual page output ---------------------------------------