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CO2Meter.py

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+"""
+Module for reading out CO2Meter USB devices
+via a hidraw device under Linux
+"""
+import sys
+import fcntl
+import threading
+import weakref
+
+CO2METER_CO2 = 0x50
+CO2METER_TEMP = 0x42
+CO2METER_HUM = 0x41
+HIDIOCSFEATURE_9 = 0xC0094806
+
+
+def _co2_worker(weak_self):
+    """
+    Worker thread that constantly reads from the usb device.
+    """
+    while True:
+        self = weak_self()
+        if self is None:
+            break
+        self._read_data()
+
+        if not self._running:
+            break
+        del self
+
+
+class CO2Meter:
+    _key = [0xc4, 0xc6, 0xc0, 0x92, 0x40, 0x23, 0xdc, 0x96]
+    _device = ""
+    _values = {}
+    _file = ""
+    _running = True
+    _callback = None
+
+    def __init__(self, device="/dev/hidraw0", callback=None):
+        self._device = device
+        self._callback = callback
+        self._file = open(device, "a+b", 0)
+
+        if sys.version_info >= (3,):
+            set_report = [0] + self._key
+            fcntl.ioctl(self._file, HIDIOCSFEATURE_9, bytearray(set_report))
+        else:
+            set_report_str = "\x00" + "".join(chr(e) for e in self._key)
+            fcntl.ioctl(self._file, HIDIOCSFEATURE_9, set_report_str)
+
+        thread = threading.Thread(target=_co2_worker, args=(weakref.ref(self),))
+        thread.daemon = True
+        thread.start()
+
+    def _read_data(self):
+        """
+        Function that reads from the device, decodes it, validates the checksum
+        and adds the data to the dict _values.
+        Additionally calls the _callback if set
+        """
+        try:
+            result = self._file.read(8)
+            if sys.version_info >= (3,):
+                data = list(result)
+            else:
+                data = list(ord(e) for e in result)
+
+            if data[4] != 0x0d:
+                """ newer devices don't encrypt the data, if byte 4!=0x0d assume encrypted data """
+                data = self._decrypt(data)
+                
+            if data[4] != 0x0d or (sum(data[:3]) & 0xff) != data[3]:
+                print(self._hd(data), "Checksum error")
+                return
+            
+            operation = data[0]
+            val = data[1] << 8 | data[2]
+            self._values[operation] = self._convert_value(operation, val)
+            if self._callback is not None:
+                if operation in {CO2METER_CO2, CO2METER_TEMP} or (operation == CO2METER_HUM and val != 0):
+                    self._callback(sensor=operation, value=val)
+        except:
+            self._running = False
+
+    def _decrypt(self, data):
+        """
+        The received data has some weak crypto that needs to be decoded first
+        """
+        cstate = [0x48, 0x74, 0x65, 0x6D, 0x70, 0x39, 0x39, 0x65]
+        shuffle = [2, 4, 0, 7, 1, 6, 5, 3]
+
+        phase1 = [0] * 8
+        for i, j in enumerate(shuffle):
+            phase1[j] = data[i]
+
+        phase2 = [0] * 8
+        for i in range(8):
+            phase2[i] = phase1[i] ^ self._key[i]
+
+        phase3 = [0] * 8
+        for i in range(8):
+            phase3[i] = ((phase2[i] >> 3) | (phase2[(i - 1 + 8) % 8] << 5)) & 0xff
+
+        ctmp = [0] * 8
+        for i in range(8):
+            ctmp[i] = ((cstate[i] >> 4) | (cstate[i] << 4)) & 0xff
+
+        out = [0] * 8
+        for i in range(8):
+            out[i] = (0x100 + phase3[i] - ctmp[i]) & 0xff
+
+        return out
+
+    @staticmethod
+    def _convert_value(sensor, value):
+        """ Apply Conversion of value dending on sensor type """
+        if sensor == CO2METER_TEMP:
+            return round(value / 16.0 - 273.1, 1)
+        if sensor == CO2METER_HUM:
+            return round(value / 100.0, 1)
+
+        return value
+
+    @staticmethod
+    def _hd(data):
+        """ Helper function for printing the raw data """
+        return " ".join("%02X" % e for e in data)
+
+    def get_co2(self):
+        """
+        read the co2 value from _values
+        :returns dict with value or empty
+        """
+        if not self._running:
+            raise IOError("worker thread couldn't read data")
+        result = {}
+        if CO2METER_CO2 in self._values:
+            result = {'co2': self._values[CO2METER_CO2]}
+
+        return result
+
+    def get_temperature(self):
+        """
+        reads the temperature from _values
+        :returns dict with value or empty
+        """
+        if not self._running:
+            raise IOError("worker thread couldn't read data")
+        result = {}
+        if CO2METER_TEMP in self._values:
+            result = {'temperature': self._values[CO2METER_TEMP]}
+
+        return result
+
+    def get_humidity(self):  # not implemented by all devices
+        """
+        reads the humidty from _values.
+        not all devices support this but might still return a value 0.
+        So values of 0 are discarded.
+        :returns dict with value or empty
+        """
+        if not self._running:
+            raise IOError("worker thread couldn't read data")
+        result = {}
+        if CO2METER_HUM in self._values and self._values[CO2METER_HUM] != 0:
+            result = {'humidity': self._values[CO2METER_HUM]}
+        return result
+
+    def get_data(self):
+        """
+        get all currently available values
+        :returns dict with value or empty
+        """
+        result = {}
+        result.update(self.get_co2())
+        result.update(self.get_temperature())
+        result.update(self.get_humidity())
+
+        return result

LICENSE

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+MIT License
+
+Copyright (c) 2017 Michael Heinemann
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+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.

README.md

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+# CO2Meter
+Python Module to use co2meters like the 'AirCO2ntrol Mini' from TFA Dostmann with USB ID 04d9:a052. There are also other modules using the same interface.
+
+This module supports Python 2.7 and 3.x.
+
+## Attribution
+Reverse Engineering of the protocol and initial code done by [Henryk Plötz](https://github.com/henryk). 
+
+Read all about it at [hackaday](https://hackaday.io/project/5301-reverse-engineering-a-low-cost-usb-co-monitor)
+
+Code derived from [this article](https://hackaday.io/project/5301-reverse-engineering-a-low-cost-usb-co-monitor/log/17909-all-your-base-are-belong-to-us)
+
+## Install
+
+With pip:
+```bash
+pip install git+https://github.com/heinemml/CO2Meter
+```
+
+Without pip:
+```bash
+python setup.py install
+```
+Remark: you don't need to install, you can also just copy the CO2Meter.py into your project.
+
+If you don't want to run your script as root make sure you have sufficient rights to access the device file.
+
+This udev rule can be used to set permissions.
+```
+ACTION=="remove", GOTO="co2mini_end"
+
+SUBSYSTEMS=="usb", KERNEL=="hidraw*", ATTRS{idVendor}=="04d9", ATTRS{idProduct}=="a052", GROUP="plugdev", MODE="0660", SYMLINK+="co2mini%n", GOTO="co2mini_end"
+
+LABEL="co2mini_end"
+```
+save it as `/etc/udev/rules.d/90-co2mini.rules` and add the script user to the group `plugdev`.
+
+This rules make the device also available as co2mini0 (increase trailing number for each additional device).
+
+## Usage
+```python
+from CO2Meter import *
+import time
+sensor = CO2Meter("/dev/hidraw0")
+while True:
+    time.sleep(2)
+    sensor.get_data()
+```
+
+The device writes out one value at a time. So we need to parse some data until we have co2 and temperature. Thus the get_data() method will initially return none or only one value (whichever comes first). 
+When you just need one measurement you should wait some seconds or iterate until you get a full reading. If you just need co2 a call to `get_co2` might speed things up.
+
+### Callback
+You can pass a callback to the constructor. It will be called when any of the values is updated. The parameters passed are `sensor` and `value`. `sensor` contains one of these constants:
+
+```python
+CO2METER_CO2 = 0x50
+CO2METER_TEMP = 0x42
+CO2METER_HUM = 0x41
+```
+
+
+### Error handling
+In Case the device can't be read anymore (e.g. it was unplugged) the worker thread will end in the background. Afterwards calls to any of the `get_*` functions will throw an `IOError`. You will need to handle any resetup, making sure that the device is there etc yourself.

example.py

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+#!/bin/env python
+import time
+from datetime import datetime
+
+from CO2Meter import *
+
+Meter = CO2Meter("/dev/hidraw0")
+while True:
+    measurement = Meter.get_data()
+    measurement.update({'timestamp': datetime.now()})
+    print(measurement)
+    time.sleep(5)

setup.py

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+from distutils.core import setup
+
+setup(name='CO2Meter',
+      version='2.3',
+      py_modules=['CO2Meter'],
+      url='https://github.com/heinemml/CO2Meter',
+      description='Library to access USB CO2Meters'
+      )