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Projects/CO2_sensor.py

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+#!/usr/bin/env python
+########################################################################                                                                  
+# Calibration and read of the CO2 sensor MH-Z16
+# according to the datasheet : http://www.seeedstudio.com/wiki/images/c/ca/MH-Z16_CO2_datasheet_EN.pdf
+# output value directly in ppm
+# Doms made                                                              
+# History
+# ------------------------------------------------
+# Author     Date      		Comments
+# Doms      13 04 15 		Initial Authoring
+# 			                                                         
+'''
+## License
+
+The MIT License (MIT)
+
+GrovePi for the Raspberry Pi: an open source platform for connecting Grove Sensors to the Raspberry Pi.
+Copyright (C) 2017  Dexter 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
+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
+'''      
+#
+########################################################################
+import os
+import serial, time
+import smbus
+import math
+import RPi.GPIO as GPIO
+import struct
+import sys
+import datetime
+import grovepi
+import struct
+from grovepi import *
+
+#
+__author__ = 'Doms Genoud'
+
+#co2 sensor
+#use an external usb to serial adapter
+ser = serial.Serial('/dev/ttyUSB0',  9600, timeout = 1)	#Open the serial port at 9600 baud
+
+#To open the raspberry serial port
+#ser = serial.Serial('/dev/ttyAMA0',  9600, timeout = 1)	#Open the serial port at 9600 baud
+
+#init serial
+ser.flush()
+
+
+############# carbon dioxid CO2 #####################
+class CO2:
+#inspired from c code of http://www.seeedstudio.com/wiki/Grove_-_CO2_Sensor
+#Gas concentration= high level *256+low level
+    inp =[]
+    cmd_zero_sensor = "\xff\x87\x87\x00\x00\x00\x00\x00\xf2"
+    cmd_span_sensor = "\xff\x87\x87\x00\x00\x00\x00\x00\xf2"
+    cmd_get_sensor = "\xff\x01\x86\x00\x00\x00\x00\x00\x79"
+    def read(self):
+        try:
+          while True:
+                ser.write(CO2.cmd_get_sensor)
+                CO2.inp = ser.read(9)
+                high_level = struct.unpack('B',CO2.inp[2])[0]
+                low_level = struct.unpack('B',CO2.inp[3])[0]
+                temp_co2  =  struct.unpack('B',CO2.inp[4])[0] - 40
+
+                #output in ppm
+                conc = high_level*256+low_level
+                return [conc,temp_co2]
+
+        except IOError:
+                return [-1,-1]
+
+    def calibrateZero(self):
+        try:
+             ser.write(CO2.cmd_zero_sensor)
+             print("CO2 sensor zero calibrated")
+
+        except IOError:
+                print("CO2 sensor calibration error")
+
+    def calibrateSpan(self):
+        try:
+          while True:
+                #ser.write(CO2.cmd_zero_sensor)
+                print("CO2 sensor span calibrated")
+                break
+
+        except IOError:
+                print("CO2 sensor calibration error")
+
+########################################################################################################
+#############   MAIN
+########################################################################################################
+# following the specs of the sensor :
+# read the sensor, wait 3 minutes, set the zero, read the sensor
+c = CO2()
+
+while True:
+    try:
+        #CO2 sensor calib
+        print("wait 3 minutes to warm up CO2 sensor")
+        time.sleep(180)
+        print("Read before calibration-->",c.read())
+
+        print("calibrating...")
+        co2 = c.calibrateZero()
+        time.sleep(5)
+
+        print("Read after calibration-->",c.read())
+
+        print("DONE")
+        break
+
+    except IndexError:
+        print("Unable to read")
+    except KeyboardInterrupt:
+        print("Exiting")
+        sys.exit(0)