library/envirophatplus/gas.py

   1 """Read the MICS6812 via an ads1015 ADC"""
   2
   3 import ads1015
   4 import RPi.GPIO as GPIO
   5
   6 MICS6812_EN_PIN = 24
   7
   8
   9 ads1015.I2C_ADDRESS_DEFAULT = ads1015.I2C_ADDRESS_ALTERNATE
  10 _is_setup = False
  11
  12
  13 class Mics6812Reading(object):
  14     __slots__ = 'oxidising', 'reducing', 'nh3'
  15
  16     def __init__(self, ox, red, nh3):
  17         self.oxidising = ox
  18         self.reducing = red
  19         self.nh3 = nh3
  20
  21     def __repr__(self):
  22         return """Oxidising: {:05.02f}
  23 Reducing: {:05.02f}
  24 NH3: {:05.02f}
  25 """.format(self.oxidising, self.reducing, self.nh3)
  26
  27     __str__ = __repr__
  28
  29
  30 def setup():
  31     global adc, _is_setup
  32     if _is_setup:
  33         return
  34     _is_setup = True
  35
  36     adc = ads1015.ADS1015(i2c_addr=0x49)
  37     adc.set_mode('single')
  38     adc.set_programmable_gain(6.148)
  39     adc.set_sample_rate(1600)
  40
  41     GPIO.setwarnings(False)
  42     GPIO.setmode(GPIO.BCM)
  43     GPIO.setup(MICS6812_EN_PIN, GPIO.OUT)
  44     GPIO.output(MICS6812_EN_PIN, 1)
  45
  46
  47 def read_all():
  48     ox = adc.get_voltage('in0/gnd')
  49     red = adc.get_voltage('in1/gnd')
  50     nh3 = adc.get_voltage('in2/gnd')
  51
  52     ox = (ox * 56000) / (3.3 - ox)
  53     red = (red * 56000) / (3.3 - red)
  54     nh3 = (nh3 * 56000) / (3.3 - nh3)
  55
  56     return Mics6812Reading(ox, red, nh3)
  57
  58
  59 def read_oxidising():
  60     """Return gas resistance for oxidising gases.
  61
  62     Eg chlorine, nitrous oxide
  63     """
  64     setup()
  65     return read_all().oxidising
  66
  67
  68 def read_reducing():
  69     """Return gas resistance for reducing gases.
  70
  71     Eg hydrogen, carbon monoxide
  72     """
  73     setup()
  74     return read_all().reducing
  75
  76
  77 def read_nh3():
  78     """Return gas resistance for nh3/ammonia"""
  79     setup()
  80     return read_all().nh3