X-Git-Url: https://zdv2.bktei.com/gitweb/EVA-2020-02-2.git/blobdiff_plain/0cf10e5bb8354458b6eac7d04d4aa6235bedcf73..8ab4cd2dbb0d51048f01e92a712e61d5da4fa120:/library/enviroplus/gas.py?ds=inline

diff --git a/library/enviroplus/gas.py b/library/enviroplus/gas.py
new file mode 100644
index 0000000..4f61940
--- /dev/null
+++ b/library/enviroplus/gas.py
@@ -0,0 +1,88 @@
+"""Read the MICS6812 via an ads1015 ADC"""
+
+import atexit
+import ads1015
+import RPi.GPIO as GPIO
+
+MICS6812_HEATER_PIN = 24
+
+
+ads1015.I2C_ADDRESS_DEFAULT = ads1015.I2C_ADDRESS_ALTERNATE
+_is_setup = False
+
+
+class Mics6812Reading(object):
+    __slots__ = 'oxidising', 'reducing', 'nh3'
+
+    def __init__(self, ox, red, nh3):
+        self.oxidising = ox
+        self.reducing = red
+        self.nh3 = nh3
+
+    def __repr__(self):
+        return """Oxidising: {:05.02f}
+Reducing: {:05.02f}
+NH3: {:05.02f}
+""".format(self.oxidising, self.reducing, self.nh3)
+
+    __str__ = __repr__
+
+
+def setup():
+    global adc, _is_setup
+    if _is_setup:
+        return
+    _is_setup = True
+
+    adc = ads1015.ADS1015(i2c_addr=0x49)
+    adc.set_mode('single')
+    adc.set_programmable_gain(6.148)
+    adc.set_sample_rate(1600)
+
+    GPIO.setwarnings(False)
+    GPIO.setmode(GPIO.BCM)
+    GPIO.setup(MICS6812_HEATER_PIN, GPIO.OUT)
+    GPIO.output(MICS6812_HEATER_PIN, 1)
+    atexit.register(cleanup)
+
+
+def cleanup():
+    GPIO.output(MICS6812_HEATER_PIN, 0)
+
+
+def read_all():
+    """Return gas resistence for oxidising, reducing and NH3"""
+    setup()
+    ox = adc.get_voltage('in0/gnd')
+    red = adc.get_voltage('in1/gnd')
+    nh3 = adc.get_voltage('in2/gnd')
+
+    ox = (ox * 56000) / (3.3 - ox)
+    red = (red * 56000) / (3.3 - red)
+    nh3 = (nh3 * 56000) / (3.3 - nh3)
+
+    return Mics6812Reading(ox, red, nh3)
+
+
+def read_oxidising():
+    """Return gas resistance for oxidising gases.
+
+    Eg chlorine, nitrous oxide
+    """
+    setup()
+    return read_all().oxidising
+
+
+def read_reducing():
+    """Return gas resistance for reducing gases.
+
+    Eg hydrogen, carbon monoxide
+    """
+    setup()
+    return read_all().reducing
+
+
+def read_nh3():
+    """Return gas resistance for nh3/ammonia"""
+    setup()
+    return read_all().nh3