Initial commit

library/grow/gas.py

@@ -0,0 +1,140 @@
+"""Read the MICS6814 via an ads1015 ADC"""
+
+import time
+import atexit
+import ads1015
+import RPi.GPIO as GPIO
+
+MICS6814_HEATER_PIN = 24
+MICS6814_GAIN = 6.144
+
+ads1015.I2C_ADDRESS_DEFAULT = ads1015.I2C_ADDRESS_ALTERNATE
+_is_setup = False
+_adc_enabled = False
+_adc_gain = 6.148
+
+
+class Mics6814Reading(object):
+    __slots__ = 'oxidising', 'reducing', 'nh3', 'adc'
+
+    def __init__(self, ox, red, nh3, adc=None):
+        self.oxidising = ox
+        self.reducing = red
+        self.nh3 = nh3
+        self.adc = adc
+
+    def __repr__(self):
+        fmt = """Oxidising: {ox:05.02f} Ohms
+Reducing: {red:05.02f} Ohms
+NH3: {nh3:05.02f} Ohms"""
+        if self.adc is not None:
+            fmt += """
+ADC: {adc:05.02f} Volts
+"""
+        return fmt.format(
+            ox=self.oxidising,
+            red=self.reducing,
+            nh3=self.nh3,
+            adc=self.adc)
+
+    __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(MICS6814_GAIN)
+    adc.set_sample_rate(1600)
+
+    GPIO.setwarnings(False)
+    GPIO.setmode(GPIO.BCM)
+    GPIO.setup(MICS6814_HEATER_PIN, GPIO.OUT)
+    GPIO.output(MICS6814_HEATER_PIN, 1)
+    atexit.register(cleanup)
+
+
+def enable_adc(value=True):
+    """Enable reading from the additional ADC pin."""
+    global _adc_enabled
+    _adc_enabled = value
+
+
+def set_adc_gain(value):
+    """Set gain value for the additional ADC pin."""
+    global _adc_gain
+    _adc_gain = value
+
+
+def cleanup():
+    GPIO.output(MICS6814_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')
+
+    try:
+        ox = (ox * 56000) / (3.3 - ox)
+    except ZeroDivisionError:
+        ox = 0
+
+    try:
+        red = (red * 56000) / (3.3 - red)
+    except ZeroDivisionError:
+        red = 0
+
+    try:
+        nh3 = (nh3 * 56000) / (3.3 - nh3)
+    except ZeroDivisionError:
+        nh3 = 0
+
+    analog = None
+
+    if _adc_enabled:
+        if _adc_gain == MICS6814_GAIN:
+            analog = adc.get_voltage('ref/gnd')
+        else:
+            adc.set_programmable_gain(_adc_gain)
+            time.sleep(0.05)
+            analog = adc.get_voltage('ref/gnd')
+            adc.set_programmable_gain(MICS6814_GAIN)
+
+    return Mics6814Reading(ox, red, nh3, analog)
+
+
+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
+
+
+def read_adc():
+    """Return spare ADC channel value"""
+    setup()
+    return read_all().adc