zdv2.bktei.com Git - EVA-2020-02-2.git/blame_incremental

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Commit	Line	Data
	1	"""Read the MICS6814 via an ads1015 ADC"""
	2
	3	import time
	4	import atexit
	5	import ads1015
	6	import RPi.GPIO as GPIO
	7
	8	MICS6814_HEATER_PIN = 24
	9	MICS6814_GAIN = 6.144
	10
	11	ads1015.I2C_ADDRESS_DEFAULT = ads1015.I2C_ADDRESS_ALTERNATE
	12	_is_setup = False
	13	_adc_enabled = False
	14	_adc_gain = 6.148
	15
	16
	17	class Mics6814Reading(object):
	18	__slots__ = 'oxidising', 'reducing', 'nh3', 'adc'
	19
	20	def __init__(self, ox, red, nh3, adc=None):
	21	self.oxidising = ox
	22	self.reducing = red
	23	self.nh3 = nh3
	24	self.adc = adc
	25
	26	def __repr__(self):
	27	fmt = """Oxidising: {ox:05.02f} Ohms
	28	Reducing: {red:05.02f} Ohms
	29	NH3: {nh3:05.02f} Ohms"""
	30	if self.adc is not None:
	31	fmt += """
	32	ADC: {adc:05.02f} Volts
	33	"""
	34	return fmt.format(
	35	ox=self.oxidising,
	36	red=self.reducing,
	37	nh3=self.nh3,
	38	adc=self.adc)
	39
	40	__str__ = __repr__
	41
	42
	43	def setup():
	44	global adc, _is_setup
	45	if _is_setup:
	46	return
	47	_is_setup = True
	48
	49	adc = ads1015.ADS1015(i2c_addr=0x49)
	50	adc.set_mode('single')
	51	adc.set_programmable_gain(MICS6814_GAIN)
	52	adc.set_sample_rate(1600)
	53
	54	GPIO.setwarnings(False)
	55	GPIO.setmode(GPIO.BCM)
	56	GPIO.setup(MICS6814_HEATER_PIN, GPIO.OUT)
	57	GPIO.output(MICS6814_HEATER_PIN, 1)
	58	atexit.register(cleanup)
	59
	60
	61	def enable_adc(value=True):
	62	"""Enable reading from the additional ADC pin."""
	63	global _adc_enabled
	64	_adc_enabled = value
	65
	66
	67	def set_adc_gain(value):
	68	"""Set gain value for the additional ADC pin."""
	69	global _adc_gain
	70	_adc_gain = value
	71
	72
	73	def cleanup():
	74	GPIO.output(MICS6814_HEATER_PIN, 0)
	75
	76
	77	def read_all():
	78	"""Return gas resistence for oxidising, reducing and NH3"""
	79	setup()
	80	ox = adc.get_voltage('in0/gnd')
	81	red = adc.get_voltage('in1/gnd')
	82	nh3 = adc.get_voltage('in2/gnd')
	83
	84	try:
	85	ox = (ox * 56000) / (3.3 - ox)
	86	except ZeroDivisionError:
	87	ox = 0
	88
	89	try:
	90	red = (red * 56000) / (3.3 - red)
	91	except ZeroDivisionError:
	92	red = 0
	93
	94	try:
	95	nh3 = (nh3 * 56000) / (3.3 - nh3)
	96	except ZeroDivisionError:
	97	nh3 = 0
	98
	99	analog = None
	100
	101	if _adc_enabled:
	102	if _adc_gain == MICS6814_GAIN:
	103	analog = adc.get_voltage('ref/gnd')
	104	else:
	105	adc.set_programmable_gain(_adc_gain)
	106	time.sleep(0.05)
	107	analog = adc.get_voltage('ref/gnd')
	108	adc.set_programmable_gain(MICS6814_GAIN)
	109
	110	return Mics6814Reading(ox, red, nh3, analog)
	111
	112
	113	def read_oxidising():
	114	"""Return gas resistance for oxidising gases.
	115
	116	Eg chlorine, nitrous oxide
	117	"""
	118	setup()
	119	return read_all().oxidising
	120
	121
	122	def read_reducing():
	123	"""Return gas resistance for reducing gases.
	124
	125	Eg hydrogen, carbon monoxide
	126	"""
	127	setup()
	128	return read_all().reducing
	129
	130
	131	def read_nh3():
	132	"""Return gas resistance for nh3/ammonia"""
	133	setup()
	134	return read_all().nh3
	135
	136
	137	def read_adc():
	138	"""Return spare ADC channel value"""
	139	setup()
	140	return read_all().adc