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Sensirion_SGP40.py
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Sensirion_SGP40.py
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import smbus
import time
from Sensirion_SGP40_VOCAlgorithm import Sensirion_VOCAlgorithm
class Sensirion_SGP40:
SGP40_ICC_ADDR = 0x59
TEST_OK_H = 0xD4
TEST_OK_L = 0x00
CMD_HEATER_OFF_H = 0x36
CMD_HEATER_OFF_L = 0x15
CMD_MEASURE_TEST_H = 0x28
CMD_MEASURE_TEST_L = 0x0E
CMD_SOFT__reset_H = 0x00
CMD_SOFT__reset_L = 0x06
CMD_MEASURE_RAW_H = 0x26
CMD_MEASURE_RAW_L = 0x0F
DURATION_READ_RAW_VOC = 0.03
DURATION_WAIT_MEASURE_TEST = 0.25
OFFSET = 0x00
def __init__(self,bus = 1,relative_humidity = 50,temperature_c = 25):
""" Module init
:param bus:int Set to IICBus
:param relative_humidity:float Set to relative_humidity
:param temperature_c:float Set to temperature
"""
self.__i2cbus = smbus.SMBus(bus)
self.__my_vocalgorithm = Sensirion_VOCAlgorithm()
self.__i2c_addr = self.SGP40_ICC_ADDR
self.__temperature_c = temperature_c
self.__relative_humidity = relative_humidity
self.__rh = 0
self.__temc = 0
self.__rh_h = 0
self.__rh_l = 0
self.__temc_h = 0
self.__temc_l = 0
self.__temc__crc = 0
self.__rh__crc = 0
def set_envparams(self, relative_humidity,temperature_c):
""" Set temperature and humidity
:param relative_humidity:float Set to relative_humidity
:param temperature_c:float Set to temperature
"""
self.__temperature_c = temperature_c
self.__relative_humidity = relative_humidity
def begin(self,duration = 10):
""" start equipment
:param duration:int Set to Warm-up time
:return int equipment condition
: 0 succeed
: 1 failed
"""
self.__my_vocalgorithm.vocalgorithm_init()
timeOne = int(time.time())
while(int(time.time())-timeOne<duration):
self.get_voc_index()
return self.__measure_test()
def measure_raw(self):
""" Get raw data
: return int collect result
:-1 collect failed
:>0 the collection value
"""
self.__data_transform()
self.__i2cbus.write_i2c_block_data(self.__i2c_addr,self.CMD_MEASURE_RAW_H, [self.CMD_MEASURE_RAW_L,self.__rh_h,self.__rh_l,self.__rh__crc,self.__temc_h,self.__temc_l,self.__temc__crc])
time.sleep(self.DURATION_READ_RAW_VOC)
raw = self.__i2cbus.read_i2c_block_data(self.__i2c_addr,self.OFFSET,3)
if self.__check__crc(raw) == 0:
return raw[0]<<8 | raw[1]
else:
return -1
def get_voc_index(self):
""" Measure VOC index after humidity compensation
:note VOC index can indicate the quality of the air directly. The larger the value, the worse the air quality.
:note 0-100,no need to ventilate, purify
:note 100-200,no need to ventilate, purify
:note 200-400,ventilate, purify
:note 00-500,ventilate, purify intensely
:return int The VOC index measured, ranged from 0 to 500
"""
raw = self.measure_raw()
if raw<0:
return -1
else:
vocIndex = self.__my_vocalgorithm.vocalgorithm_process(raw)
return vocIndex
def __data_transform(self):
""" Convert environment parameters
"""
self.__rh = int(((self.__relative_humidity*65535)/100+0.5))
self.__temc = int(((self.__temperature_c+45)*(65535/175)+0.5))
self.__rh_h = int(self.__rh)>>8
self.__rh_l = int(self.__rh)&0xFF
self.__rh__crc = self.__crc(self.__rh_h,self.__rh_l)
self.__temc_h = int(self.__temc)>>8
self.__temc_l = int(self.__temc)&0xFF
self.__temc__crc = self.__crc(self.__temc_h,self.__temc_l)
def __measure_test(self):
""" Sensor self-test
:return int self-test condition
: 0 succeed
: 1 failed
"""
self.__i2cbus.write_i2c_block_data(self.__i2c_addr,self.CMD_MEASURE_TEST_H, [self.CMD_MEASURE_TEST_L])
time.sleep(self.DURATION_WAIT_MEASURE_TEST)
raw = self.__i2cbus.read_i2c_block_data(self.__i2c_addr,self.OFFSET,2)
if raw[0] == self.TEST_OK_H and raw[1] == self.TEST_OK_L :
return 0
else:
return 1
def __reset(self):
""" Sensor reset
"""
self.__i2cbus.write_i2c_block_data(self.__i2c_addr,self.CMD_SOFT__reset_H, [self.CMD_SOFT__reset_L])
def __heater_off(self):
""" spg40 Heater Off. Turn the hotplate off and stop the measurement. Subsequently, the sensor enters the idle mode.
"""
self.__i2cbus.write_i2c_block_data(self.__i2c_addr,self.CMD_HEATER_OFF_H, [self.CMD_HEATER_OFF_L])
def __check__crc(self, raw):
""" Verify the calibration value of the sensor
:param raw : list Parameter to check
:return int Check result
:-1 Check failed
: 0 Check succeed
"""
assert (len(raw) == 3)
if self.__crc(raw[0], raw[1]) != raw[2]:
return -1
return 0
def __crc(self,data_1,data_2):
""" CRC
:param data1 High 8 bits data
:param data2 LOW 8 bits data
:return int Calibration value
"""
crc = 0xff
list = [data_1,data_2]
for i in range(0,2):
crc = crc^list[i]
for bit in range(0,8):
if(crc&0x80):
crc = ((crc <<1)^0x31)
else:
crc = (crc<<1)
crc = crc&0xFF
return crc