takeTempAndHumidity/readTempAndHumidity.py at master · jimfinoc/takeTempAndHumidity · GitHub

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#!/usr/bin/python
import struct, array, time, io, fcntl

I2C_SLAVE=0x0703
HTU21D_ADDR = 0x40
CMD_READ_TEMP_HOLD = "\xE3"
CMD_READ_HUM_HOLD = "\xE5"
CMD_READ_TEMP_NOHOLD = "\xF3"
CMD_READ_HUM_NOHOLD = "\xF5"
CMD_WRITE_USER_REG = "\xE6"
CMD_READ_USER_REG = "\xE7"
CMD_SOFT_RESET= "\xFE"

class i2c(object):
    def __init__(self, device, bus):
        self.fr = io.open("/dev/i2c-"+str(bus), "rb", buffering=0)
        self.fw = io.open("/dev/i2c-"+str(bus), "wb", buffering=0)
        # set device address
        fcntl.ioctl(self.fr, I2C_SLAVE, device)
        fcntl.ioctl(self.fw, I2C_SLAVE, device)
    def write(self, bytes):
        self.fw.write(bytes)
    def read(self, bytes):
        return self.fr.read(bytes)
    def close(self):
        self.fw.close()
        self.fr.close()

class HTU21D(object):
    def __init__(self):
        self.dev = i2c(HTU21D_ADDR, 1) #HTU21D 0x40, bus 1
        self.dev.write(CMD_SOFT_RESET) #soft reset
        time.sleep(.1)
    def ctemp(self, sensorTemp):
        tSensorTemp = sensorTemp / 65536.0
        return -46.85 + (175.72 * tSensorTemp)
    def chumid(self, sensorHumid):
        tSensorHumid = sensorHumid / 65536.0
        return -6.0 + (125.0 * tSensorHumid)
    def crc8check(self, value):
        # Ported from Sparkfun Arduino HTU21D Library: https://github.com/sparkfun/HTU21D_Breakout
        remainder = ( ( value[0] << 8 ) + value[1] ) << 8
        remainder |= value[2]
        # POLYNOMIAL = 0x0131 = x^8 + x^5 + x^4 + 1
        # divsor = 0x988000 is the 0x0131 polynomial shifted to farthest left of three bytes
        divsor = 0x988000
        for i in range(0, 16):
            if( remainder & 1 << (23 - i) ):
                remainder ^= divsor
                divsor = divsor >> 1
            if remainder == 0:
                return True
            else:
                return False
    def read_temperature(self):
        self.dev.write(CMD_READ_TEMP_HOLD) #measure temp
        time.sleep(.2)
        data = self.dev.read(3)
#        print "temp data"
#        print data
        buf = array.array('B', data)
#        print "temp buf"
#        print data
        if self.crc8check(buf):
            temp = (buf[0] << 8 | buf [1]) & 0xFFFC
            return self.ctemp(temp)
        else:
            return -255
    def read_humidity(self):
        self.dev.write(CMD_READ_HUM_NOHOLD) #measure humidity
        time.sleep(.1)
        data = self.dev.read(3)
#        print "humidity data"
#        print data
        buf = array.array('B', data)
        if self.crc8check(buf):
            humid = (buf[0] << 8 | buf [1]) & 0xFFFC
            return self.chumid(humid)
        else:
            return -255

if __name__ == "__main__":
    obj = HTU21D()
    print "Temp:", obj.read_temperature(), "C"
    print "Humid:", obj.read_humidity(), "% rH"