# Voltcraft IR thermometer serial communication initialization
ser = serial.Serial()
ser.baudrate = 9600
ser.port = '/dev/ttyUSB0'

try:
    ser.open()
except:
    print "Thermometer is not connected, can't open /dev/ttyUSB0"
    sys.exit()

# ### INITIALIZATION  ###

# read line to overcome possible corrupted data
def detect_frame():
    print "> Detecting frame"
    while True:
        data = ser.read(1)
        #print data[0].encode('hex')
        if data[0].encode('hex') == "aa":
            print "> Frame Detected"
            break

detect_frame()

# ### UTILS  ###

# Voltcraft IR 2200-50D USB data stream decoding (should be compatible with other Voltcraft IR USB thermometers)
def temp_get():
    # read data from the serial port - 17 bytes
    data = ser.read(17)
    #for character in data:
    #    print character.encode('hex'),

    if data[16].encode('hex') != "aa":
        print "> Frame Lost"
        detect_frame()
        return temp

    return float (struct.unpack("<L", data[4]+""+data[3]+"\x00\x00")[0]) / 10

temp_start = temp_get()