MH-Z19B

py

#!/usr/bin/python
import serial, os, time, sys, struct

def crc8(a):
    crc=0x00
    count=1
    b=bytearray(a)
    while count<8:
        crc+=b[count]
        count=count+1
    #Truncate to 8 bit
    crc%=256
    #Invert number with xor
    crc=~crc&0xFF
    crc+=1
    return crc

ser = serial.Serial()
ser.port = "/dev/ttyUSB0"
ser.baudrate = 9600
ser.open()
ser.write(serial.to_bytes([0xFF,0x01,0x86,0x00,0x00,0x00,0x00,0x00,0x79]))
time.sleep(0.1)
s = ser.read(9)
print hex(int(s.encode('hex'), 16))
print hex(crc8(s))