Display the PM 2.5 numbers on 1602 LCD via I2C Bus

pm25.py

#!/usr/bin/env python

import RPi.GPIO as GPIO
import serial
import pylcdlib
# pylcdlib from https://gist.github.com/gnawux/4f68b8e301b203489336

def readbe16(s, pos):
    return ( ord(s[pos])<<8) + ord(s[pos+1])

GPIO.setwarnings(False)
GPIO.setmode(GPIO.BCM)
GPIO.setup(17, GPIO.OUT)
GPIO.output(17, True)

# define bus address, port, and pins
display = pylcdlib.lcd(0x27,1, Rs=0, Rw=1, En=2, Backlight=3, D4=4, D5=5, D6=6, D7=7)
display.lcd_clear()

ser = serial.Serial("/dev/ttyAMA0")
ser.baudrate=9600
data = ser.read(32)
pos  = 0
while True:
    pos = data[pos:].index(chr(0x42))
    if ord(data[(pos+1)&31]) == 0x4d:
        print('found BM at %d' % (pos))
        ser.read(pos)
	break
    pos = pos + 1
    if pos > 31:
        print('frame format error')
        exit(1)

l1d=-1
l2d=-1

while True:
    data = ser.read(32)
    if data[0] != 'B' or data[1] != 'M':
        print('frame format error while reading data: %s, %s' % (data[:2], data))
        exit(1)
    length = readbe16(data, 2)
    if length != 28:
        print('length error : %d' % (length))
        exit(1)

    pm25std = readbe16(data, 6)
    pm25atm = readbe16(data, 12)

    if l1d != pm25std:
        l1d = pm25std
        display.lcd_puts('std: %d ug/m3' % l1d,1)
    if l2d != pm25atm:
        l2d = pm25atm
        display.lcd_puts('atm: %d ug/m3'% l2d,2)