Read an SDS011 Laser PM2.5 Sensor (Nova PM Sensor) with Python

sds011.py

#!/usr/bin/python
# -*- coding: UTF-8 -*-

import serial, time, struct
import httplib, urllib

ser = serial.Serial("/dev/ttyUSB0", baudrate=9600, stopbits=1, parity="N", timeout=2)

ser.flushInput()

KEY = 'your_thingspeak_write_key_here'

byte, lastbyte = "\x00", "\x00"

while True:
    lastbyte = byte
    byte = ser.read(size=1)
    
    # We got a valid packet header
    if lastbyte == "\xAA" and byte == "\xC0":
        sentence = ser.read(size=8) # Read 8 more bytes
        readings = struct.unpack('<hhxxcc',sentence) # Decode the packet - big endian, 2 shorts for pm2.5 and pm10, 2 reserved bytes, checksum, message tail
        
        pm_25 = readings[0]/10.0
        pm_10 = readings[1]/10.0
        # ignoring the checksum and message tail
        #pm_25 = (ord(sentence[0]) | ord(sentence[1])<<8) / 10.0
        #pm_10 = (ord(sentence[2]) | ord(sentence[3])<<8) / 10.0

        params = urllib.urlencode({'field1': pm_25,
                                   'field2': pm_10,
                                   'key':KEY})

        headers = {"Content-type": "application/x-www-form-urlencoded","Accept": "text/plain"}
        conn = httplib.HTTPConnection("api.thingspeak.com:80")                
        try:
            conn.request("POST", "/update", params, headers)
            response = conn.getresponse()
            data = response.read()
            conn.close()
        except Exception, e:
            print "error sending data to thingspeak"

        print "PM 2.5:",pm_25,"μg/m^3  PM 10:",pm_10,"μg/m^3"

I changed the byte order, as the first byte is the low byte, and the second the high byte.
I've also set the parameters as args for the serial.Serial instanciation.

Now added upload to thingspeak.