airco2ntrold.py

#!/usr/bin/env python

# based on code by henryk ploetz
# https://hackaday.io/project/5301-reverse-engineering-a-low-cost-usb-co-monitor/log/17909-all-your-base-are-belong-to-us

import os, sys, fcntl, time
import paho.mqtt.publish as publish

def callback_function(error, result):
	if error:
		print(error)
		return

	print(result)

def decrypt(key,  data):
	cstate = [0x48,  0x74,  0x65,  0x6D,  0x70,  0x39,  0x39,  0x65]
	shuffle = [2, 4, 0, 7, 1, 6, 5, 3]

	phase1 = [0] * 8
	for i, o in enumerate(shuffle):
		phase1[o] = data[i]

	phase2 = [0] * 8
	for i in range(8):
		phase2[i] = phase1[i] ^ key[i]

	phase3 = [0] * 8
	for i in range(8):
		phase3[i] = ( (phase2[i] >> 3) | (phase2[ (i-1+8)%8 ] << 5) ) & 0xff

	ctmp = [0] * 8
	for i in range(8):
		ctmp[i] = ( (cstate[i] >> 4) | (cstate[i]<<4) ) & 0xff

	out = [0] * 8
	for i in range(8):
		out[i] = (0x100 + phase3[i] - ctmp[i]) & 0xff

	return out

def hd(d):
	return " ".join("%02X" % e for e in d)

def now():
	return int(time.time())

if __name__ == "__main__":
	"""main"""

	key = [0xc4, 0xc6, 0xc0, 0x92, 0x40, 0x23, 0xdc, 0x96]
	#fp = open(sys.argv[1], "a+b",  0)
	fp = open("/dev/hidraw0", "a+b",  0)
	HIDIOCSFEATURE_9 = 0xC0094806
	set_report = "\x00" + "".join(chr(e) for e in key)
	fcntl.ioctl(fp, HIDIOCSFEATURE_9, set_report)

	values = {}
	stamp = now()

	while True:
		data = list(ord(e) for e in fp.read(8))
		decrypted = decrypt(key, data)
		if decrypted[4] != 0x0d or (sum(decrypted[:3]) & 0xff) != decrypted[3]:
			print hd(data), " => ", hd(decrypted),  "Checksum error"
		else:
			op = decrypted[0]
			val = decrypted[1] << 8 | decrypted[2]
			values[op] = val

			if (0x50 in values) and (0x42 in values):
				co2 = values[0x50]
				tmp = (values[0x42]/16.0-273.15)

				# check if it's a sensible value
				# (i.e. within the measuring range plus some margin)
				if (co2 > 5000 or co2 < 0):
					co2 = -1

				if now() - stamp > 15:
					print "CO2: %4i TMP: %3.1f" % (co2, tmp)
					msgs = [{'topic':"lab/sensor/co2/co2", 'payload':co2, 'qos':0, 'retain':True},{'topic':"lab/sensor/co2/temperature", 'payload':tmp, 'qos':0, 'retain':True}]
					publish.multiple(msgs, hostname="fabserver.fablab.lan", client_id="co2")
					stamp = now()