airco2ntrol.py

#!/usr/bin/env python3

# 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, struct

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]
	params = [0x00] + key

	#fp = open(sys.argv[1], "a+b", 0)
	fp = open("/dev/hidraw5", "a+b", 0)

	HIDIOCSFEATURE_9 = 0xC0094806
	set_report = struct.pack('B' * len(params), *params)
	fcntl.ioctl(fp, HIDIOCSFEATURE_9, set_report)

	values = {}
	stamp = now()

	while True:
		data = list(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 > 5:
					print ("CO2: %4i TMP: %3.1f" % (co2, tmp))
					stamp = now()