Munin plugin based on https://github.com/KristofRobot/openhab-config/blob/master/co2mon/co2mon.py

co2mini

#!/usr/bin/env python2

import sys, fcntl, time

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)

if __name__ == "__main__":
    if len(sys.argv) == 2 and sys.argv[1] == "config":
        print("co2mini.label CO2 in ppm")
        print("graph_vlabel ppm")
        print("graph_title CO2-Niveau")
        print("graph_category wohnung")
        sys.exit(0)
    fp = open("/dev/co2mini0", "a+b",  0)
    
    HIDIOCSFEATURE_9 = 0xC0094806
    # Key retrieved from /dev/random, guaranteed to be random ;)
    key = [0xc4, 0xc6, 0xc0, 0x92, 0x40, 0x23, 0xdc, 0x96]
    set_report = "\x00" + "".join(chr(e) for e in key)
    fcntl.ioctl(fp, HIDIOCSFEATURE_9, set_report)
    
    values = {}
    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
            
            ## From http://co2meters.com/Documentation/AppNotes/AN146-RAD-0401-serial-communication.pdf
            if 0x50 in values:
                print("co2mini.value %i" % values[0x50])
                sys.exit(0)