Attempts to parse obd data from the zaicus-gps-tracker

obd_shim.py

# written for obd==0.4.1
# this will need a few modifications once 0.5.0 rolls out


import obd
from obd.utils import Response, unhex
from obd.protocols.protocol import Message


def parse(data):
    """ converts hex string into dict of OBDCommands and Responses """

    output = {}

    # removes and returns the first N characters of a string
    take = lambda s, n: (s[:n], s[n:])

    while data:
        pid, data = take(data, 2)
        pid = unhex(pid) # convert hex to integer

        # check that it's supported
        if not obd.commands.has_pid(1, pid):
            print("WARNING: unknown PID: %d" % pid)

            # WARNING: these are sensors that python-OBD can't decode yet
            # I'm skipping them manually for now
            if pid == 99:
                value, data = take(data, 2*2) # chop off the correct amount of data. Happens to be 2 bytes for PID 99
                continue
            # elif pid == xx:
                # consult the OBD-II PID tables if you run into more

            # if we've come this far, then there's nothing we can do to recover
            # from this (without knowing the size of the unknown command's return data).
            # Return all we have
            print("ERROR: cant parse PID %d, stopping..." % pid)
            return output

        command = obd.commands[1][pid] # lookup the corresponding command

        # consume the data
        value, data = take(data, (command.bytes * 2)) # x2 because 1 byte = 2 hex chars

        # parse the message
        response = Response(command) # make a new response object
        response.value, response.unit = command.decode(value) # decode the hex data
        output[command] = response

    return output


def query(obd_data, command):
    """ returns null responses when no data is available """
    if command in obd_data:
        return obd_data[command]
    else:
        print("No data for %s" % str(command))
        return Response() # empty response



if __name__ == "__main__":
    obd_data = parse("05830b5e0c95630d630f05111f0e4e074e630163145b63428c54")

    # example
    r = query(obd_data, obd.commands.RPM)
    print(r.value, r.unit)

    r = query(obd_data, obd.commands.COOLANT_TEMP)
    print(r.value, r.unit)