Allow NMEA 0183 file input/output

[PaddyB]

Thanks!

OK, getting somewhere

To strip the "$" off the front of the message and the "*" and chcksum from the end try a function like:-

Code:

var nmeaFull=msg.payload;

var nmeaStripped=nmeaFull.substring(1, nmeaFull.indexOf("*"));     //cut of the leading "$" and the bad checksum
msg.payload = nmeaStripped;
return msg;

Then to calculate a new checksum try a function like :-
Seems to work OK checking against http://www.hhhh.org/wiml/proj/nmeaxor.html

Code:

var nmea = msg.payload;
var checksum = 0; 

for(var i = 0; i < nmea.length; i++) { 
  checksum = checksum ^ nmea.charCodeAt(i); 
}
checksum = checksum.toString(16);    //convert to hex
nmea = '$' + nmea + '*' + checksum;  //make the full nmea sentence again

message = 'Full message =' + nmea + '\r\n' + 'Checksum = ' + checksum;
msg.payload = message;

return msg;

And the node-red code :-

Code:

[
    {
        "id": "a91ed12.b0a903",
        "type": "inject",
        "z": "d26052b1.ec666",
        "name": "",
        "topic": "",
        "payload": "$WIMDA,30,I,1.02,B,10.1,C,,C,,,,C,158.69,T,,M,3.89 ,N,2,M*37",
        "payloadType": "str",
        "repeat": "",
        "crontab": "",
        "once": false,
        "x": 150,
        "y": 720,
        "wires": [
            [
                "51fc3a3c.0d9534"
            ]
        ]
    },
    {
        "id": "51fc3a3c.0d9534",
        "type": "function",
        "z": "d26052b1.ec666",
        "name": "Strip front and back",
        "func": "var nmeaFull=msg.payload;\n\nvar nmeaStripped=nmeaFull.substring(1, nmeaFull.indexOf(\"*\"));     //cut of the leading \"$\" and the bad checksum\nmsg.payload = nmeaStripped;\nreturn msg;",
        "outputs": 1,
        "noerr": 0,
        "x": 340,
        "y": 720,
        "wires": [
            [
                "6a1166f7.40d818",
                "f4310649.47dad8"
            ]
        ]
    },
    {
        "id": "6a1166f7.40d818",
        "type": "debug",
        "z": "d26052b1.ec666",
        "name": "",
        "active": true,
        "console": "false",
        "complete": "false",
        "x": 570,
        "y": 600,
        "wires": []
    },
    {
        "id": "f4310649.47dad8",
        "type": "function",
        "z": "d26052b1.ec666",
        "name": "calc checksum",
        "func": "var nmea = msg.payload;\nvar checksum = 0; \n\nfor(var i = 0; i < nmea.length; i++) { \n  checksum = checksum ^ nmea.charCodeAt(i); \n}\nchecksum = checksum.toString(16);    //convert to hex\nnmea = '$' + nmea + '*' + checksum;  //make the full nmea sentence again\n\nmessage = 'Full message =' + nmea + '\\r\\n' + 'Checksum = ' + checksum;\nmsg.payload = message;\n\nreturn msg;",
        "outputs": 1,
        "noerr": 0,
        "x": 560,
        "y": 720,
        "wires": [
            [
                "6a1166f7.40d818"
            ]
        ]
    }
]

That was fun over morning coffee :  Sooooooo,,, how on earth do we get that into kplex!!! 

PS - I'm not a programmer but tend use CNP (cut and paste from google ) so - if any of you clever people want to point out beter ways of any tips or tricks please, please take a moment to spread the wisdom, these forums are a great place to learn, thanks

---

YAY!!! At last, so simple - Doh!   All that was missing was a line feed. This works from node red showing up in the nmea diagnostic. Note, I had to manually edit the kplex file to create a UDP input with no address:

Code:

[udp]
name=nodered
direction=in
optional=yes
port=10108

And the node-red function needs a carriage return/ line feed added like :-

msg.payload = msg.payload+"\r\n"
But it works at last!