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Tank Adapter YDTA-01N to SK via Shipmodule Miniplex
#1
Hi all,
I have connected a YDTA-01N tankadapter on my tanksensor.
The divice seems to work OK, on the SD card it's writing the correct tank content (80% ~ 88 liter)

I connected the sensor to the N2K network.
The Shipmodule miniplex 3E N2K is getting the input from the tankmodule and from the logfile I can see for example:

$MXPGN,01F211,68BB,FF0000044C4EA800*60

The miniplex send this to UPD 10120

in the SK log I find:

Aug 17 11:54:21 2021-08-17T09:54:21.871Z canboatjs:fromPgn parsed pgn {"prio":0,"pgn":127505,"dst":255,"src":391,"input":["$MXPGN,01F211,68BB,FF0000044C4EA800*60"],"fields":{"Level":0,"Capacity":282370355.6,"Reserved1":"0"},"description":"Fluid Level","timestamp":"2021-08-17T09:54:21.871Z"}

So it look like the data is recieved in SK, however not the values like 80% and/or 88Liter


Now I have some questions:
1) How is propriatarie MXPGN recognized as N2000?
2) How is the data being read from the MXPGN sentence?


Thanks in advance
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#2
src could never get higher than 255 but that doesn't matter.

If you change the direction of the 8 data bytes (00 A8 4E 4C 04 00 00 00 FF)
00 -> instance 0 and type of tank fuel
A8 4E = 168 + 78*256 = 20136 (this must be multiplied with 0,004) -> 80,544 % level
4C 04 00 00 = 76+1024 = 1100 (multiplied with 0,1) -> 110 liter capacity

8BB
8 - length = 8
BB - src = 187

Are you shure you have the latest version of Signal K?
File /usr/lib/node_modules/signalk-server/node_modules/@canboat/canboatjs/lib/stringMsg.js changes the data byte direction. This fix was done on Mar 3, 2021.
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#3
Thanks E-sailing.
Got a simulair answer from Shipmodule support in meantime as well.
But always good to share some knowledge here.

I have SK version 1.40

I found the file it was timestamped 10/26/1985 09:15 so I asume the date is not valiid

The MXPGN code in my server is:
Code:
// $MXPGN,01F801,2801,C1308AC40C5DE343*19
exports.isMXPGN = startsWith('$MXPGN,')
exports.parseMXPGN = (input) => {
 const [ prefix, pgn, attr_word, data ] = input.split(',')

 const send_prio_len = (parseInt(attr_word.substr(0,2), 16).toString(2)).padStart(8, '0');
 const addr = (parseInt(attr_word.substr(2,2), 16));
 const send = parseInt(send_prio_len.substr(0,1), 2);
 const prio = parseInt(send_prio_len.substr(1,3), 2);
 const len = parseInt(send_prio_len.substr(4,4), 2);
 let src, dst;
 send ? dst = addr: src = addr;
 
 return buildMsg(
   buildCanId(0, parseInt(pgn, 16), 255, parseInt(src, 16)),
   'MXPGN',
   Buffer.from(rmChecksum(data), 'hex'),
   { coalesced: true, prefix },
 )
}

exports.encodeMXPGN = ({ prefix = '$MXPGN', pgn, prio, src, data }) => {
 if (src > 255) src = 255;
 if (!prio) prio = 3;
 if (!src) src = 255;
 const dataLength = hexByte(128 + (prio * 16) + (byteString(data, '').toUpperCase().length / 2)).toUpperCase()
   const attribWord = dataLength + hexByte(src).toUpperCase()

   var buff = Buffer.from(byteString(data, ''), 'Hex');
   for (var i = 0, j = buff.length - 1; i < j; ++i, --j) {
       var t = buff[j]

       buff[j] = buff[i]
       buff[i] = t
   }

   const sentence = [prefix, toPaddedHexString(pgn, 6), attribWord, buff.toString('Hex').toUpperCase()].join(',')
 return sentence + compute0183Checksum(sentence)
}

The only reference I found on MXPGN in gethub is this commit
https://github.com/canboat/canboatjs/com...df17fa3edf

As far as I see I have this commit installed.
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#4
If you have checked that you have the latest firmware on your shipmodul, you can try the original series (comment out two lines of the code).
Code:
  for (var i = 0, j = buff.length - 1; i < j; ++i, --j) {
      var t = buff[j]

      //buff[j] = buff[i]
      //buff[i] = t
  }
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#5
Hello,
I was having a look again in this issue tonight.
I do not understand the code.

I tried to comment-out the 2 buf lines, but it still does not give the correct result.
Actually I do not see difference in the output

Currently I have this in the log:

Code:
canboatjs:fromPgn parsed pgn {"prio":0,"pgn":127505,"dst":255,"src":391,"input":["$MXPGN,01F211,68BB,FF0000044C42B600*1A"],"fields":{"Level":0,"Capacity":305779814.8,"Reserved1":"0"},"description":"Fluid Level","timestamp":"2021-10-08T20:29:06.326Z"}



As you explained before the correct translation should be:
LEVEL: 42B6=17078x0.004= 68.312%
Capacity: 044C = 1100 = 110l lit

Is there a way I can add more detailed logging in this function in order to see what happens exactly?

Thanks for your help!
Reply
#6
Boat is on the dry so started to use the http://localhost:3000/admin/#/serverConfiguration/datafiddler to further investigate.

I added logging to stringMSG.js
I found exports.encodeMXPGN code mentioned above is not used.
Only exports.parseMXPGN is being used.

Also I tried to reverse the HEX words manualy so tested:
$MXPGN,01F211,68BB,004EA80000044CFF

Then I get at least some valid data:
Code:
"values": [
  {
    "path": "tanks.fuel.0.currentLevel",
    "value": 1.7234399999999999
  },
  {
    "path": "tanks.fuel.0.capacity",
    "value": 127533.056
  }
]

this looks better however values not yet correct.

==> which piece of code should reverse the HEX words?
==> where are the values calculated

to be continued.
Tips are welcome Tongue
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