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Old 07-01-2016, 15:52   #1
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MWV sentences not working in dashboard

I have a Nasa NMEA wind sensor - Accessories: NASA Marine Instruments

Connected to opencpn I can see these sentences coming in the nmea debug window.

Code:
$WIMWV,27,R,00,N,A*0C
$YXXDR,C,22,C*49
$WIMWV,27,R,00,N,A*0C
$YXXDR,C,22,C*49
$WIMWV,27,R,00,N,A*0C
$YXXDR,C,22,C*49
In the dashboard, however, I can't get anything showing with any of the apparent wind or true wind instruments.

I must be doing something wrong, or is the data badly formatted?

Any ideas? VDR file attached
nasa_sensor.txt.pdf
TIA
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Old 07-01-2016, 16:43   #2
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Re: MWV sentences not working in dashboard

Think I *might* have found the issue - google came up with some example MWV sentences which worked when played back through the VDR ..
$WIMWV,200.0,R,11.0,N,A*11

Almost the same but the degrees and windspeed are to 1 decimal place.

The nasa is just integers without the trailing ".0"

That's annoying, but not the end of the world as it will be going through an arduino anyway which should be able to add those in on the way.
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Old 07-01-2016, 23:36   #3
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Re: MWV sentences not working in dashboard

conachair..
Very good. Many thanks for sharing the info about the Nasa wind sensor. I've that one on my list for a possible replacement. The prize is not bad. Now I know what to do if I go for that one.
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Old 08-01-2016, 00:55   #4
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Re: MWV sentences not working in dashboard

If anyone knows an easy way to add ".0" to the data I'm all ears

First thoughts are to take the sentences apart with the arduino tinygps++ custom object then sticking them together again after adding the ".0" where required.

Assuming that is the problem....

TIA
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Old 08-01-2016, 01:17   #5
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Re: MWV sentences not working in dashboard

Quote:
Originally Posted by conachair View Post
If anyone knows an easy way to add ".0" to the data I'm all ears

First thoughts are to take the sentences apart with the arduino tinygps++ custom object then sticking them together again after adding the ".0" where required.

Assuming that is the problem....

TIA
Maybe the NMEA converter plugin will do the job ??
Plugins for OpenCPN 4.1 | Official OpenCPN Homepage
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Old 08-01-2016, 03:07   #6
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Re: MWV sentences not working in dashboard

Quote:
Originally Posted by petter5 View Post
Maybe the NMEA converter plugin will do the job ??
Plugins for OpenCPN 4.1 | Official OpenCPN Homepage
Thanks, I hadn't thought of that one.

Close, it works "statically", if I use the repeat each second option with a fixed "old" sentence, the NMEA converter adds the extra ".0"'s automatically but doesn't seem to want to make a new MWV sentence from itself.
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Old 08-01-2016, 04:20   #7
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Re: MWV sentences not working in dashboard

Update - the data coming out of the nasa unit seems to have the wrong checksums. The decimal point was a red herring.

$WIMWV,27,R,00,N,A*0C should be...

$WIMWV,27,R,00,N,A*26


So looks like it definitely needs some processing before being useful.
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Old 08-01-2016, 05:03   #8
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Re: MWV sentences not working in dashboard

Quote:
Originally Posted by conachair View Post
If anyone knows an easy way to add ".0" to the data I'm all ears

First thoughts are to take the sentences apart with the arduino tinygps++ custom object then sticking them together again after adding the ".0" where required.

Assuming that is the problem....

TIA
Too bad It's not the problem. How old is your instrument (still under warranty)? It's a known issue with some nasa Clipper Wind Sytem, at least since 2007.

Your instrument is computing the checksum with the '*' included and it's wrong...
For example replace

$WIMWV,32,R,00,N,A*08
with
$WIMWV,32,R,00,N,A*22

and it works, 22 is 8 XOR '*' in hexa

BTW there's no wind speed in your capture, is it normal?

options setting 'Control Checksum' doesn't help, dashboard plugin always computes and uses checksum.
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Old 08-01-2016, 06:06   #9
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Re: MWV sentences not working in dashboard

Quote:
Originally Posted by did-g View Post
Too bad It's not the problem. How old is your instrument (still under warranty)? It's a known issue with some nasa Clipper Wind Sytem, at least since 2007.
Good few years old now, and in fairness is designed to work with their own display. I've a soft spot for nasa but they are cheap and cheerful so can't really complain much.


Quote:
Your instrument is computing the checksum with the '*' included and it's wrong...
For example replace

$WIMWV,32,R,00,N,A*08
with
$WIMWV,32,R,00,N,A*22

and it works, 22 is 8 XOR '*' in hexa
Well spotted!!!


Quote:
BTW there's no wind speed in your capture, is it normal?
Is when the sensor is sitting on the chart table, but definitely not outside


Quote:
options setting 'Control Checksum' doesn't help, dashboard plugin always computes and uses checksum.
Ah, I had a quick play with that and wondered why it wouldn't work turned off, thanks.

I wrote a quick arduino sketch with the correct checksum and all seems well with the dashboard when reading that data, so end of the day no great drama, the feed would go though an arduino anyway after the display so a few lines of code should make it well behaved again.


Quote:
/*

This example code is in the public domain.
*/
String NMEA0Deg="WIMWV,0,R,00,N,A";
String NMEA90Deg="WIMWV,90,R,05,N,A";
String NMEA180Deg="WIMWV,180,R,10,N,A";
String NMEA270Deg="WIMWV,270,R,15,N,A";
int CheckSum;


// the setup routine runs once when you press reset:
void setup() {
// initialize serial communication at 9600 bits per second:
Serial.begin(4800);

}

// the loop routine runs over and over again forever:
void loop() {

CheckSum=checkSum(NMEA0Deg);
String NMEA0DegOut="$" + NMEA0Deg + "*" + String(CheckSum, HEX);
Serial.println(NMEA0DegOut);

delay(1000);

CheckSum=checkSum(NMEA90Deg);
String NMEA90DegOut="$" + NMEA90Deg + "*" + String(CheckSum, HEX);
Serial.println(NMEA90DegOut);


delay(1000);

CheckSum=checkSum(NMEA180Deg);
String NMEA180DegOut="$" + NMEA180Deg + "*" + String(CheckSum, HEX);
Serial.println(NMEA180DegOut);


delay(1000);

CheckSum=checkSum(NMEA270Deg);
String NMEA270DegOut="$" + NMEA270Deg + "*" + String(CheckSum, HEX);
Serial.println(NMEA270DegOut);

delay(1000);

}


//-----------------
char checkSum(String theseChars) {
char check = 0;
// iterate over the string, XOR each byte with the total sum:
for (int c = 0; c < theseChars.length(); c++) {
check = char(check ^ theseChars.charAt(c));
}
// return the result
return check;
}
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Old 09-12-2017, 21:39   #10
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Smile Re: MWV sentences not working in dashboard

Hi, got a similar problem trying to feed an NMEA WMV from an Arduino into a NASA Meteoman. It was just not responding. I was trying to emulate the NASA wind sensor output (3wire) to see if the problem was in the Meteoman before climbing the mast.

In the end I found out I had to 'invert' the TX signal to get it to work.

Now I have to climb the mast and find why the wind sensor is not working.


//**************************************************

#include <SoftwareSerial.h> CR = 13 LF = 10
SoftwareSerial altSerial(8, 9, 1); // RX=8, TX=9, Invert=YES
// ***************
String sensordata1 ="$WIMWV,316,R,6.8,N,A*37";
String sensordata2 ="$YXXDR,C,26,C*4D";
String sensordata3 ="$WIMWV,247,R,14.1,N,A*08";
String sensordata4 ="$YXXDR,C,26,C*4D";
String sensordata5 ="$WIMWV,250,R,20.9,N,A*01";
String sensordata6 ="$YXXDR,C,26,C*4D";
String sensordata7 ="$WIMWV,282,R,24.7,N,A*04";
String sensordata8 ="$YXXDR,C,26,C*4D";
String sensordata9 ="$WIMWV,321,R,26.3,N,A*0A";
String sensordata10 ="$YXXDR,C,26,C*4D";


/* =============================================*/
void setup() {
/* ============================================ */

altSerial.begin(4800);
delay(1000);

while (!altSerial) {
; // wait for serial port to connect. Needed for native USB port only
}
}

/* ============================================ */
void loop(){
/* ============================================ */

while (altSerial.available() <= 0)
{
altSerial.println(sensordata1);
altSerial.println(sensordata2);
altSerial.println(sensordata3);
altSerial.println(sensordata4);
altSerial.println(sensordata5);
altSerial.println(sensordata6);
altSerial.println(sensordata7);
altSerial.println(sensordata8);
altSerial.println(sensordata9);
altSerial.println(sensordata10);
}

}
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Old 10-12-2017, 01:00   #11
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Re: MWV sentences not working in dashboard

Quote:
Originally Posted by mwau032 View Post

In the end I found out I had to 'invert' the TX signal to get it to work
That's because the arduino serial works on TTL which is different to rs232 NMEA 0183 which the nasa works on, there are other differences but inverted logic is one.
Better off with a rs232/ttl adaptor from eBay which will look after voltage differences as well.
Same listening to the NASA sensor, the voltages it uses might not work with the arduino software serial library straight onto a pin, might even blow the pin if you are unlucky.
Also, I have an older nasa wind sensor which sends the wrong nmea checksum, it works going into the meteoman but some other kit might not be so forgiving. I have a bit of arduino code somewhere to replace the checksum with a correct one , I'll post later if I can find it.(edit - found it, it's 2 posts up )
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Old 15-12-2017, 03:51   #12
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Re: MWV sentences not working in dashboard

Conachair:
Update - the data coming out of the nasa unit seems to have the wrong checksums. The decimal point was a red herring.

You took the $ and checksum *26 off when you calculated the checksum?

Bdcat recently reminded me of this!

Nmeaconverter should work.
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Old 15-12-2017, 05:19   #13
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Re: MWV sentences not working in dashboard

Quote:
Originally Posted by rgleason View Post
You took the $ and checksum *26 off when you calculated the checksum?

Bdcat recently reminded me of this!

Nmeaconverter should work.
Yep, checksum is correct coming out, assuming that's the right code I found stashed away in dropbox, looks OK.

Code:
// replace a wrong nmea checksum with a good one. 


 String nmeaGood;
 String nmeaBad;
 
// the setup routine runs once when you press reset:
void setup() {
  // initialize serial communication at 4800 bits per second:
  //serial1 is available on the mega board
  Serial.begin(4800);
  Serial1.begin(4800);
}

// the loop routine runs over and over again forever:
void loop() {
if(Serial1.available())
  {
    char c= Serial1.read();
    

    if( c=='\n')     // if char is new line then it's the end of a sentence so do something
    {
      nmeaBad=nmeaBad + '\n'; // put back the missing linefeed before parsing
      parseNmea(nmeaBad);
      nmeaBad="";    // empty the string
    }
    else             // else fill up the straing with nmea sentence
    nmeaBad+=c;
  }  
          
//End of loop
}




//-----------------
void parseNmea(String nmeaBad)
{
  //Serial.print(nmeaBad);
  nmeaGood=nmeaBad.substring(1, nmeaBad.indexOf("*"));     //cut of the leading "$" and the bad checksum

int  CheckSum=(checkSum(nmeaGood));                //create a good checksum
  nmeaGood="$"+nmeaGood+ "*" +  String(CheckSum, HEX);     // make the good nmea string

  Serial.println(nmeaGood);               
}


//---
char checkSum(String theseChars) {
  char check = 0;
  // iterate over the string, XOR each byte with the total sum:
  for (int c = 0; c < theseChars.length(); c++) {
    check = char(check ^ theseChars.charAt(c));
  } 
  // return the result
  return check;
}
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Old 16-12-2017, 11:21   #14
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Re: MWV sentences not working in dashboard

That's a nice piece of code. I suppose if nmeaconverter had the ability to calculate checksums and correct them, some expert users would advise that that is a very bad thing to do. The entire reason the checksum is there, is to get bad data kicked out.
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