Displaying non-standard NMEA data on plotter?

[jdc]

I have constructed a strain-gauge (0-1000kg to 1kg resolution and ~5kg accuracy), which potentially has multiple uses but which I first want to use to measure and display the anchor rode tension in real-time. It outputs NMEA style sentences (but I can make it send any format really). It sends serial data via Bluetooth SPP.

My question is what should I display the readings, or graph of readings vs time, on?

I'd ideally like it to be my chart plotter as that's the only built-in graphical device. Of course I could use my lap-top, but that's a palaver and I don't always take it on board (expensive and fragile and mission critical for work). However NMEA183 or 2000 sentences don't seem to support strain as a measurement, and neither do they allow an arbitrary sentence to be displayed. Any ideas? Represent it as fake 'engine temperature' or other quantity which is supported in NMEA?

FWIW the chart plotter is Raymarine A95.

 

[Minerva]

sounds interesting; what did you use for the strain gauge?

I’d imagine the most useful would be to track and record the dataset alongside apparent wind speed to plot them together

 

[jdc]

Strain gauge was from eBay, S TYPE Load Cell Scale Sensor Weighting Sensor With Cable High Accuracy PSD-S1 | eBay

Electronics, firmware, and the attachments to anchor rode home made.

I agree 100% that wind speed is the most useful data to correlate anchor rode tension with.

 

[Hoolie]

If you can select the data source on your plotter you could, for example, scale and address the output of the strain gauge as depth where 1kg = 1metre.

 

[ylop]

Can you use XDR? I think designed for any transducer - and you can label it and the units yourself.

 

[Hoolie]

That's possible but I think it's unlikely the existing A95 plotter will know what to do with it.

 

[jdc]

XDR is an excellent suggestion, and there's even a reserved unit of Newtons. Thank you for the suggestion, I think this is the 'accepted' way to do the strain sensor in NMEA.

But as Hoolie said, we'll have see if the Lighthouse S/W can recognise and display it!

 

[Martin_J]

You could use the XDR NMEA 0183 sentence as Ylop suggests..



And then use the YachtDevices NMEA2000 gateway to convert it to NMEA2000 which you're then more likely to find a PGN that's supported by your MFD.

Yacht Devices News: New firmware for NMEA 2000 gateways

 

[KompetentKrew]

B&G Vulcan allows some NMEA data to be displayed as a line chart:

 

[Martin_J]

Indeed, as do the Zeus range but I think they'll all need it as an NMEA2000 PGN and then as you show, display it as Pressure.

 

[Martin_J]

It's starting to sound like it might be easier to go direct to NMEA2000 with an Air Pressure PGN... saves all the NMEA0183 issues and will get you into creating an NMEA2000 circuit.

Hard to remember (it was so long ago that I built it) but I think I use a BMP180 on board with a raspberry Pi and canbus interface direct to NMEA2000.

I know the numbers will be different but at least it'll be future proofed..

 

[GHA]

get a raspberry pi & run openplotter. Perfect for this kind of stuff, will run without a monitor & save the data to a database. All set up, no programming required. It can take data from wifi or serial or convert it to nmea2k Welcome to OpenPlotter’s documentation! — OpenPlotter 3 documentation
Graphing really is an eyeopener >

 

[jdc]

I can certainly run a small computer aboard, for instance a raspberry-pi, but monitors are a pita so this question is about how, if poss, one could display as an integrated data source on the MFD.
For graphing we all have our preferences, mine being Matlab.

 

[GHA]

no need for a monitor, openplotter ships with realvnc installed so view from a tablet/laptop (or at home if you have internet on the boat), burn onto a sd card, reboot & wifi network is there waiting. though once set up most stuff is on a webpage. No real need for matplotlib, signalk app writes whatever you tell it to into influxdb & view in grafana, extremely powerful, must be pretty much world leader combination in ITO data these days. . All installable with a click of a mouse & sources known to play nice with each other. Signalk will write pretty much any data format to any output you have connected to the Pi, node-red built so if an app doesn't already exist a javascript function is simple to implement. Depends what the MFD will accept.

 

[rogerthebodger]

Is it possib

no need for a monitor, openplotter ships with realvnc installed so view from a tablet/laptop (or at home if you have internet on the boat), burn onto a sd card, reboot & wifi network is there waiting. though once set up most stuff is on a webpage. No real need for matplotlib, signalk app writes whatever you tell it to into influxdb & view in grafana, extremely powerful, must be pretty much world leader combination in ITO data these days. . All installable with a click of a mouse & sources known to play nice with each other. Signalk will write pretty much any data format to any output you have connected to the Pi, node-red built so if an app doesn't already exist a javascript function is simple to implement. Depends what the MFD will accept.

le to do the same monitoring using OpenCPN running on a Windows PC as I already have this setup which works very well including remode screen in my cockpit

 

[GHA]

Is it possib

le to do the same monitoring using OpenCPN running on a Windows PC as I already have this setup which works very well including remode screen in my cockpit

signalk will run on a PC which will do anything you can think of with data on a boat Run all the data though signalk which then sends it to opencpn.

 

[jdc]

Thanks to all for the suggestions, but not having the display and taking the data home on an SD card, or even via the cloud, for display later isn't what I want. My question was how to make it display on the MFD in real time, just like any other instrument data. Some fake Pressure (or engine temperature perhaps) can do it, and I can output CAN bus sentences, so that may be a solution.

BTW: I didn't say matplotlib (I do Python, and use matplotlib on many of our cloud servers, but that's not the point), I said Matlab (mind you, an individual licence costs ~£1k p.a. but we've already an unlimited licence at work).