The Navigatrix has been updated. The new website can be found at navigatrix.net.




Post new topic Reply to topic  [ 14 posts ] 
Author Message
 Post subject: NMEA For Dummies ? (Moe, I hope you're out there)

Joined: 03 Jul 2013, 08:30
Posts: 59
First off, glad I found Navigatrix. Been in the process of trying to set up a super low power nav system at a minimal price. Linux as an OS was a given, but Navigatrix has all the bells and whistles in a fairly light weight distro. (Love the option of spinning down the HD underway. Amps is Amps)

As I said, this is a low budget project, as I am trying for a full refit of my little pocket cruiser for a fall departure to points south and beyond. Always use paper charts, try to take a noon shoot to stay in practice, etc. That being said, while I am not big on Chart Plotters GPS is a wonderful thing, and OpenCPN is great for passage planning and those times where I end up somewhere other than where I expected to be. Those kap files don't take up much space on the boat. Anyway, the old Solitaire needs all new electronics. Depth sounder, VHF, GPS minimum. Radar has never been one of my priorities, expensive and big power draw. AIS on the other hand sounds pretty spiffy... Easy to stay out of the big boys way. (Gross tonnage rule and all) Need a way to wrap all this up, and display at least a minimum of realtime info in the cockpit.

Ran across the Std Horizon GX2150 which seems to have the ability to kill several birds with one stone. VHF / AIS receiver. Waterproof display. When tied to GPS (barewire RS232) will display AIS contacts and basic GPS info (lat / lon sog / cog) RS232 output for AIS and DSC info.

Problem is, NMEA (like the jitterbug) is so simple, it's plumb evaded me. This is what I would like to do, and how I would like to do it. Now its up to you to tell me why I can't.....

Netbook
Assus eee PC 1015PE
OS Navigatrix (Duh!)
Very low power consumption. Cheap, readily avail on Ebay Craigslist etc.
3 USB ports

GPS Receiver
USGS Br353
RS232 input/output
5V dc

VHF / AIS
Std Horizon GX2150
NMEA interface RS232 Hardwire
GPS in
AIS/DSC out

Additional Equipment
5V power supply (Br353 power)
Terminal Block
2 - RS232 (bare wire) to USB cable (FTDI chip)

Pictures worth a thousand words. Click to enlarge
Image
Point of connecting puck direct to gx2150 is to avoid having to run netbook all the time in order to rcv basic gps and ais info. Saves power and wear. Also will function if Netbook emits "Magic Smoke" Still tracking on paper charts anyway. Should (I hope) be able to fire up the Netbook to pump into OpenCPN etc when I want/need to.

What simple item am I missing? Seems way too easy

TIA
David
(aka Cap' Couillon)


Top
   
 
 Post subject: Re: NMEA For Dummies ? (Moe, I hope you're out there)

Joined: 04 Nov 2010, 20:51
Posts: 1062
Got some NMEA for me?

My father's advice was, "...if you don't know what you're doing; don't do it."

Some how in my mind that got translated into a decision process, "eh, what's the worst that could happen?"

The follow up is that sometimes education is expensive. If that's what you want to do...what's the worst could happen?

Then pragmatically, is the expense worth the return?

To give you an idea; fire up Navigatrix on your laptop. Unplug it and run it on batteries. Go to the terminal (Menu> Accessories> Terminal Emulator, or <ctrl><alt><t>keys simultaneously). Enter: sudo powertop.

It will look something like the screenshot below. Notice the red arrow. This is the power consumption of a netbook with Navigatrix running at idle.
Attachment:
Workspace_002.png
Workspace_002.png [ 177.74 KiB | Viewed 24414 times ]
If I blank the screen it putters along at 6.6something watts. If I plug in a gps hockey puck and fiddle it's around 10 watts.
Attachment:
powertop.png
powertop.png [ 76.4 KiB | Viewed 24412 times ]
Disk grinding will shove it to 12 and a half....about an amp. If I turn off the WiFi it obviously drops.

The computer power draw is only part of it. Unfortunately, powertop doesn't calculate power draw when the machine is plugged in. It also doesn't tell you the loss going from ship's mains to power plug in the side. You're going to loose something because there is no free lunch; that's the second law of thermodynamics...which, incidentally, is not #2 for me, but still big on my list.

The boat's computer is hardwired and takes a bit over 1 amp..with the monitor off (on, add 1.5amp). This little netbook is powered via a 12-19volt dc-dc converter. All told it is about 1.5 amps. The firstmate runs her machine through an inverter-wall wart (DC-AC/AC-DC) and as I recall was around 2 amps. The biggest problem is I'm not set up to measure with enough accuracy as the ampmeter measure the whole system.

I've not isolated the vhf radio to know its current draw; it's on so little.

I ran a RS232 gps split it with one branch going to a USB/serial converter. This went into the computer USB. The other branch repeated on the sailing instruments in the cockpit.

It worked if either the sailing instrument or the computer were off. I've never yoked the computer with the sailing instruments...couldn't be bothered.

One guy (an EE) told me that unshielded terminal blocks can allow the injection of noise that can interrupt the data stream. It might be the case, but I thought, "what's the worst that could happen?"


Top
   
 
 Post subject: Re: NMEA For Dummies ? (Moe, I hope you're out there)

Joined: 03 Jul 2013, 08:30
Posts: 59
Interesting screenshot..... :?

Lessee PowerTop running Looks like a package install running in the terminal, and some sort of a sourceforge download in Firefox?

Looking forward for the "Text to Follow"


Top
   
 
 Post subject: Re: NMEA For Dummies ? (Moe, I hope you're out there)

Joined: 04 Nov 2010, 20:51
Posts: 1062
That would be powertop in the terminal. Precompilation configuring of wxPython2.9something just downloaded from Sourceforge..and the Package Manager which just fetched Shutter so I could draw a nice red arrow rather than staggered squiggle.


Top
   
 
 Post subject: Re: NMEA For Dummies ? (Moe, I hope you're out there)

Joined: 03 Jul 2013, 08:30
Posts: 59
You're right Moe....... What's the worst that could happen? Been over thinking the whole thing. (Nice arrow by the way)
Have gotten really wrapped up in the cost thing. First cause I gots not a lot of money. Second cause I am frugal (cheap, tightwad, etc) Just hate to pay 4 times the reasonable price for a piece of equipment just because it says "marine" on it. Liked your thread on AIS by the way. Know some guys are playing round with cheap radio dongles as well. Spent a long time cruising a bigger boat, and found out just how much I didn't need over the years. Energy is expensive.... ergo no AC (open a hatch) no reefer (spend money on good beer you can drink at bilge temp) no 1st Mate (lots of different savings there). Even so, that pesky 2nd law (Can't win, can't break even. can't even get out of the game) rears it's head all over the place. Planned to take your same route with a 12V to 19V buck converter to power the netbook. Been wondering lately what the actual required voltage is for the power supply. 5V? 3V? ... 19V seems such an odd number, can't help but think that is needed to charge batteries. Then again would be power savings going 12V - 9V be more than 12V - 19V ????? Some guys spend all their time trying to get another 1/2 knot out of the boat... me, I am trying to save 1/2 amp. I got plenty of time (I hope). Once raced another single hander from Colon to Isla Mujeres. First one there had to buy the beer. Thought I had Roland beat as I laid up in Providencia for a couple days. Turned out Roland cheated... Was making such good way, he sailed right by Isla Mujeres and straight on to the Azores. I fooled him though, I drank all the beer I bought for him.

Thanks for your input, have enjoyed reading your forum posts. Will (eventually) post back here the results of the grand experiment. Looking forward to playing with Navigatrix and have already made copies for friends.

David


Top
   
 
 Post subject: Re: NMEA For Dummies ? (Moe, I hope you're out there)

Joined: 04 Nov 2010, 20:51
Posts: 1062
It's a question of personal preference. I would rather see the looping squiggle of my wandering track than a constantly updated numerical lat/lon.

The First mate transcribes lat/lon into a paper log every 4 hours for two reasons;
    it impresses the rare customs official who ask to see it
    if everything craps out we have something to reconstruct on the paper...otherwise we don't bother.

A few days ago I was having a beer with another sailor who preparing for a circumnavigation of Australia. He was just astounded that his old VHF can be modified to receive AIS. I think he went home that night and converted it.

Good luck with your preparations.


Top
   
 
 Post subject: Re: NMEA For Dummies ? (Moe, I hope you're out there)

Joined: 03 Jul 2013, 08:30
Posts: 59
Tks Moe.... Myself, post position to log book every hour. Post position to paper chart every 4 hour. Just a born-again Luddite I guess. If it can go wrong, it will.... Just a matter or when (Murphy was an optimist). But the GPS is way more accurate than my sextant has ever been.

Fair Winds
David


Top
   
 
 Post subject: Re: NMEA For Dummies ? (Moe, I hope you're out there)

Joined: 04 Nov 2010, 20:51
Posts: 1062
My good sights are within 15nm of the GPS reading. That's nautical miles not nanometers.

The gps *supposedly* is with 30 meters. I've heard 10meters 95% of the time; within 2 meters 50% of the time.

I don't know if the sources I made up that data from knew what they were talking about; or that even remember correctly. I do know that my GPS position matches my amazement to the Google Earth satellite images.

Take a look at (which is identical to the paper)this chart from a 'friend'...
Attachment:
e-chart-1.jpg
e-chart-1.jpg [ 117.21 KiB | Viewed 24376 times ]
Compared to...
Attachment:
e-chart-google-overlay.jpg
e-chart-google-overlay.jpg [ 178.5 KiB | Viewed 24376 times ]
The Red Arrow points to the kink in the black exit path...where 'they' went aground.


Top
   
 
 Post subject: Re: NMEA For Dummies ? (Moe, I hope you're out there)

Joined: 21 May 2013, 14:53
Posts: 93
Hello!

There is nothing wrong with the accuracy of the GPS.
The problem is with the charts. It is very usual to have the longitude out by a mile or so. This comes from the difficulty of obtaining accurate time signals for chart making. (old charts)
It is always useful to take bearings from fixed points, to determine the offset of every single chart in your chartplotter or charting software. Some softwares can correct for this, but be very carfeul when you move across different charts.
This error does not compromise the accuracy of your navigation, as long as you aware of the offset.
I frequently use my radar to determine the degree of error.
Almost all charts have this problem, in Chile, and most of the Polynesian islands..


Top
   
 
 Post subject: Re: NMEA For Dummies ? (Moe, I hope you're out there)

Joined: 07 Jul 2013, 12:24
Posts: 1
David,
I just saw your post David and this CAN be done. I have a very similar setup. I use a small Garmin GPSMap 441 at the helm. It is a small chart plotter and few years old now. I think they went for about $400, 8 years ago. I also replaced my VHF radio a while back with the Standard Horizon Matrix GS2150 that has AIS and VHF on it. It was also fairly inexpensive at the time as well (bought about 2 years ago on sale at West Marine (under $300 if I recall).

Fairly recently I connected the Garmin GPS Chartplotter to the Radio so that it could use DSC for emergencies and also so that the AIS would know where I am. Then I also connected the AIS high speed output from the radio to both the Chartplotter input as well as to an old outdated Dell laptop running Navigatrix. That part takes a little bit of explaining. I purchased a USB to Serial cable at a local electronic Component store (EPS in Webster TX) for about $10. Similar functionality for "Marine" use are about $75-$100 on the low side. I just bought 4 of these things at a total of $40 and figured I would have some spares.
I cut an old RS-232 cable in half and stripped the wires to find the right pins to connect it so. Pin 2 is receive and pin 3 is transmit. (Here is a pin out diagram) - Image).
I used a continuity tester and a paper clip stuck in each hole of the RS232 cable to find the right wires. In my case I didn't have to load any drivers or anything to use the USB/Serial cable. Navigatrix recognized it as a com port with no issues.

I did have to play around a little bit with which of the outputs from the GS2150 I needed to use. IF I recall there is a slow and high speed. I used the high speed output wire from the GS2150 AIS/VHF and connected it to PIN 2 of that RS232 cable. Then plugged the RS232 cable into the USB adapter (I had to do this because the laptop I had did not have a serial cable on it)

In OpenCPN, Under settings, Connections, I clicked on Add Connection and chose type "Serial" and then the data port on my laptop was /dev/ttyUSB1. I was able to choose it from a drop down. I set the Baudrate to 38400. If that doesn't work, try the other /dev/TTYUSB dataports in your drop down list.

When you are working on setting it up, it is best to go into settings, connections, then put a check box next to "Show NMEA Debug Window" That will open a window and you will start to see sentences scrolling by when you get the buad rate and port right.

I hope this helps. Once setup, this worked GREAT. I can see all of the other boats in the area, you can also filter out boats that are not under way and set parameters around how to handle possible collision scenarios.


Top
   
 
 Post subject: Re: NMEA For Dummies ?

Joined: 03 Jul 2013, 08:30
Posts: 59
Thanks so much for the info... Nice not to have to re-invent the wheel as it were. Have some standing rig issues that are absorbing more cash than I want (ain't it always that way) and am going to have to put off departure for probably a month. The 2150 will have to wait for a bit, but I have managed to come up with a Garmin 126 (elderly but works good) to intigrate with OpenCpn. No chartplotter on the GPS which suits me fine as I use paper charts religiously off shore. OpenCpn is used primarily for passage planning and as a cross check on current position. With your diagrams and explanation, as well as a little planning, it looks simple enough to set up to add the 2150 into the system at a later date. Hope to have it before I go, but if not, maybe next port of call. Will probably add a usb "hocky puck" gps rcvr as a backup. At $30.00 or so its cheap insurance. My sextant work is a bit rusty.

Busy right now stuffing Nx on the new (to me) Dell laptop that will serve as the boat computer and as soon as I get all my files transfered I can start playing. Will be fun to be doing something that does not require skinned knuckles and bilge bottoms.

Thanks again, will post results for all.

David
"I'll be leaving soon" (really)


Top
   
 
 Post subject: Re: NMEA For Dummies ? (Moe, I hope you're out there)

Joined: 04 Nov 2010, 20:51
Posts: 1062
Quote:
In OpenCPN, Under settings, Connections, I clicked on Add Connection and chose type "Serial" and then the data port on my laptop was /dev/ttyUSB1. I was able to choose it from a drop down. I set the Baudrate to 38400. If that doesn't work, try the other /dev/TTYUSB dataports in your drop down list.
One of my favourite things running in the background is gpsd. It is a gps daemon that looks for gps data, regardless of location or order in which the device is attached. When it finds it, it will magically negotiate all the nitty gritty with most any gps you attach to the computer. It also handles ais data. After it transparently handles the input, it shares the data with any application that calls for it. Opencpn demuxes, unravels, the datastream from the gpsd.

Setting your gps/ais data ports to something other than gpsd, without turning off the gpsd (why would you do this?), will lead to a bloody conflict that no one wins. Left alone there is no port guessing; no protocol guessing; no baud rate guessing; no blood.

AIS through the soundcard is a different matter.


Top
   
 
 Post subject: Re: NMEA For Dummies ? (Moe, I hope you're out there)

Joined: 04 Jan 2014, 03:19
Posts: 34
I am new to Navigatrix but I have OpenCPN on a Windows computer at the moment connected to my Standard Horizon GX2100.

I have a GPS puck powered by a 12v to 5v converter sending it position. I wanted a redundant system as I have a back up battery for the VHF, so if the water level had reached the main batteries I could still send a DSC Mayday.

This goes in the input NMEA of the GX2100 Blue wire. There are two outputs. The Brown one ins NMEA HS at 38400 baud and that caries the NMEA AIS data VDM. The other one Grey, according to the manual, only outputs DSC sentences at the standard 4800 baud NMEA DSC and DSE.

See page 12 of the manual.

So you need two serial ports on your computer to get both of these, but also a separate GPS input (sorry perhaps this has already been covered above). In my case I use a cheap USB GPS dongle for that. My various GPS devices tend to agree with about 3m.

I don't have the Grey one connected yet but, but will when I have fitted a computer running Navigatrix. I assumed I just had to tell OpenCNP to listen on another port and DSC position reports would pop up.


Top
   
 
 Post subject: Re: NMEA For Dummies ? (Moe, I hope you're out there)

Joined: 04 Jan 2014, 03:19
Posts: 34
Moe wrote:

Setting your gps/ais data ports to something other than gpsd, without turning off the gpsd (why would you do this?), will lead to a bloody conflict that no one wins. Left alone there is no port guessing; no protocol guessing; no baud rate guessing; no blood.


I am still trying to understand this. As I said the MX2100 puts out AIS and DSC NMEA on two different ports at different rates and GPS will be on another port. Are there demons for handling those NMEA streams as well or should they be handled by OpenCNP (as I am doing on Windows at the moment).


Top
   
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 14 posts ] 


Search for:
cron

Credits © 2010 - 2022