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Old 10-11-2013, 11:01   #31
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Re: Inexpensive heading sensor?

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Originally Posted by bcn View Post
Some modern do combine both - to get the best from the two worlds:
- high precision and bandwidth from gyros and accelerometers
- no drift and precise timing from GPS

for example:
| Coda Products

non marine aplications (from the manufacturer of the Coda stuff):
OxTS

Hubert
If you will notice in the descriptions, they refer to it as an inertial navigation system aided by GPS. An inertial navigation system does not use a GPS. However, systems that combine inertial navigation with a GPS are very common.

In the case of the marine applications, I can see that because it is under water, it can't use the GPS. Through a wire, it CAN use the timing signal of the GPS. SO, even though it is using a GPS for timing, it is not using it for position. So, I can see calling it an inertial navigation with out qualifying that is also uses GPS. This situation had not occurred to me. But again, I would not refer to this a an inertial nav system with GPS, because most people would assume it means the system is using the position from the GPS as well as the timing.

Basically, the very definition of an inertial navigation system precludes it from using a GPS for position. It uses inertia. Accelerometers and gyros.

But there is absolutely nothing keeping people from combining all the different technologies into a piece of equipment they want to. As they do, sometimes they start getting sloppy with what technology the refer to it as. It gets sloppy.

So, they refer to AIS Radar, when more accurately it is a Radar with AIS.

Sorry, you have been posting excellent information. I was just getting picky about the definition of inertial navigation.

-dan
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Old 10-11-2013, 18:19   #32
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Two GPS units cannot be used to accurately compute heading , despite what Tim Bartlett says. Fundamentally the standard deviation of the errors is not consistent. Hence significant errors are seen on heading by comparing locations in an attempt to determine it. I have a satellite compass on my desk at the moment ( hemisphere GPS unit ) it's uses the RTK principle , using phase difference between two GPS antennas.

It can determine heading at 10hz completely stationary. It's fantastic.

Of I could cost reduce it. , I bring a low cost version to market. Not easy though.


Dave
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Old 11-11-2013, 01:25   #33
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Re: Inexpensive heading sensor?

Dave,

yes, really nice "toys". We had an OxTS RT2502 on the boat and the data you are getting are very impressive.

For instance data about forces when you "fall" into the bottom of a wave. The guys that designed the engine supports were very happy to get real data.
Or knowing with a precision of 0,1 degrees how the pitch is changing under load.

But as the OP asked for inexpensive solutions for heading, we are far off: this is an equipment in the 18.000€ range (w/o taxes).
And as a dual purpose technology product it is export controlled. So you will have to look where you are travelling to...
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Old 11-11-2013, 17:21   #34
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Re: Inexpensive heading sensor?

there are specialized ways to determine both heading and attitude from gps signals, but not with two standard antennas and nmea.

I have developed a working heading sensor using i2c inertial sensors on raspberry pi. The cost for the pi $25 and the inertial sensors $20 and only 8 solder connections.

The raspberry then runs the autopilot algorithms and controls the rudder as well (in my case a small motor controls the wind vane rudder). It can also run opencpn, or just relay the information (via wifi) to a laptop.

http://github.com/seandepagnier/rpi_autopilot
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Old 17-11-2013, 09:41   #35
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Re: Inexpensive heading sensor?

Sean, Yes, you've been busy! This appears to be headed towards implimentation of your CruisePro program.

PS May we list you for attribution on your many plugins, but not have you get emails for tasks, so you don't get bothered with your intermittent internet service? Thanks.
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Old 17-11-2013, 10:06   #36
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Re: Inexpensive heading sensor?

Surely there's an iPhone app that can output NMEA over WiFi for GPS and heading?
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Old 17-11-2013, 10:29   #37
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Re: Inexpensive heading sensor?

CMPS10 - Tilt Compensated Magnetic Compass add a small SBC of your choice. $35
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Old 17-11-2013, 10:56   #38
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Re: Inexpensive heading sensor?

CMPS10 - Tilt Compensated Magnetic Compass
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Old 18-11-2013, 14:32   #39
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Re: Inexpensive heading sensor?

Another option is the Lowrance Point-1 which outputs heading as well as GPS on NMEA 2000. It lists for $200, and is plug and play and designed for a marine environment.
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Old 18-03-2014, 11:03   #40
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Re: Inexpensive heading sensor?

Hi
This is to share my compass installation using the CMPS10 earlier referred to if of any interest.
I used the CMPS10 since it's stated accuracy is fairly good. Better then a lot of offered Fluxgates on the market. The inbound pith and roll parameters is used for heading calculations and can be read out to a message of your choice. I used a Arduino Uno for the NMEA communication but if you like to make it smaller the Arduino Mini can do as well.

Since I've a Simrad IS15 system in my boat I'd to install a serial TTL circuit to convert Arduino 5V-TTL to IS15 12V-RS232. Then I could connect the compass direct to a IS15 instrument. The IS15 system is already connected to OpenCPN.

The box in the pictures is from a scraped Simrad compass. The outside has a professional look while the lid is on though the inside is less of that.
My connection scheme, the Arduino program and some pictures are attached. (Use it as you like as I did with some parts of the program.)

Håkan
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File Type: pdf Compass_Arduino_con_diag.pdf (12.4 KB, 328 views)
File Type: pdf Compass_cmps10_Momo_Arduino_code.pdf (73.8 KB, 504 views)
File Type: pdf Compass_pict.pdf (64.0 KB, 184 views)
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Old 18-03-2014, 23:38   #41
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Re: Inexpensive heading sensor?

Great work Hakan.

Can you tell us something how you your IS15 network looks aboard?
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Old 19-03-2014, 00:45   #42
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Re: Inexpensive heading sensor?

Well - The now rather dated IS15 system is a couple of instruments connected by a two wired cable looping around between them. The Simrad system use a bus called "Roblinc" with its signal superposed on the 12 V power distribution. See the figure below. There haven't been any reason for further investigation of the bus structure so I don't know anything about that. On every instrument is one NMEA connection (in or out) so the more instrument used the more NMEA connections are available. Every signal type floating around in the system is also available as a NMEA message and also is the most relevant incoming NMEA messages viewed on that IS15 instrument having the particular data viewer.
I've four IS15 instruments. One at the nav desk, two in the cockpit (Wind and multi text) and now also a compass viewer. The compass I put in the saloon to be able to see the course when I'm down there. In the cockpit I've the magnetic compass and I can see the saloon compass from the cockpit If I like. My IS15 system is feeding OCPN with various data now thus completed with heading for future radar plotting use. The IS15 wind data is already used by the auto pilot forwarded by OCPN. (My also dated AP don't serve its inbound heading out on its NMEA bus.)
I've now been able to learn quit a lot of the IS15 system so if any more questions I will try to answer them.
Håkan
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Old 19-03-2014, 01:42   #43
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Re: Inexpensive heading sensor?

Thanks for explaining Hakan. Based on the scheme, you don't have a tillet pilot connected to the IS15?
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Old 19-03-2014, 02:02   #44
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Re: Inexpensive heading sensor?

George...
Not a tiller but a wheel pilot and its connected to OCPN multiplexing way points, course offset etc and wind data originating from the IS15.
Håkan
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Old 24-03-2014, 03:11   #45
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Re: Inexpensive heading sensor?

Ah, I see. Was hoping one got a tilled compensated compass to work with the TP30.
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