Dedicated GPS receiver for VHF?

concentrik

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I've missed out the word 'cheap' but it is an important consideration! I already have two GPS receivers, one is a handheld with charts card, the other is a £20 usb 'dongle' feeding my laptop chartplotter, but my DSC VHF is feeling very left out because it's not in on the conversation.

I've searched the forums, 150 posts deep, but can't find an inexpensive way to assign a dedicated gps receiver to the VHF. I'm happy to chop some wiring around (to supply separate 12v for example) but I don't want any electronic interfaces (converters etc).

Again, I only need gps data, not any kind of display, I have these already. I don't want to use either of my existing systems to feed the VHF, details here:

OCEANUS NMEA0183 GPS Input Connection
Specification
This section is useful when attaching an external GPS to the OCEANUS
DSC radio. Many GPS units have a setup menu to be able to configure
the NMEA0183 serial data output. This output can be used to supply
information to other devices on the vessel, such as the POLARIS DSC
VHF radio, auto pilots, chart plotters, etc.
To setup the GPS to be used with the OCEANUS DSC radio, the
following items need to be considered for proper operation:
1. Baud Rate – Set the Baud rate to 4800.
2. Data Bits – Set the Data Bits to 8.
3. Parity – Set the Parity to None.
4. Stop Bits – Set the Stop Bits to 1.
5. GPRMC Command – This command is used by the OCEANUS
DSC and includes the UTC Time, Latitude, Longitude, Speed,
Direction, and Date information.
The data amplitude : Over 3.0V
Drive capability : Over 10mA



and the connections here:


Thanks,
 

ostell

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Why use a seperate GPS for the DSC radio? Long cable between your handheld and the radio. Allows you to continue to use the GPS and the vhf to use the GPS signal.

You're still talking about £100 for another (disregarding the build it yourself options).

Make of handheld would be helpful (and the connections didn't appear).
 

ostell

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I've been running with a Garmin handheld and a Navman VHF. It hasn't been a problem, the GPS connection still allows its use in the cockpit, and also use the boat 12V to power it.
 

fireball

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If you want a fit and forget solution then you may do best with a 3rd GPS - just search for GPS serial - there are a number of GPS buttons available with serial connectors and NMEA0183 compliant - don't go for a USB one.

Otherwise you're either after outputing the data from the laptop - for which there are loads of options or using a cable from your handheld ...

If your laptop doesn't have a serial connector you'll need a USB to Serial port adapter to give you that interface.
 

ProDave

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Are you TOTALLY discounting any sort of DIY?

If not, try this: http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=180581292221&ssPageName=STRK:MEWAX:IT

All you will have to do is make or buy a 12V to 5V regulator to power it, and connect it to your radio.

I've ordered one and waiting for it to arrive (usually takes a couple of weeks from Hong Kong) so I can't guarantee it will work until I have tried it on my own radio, but I doubt you will find anything cheaper.

As it's just a module, and in no way waterproof, I intend to mount mine on the inside of the drop down wooden electrical panel on my boat, which will place the aerial immediately under the GRP coachroof. On the basis radio signals pass through GRP I'm hoping that will work, and it will be right next to the radio so easy to connect.
 

ProDave

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ProDave: Not totally, I am looking at one of these:

http://bit.ly/i4iinZ

That looks like a very similar thing, already mounted in a case, and ready to operate from 12V.

So that should be easier to connect up that the one I have ordered (and a lot quicker to get to you since it's in the UK)

The only doubt I have with the one I have ordered is does it continuously send data without a data request. The documentation he sent when I bought it doesn't answer that question.
 

Playtime

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ProDave: Not totally, I am looking at one of these:

http://bit.ly/i4iinZ

and I'm happy to do a bit of jigg/poke with the bare ends. Like you I will post results if it works (and if it doesn't).

The nice man from Cashcow has sent me the PDF, which I have promptly uploaded here:

http://www.mediafire.com/?mk1k9xkoy7ef0y5

Looks like a good bit of kit. However, I have one concern - do you need to set-up the configuration parameters at initial power on? It is not immediately clear from the pdf manual what the defaults are.

If they are not OK 'as is' then I think you have a problem. You will need a computer and the Garmin Configuration Software (available from the Garmin website apparently) to set up the device with the required parameters. These are stored in non-volatile memory so, in theory, once set up correctly, you will not need the computer again and power up thereafter should be OK.

However, if the parameters ever 'get lost' or corrupted then you will need to reprogramme the device from the computer. Not good in a MayDay situation. :eek:

Maybe someone with a Computer Science degree can take a closer look at the pdf manual and advise?
 

concentrik

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Playtime: good point, thank you. As the device is relatively recent I'm pretty sure the config settings will be held in flash memory (NVRAM) so should stick after power off. I'll put a little 7805 regulator in a 35mm film can (my inline power supply method!) for the DC supply.

I downloaded the Garmin serial config program, still available from the Garmin website, in case I need to change baud rate or somesuch.

I will set the alarm on the VHF to go off if it loses valid NMEA data so that should take care of failure due to corrupt config settings. Of course if it fails during an emergency.... I'm stuffed, but then I probably would be anyway!

Cheers, guv.
 

ProDave

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My little module arrived yesterday, just to remind you, it's this one: http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=180581292221&ssPageName=STRK:MEWAX:IT

Well I had a frustrating day trying to get it to work, with no success.

Firstly I set up a regulator to provide it's 5V supply then tried it on the workbench. I can confirm as soon as the unit is powered up, it is sending bursts of data at 1 second intervals, but I don't know what (just looked for a signal with my oscilloscope).

Now I know my handheld GPS won't get a signal indoors, so I thought further testing in the workshop was futile, so I moved it out to the boat with it's data out connected to my VHF DSC.

It's been there for 12 hours now powered up (left it on overnight) and all I can say is the radio has not seen any position data.

However, I'm not even convinced it has got a position fix yet. The rather pigeon English instructions says:

"Powerup: Red light Flashing
Green light Flashing GPS signal received
Positioning completed: Green lighting"

Well after 12 hours the green light is flashing at a rate of 1 flash per second. That says to me it still hasn't got a position lock?

But I tried my handheld GPS at the same position (inside the cabin of the boat, with the boat on the trailer at home in between my garage and next doors garage, about 50% of the sky visible) and my handheld GPS got a position fix in just a couple of minutes.

I've nothing to lose by leaving it powered up for the rest of today, but I doubt anything will change.

Obviously what I really need to do is connect the unit up to a PC and use the diagnostic program that came with it to see what it's doing, but the logistics of that are tricky. The only PC in the house with an RS232 port is in my office in a downstairs room of the house. The GPS would not get a signal there, so I would have to move the PC somewhere else. Then add the fact that the GPS module outputs TTL level "rs232" but of course the PC would expect proper rs232 levels, so I would have to knock up a level converter. With all that hassle my interest in proceeding has diminished.

So that's a very long winded way of saying it didn't do what I had hoped it would do (just power up and send position data in the correct format for the VHF DSC) so I cannot recommend this unit to anyone else.

Also another warning for anyone buying one of these modules. The supplied cable uses BLACK for +5V and RED for ground. I wonder how many people have bought one of these and blown it up with reversed power?

Of course there's still one big unknown, that nobody has yet answered. What is the signal level expected by the DSC radio? The user manual does not tell me. It could be it's expecting real RS232 levels, which of course this module does not provide.
 
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Red Admiral

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I have run a data buss bar around my chart table and cockpit - sounds complicated but is just a length of well hidden twin with earth household cable The red and black (brown and blue) are 12v live and return. The earth carries data from cockpit mounted handheld GPS (Garmin 12 off e-bay) and uses same return.

This arrangement powers and distributes data for GPS, Icom 505 DSC radio, Yeoman Sport plotter, and Tiller Pilot. Each has its own separate plug that taps into the buss bar. Strangely, for me, it all works!

Added more recently is a netbook running MemoryMap charts but that has its own power supply and gps dongle. I have yet to gain full confidence in this system as there was quite a lot of electrotrickery in convincing the netbook that it has a virtual serial port - whatever that is.
 

Playtime

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Obviously what I really need to do is connect the unit up to a PC and use the diagnostic program that came with it to see what it's doing, but the logistics of that are tricky. The only PC in the house with an RS232 port is in my office in a downstairs room of the house. The GPS would not get a signal there, so I would have to move the PC somewhere else. Then add the fact that the GPS module outputs TTL level "rs232" but of course the PC would expect proper rs232 levels, so I would have to knock up a level converter. With all that hassle my interest in proceeding has diminished.

Even though you probably won't get a position lock in your office, it would still be worthwhile connecting up to the PC to see what is being output by the chip.

Are there any parameters that need setting up (from a PC) to establish the receive mode you need? Once these are properly set, the device may power up and get a position lock outside.
 

ProDave

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Some Progress with my little stand alone GPS module:

I now have an old chart plotter that I've just been given (still needs a bit of a repair), and I've just connected that, and at first attempt with no problem, it sends position data to the VHF DSC,

Crucially, I connected the oscilloscope and had a look at the data, and I think I have found the problem.

The chart plotter is outputting a logic low, pulsing to a TTL high with each burst of data.

But my stand alone unit is outputting a logic high, pulsing to low with each data burst.

So I need to invert the output, which a simple mosfet should do, then I'll try it again. With the data inverted, it's no wonder the radio didn't recognise the data.

At least it confirms the VHF DSC is expecting TTL level data, something I have never found documented anywhere.

I'll report back when I try it, but that might not be for a day or two (will probably knock up the inverter this evening, and try it on the boat tomorrow)
 

ProDave

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Well I have to report failure again.

Rather than use a mosfet for the inverter (couldn't find one in my transistor drawer) I used a 7400 as in inverter.

So now it's sending TTL data with the correct polarity. It's even the correct baud rate (comparing pulse widths with the plotter using my oscilloscope)

But still the DSC VHF does not see any position data. So either it's sending data in the wrong format, or it's not getting a position fix so not sending the position.

One day (but not very soon) I might make a level converter and hook it up to the PC to see what's going on, but I have spent enough time on it and don't feel like spending more. Even if it's possible to configure it via the PC to send the correct data format, that would be no good for this application, because according to the instructions, it will revert to factory settings if unpowered for 20 minutes.

The acquisition of the old plotter has kind of made the need for a stand alone GPS for the radio redundant in my particular case and I only continued to see if this unit was viable as a stand alone GPS for a VHF DSC radio. Unless someone else proves me wrong, it is not.
 
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Playtime

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Well I have to report failure again.
-----
One day (but not very soon) I might make a level converter and hook it up to the PC to see what's going on, but I have spent enough time on it and don't feel like spending more.

That's a pity - I was hoping you would succeed as I would like to try something similar.

I wonder when a DSC radio manufacturer will include a GPS chip inside the radio? Seems an obvious next step - I'm surprised it's not been done yet.
 

elton

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That's a pity - I was hoping you would succeed as I would like to try something similar.

I wonder when a DSC radio manufacturer will include a GPS chip inside the radio? Seems an obvious next step - I'm surprised it's not been done yet.

A "GPS chip" wouldn't be any use inside a radio beneath a steel deck.
 
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