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docphi

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Guys,

I've hooked up a Royaltek Sapphire GPS unit to the ICircuits OSD-GPS board. The wiring isn't complicated. The RX wire from the GPS unit is connected to the Serial In on the OSD board. However, I'm not getting any data displayed. The GPS is compatible with the OSD (NMEA-0183, GPGGA, 4800 baud). What could be the problem? Thanks!

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Does the Saphire work when plugged into the serial port on your PC?

Keep in mind that if you don't have a Satellite lock, some GPS units will appear to not work. During your debugging, obtain a Satellite lock while using the PC, then swap the RS-232 signal over to the OSD board (or connect the PC and OSD as a pair for simultaneous data).

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Yes, it works great with my PC. It's actually connected via the USB port. I'll try the signal swap from PC to OSD. Thanks!

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No luck. I've got the NMEA data stream on my PC, but, when I switch over to the OSD, I get nothing. The OSD board keeps displaying "Searching for Satellites." I definitely have a lock. The second field of the GPRMC sentence is an "A". It won't even transmit simultaneous data to the OSD when connected to both the board and the PC. Aaarrrghh!!!! <_<

Edited by docphi

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I remember having difficulty with Saphire GPS as well. It was awhile ago - I don't remember all the details. I believe the otuput of Saphire is lacking GPGGA sentence necessary to reconstruct altitude info - may be that's what confuses the OSD board. Again, I am not exactly sure - let me know what you find out.

Edited by cyber-flyer

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The sad thing about the NMEA standard, is that it isn't a strict standard. I've come across a variety of differences in the data that the various receivers send. It really makes it harder to design a device that plays nice with them all. Can you capture a few sentences into a file and then post it as an attachment?

Edit: BTW, if you have the USB Saphire, how are you connecting it to the OSD board? I believe you will need Royaltek's Serial dongle to do that.

Edited by Mr.RC-Cam

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Edit: BTW, if you have the USB Saphire, how are you connecting it to the OSD board? I believe you will need Royaltek's Serial dongle to do that.

I've got it connected using the bare wires from the GPS module. IE, I've removed the case to save weight. NMEA file is attached.

NMEA.txt

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I've got it connected using the bare wires from the GPS module.

I could be wrong, but I was under the impression that the bare module used non-inverted 3V TTL "RS-232" signaling and that the optional RS-232 dongle (that Royaltek provides) is needed for standard serial interfacing. If true, then the OSD board would not work if connected to the native wiring on the little GPS mouse.

If you can make it work on the PC's serial port, without the USB dongle, using the native GPS wires and a 5V power supply, then I'm definitely wrong. Beyond that, maybe Cyber-flyer can offer some insight into this since he has used it before.

From looking at the file, the GPS sentences are the same as the Royaltek Module that I played with early in the Gecko project. The Intuitive board needs the GPRMC and GPGGA sentences, which are present.

One of the things that tend to be a wild-card is the UTC field. Royaltek uses a 10 character field, where the common handhelds tend to use only a 6 character long field. If the Intuitive code is blind to this, it might make it choke. Do you by chance have a copy of the OSD board's NMEA sentence specs? What they have on their web site did not help at all.

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If you can make it work on the PC's serial port, without the USB dongle, using the native GPS wires and a 5V power supply, then I'm definitely wrong.

I'm not sure of this. PC UART's tend to be extremely tolerant. I've already been able to send data to a PC serial port successfully using non-inverted 0V-3V levels! :blink:

That might not work with the board as they would have used a level translator. The good thing would be to see the GPS' output signal... but I remember having had a hard time in finding a module that would send true RS232 levels.

Edited by Kilrah

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I'm a bit more optimistic about the PC serial comm test. That would prove that the serial signal is correctly inverted (per RS-232). If my reasoning is correct, it couldn't work on a PC's serial port since the data would non-inverted (missing the RS-232 driver). On the other hand, if it works on a PC, but not the OSD, and it is a signal amplitude problem, then we have ways to fix that. :)

Just thinking out loud here. If the Saphire's "bare wires" are providing industry standard RS-232 signaling, then all my comments are useless noise. But, I have a feeling that the optional serial dongle provides this, and the Saphire's bare wires are not RS-232 compatible. Cyber-Flyer should be able to straighten us out on this.

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If the Saphire's "bare wires" are providing industry standard RS-232 signaling

As far as I can remember Saphire bare wires output has correct polarity for PC port, no inversion was required .

But I do remember having issues with Saphire. Ok, it's not GPGGA sentence - file dump disproves that. My own NMEA parser (on ATMega128) would only get part of GPS data from Saphire while it was working fine with Gecko-201 and instead of figuring out why, I just put Saphire on the shelf and moved on.

I am interested in making my Saphire module to work as well, but it will be one-two months before I get to it.

One of the things that tend to be a wild-card is the UTC field. Royaltek uses a 10 character field, where the common handhelds tend to use only a 6 character long field

Good point - I can go over my code and see if that could be the reason for me, but only Intuitive's engineers can confirm why their board is rejecting the signal.

I'd try increasing Saphire output amplitude first since it's an easy thing to do.

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As far as I can remember Saphire bare wires output has correct polarity for PC port, no inversion was required .

That is good news (and a bit unexpected, at least by me. :) ).

Docphi, if you need more help then just let us know. If you do, then one helpful thing (at least to me) would be to post clear closeup photos of the top and bottom sides of the OSD board. If it is a inadequate signal level problem, then we can determine what needs to be changed.

It would also be good to contact IC and ask them if your GPS sentences are compatible with their OSD. If they are unable to provide details to their data expectations, then you could send them the $GP file for their review.

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That is good news (and a bit unexpected, at least by me. :) ).

Docphi, if you need more help then just let us know. If you do, then one helpful thing (at least to me) would be to post clear closeup photos of the top and bottom sides of the OSD board. If it is a inadequate signal level problem, then we can determine what needs to be changed.

It would also be good to contact IC and ask them if your GPS sentences are compatible with their OSD. If they are unable to provide details to their data expectations, then you could send them the $GP file for their review.

I'm waiting for the serial cable (backordered) for further testing. I've sent a sample $GP file to IC and they have said it is compatible.

In the meantime, I'll take pix of the OSD board for reference. And I've also got your great mini-GPS module to tinker with! :)

Edited by docphi

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