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Daniel Wee

My little NAV/OSD project - under construction

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Ok, Here are a few more answers to my problem with the EB85A GPS module.

I am using a DragonOSD board I bought from Mark that has the coin battery cell for the GPS on board. In addition to the DragonOSD I have the BOB4 board mounted on the DSOD and am running the system from a 2S battery that the display says is at 7.34v. I am now using goggles to monitor the output rather than a TV.

With the GPS and DragonOSD/BOB4 left outside in clear air for about 15minutes it acquired no satellites, the display showing 176.0m, 90.000000N, 00.000000E and 23:59 time.

I have tried the module with an RS232 convertor and the Etek GPS Locator Utility and after about 2minutes it had a 3D lock and acquired 7 satellites, and that was inside but close to a window. This was running at 4800baud. This was using the DragonOSD/BOB4GPS powered up as normal but the GPS TX1/RX1 connected to the level convertor. Moving the GPS connections from the level convertor to the DragonOSD and restarting everything there was no satellites acquired after three minutes.

Once again I notice that the setup routine on the DragonOSD is quite variable, sometimes sticking at Home not Set with just the time displayed, sometimes with the Home not Set screen fully displayed, sometimes stuck at the Waiting for GPS screen and a few times stuck at the GPS Startup 0 screen.

I am going to try shortening the GPS leads and see if that does the trick but any other suggestions would be welcome although with the dodgy startup I am beginning to suspect the DSOD board.

hoping expectantly for enlightment, regards Peter

Edited by pseddon

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Have you re-written the code? Reason I ask is because you are talking about baud rates, which I thought were changeable only in software. If that's the case, then maybe look at possible software bugs.

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No no I have not rewritten anything!!

The default baud rate on the GPS is 4800. With GPS Locator it seems only to want to run at the default, which is a shame as it does not provide the opportunity to try it at other speeds.

The DOSD changes from default 4800 to 115000 (or thereabouts) during initialistion and setup of the GPS.

regards Peter

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Okay, let me see - you got your own BOB4 board, is this correct? I can't be sure from your post. If so, can you check if the crystal on your BOB4 is marked 74.25MHz rather than 75MHz. If it does not say 74.25MHz, you may want to confirm that it is not 75MHz. From your description it sounds like it is possible that your BOB4 is running on 75MHz, in which case the 21st harmonic will be jamming the GPS signal. This should not be a problem if you got an RTF board.

Secondly, the altitude should be 137.0m. I'm not sure why yours reads 176.0m. You may want to check that as well and confirm the correctness of that info. In any case, the fact that you are acquiring satellites suggests that there is nothing wrong with the connections so in the absence of more comprehensive information about your setup, I can only guess that your unit came without the BOB4 and you added your own BOB4, and it is possible that your BOB4 is not running the modified crystal and is therefore jamming the GPS signal.

I also notice that you mentioned a level converter. What exactly are you talking about here? Are you referring to the USB unit?

Daniel

Edited by Daniel Wee

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Thanks you Daniel for coming back to me.

I have a 75MHz BOB4 - probably because I bought it some time ago before the DragonOSD existed!

176 was a mistype - should have been 137.0.

The only reason I am confused as to why the BOB4 is jamming the GPS is that to check the GPS all I did was to remove the RX1 and TX1 signals from the DOSD pcb and connect them to the RS232 convertor. The power and everything else to the GPS is still coming from the DOSD. I also did not move the physical position of anything when I connected the GPS to the PC.

Is it the relative position of the BOB4 and the GPS that causes problems or is it conducted radiation via the wiring that causes the problem. I could try, when the GPS is connected to the PC, bringing the BOB4 close to the GPS.

Thanks for your patience, regards Peter

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Well, you're just not going to get anywhere with the 75MHz version of BOB4, short of sealing the whole thing in a metal can. I know, I've tried. What you need to do is to either send it back to Decade Engineering and pay them to re-work it for you, or do it yourself. There is no easy way around this if that's what you're hoping for. The 21st harmonic of the 75MHz oscillator lands dead on the GPS frequency so you can have it out in the open for days and it will not lock. If you read through the thread really carefully, I think I mention this issue in the earlier parts.

Daniel

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Thanks Daniel,

You did mention it in an earlier thread and I did do some checking but concluded wrongly that a standard BOB-4SG could be used.

A warning for anyone else and maybe it ought to be clear on the websites that sell the DOSD that a standard BOB4SG will not work.

thanks again, Peter

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Sorry Mark, I got no email from you.

I was asking in my email when should i aspect my order to be here?

I was under the impression i will get a tracking numer or so, so i can check the status with the people from the post office....

Edited by mugur

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Mugur,

When ordering, you chose Internation Parcel Post - AIR. This is uninsured and does not offer tracking of any sort just as started on the confirmation of your order being posted :)

As it is christmas time, Australia Post are saying it may take up to 20 days for delivery rather than the standard 7-9 days.

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Success!! - the problem with my DragonOSD being unable to obtain any satllites was indeed because of the BOB-4 having the wrong crystal. Everything now seems to be working correctly and Home is Set!

Mike Hardwick at Decade Engineering was most helpful and has sent me a replacement crystal - the 74.25MHz crystal is now standard fit to all boards.

Thanks to all the suggestions to get things working!

regards Peter

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I'm trying to get my hands on a Dragon OSD. My application is an iceberg study which will take place in Antarctica next year. We'll be flying a couple of RPVs to drop Iridium/GPS locator tags on the tops of icebergs to track them. We'll also be flying an ROV under the icebergs for video and samples, but that's another story.

I really like the Dragon OSD's features, particularly the ability to bring our RPV towards home if we lose contact. I also appreciate the source code being available so I can mess with it if I need to. Like some (many?) on this forum, I'm an EE and embedded systems engineer. Daniel, you've done an amazing job!

Intelligent Flight is out of stock on the Dragon OSD, and I got no response to an email asking about it. Is there any other source for these boards? Can anyone point us in the right direction?

Thanks,

Paul

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Paul,

Very interesting application! As for the Dragons, last I heard they were still quite a few weeks away, the order for the PCBs for the v1.1 has just been sent to the factory as I've been told. However, are you able to build one yourself perhaps? From personal experience I can tell you that's an easy task for any EE.

If needed I'd be happy to offer my assistance if you go down that route. I actually have a working 3V3 design using the dsPIC30F4012 and am currently drafting a PCB with the 4011 to be mated with the BOB-4-H (the header version). PM me if you need any additional details.

Cheers,

Sander.

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Hi Paul,

That sounds like a great project. I'd be happy to assist in any way that I can. We are currently out of boards but they are being made right now. However, if you need something urgently please let me know. Additionally if you want some assistance in modifying the code or hardware (such as adding a temperature sensor), please let me know also.

Daniel

p.s. I did not receive any e-mails on this.

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Thanks to Sander's excellent advices, help and tutoring - I have my Dragon up and running. Daniel, thank you for this wonderful product.

Please see the pictures below.

post-6-1197093603_thumb.jpg

Edited by oxxyfx

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What version of the board is that? Or is it your own? It doesn't look like the images I've seen.

BTW, I like your idea of using ribbon cable for the GPS. How long do you think you can make the wires without causing RF problems?

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Well, what can I say? I didn't expect anything less than for you to get it working, great job :D

As a for your information, the board is a custom design using the 4012 in SOIC28 package running on a slightly modified version of DragonOSD 4.5.

Cheers,

Sander.

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Well, I think this is one of the best Dragon design's to date :) - thanks to Sander again for his expert contribution.

Other than the regular Dragon design this board also features:

- it is a 5V design - I prefer this over the 3.3V version even though that would have less part count. Everything else in my plane runs on 5V.

- Jumper to select between powering the Dragon board form the Flight battery pack or from a separate battery.

- Jumper to power your KX131 from the Dragon board - using only one cable for the camera. This will work only with 5V cameras - so the reason for the jumper is -that if I want to use this with for ex. the IF camera - then I switch the 5V off so no power is going to the camera from the Dragon.

I finished building this last night, and I was happy to see it working around 1AM in the morning. I didn't even have time to take a good look at it, this morning I had to go help a friend move. However, I just got home and took some more pictures for you - here are the jumpers I was talking about.

twinturbostang:

I am not sure how long the ribbon can be before picking up interference. I left this fairly long - so I can shorten in later in case I need it. Since I crimp the connector on it myslef - that should not be a problem later on.

post-6-1197159618_thumb.jpg

Edited by oxxyfx

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And a better picture showing you the jumpers and the power connectors. I have to change the 10mH choke to a different one, this one cannot handle the load of the camera and the dragon as well. For now I have it shorted on the bottom.

post-6-1197159920_thumb.jpg

Edited by oxxyfx

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