doomtroll

GPS USB Receiver DIY Question

13 posts in this topic

So...since I'm a really poor bastard that has all his money saved to move out of New England..I can not afford to buy certain things for my trip..

SO!!!

I'm looking to build a GPS receiver for my laptop, I say USB but serial will work.

Problem being is I have combed Google & a myriad of forums with no info on circuits or even hacks......

Now would ANYONE have info, links, a guess on how one may go about building one??????

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I'm looking to build a GPS receiver for my laptop, I say USB but serial will work.

The way GPS works is that there is a psuedo random signal containing a time stamp transmitted from all satellites on a given frequency (L1=1.575GHz). The GPS unit has to receive these signals, phase lock onto them and then calcaluate all the possible locations (accounting for interger ambiguity) that the receiver could be and disregard the obviously wrong ones.

After a lot of maths an answer pops out in UTM, which then has to be converted to local reference system.

Obviously this isn't that easy.... but I guess if you have a suitable RF front-end/antenna you could do all the math in software.

If all you're wanting is a rough (10ft - 100ft) precesion then I would suggest buying a second hand USB device off ebay, or a old handheld. The yellow etrex are basic, but perfectly functional to war drive/geocache with. Even damaged handhelds (i.e. cracked screen, etc) may be good fodder for your project.

Almost all GPS receivers have a NMEA output, which is simple serial strings containing information on location/heading/speed/etc... and can easily be parsed.

Mungewell.

Edited by mungewell
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Appologies for saturating this thread.... but browsing Hack-a-day around the subject there a link for hacking into OnStar units to get GPS data out.

http://members.cox.net/onstar/

Me thinks it's time to take the soldering iron out to the truck.

Mungewell.

PS. Might just be a really cheap source of GPS units, just head down to the breaker's yard. Though don't forget to find the GPS antenna as well....

Edited by mungewell
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Have your tried ebay? I just bought (like 2 hours ago) a USB GPS Receiver for under 40 dollars after shipping, you might save yourself a lot of time with the ebay...

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cool...I may hit up a junkyard & see if I can find one of those Onstar units...there has to be a few newer wrecks in there

and FYI...I'm also very eager to build/hack one....even if it makes more sense to buy...I want to learn about it more

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The problem with building one is that even if you did it might be kindof usless unless you tuned it well to get good acuracy. The best thing to do is probably just to buy a cheap one and hack it, maybe a book on GPS technologies might help.

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Does the laptop have a serial port??? if so... just screw the usb idea and let the NEMA sentences just come across rs232

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Does the laptop have a serial port??? if so... just screw the usb idea and let the NEMA sentences just come across rs232

it does have a serial port...but not an option I have found allot of info on as far ass GPS goes.

I would even consider purchasing a Serial GPS receiver if I could find one...even eBay comes up short lately...

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do you have an old nextel phone? you could use it as a gps receiver.

I had never thought of that...I'm sure I could get one off somebody easily...VIA: Freecycle!!!

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do you have an old nextel phone? you could use it as a gps receiver.

I had never thought of that...I'm sure I could get one off somebody easily...VIA: Freecycle!!!

good idea... and if it's an old i305 (it has GPS) that hasn't been 'updated' NEXTEL will send you a free cable... Seems it had a bug in it where if you dialed 911 when they queued you for the GPS position fix it would hang up.... That's how I got my cable.

but you're not gonna have the best positioning with that... and it is slllllllooooooooooooooooowwwww to get a fix.

I have an old Lowrance globalnav 12 around here somewhere... it has a serial out... the cable is kinda funky to match up nicely, but ya can do the 'wire spring' trick and make it work... it'll be ugly... but it's cheap. (i gave 200 for it when it was new like back in '96 or whatever) oh yeah.... it eats batteries... 4 AAs will get ya about 3 or 4 hours. so figure on wiring it to the 12v source. How about 20 bucks to cover the shipping and my excavation fees (my apartment is trashed... I think I know where it is within 5 cubic foot area)

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