Thursday, August 26, 2010

Hacking a USB GPS

As regular readers will know, I've been playing about with APRS quite a lot in recent weeks and I'm starting to get the urge to build something APRS related. I'm planning to order one of the inexpensive FoxTrak kits, which lets you use a standard VHF FM radio to transmit position reports. To do that you also need a serial GPS and on searching eBay I became aware that serial GPSes seem to be rather more expensive than USB or even Bluetooth devices. This led me to wonder whether it would be possible to hack a USB GPS to use with a tracker like the FoxTrak. My investigations led me to this article by Primiano Tucci on GPS Hacking.

This post is basically an un-loseable bookmark to myself, since it will probably be a few weeks before I get around to working on this and by then I'll have lost the article and never be able to find it again. But it might be of interest to someone else or provoke some interesting comments.

Although I'll probably build the the FoxTrak as-is and test it with one of my 2m rigs I'm really interested in trying HF APRS on the move without having to buy an expensive TNC or lug a laptop around me so I can use AGWPE to generate the 300baud audio. So I'd also be interested to know whether anyone has modified the FoxTrak (or the TinyTrak which I believe is very similar) for the 300baud tones? I know the OpenTracker+ from Argent Data does 300baud "out of the box" but it's quite a bit more expensive, enough more expensive to attract the punitive import fees that will almost double the price.

5 comments:

Steve Bunting said...

Julian, I have a fox digi which works just fine. I have read that the fox trak can be used like a TinyTrak 3 clone, but don't know for sure.

I had a TT3+ and it was very susceptible to RF - even with the mods of the decoupling SMD caps. I ended up switching to an opentracker and ithis has run in my car for >2yrs now.

Was a little surprised about your price comments so took a look the relevant websites: The TT3+ kit is $33 whilst the OT1+ kit is $32. Have I missed something? Perhaops the postage is the difference 73 Steve M0BPQ

Julian said...

Hi Steve. Anything over about $29 becomes liable for VAT which means it also incurs the £13 tax collection fee. The Fox kit is $20.

Anonymous said...

Have you seen the nex VX-8 with optional GPS Julian?

G7FRI said...

You can get a native RS-232 Garmin unit from ebay for 25 quid...

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=170532915819&ssPageName=STRK:MEWAX:IT

6-40v DC supply and true RS-232 output levels. I bought one a couple of months ago from the same seller. They're good units.

Cheers,
Jim

Julian said...

ZL1VFO has a page about modifying a USB GPS too.