GPS Bluetooth Hacking

I was having a bit of a clear out this evening and came across this little device, it’s an old GPS bluetooth adaptor that I purchased years ago to use with my ancient SPV Smartphone (I was an early adopter).

Bluetooth GPS

I haven’t used it for a long time so I figured I’d take it a part and have a closer look.

Bluetooth GPS Circuit Board

At a glance it all looks fairly standard, they seem to be using a standard Bluetooth module on the left, note the Bluetooth antenna trace on the top left of the board. On the right of the device is the GPS module with a separate antenna board. However there are a couple of suspicious unpopulated headers one centre bottom (5 pins) and another vertical next to the Bluetooth module.

It would be great if I could get some data out of this, GPS time or even some coordinate data. Having a very accurate time source could be handy.

The first problem was powering it on, I’ve long since lost the charger cable so I had to attach a couple of wires and charge it from my bench supply.

Bluetooth GPS Circuit Board

After powering it on, I started probing around the unpopulated headers, nothing much on the Bluetooth module header (likely an ISCP header), however the 5 pin header was far more interesting. One of the pins clearly had some data on it. Here’s the output from my scope.

Bluetooth GPS Scope Trace

If we look at the frequency it’s showing 4.72Khz which is suspiciously close to the 4.8Khz required for 4800 baud serial data, my scope is not that great so it’s certainly within the margin of error. The signals are at 3.3v CMOS Logic levels and I can’t find my adapter at the moment, so I’ll get one ordered and do some further investigation, however it looks quite promising that I’ll be able to get some useful data out of this little old box.

Once the level converter arrives we’ll take a look at what the data could be. Stay tuned.



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I'm James, a radio amateur, software engineer and professional geek. I'm the IT Director for a software company and Director and part owner of a web design, hosting and media business.

4 CommentsLeave a comment

  • Hello , I have one of these. I also occasionaly use RFO BASIC which has a bluetooth program in its examples folder. So I tried adapting it a little to print the output from this device. It spews out a lot of types of GPS data which I have found a document which gives an explanation for the various types of data. If you would like to share your experiences I would be willing to share what I know.

  • Hey buddy, I read your post. I have a question for you. I have a car Garmin GPS, and it doesn’t pair with my helmet bluetooth headset (I’m a motorcyclist). turns out Garmin planned it that way so we would be forced to buy a 1000 dollar Zumo unit. I want to hack the GPS I have. I need to add a Bluetooth that transmits in HFP, so that my headset will receive it as a GPS (otherwise it would be on the same ‘lane’ as my phone, and the instructions wouldn’t be heard). Can you help me? Is it possible to attach an HFP transmitter? If so, which one? and where!?

    Thanks so much!

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