Bluetooth GPS

[Mike_cj0]

Hi,

This is my first post so please be gentle!

I've been doing a lot of seraching over the last few days but dont seem to be able to find a definitive answer for my question so im hoping someone can either point me to a thread i have missed or point me in the right direction/

Im planning on building a GPS data logger for use in my car. I have worked out pretty much all the parts i need except for how to get the GPS data.

I have been looking at two options. My preferred option would be to add a bluetooth interface and receive the data from the bluetooth GPS that i already have in my car.

Is it possible to connect a 28x1 PICAXE to a GPS like this and use serial over bluetooth to receive the data?

My other option would be to buy another bluetooth module and connect that directly to the PICAXE and get the data that way.

I would prefer to use bluetooth as i already have a working gps reciever and it seems a waste to buy a second one if i can get the one i already own to work, even if it does cause a few headaches.

Any help would be greatfuly received!

Mike

 

[Gavinn]

Hi Mike,

I can't answer your question but thought I would mention I'm looking at BT GPS modules for a similar project. I'm planning to open the GPS module and find points I can tap where the serial data from the GPS module goes to the BT chip and feed that into my PIC.

Gavin.

 

[Mike_cj0]

Hi Mike,

I can't answer your question but thought I would mention I'm looking at BT GPS modules for a similar project. I'm planning to open the GPS module and find points I can tap where the serial data from the GPS module goes to the BT chip and feed that into my PIC.

Gavin.

Now that sounds like a cunning plan! The holox BT GPS i have was nice and cheap so it that coule work it would be great. You will have to keep us updated with your progress.

Im going to still try and investigate the bluetooth option in the first anstance though.

 

[papaof2]

Be aware that the PICAXEs do NOT have string capability. Receiving character data (ASCII from a GPS) requires a byte variable for each character in the string to be received. If you have enough variables available for both the GPS data and any processing you want to perform on that data, you should be OK. You will probably only be able to process one of the GPS strings (GPGGA, GPRMC, GPGSA, GPGSV, etc).

Tapping into a serial stream, if available, may be the simplest method - you will not have to ensure that the BT devices pair up before you can get the data (sometimes works beautifully, sometimes doesn't). Depending on the chipsets used, the BT GPS may not have an internal point that provides access to the serial output of the GPS receiver chip.

John

 

[staylo]

The iBlue 737 and 747 are two small bluetooth GPS devices which have very good points to tap into the TTL serial feed. See http://www.gpspassion.com/forumsen/topic.asp?TOPIC_ID=81990&whichpage=1

The 737 is simply a bluetooth GPS (no other functions), but the 747 (despite being the same size) is a logger with 2Mbit memory. There is an open source program to control the logger functions at http://bt747.wiki.sourceforge.net

 

[krypton_john]

You could try a bluetooth module such as this:
http://www.sparkfun.com/commerce/product_info.php?products_id=8461

Reading and parsing NMEA-0183 GPS sentences has been discussed here a lot - just search the forums.

However the amount of effort involved in faffing around with BT would put me right off. I would personally just go for a cheap serial GPS puck.

 

[Mike_cj0]

Thanks for all the help and advice.

It looks a lot like using bluetooth is just going to be to complicated and also with the cost of a bluetooth module i may as well just get another GPS.

Would this one be any good? http://194.201.138.187/epages/Store.storefront/?ObjectPath=/Shops/Store.TechSupplies/Products/GPS001 ?

It looks like it should do i want.

 

[krypton_john]

Here's an eBay cheapie:

http://cgi.ebay.co.uk/SiRF-III-GPS-PUCK-RECIEVER-RS232_W0QQitemZ300266131375QQcmdZViewItem?hash=item300266131375&_trksid=p3286.m63.l1177

As it has a serial cable you can use it elsewhere too.

 

[Jeremy Leach]

Just to mention - I've proved that it is possible to fully decode NMEA sentences on a 28X1, properly parsing the strings (reading commas etc), but it uses a fair amount of code. So it's not like picaxes haven't got the capabilty.

 

[dorkygrin]

So nobody has done a GPS logger with a picaxe?

Seems like a very cool gps logging project for people that have a serial gps. I've got one, it's too bad I don't have the smarts to develop it.

Can a picaxe save serial data to a SD card? Easily?

 

[Mike_cj0]

The plan i have is to write to an SD or transflash card.

It can be done using an uALFAT. There is some really good information on this forum about it.

krypton_john, thanks for the link!

Jeremy, its good to know the 28x1 has the capability to process the NMEA sentances. Looking at a few other posts it looks pretty processor intensive. Would a coprocessor make a noticable improvement in the processing time?

 

[Jeremy Leach]

Well, I'm saying that 28X1 (@16MHz) can read single NMEA sentence that's chucked out every second from GPS module and do 'other stuff' too. Haven't got any figures of exact timing though, and how much processing time left to do other things. Need 28X1 picaxe or higher really though, to use HSerin into the scratchpad.

All depends on exactly how much you want to process and the timing. To play it safe you could have a 28X1 dedicated to dealing with the NMEA reception and translation, and this picaxe outputs the result to another picaxe that deals with interface to SD etc.

But just thinking ...If you are logging to SD, then do you even need to decode the NMEA sentences?? Maybe you just need to save the raw data??

 

[Mike_cj0]

One thought was to write just the raw data and i already have a vb progra i have writen that can decode the raw data and output what i want as a csv file but i would like a solution that doesnt involve an extra step if i can avoid it.

I need to dig out my source code and check exactly which parts of the sentence i need.

 

[dorkygrin]

Mike, take a look at this: http://www.semifluid.com/?p=43

Looks like exactly what you might want to do. Wonder if the Pic code he has can be adapted for use with a picaxe?