I know lots about electronics and all, and want to try something new. I would like to know what I need to make a simple, GPS receiver to use inline with a program called Roadnav(http://roadnav.sourceforge.net/index.php). If any one can help with suggestions I would really appreciate it. BTW, am only 16, and will be doing this as a school project, am really interested in all this.
I have been looking around and have come to the conclusion that I might be needing a EM406/ET301 SiRF III Evaluation Kit. Or maybe just a different Eval kit that uses NMEA. Would like it to be as cheap as possable(public school :(. )
As I understand it (someone correct me if I’m wrong), all you need is to establish a serial connection to the GPS. There’s a bunch of different ways out there to hook up to a serial or USB port, including the eval boards available from sparkfun.
In terms of software, there shouldn’t be much more to it than getting the software to talk to the right serial port or USB device.
[ I may be speaking from ignorance here, but it’s usually easier to get someone to correct you than to get them to lay out info in the first place. ]
Pretty much anything that looks like a GPS will spit out the NMEA data that Roadnav wants. You should be able to take any of the eval boards, connect it to your computer (and possibly a power supply, and antenna), run Roadnav and it will just work.
Depending on what your project is, you might want to look at an off-the-shelf GPS mouse. They are basically the same as the USB evaluation boards, but they’re packaged in a nice magnetic waterproof enclosure, so you can stick it directly on your roof. They’re a little smaller and little cheaper than the eval boards.
Quite a few handheld GPSes come with a data cable and will give you the same NMEA output as you’d get from one of the GPS eval boards. If you have one of those handy, you may be able to prototype using that, then decide what to buy later on in the project.
I think I might go with a GPS mouse, but will I be able to tie in a antenna that I want, I have one on the roof(for onstar), and would like to use that as the antenna.
saknife:
I think I might go with a GPS mouse, but will I be able to tie in a antenna that I want, I have one on the roof(for onstar), and would like to use that as the antenna.
The plot thickens…
A GPS mouse would have a built-in antenna, so you wouldn’t be able to use the onstar one with it.
If you have a working onstar system and you’re willing to void your warranty, are a few easy-to-find sites out there that show how to solder a few wires to your onstar system and get it to give you the NMEA data directly… all you need is an RS-232 level shifter, which you can buy or build with a few dollars worth of parts. [edit] Looks like you can switch the oncore module back and forth between spitting out its own binary format and NMEA data, so when you were getting data you could use, the built-in onstar stuff wouldn’t work, and vice versa.
It should be possible to get a GPS antenna splitter and split the signal from the onstar antenna, feeding both the existing onstar module and a GPS module from SparkFun, but it won’t be cheap… off-the-shelf splitters cost a ton, and you’d probably have to convert to a different style connector to use one, and the cost of all of those converters adds up (in $ and in signal quality). I’d avoid going this route.
If you just want to unplug your onstar antenna and feed it into a GPS module, that should be pretty straightforward.
Yeah, I was looking into the onstar hack, although I have only found hacks for the 2 piece system. This is a one piece onstar unit, from 2003. If you could help me with finding the sites, that would be great. Also It would have to be USB since I would be using a mac, and well the days of RS232 are long gone for them. Any idea?
saknife:
Yeah, I was looking into the onstar hack, although I have only found hacks for the 2 piece system. This is a one piece onstar unit, from 2003. If you could help me with finding the sites, that would be great. Also It would have to be USB since I would be using a mac, and well the days of RS232 are long gone for them. Any idea?
Hm… Haven’t seen anything about one piece units, but that doesn’t mean the info isn’t out there. I did come across this thread (http://www.mp3car.com/vbulletin/showthread.php?t=75346) about using the antenna with another GPS Receiver.
I don’t know much about Macs, but my guess is an off-the-shelf RS232 → USB converter would work well if you’re interfacing with an off-the-shelf device. If you’re interfacing with a GPS module that has TTL-level outputs, you’d end up using something like the FT232RL sold here (or the USB eval boards which have that chip built in).
I have soldered everything correctly (pretty sure) and nothing has burned up. my problem like usual is connecting a serial device to the computer. (i was never able to succesfully connect the serial dongle programmer)
