Can I implement a GPS receiver?

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Hi Freaks,

I am thinking of making a project which would be something like the run of the mill GPS but with an AVR

It will have a GPS receiver and an 8 bit AVR.

Can I implement this for personal use or do I need permission from the FCC (I am in the US) to build this? Also any suggestions of good working ideas of which receiver to use, etc. would be appreciated.

Thanks.

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Well, you have a lot of reading ahead. There are 667 Threads on the Freaks when I search for GPS!

Incorporating a commercial GPS module which outputs NMEA data into your product is certainly doable, and a fun project. If you aren’t selling it, the FCC has nothing to do with it.

Spark Fun Electronics sells a number of commercial GPS modules, and also some on breakout boards. Take a look at their site. My favorite is the EM-406, but there are certainly newer modules available.

I would suggest you get a module with a built-in antenna for starters. By the time you order a separate antenna, and cable, and make sure the connectors all match, and make sure the power is correctly supplied for an active antenna, you might just as well have purchased a module with an antenna to begin with. If you have special antenna requirements you can deal with them after you have made your initial investigation into GPS.

Look closely at the output from the various modules. Most will output NMEA at 4800 baud, “the standard”. See if the output is 3V or 5V, as it will be easier if your project runs on the same supply voltage. I would start with a character LCD, (2x20), which also runs on the same supply voltage, to display the Time, Date, Lat, Long, Number of active satellites, etc.

Later you can add a Graphics LCD and plot your position, or track your course.

A uC with 2 USARTs would be useful, one to read in the GPS data, one to dump it to a PC, to either read in Hyperterminal, or to feed to a PC GPS program. Select the correct Max232 chip, again based upon the supply voltage of the GPS, micro, and LCD, for dumping the data on the PC.

Just a few thoughts to get you started.

JC

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Thanks for the feedback,JC. That is great for me to start with.

I looked at the EM406 and it is a little expensive at $60 a pop. Are there any cheaper ones in the $20-25 range? I will search too.

I agree with using the entire package as one unit. I have seen too many threads here where people have tried to make the antenna work..

Eventually when I get it to work, I am thinking of building a handheld device so I will be looking at size too.

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FCC is not involved unless you wish to sell it. And, then, their involvement has nothing to do with GPS, but with possible emissions by your hardware which, by the way, happens to have a GPS receiver.

GPS modules with NMEA (async serial) are pretty easy to work with. The NMEA sentences are well documented and straight forward to parse. There are other interface schemes, including I2C. Make sure what interface you want when you go shopping for a module.

For the most part, you don't have to deal much with high precision floating point math, unless you want to determine distances and headings (with some accuracy) over long paths (say, greater than 50-100 miles). Generally, for shorter spans, you can assume a rectangular coordinate system with little error.

Importing and displaying maps, which many GPS units do, is challenging as most of the commercial maps for GPS units are proprietary.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Thanks,Jim.

Quote:

Importing and displaying maps, which many GPS units do, is challenging as most of the commercial maps for GPS units are proprietary.

What if I used Google maps? Those are free, right? I don't see much use for a GPS that only reports numbers. (lat,long,elevation,etc.)

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Quote:

What if I used Google maps? Those are free, right?

Define "free":

http://code.google.com/apis/maps...
http://code.google.com/apis/maps...

(suggest you read the ENTIRE licence!). Note that you are ONLY allowed to access the map data ONLINE with a browser. You cannot snapshot/cache the maps.

A lot of the cost you pay for a commercial GPS is a licence to use someone's map data - it is extremely labour intensive to produce it and on the whole it's not done by philanthropists or for the goodness of their health.

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Actually, there are applications where simple lat/lon are useful. For example, reporting a vehicle location by radio.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Just one observation I made when playing with GPS modules. GPS reception can be very patchy or nonexistent. You may be better off with an external antenna with a sufficiently long cable to go out the window. I did use a 5m cable and placed my module outside as I had no reception in my office. As the communication with the modules is usually a 4800baud NMEA data stream a cable of a couple of m works fine and placing the module outside might be as good as the long antenna cable.

Markus

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A long serial cable should be far preferable to a long antenna cable, performance wise. GPS is around 1200MHz to 1500MHz. Cables have a LOT of loss at such high frequencies. You do much better with a short antenna cable and a long serial cable, where loss is not much of a problem.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Quote:

A lot of the cost you pay for a commercial GPS is a licence to use someone's map data - it is extremely labour intensive to produce it and on the whole it's not done by philanthropists or for the goodness of their health.

http://www.openstreetmap.org/

'nuff said :)

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Xantor wrote:
http://www.openstreetmap.org/

'nuff said :)

Almost. See the winner (not me) at http://www.stm32circle.com/hom/i...

Stealing Proteus doesn't make you an engineer.

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Xantor wrote:
http://www.openstreetmap.org/

'nuff said :)


It'll be nice if they ever finish it - I live in one of the more boring bits of planet Earth apparently - a red arrow in the middle of nowhere...

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clawson wrote:

It'll be nice if they ever finish it - I live in one of the more boring bits of planet Earth apparently - a red arrow in the middle of nowhere...

That's the good thing about it... take your GPS for a walk, upload the trace and wait for someone to make nice streets out of it (or if you feel adventurous or in a hurry, do it yourself) A couple of hours later and see... no more lonely arrow

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$10 - so whats the catch?
I have seen these on ebay for past 6 months, I have not been able to commit. Have you bought and tried these?

I don't mind slow (1Hz), large, power hungry with just a few channels. As long as it is decently sensitive and no other catches.

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Don't have one yet. There were about 430 of them about a year ago. No reason to suspect anything is wrong with them, just old technology from a cancelled navigation system.

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visnwbs wrote:

$10 - so whats the catch?
I have seen these on ebay for past 6 months, I have not been able to commit. Have you bought and tried these?

I don't mind slow (1Hz), large, power hungry with just a few channels. As long as it is decently sensitive and no other catches.


You need an antenna. That'll add a significant amount of cost. Plus I doubt you could ever go into production with those things - sounds like they're just leftover stock.

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Fewer channels tends to mean lower accuracy.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Not really, as there are never ever more than 12 satellites visible simultaneously, having more channels only looks good in the ad.

Newer ones do have better signal processing and sensitivity though, so usually perform better, but not for having more channels.