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Old Jan 30, 2009, 07:49 PM
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rich smith's Avatar
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Low cost DIY XBee/GPS plane locator

Due to many email requests I've put together plans for a low cost XBee/GPS interconnect circuit that lets you know where your plane is even when it goes out of sight. Parts only cost a couple bucks and take a few minutes to assemble. A wiring diagram is shown below. Four components are required: regulator, two caps, and a resistor. The LEDs are optional but help show power, RF link status, and GPS lock.

The idea is to connect output from a low cost Globalsat GPS receiver to input of an XBee 2.4ghz radio module. GPS and RF modules can be had for as low as $20 each. A ground tracking station consists of any laptop with serial or USB ports and another XBee module. I found the best software to track position of the plane is Delorme Street Atlas but many prefer Google Earth.

The GPS receiver is used as-is but the XBee requires some configuring so it will have the same baud rate as the GPS. This is done by connecting to a PC and using so called AT modem commands as follows:

+++ (put in command mode)
ATCTFFFF (set max command timeout)
ATBD2 (sets baud rate to 4800)
ATAC (apply changes)
ATWR (write to non-volatile memory)

ATCTFFFF is not absolutely necessary but makes it easier to enter commands so you don't have to hurry.

Attached is a picture of the assembled unit and Delorme screen capture of a test flight of my Solar UAV. Let me know if you see any errors or have questions.
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Last edited by rich smith; Oct 06, 2009 at 07:55 AM. Reason: new schematic
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Old Jan 30, 2009, 08:38 PM
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Do you know where they can be found for around $20 each? I looked up the EM406 module and the lowest price I found was $48.

Thanks,

Vas
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Old Jan 31, 2009, 12:01 AM
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Yea, tell us where we can get them for $20!!!
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Old Jan 31, 2009, 12:10 PM
7000mw of raw power!
rich smith's Avatar
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About 5 yrs ago I bought up couple dozen Trimble 502 from BG Micro for $11 shipped. They're only 4ch and a bit heavy but work. More recently I got a dozen or so Globalsat BU353 units on Fleabay for $22 ea that had USB em4xx easy to convert to RS232. Last year a fellow was selling em410? here on RCG pretty cheap but don't remember exactly how much. A client I did the autopilot for purchases em406 in quantity for about $12 ea on a slow boat from China. Sometimes I piggyback. Couple months ago on black friday Boost i425 cel phones were on sale for $10 w/rebate so I picked up a bunch of those, pulled the GPS, and used the included time for my cel. Sparkfun charges $60 for em406 so they make a hefty profit but have excellent service.

The deals are around if you shop. FWIW $48 don't sound too bad considering commercial tracking systems like this cost hundreds or even thousands.
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Old Feb 02, 2009, 10:45 AM
7000mw of raw power!
rich smith's Avatar
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In another thread more info was requested on the PC end of the link so I updated the schematic to include a low cost interface. It's pretty much the same as the one for the plane but with N-FET inverters instead of the GPS. Note that the XBee eval kit (Digikey) and a modified FTDI adapter can also be used.

I also got requests for more on the Trimble 502 GPS units so will try to dig up that soon.
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Old Feb 02, 2009, 11:23 AM
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Is this 2.4 GHz application compatible with Spektrum DSM2 radios?
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Old Feb 02, 2009, 11:51 AM
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What sort of range are you getting out of that Rich??

I think one of the magazines like Radio Control Models and Electronics, the UK one http://www.modelflying.co.uk would love to run a how to with this.

Cheers

G
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Old Feb 03, 2009, 12:57 PM
7000mw of raw power!
rich smith's Avatar
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Quote:
Originally Posted by Kadath
Is this 2.4 GHz application compatible with Spektrum DSM2 radios?
Yes, there is no frequency conflict. Last summer while testing Spectrum with 6200 RX the plane went out of TX range and went down about 2/3 mile from launch. We still got GPS track w/Delorme which made it real easy to find the plane on the ground. So XBee range is longer than that.

At first I though XBee was interfering w/RX because they were both 2.4ghz but tests w/o the XBee showed that was the limit for Spectrum in the area. I think trees cut the signal. We switched back to 72mhz for longer range.
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Old Feb 03, 2009, 08:11 PM
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May seem a silly question.

But what software do you use to get the received data from the ZigBee to your computer?
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Old Feb 04, 2009, 12:06 PM
7000mw of raw power!
rich smith's Avatar
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I get about 1/2 mile with standard antennas and a little over 1.5 mile with MR RCCAMs $1 patch antenna. Depends on conditions/geography, actually got over 2 miles at one site. "Better than idea conditions" like they say in the commercial.

Magazine article would certainly reach a wider audience. If anyone else builds one of these it will tell us if there's any bugs in the docs.


Quote:
Originally Posted by Gary Mortimer
What sort of range are you getting out of that Rich??

I think one of the magazines like Radio Control Models and Electronics, the UK one http://www.modelflying.co.uk would love to run a how to with this.

Cheers

G
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Old Feb 04, 2009, 12:10 PM
7000mw of raw power!
rich smith's Avatar
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Quote:
Originally Posted by dellarb
May seem a silly question. But what software do you use to get the received data from the ZigBee to your computer?
No software at all. GPS connects directly to XBee.

I use either Procomm under DOS or Hyperterm under WINDOWS to capture GPS data and Delorme Street Atlas to show maps. Google Earth works too.
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Old Feb 05, 2009, 12:06 PM
7000mw of raw power!
rich smith's Avatar
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Paul and Razor,

Per your request here is more info on the $20 Trimble model SVee-Six-CM3. Here's a link to one person who used it as a mobile GPS:

http://juliepalooza.8m.com/sl/trimble.htm

Attached is the software I used to set up for NMEA and a pdf with wiring. Note that the MAX232 chip is not needed to talk to the Xbee which has inverted serial.
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Old Feb 05, 2009, 12:26 PM
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What GPS module is in the i425?
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Old Feb 05, 2009, 05:01 PM
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Very cool. I was thinking of something like this but for a different purpose - locating my son when he runs away at the shopping malls, theme parks etc. Do you think it would have the resolution and accuracy? Is it possible to connect it to say a handheld and have realtime updates?

I work in product development, and we had a client come to us and ask if we could develop a device which you clipped onto your child's clothes, sewed into his pants or whatever, however there is a plethora of patents preventing us/him from doing it, but for an individual non-commercial application it's wide open. We never went any further than an IP search, but it would be a cool thing to have if you have a child who is difficult to keep close at hand (like my son!), nothing more scary than realising you can't see him in the crowd any more, terrifying, actually.

Stu.
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Old Feb 05, 2009, 05:14 PM
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Quote:
Originally Posted by stumax
Very cool. I was thinking of something like this but for a different purpose - locating my son when he runs away at the shopping malls, theme parks etc. Do you think it would have the resolution and accuracy? Is it possible to connect it to say a handheld and have realtime updates?

I work in product development, and we had a client come to us and ask if we could develop a device which you clipped onto your child's clothes, sewed into his pants or whatever, however there is a plethora of patents preventing us/him from doing it, but for an individual non-commercial application it's wide open. We never went any further than an IP search, but it would be a cool thing to have if you have a child who is difficult to keep close at hand (like my son!), nothing more scary than realising you can't see him in the crowd any more, terrifying, actually.

Stu.
The limit with this GPS device is you are limited to the range of the Xbee module. It does no logging in itself. However it would not be hard to use a PIC or something to interface an SD card for logging. There are examples out there.
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