Xbee Long-Range

jakethesnake

Hello,

I would greatly appreciate any answers to the following questions. I am fairly new to the world of microcontrollers but i have learned quickly and want to embark on a rather large project of building a UAV. First though i need a smaller task to create a GPS tracking device that i can communicate with via radio. The tracking device would be placed in the payload of a weather balloon to be tracked so it can be retrieved for landing-i can do this with a cell phone but would like it if i could build my own device to get some experience.
First:
The Parallax Xbee modules do not have the range i need for my project-is there any way to build a signal amplifier?
Second: How hard is it to connect a Xbee to a BASIC Stamp module and set it up to transmit the data from a GPS module?
Third:
Can a Xbee module remotely turn on and off a simple switch that is isolated electronically from the BASIC Stamp? Could I use a Digital Potentiometer?
Thank You!
-jakethesnake

Franklin

http://www.sparkfun.com/products/10138

jakethesnake

Thank You!
However i would rather not deal with cell networks-any ideas how to at least double the range and keep it cell network free?

Duane Degn

I have a couple of 900mHz XBee XSC modules. Supposedly they have a 14 mile range. I did a range test by leaving one unit it the house and I walked down the street with the other unit. I started having trouble about a block away. I lost all signal once I turned the corner had a full blocks worth of houses between modules.

These modules should do a lot better in an open area. I'm not so sure about getting a full 14 miles out of them. They should work better if one or both units had a directional antenna.

It would be fun to get a couple of the XTend modules. 40 miles! Now were talking.

Duane

sylvie369

One of the longer range XBee modules (like what Duane is talking about) will be a better bet than trying to rig some kind of signal booster. I have worked with a company that uses the 900 MHz modules successfully to transmit GPS and telemetry from high altitude weather balloons.

If _all_ that you want to do is to send GPS information from an XBee, it's possible to directly connect the GPS output to the XBee's data in line, and go without an onboard computer of any sort. The rather big downside of that, though, is that it will transmit almost constantly, which uses a lot of power. Your power supply will need to be pretty significant.

Here is some information on how to set up an XBee so that the digital state of a pin on the transmitting XBee will be reflected in the digital state of the corresponding pin on the receiving XBee:

http://www.ladyada.net/make/xbee/arduino.html

That's a start for your "switch" question.

jakethesnake

Thank you all! I greatly appreciate your help! However, like i said, i am new to the world of microelectronics, and some of what you have posted is greek to me. For example is connecting the xbee to the GPS module as simple as plug and play? and do i have to have a device to "understand" the information on the receiving end? Thank you
-jakethesnake

Mike Green

I wouldn't call it "plug and play". It's almost that easy, but if you have any problems, as a beginner, you'd have a tough time. I'd stick with worked examples that you can duplicate, then modify little by little to do just what you want.

Duane Degn

Jake,

As you said, a UAV is a "rather large project." I think a Basic Stamp is going to be hard pressed to do everything you'll need in this project. You ought to consider using a Propeller. Dividing up tasks among the eight cogs makes writing complex programs much easier than using a single core uC.

Duane

jakethesnake

Once again thank you-truthfully right now I have my goal set as building a GPS tracking device for a project in involving a high altitude weather balloon. It has been done before (see www.1337arts.com), and the original project was done using a GPS enabled cell phone which used a cell network to display it's current position on google maps. However, cell reception is lost at a relatively low altitude, meaning they had little warning where it was going to come down. I wanted to solve this by having a radio-based tracker that didn't rely on cell towers. Can anyone help me with designing this tracker? I would like it to have the option on the transmitting end to send coordinates at an interval rather than constantly for battery purposes (like sylvie369 said), and on the receiving end to put the coordinates onto a display of some kind- probably google maps. And last I need at least ten miles of range. Any help is appreciated! Thank you!
-jakethesnake

Duane Degn

I was going to point you to the SparkFun tutorial but I see a comment by you there so obviously you already know about it.

They were using a Xtend module. It didn't have enough range to allow tracking the payload all the way to ground (I think they lost their payload).

My suggestion is to get a ham radio license. You'll probably need it for a radio powerful enough to meet your needs and you'll probably learn a lot more about radios and know which one to use by the time you have your license. (I've been think of doing this too.)

Duane

jakethesnake

So let's say I completely skip the gps tracker idea- I start working towards a UAV- if I bought a realatively inexpensive rc airplane, how would I get into the controls to allow it to be controlled by a onboard computer (BASIC Stamp)? And where should I go next technology-wise? I currently have the "Whats a Microcontroller?" kit. Should I buy a GPS unit and play with that for a while? Or should I get the whole GPS data logger kit?
-jakethesnake

Mark_T

For simple dipole or 1/4 wave aerials the range of a radio link depends on the wavelength - the longer the wavelength (and hence aerial) the longer the range for the same power. This suggests using a much lower frequency than 2.4GHz, perhaps the 433MHz ISM band - ought to give 5 times the range for same battery power, all other things being equal.

Alternatively/additionally consider a high-gain receiving antenna (yagi or dish), but that requires careful aiming (given you have recent GPS location data its an exercise in applied geometry 8). Gains of 20dB or more are readily achievable, and since this is purely a line-of-sight situation that translates to ten or more times the range.

Be careful when transmitting down to the ground that the aerial is oriented correctly (a vertical dipole has nulls in the vertical direction). The polarization of the transmitter is going to vary as it turns, which will again cause nulling (the solution to this is using helical antennas).

andrew1023

I just put up a post about extending the range of my system using a reflector behind the antenna... this is for the 2.4ghz XBee modules (not pro modules):

You can make it out of a soda can: http://solarstatus.com/?p=58