SparkFun Forums

[ebrandt]

Hi,

Just a quick question before I buy a handful of xbee modules...I need to find out if I'm setting myself up for disappointment or success.

My aim is to have a mesh network of sensors distributed throughout a building and nearby outbuilding. Initially, the worst case distance will be ~100-150 feet but will be through 2 exterior + 2 interior walls.

so, onto my questions:
Will xbee do this? If so, which power is appropriate? How do I select which antenna style is appropriate? The chip antenna seems most convenient, but the wire antenna would be fine too. The U.FL or SMA would be ok for the design, but that'd be one more part to find/buy/test etc.

Thanks in advance,
E.

[whoismaha]

Should work just fine. I'd suggest you start with 2x 2mW rpsma Xbees and experiment a little. Since these points sound fixed, you can use directional antennas. If you aren't interested in directional antennas, i'd say just go with wire Xbees.

[waltr]

I've had success withe XBee series 2 modules through interior and exterior, plaster and brick walls of the house.

The garage is another story. The garage has foil lined foam board in the walls and it totally blocks the XBee signal.

[groggory]

If you need to get out of a faraday cage (the aluminum lined walls) you can always hard wire a cable, run it as RS232 and then put an xbee on both sides of the wall.

[stevech]

Hi,

Just a quick question before I buy a handful of xbee modules...I need to find out if I'm setting myself up for disappointment or success.

My aim is to have a mesh network of sensors distributed throughout a building and nearby outbuilding. Initially, the worst case distance will be ~100-150 feet but will be through 2 exterior + 2 interior walls.

so, onto my questions:
Will xbee do this? If so, which power is appropriate? How do I select which antenna style is appropriate? The chip antenna seems most convenient, but the wire antenna would be fine too. The U.FL or SMA would be ok for the design, but that'd be one more part to find/buy/test etc.

Thanks in advance,
E.

XBee Series One Pro. Chip antenna on both. Will likely work. Else buy both with an ext. antenna connector, use $2 antenna to start, improve one end if needed. From what you said, you probably won't need more.

You can get a feel for this at 2.4GHz. Put WiFi access point/router at one place, take laptop to other. If you get any signal at all, the 802.15.4 will work. It's 2MHz bandwidth versus WiFi at 20MHz so it can use a -95dBm signal whereas WiFi needs at least 10dB more. Also, 802.15.4 at 2.4GHz uses QPSK modulation which works at far poorer signal to noise than does WiFi.

Interior walls, if drywall not lath/plaster, don't attenuate a great deal. Exterior walls are usually are low attenuation, comparatively, even stucco + chicken wire. . Brick can be a bit more. But often, there's enough windows or leakage up through attic and out through plywood to work well. Brick/masonry is not a huge attenuator. Heavy foliage in the path can be worse. But 150 ft. is not much at all.

[ebrandt]

Thanks to all who replied, sounds like success is likely enough that I'll pull the trigger. Thanks!

[ebrandt]

BTW, please tell me more about these '$2 antennas' that I should try first. Where can I get such a thing at such a price?

Thanks!
-Eric.

[stevech]

BTW, please tell me more about these '$2 antennas' that I should try first. Where can I get such a thing at such a price?

Thanks!
-Eric.

Like those you find on cheap WiFi routers. Reverse SMA connectors.
Get an XBee with U.FL to RP-SMA.

[ebrandt]

cool....any idea where I can score such an antenna (roughly) as cheap as you mention? sorry to keep coming back with silly q's, but a google of '2.4ghz antenna' yields a pile of hits, mostly in the fancy price range.

[groggory]

I don't know where to get those antennas at that price, but you can commonly find them for $6-$10. Then it'll be another ~$5 for the surface connector -> panel connector.

[stevech]

take one off of a old WiFi device.
Or
http://www.l-com.com/productfamily.aspx?id=6350