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Topic: methods of preventing RF/wireless crosstalk? (Read 987 times) previous topic - next topic

ttylbrah

Im a bit of a noob. I know for RC stuff, if you are racing with others, normally you'd switch over to another frequency band so you prevent cross talk between competitor controls-vehicles.

For arduino using RF communications, what are the methods you would use to prevent similar cross-talk scenarios in an environment where there may be more than one similar device also using the same wireless frequencies trying to communicate? I guess one method may be the baud rate but you are still limited there and sometimes you can still get cross talk by picking up the data. So what method do you suggest?

Encryption? Appending special start and end data that must be recognized to register a dataset? How does the receiver pull the correct signal in an environment drowned with the same frequency signals?

CrossRoads

You could use frequency hopping.
Take a look at parts like DNT24P
http://www.rfm.com/products/spec_sheet.php?record=DNT24P
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

oric_dan

This is a common problem today for the 2.4-Ghz wifi band. Total BW [bandwidth] is only 80-Mhz,
which can accomodate only 3 wifi channels without severe overlap. And obviously, if you look
in your PC's "View Wireless Networks" window, you'll typically see a dozen of so wifi routers
within close proximity. Plus, XBee works in the same band, plus microwave ovens work at
the top of the same band.

Why does this even work at all? Mainly through something called spread-spectrum DSSS [not
the same as frequency-hopping, BTW],

http://en.wikipedia.org/wiki/Direct-sequence_spread_spectrum
http://en.wikipedia.org/wiki/Frequency-hopping_spread_spectrum

They also use multiple-access techniques to prevent conflicts.

http://en.wikipedia.org/wiki/Multiple_access






ttylbrah

Cool thanks for the info.

How do you actually implement this in software using simple cheap RF transmitter/receiver pair or transceiver modules sending vial serial?

Or is this stuff usually done at hardware level by a dedicated controller?

CrossRoads

Usually done at hardware level by a dedicated controller - by a part like the DNT24P.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

oric_dan

We just buy off-the-shelf devices like Bluetooth, Zigbee, and other 2.4-Ghz transceivers,
available from many sources.

Popular with Arduino are the XBee shields, which were first designed to mount the XBee zigbee
module from digi [old Maxstream], but now there are many modules that mount on the same shield,
with some working at other frequencies, BT, and also wifi.

http://www.digi.com/products/wireless-wired-embedded-solutions/zigbee-rf-modules/zigbee-mesh-module/

http://www.seeedstudio.com/depot/index.php?main_page=advanced_search_result&search_in_description=1&keyword=beefamily

http://rovingnetworks.com/products/RN_XV

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