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Topic: WiFi Signal Strength Sensor (Read 12826 times) previous topic - next topic

jwagg34

For my college final project, I am building a robot that will sense WiFi signals and travel to find HotSpots.
What I'm looking for is advice on what sensors I would need to find WiFi signal strength? I am also building a Sumo bot from scratch and am adapting this to work off of that platform. Any advice would be awesome, as well as possible code that might be useful. I am fairly new to Robot-C but I have taken a course in C++. In particular code in using arduino interupts would be the most helpful.
Thanks a lot to all who can help, I really appreciate it!

spambake

I just sent for samples of the Linear LT5534 detector.  It's probably not exactly what you want since it detects a wide range of frequencies.  You might be able to limit it somewhat to WiFi frequencies and direction with antenna design.  I've read of others altering cheap WiFi detector gadgets but I know little about this.

Might get you started anyway.

jwagg34

Thanks a lot for your help! If you have any more advice, please dont be shy on sharing :P

spambake

Sure, I can share a bit more.  I've been looking into making a simple EMF detector that will detect in the common wifi, cell phone, cordless phone and other frequencies used around the home for a neighbor who is paranoid about the new smart meters being put in around here.  Searches in these forums and on google provided plenty of fodder.  Here's some links that might apply to your project.  You should do similar searches since there's plenty of info out there.

The Linear LT5534 is tiny.  Your college might have resources for utilizing surface mount components.  If not here's the coolest (maybe not the easiest) wiring method I've seen for one-off SMT projects:
http://elm-chan.org/docs/wire/wiring_e.html
http://elm-chan.org/docs/wire/wcd.jpeg

Here's a site that has some info about antenna loop length vs. frequency, connecting to an Arduino, and connecting the sensor to a speaker to hear the sounds different devices make.  This might give you some clues to how to differentiate Wifi from the other devices in the same frequency range:
http://interface.khm.de/index.php/lab/experiments/radio-signal-strength-sensor/

This guy made a detector with a cool antenna:
www.w1ghz.org/small_proj/Power_detector_board.pdf
http://www.wa5vjb.com/services.html

I keep thinking of a robot in the shape of Mothra with feathery moth-like antenna.

That's all I know.  Others on this forum are more expert than I.  There's tons of info out there on moving a robot in a particular direction based on the signal strength info from two light, sound or other sensors but you'll have to search that out on your own.  Forum searches and Google are your friends!

bilbo

I finished the prototype of a wireless spectrum analyzer that works in the 2.4ghz (Wi-Fi) spectrum. Visually, I am able to very clearly see wi-fi signals when I come across them. I could see how you could use something similar to recognize activity on the Wi-Fi channels... http://arduino.cc/forum/index.php/topic,52655.msg397680.html

TeslaFan

I'm using the Sparkfun Wifly Shield in my latest project, it uses the Roving Networks RN-131C module.

From command mode, you get the signal strength in dBm of all stations it can scan.

And, as a bonus... it's also connects via WiFi and is already Arduino ready.

cpixip

Hello jwagg34 - there are a lot of 2.4 GHz scanners around using the Cypress CYWM6935. The advantage of this chip is that it features a dedicated RSSI signal and it's easy to turn that into a scanner.

In case you want to try something simpler, have a look at this quick project I made some time ago (http://arduino.cc/forum/index.php/topic,54795.msg392325.html#msg392325). It uses a readily available breakout-board with an nRF24L01p-chip. The interesting part: it works even so this chip has only a single reception flag, not a dedicated RSSI-signal.

Note however the following: all these setups will give you RF-strength in the 2.4GHz band - and there is a lot going on there which does not correspond to a WiFi transmitter.

In my post above, for example, there's a diagram showing the interference of a Bluetooth-device with a WLAN. Other devices which transmit in this band include wireless TV-cams, keyboard and mouses, as well as every microwave oven.

In case you only want to scan WLAN-channels, it might be necessary that you look at more expensive WLAN shield for the Arduino. Seems that a Sparkfun WLAN shield feature an RSSI-indicator (look here http://www.sparkfun.com/datasheets/Wireless/WiFi/WiFlyGSX-um2.pdf at page 35).

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