Panoramic Wifi Camera
Panoramic Wifi Camera creates a live panoramic image of a space seen through Wifi radio and other 2.4 GHz radio signals - how they bounce back form the architecture, composing an image, just as light would do.
However, the 'light sources' in this case are laptops, wifi hoptpots, iPhones, and even microwave overs (see the video for more on this).
20 home made directional antenna are placed in a careful array, each at a slightly different angle, to evenly cover a vertical view. This array is than rotated slowly around, scanning the space and building up an image of the space column by column.
Watch a quick video of the project:
The 20 cans scan the space, each responsible for a horizontal segment in the final images
This image is an actual view of the space at 2.4GHz - wideband, looking at 2.402-2.470 all overlaid.
The screen shows the panoramic image of the actual space, seen through Wifi - the white line shows the live position of the camera and updates the image.
The slider used to choose the frequency the visitors look at is reused from an old project we did in Tokyo - reconfigurable house. Originally we found it on a flee market - it is the fader of an old analog video mixer.
The wooden box contains a continuously rotating motor which also provides power for the laptop - using a 'slipring' inside.
The rotating panel is made with a sandwich technique: a light foamboard in the center reinforced by 2 thin wooden plates on the sides - creating a really strong and light structure - a placeholder for all the parts, computer, etc...
Our 20 2.4 GHz radio sniffer boards - they where all powered from a single USB port via unpowered HUBs
We used spice cans that where available in Tokyo and had the right diameter. Pepper, garlic, and a team mix.
Production CAD drawings
More about the technology
The sensing of radio activity and control is trivial to do with the tokyo1 boards. They cost about 30 euros a piece to manufacture and can take about 5000 measurements of signal strengths a second in 1MHz bands from 2400 to 2482 MHz. When we use them we measure just 11 of those channels at the center frequencies of wifi channels(which are 22MHz wide and overlapping) giving about 450 measurements per second for each of those channels.
To drive a motor though you might need a motor driver of some sorts and depending on the size of the motor that might be quite a different beast, from a digitally controlled continuous rotation servo(which the tokyo1 board could control directly but which i guess is just too slow), via hexfets or motor driver circuits to some monster mosfets for driving many many amps or perhaps an of the shelf motor driver that is controlled by analog or digital signal and can control the speed of a motor. If i would build that it would just be a couple of hexfets driving a dc motor with pulse width modulation i think - if speed control is enough. With a tight control and a very strong stepper motor i guess some quite amazing things could be done like fairly sharp turns on that wire.
Signal strength measurement output is in the range from 0 to 31 ie 5 bits and quite noisy so you want many measurements to increase quality of signal(so the high frequency of measurements is very useful). But one thing to know also is that wifi base stations sends beacons about 10 times a second so normally you just have say for 100 networks a 1000 very short blips per second which is the beacons and then if there is traffic you get a whole lot more of activity but to get continuous activity you have to download large files or so but this is of course just a matter of filtering the output and scaling the response between no activity and how much response you want at a certain amount of activity in the radio band.
Also note that since it can only listen to and analyze one such channel at a time, jumping between 11 channels means missing 10/11 of the traffic theoretically but since we jump fast we only miss very short events - the alternative would be multiplying to paralell receivers which is really just a matter of cost and space.
And of course you see bluetooth, zigbee, 2.4ghz wireless cameras, microwave ovens and such things that also exist in the 2.4GHz spectrum. And in our experience microwave ovens are much stronger transmitters than all the others.