Here's a trick question: can you make a motion detector using a pair of Moteinos and no additional components ?
Answer: kind of, sort of. At least one way: send a string of packets and monitor received RSSI. Walking between the antennas (in this case about 11 meters apart) gives a small signal change. On average only about 1 dB unit, but averaging over 100 packets it makes a visible difference whether I am standing there, or not. My Tx unit was sending a 1-byte packet every 150 msec, so this wouldn't be too practical with batteries. Well, the whole thing is not too practical, there are more robust ways to do this, but I thought it was interesting.
(https://lh4.googleusercontent.com/-ogo98Y40qn0/Um9J5sXCDdI/AAAAAAAADMA/GPEmK8LLSQU/s640/Kst%20-%20CDocuments%20and%20SettingsJohnMy%20DocumentsRPiMoteino-PwrProfile-Oct28.kst%2010282013%20103422%20PM.jpg?gl=US)
https://picasaweb.google.com/lh/photo/SxDKhBs59pG_CFnZDdovctMTjNZETYmyPJy0liipFm0?feat=directlink
( If you're interested in a somewhat more practical sensor, here is an X-band doppler radar for motion detection, for $30.
https://solarbotics.com/product/35007/ )
I've seen a university research project about this, but it was using wi-fi. Some kind of security thing where you could detect if someone is present in the home by the altered wi-fi signals, can't remember the link, but I think it was the same principle.
Here is one reference to the wifi radar idea:
http://www.extremetech.com/extreme/133936-using-wifi-to-see-through-walls
Quote from: jbeale on October 29, 2013, 01:48:33 AM
Here's a trick question: can you make a motion detector using a pair of Moteinos and no additional components ?
Answer: kind of, sort of. At least one way: send a string of packets and monitor received RSSI. Walking between the antennas (in this case about 11 meters apart) gives a small signal change. On average only about 1 dB unit, but averaging over 100 packets it makes a visible difference whether I am standing there, or not. My Tx unit was sending a 1-byte packet every 150 msec, so this wouldn't be too practical with batteries. Well, the whole thing is not too practical, there are more robust ways to do this, but I thought it was interesting.
(https://lh4.googleusercontent.com/-ogo98Y40qn0/Um9J5sXCDdI/AAAAAAAADMA/GPEmK8LLSQU/s640/Kst%20-%20CDocuments%20and%20SettingsJohnMy%20DocumentsRPiMoteino-PwrProfile-Oct28.kst%2010282013%20103422%20PM.jpg?gl=US)
https://picasaweb.google.com/lh/photo/SxDKhBs59pG_CFnZDdovctMTjNZETYmyPJy0liipFm0?feat=directlink
( If you're interested in a somewhat more practical sensor, here is an X-band doppler radar for motion detection, for $30.
https://solarbotics.com/product/35007/ )
I suppose if you were to put a directional antenna on both Tx and Rx, then it might almost be like an electric eye?