When I first wired my Xbee units together and uploaded the send/receive sketches I realized signal would be unstable due to a number of factors;
- range of the Xbee
- line of site and obstructions
- type of power source
The first system I have rigged uses two Arduino Duemilanove, two Xbee shields and two xbee series 1's. Both units in this example are plugged in to computers via USB cable. The next trial will feature a mobile power source -probably a 3.7 V lipo. This will make the receiver unit modular and will give me an idea of performance difference between hardwired vs modular power sources for the Xbee.
My first trial was conducted in the computer lab at AUT in anything but controlled conditions;
- Stable signal for about 6 meters. Aprox 1 room
- Intermittent, fairly frequent signal for another 14-15 meters
- My body being in the line of sight between devices made considerable difference to signal
- Certain walls had greater impact on signal. The granite main pillars seem to block a lot of signal (who've thought).
- Walking around with the Arduino plugged into computer is fairly unsuitable power source and will be restrictive in most applications.
- Repeated tests under these conditions revealed very similar results;
Estimated range in indoor areas measured;
- Computer Lab; 0-6m strong signal, 6m-18/20m fickle signal, 20m signal lost. Signal only constant when sender and reciever units are in the same room.
- Studio; 0-12m strong signal, 10-12m+ very unstable, 20m signal lost. Signal only constant when sender and reciever units are in the same room. Immediate signal instability when receiver is carried out the door.
- Home (Lounge); 0-10 meters strong signal through 1 wall layer, through 2 walls or 10m+ signal unstable, signal lost at aprox 22meters. Strong signal range varied greatly as I moved amongst rooms in my house. Glass lounge doors seemed to have little effect on signal strength.
- Home (Room); 0-10 meters strong signal through 1 wall layer, through 2 walls or 10m+ signal unstable, signal lost at aprox 20meters. Strong signal range varied greatly as I moved amongst rooms in my house.
Line of sight seems to be a clear factor in the accuracy and range of my RF trigger system.
Notably, during this trial, I moved to the into the main studio where another student was working on an Xbee project. Whenever they were broadcasting serial data my receiver unit would switch on. This could be a problem if you were looking to trigger specific systems individually, wirelessly and within the same range. This is one potential downside to using Xbee for this application (RFID or wifi may be more appropriate for you if this is the case).
Make sure no one else is broadcasting serial data within range of your units or the receiver will be confused!!!