The Xbee protocol

The previous post introduced you to the Ardupilot, an autopiloting system. The Ardupilot after the initial setup is ready to send the raw as well as processed sensor data.This data is crucial as it affirms the fine movement of plane. Data such as the gps locations over which the plane has to fly (it's called waypoints) also has to be sent to the Ardupilot.  One may ask how is data transmitted to and from the plane in air, back to the ground. The answer is the telemetry unit, it is a communication link between the computer and the Ardupilot unit. The telemetry unit consist of a pair of xbee's.

Basically xbee is a transreciever with a powerful microcontroller. The microcontroller holds a unique network ID of the network therby enabling only other xbee's having same network ID to communicate to each other. The protocol used for the communication is called the zigbee protocol. Digi is the creator of this tiny master-piece. The above picture shows a xbee with pig-tail antenna. These are efficient for small range but as the projects demand is a larger range we chose an xbee whose antenna can be attached externally, that is xbee with an SMA connector. Currently we are using antenna of gain 5db and frequency 2.4 GHz(This frequency is legally free in India).

Xbee with SMA Connector

  

5db Antenna with SMA Connector