XBee is a small hardware module that employ radio technology for communication among a wireless network of two or more XBee modules.
So, to summarize, besides simply passing data between nodes for microcontrollers, the XBee has other features that can aid in process monitoring and control.
The modules have digital I/O, analog input and PWM output that may be used in a variety of ways:
• Direct digital output control: Through AT commands, the I/O may be set to digital output and controlled as high or low. For example, the command “ATD0 4” would set D0 to be a low output and “ATD0 5” would be a high output.
• Digital and Analog input for transmission: The inputs may also be set to be digital inputs or 10-bit analog to digital input. Using sampling, the values of the inputs are sent as data to a receiving XBee in API mode where the ADC data is extracted.
• PWM/analog output: The 10-bit PWM value of an output may be set and optionally filtered for analog output of the unit.
• Line Passing: The digital inputs can control a digital output on a remote unit, and analog input can control a PWM output on a remote unit.
Using AT commands, the configuration of a remote module may be changed by sending the command in an API packet. This could be used to control remote digital or PWM outputs, or change other parameters of the remote XBee.
Some links to XBee material for further study:
Cool norwegian project that shows the power of a Perl library: http://jager.no/news/digi-xbee-part-2-using-xbee-perl-modules-to-control-a-relay-board