Purpose

I would like a wireless data network for my mobile robots in order to provide telemetry data and robot coordination. I've considered 802.11, Bluetooth and Zigbee.

802.11 is a posibility given the availability of SDIO cards, but creating an SDIO driver would be a considerable task.

Bluetooth suffers from feature creep and requires considerable resources to implement a software stack.

Zigbee offers mesh networking, low power, low cost modules and one module in particular offers an easy AT or API command interface.

This document disucsses the use of the Digi (formerly MaxStream) XBee Series 2 module for mobile robot data networking.

Equipment

I use the following equipment to create a link between my host computer and the mobile robot:

Make	Model	Street Price	Picture
NewMicros	USB-XBEE-DONGLE-CARRIER	39.00
NewMicros	XBEE-CARRIER-5V	9.00
MaxStream	XB24-BWIT	21.00
Grand Total (includes 2 XB24-BWIT modules)		90.00

The XBee module comes with a selection of antennae. To chose which antenna best suits your needs, read Digi's Application Note on XBee Antenna. I chose the wire antenna for its improved performance over the chip antenna in outdoor applications.

The host computer uses an XB24-BWIT module installed in the USB Carrier. I plug the USB Carrier directly into the USB port on my computer.

The mobile robot uses an XB24-BWIT module installed in the 5V Carrier. I connect the wires from the 5V Carrier to the 5V serial lines on my MMB103.

A Better Breakout Board

After I bought the XBee carrier board above, a new board has become available. It makes all 20 XBee pins available, it is cheaper and most importantly, all the pins are labled!

The Firmware

The XBee modules have 4 different versions of firmware depending on whether you want a cross between AT or API mode and Coordinator or Router device. There must be exactly 1 coordinator per network.

XBee Series 2 ZigBee Firmware: