XBee radio communication between PICs
Revision as of 19:22, 5 February 2008
Two wired PICs can communicate by RS-232. We can replace the wires with a wireless link. In this project, that wireless link will be implemented using Zigbee radio modems that use the IEEE 802.15.4 protocol. The demonstration will show two PICs talking to each other over wireless, and a PIC talking to a PC by wireless. This demonstration has the user typing in data into hyperterminal and the PIC responding. For example, the user might type "1+5 [enter]" and the PIC responds with "6".
It is common for two pics to communicate by RS-232, a wired transmission. However, it may be desirable to communicate via a wireless link. This wiki page discusses this option by using XBee radio modems using the IEEE 802.15.4 protocol. This will allow for two pics to communicate wirelessly as well as a pic and a PC to wirelessly communicate.
The IEEE 802.15.4 is a point-point/point-multipoint communications protocol(similar to Bluetooth) designed for low-power devices. Like Bluetooth, the IEEE 802.15.4 specification also uses the 2.4 GHz ISM band. The ZigBee protocol, which deals with mesh networking and routing, is built upon the IEEE 802.15.4 specification.
The XBee radios, made by Digi (formerly Maxstream), are shipped with firmware implementing the IEEE 802.15.4 protocol, but can be loaded with the ZigBee protocol stack, which can be downloaded from the Digi website. Note that ZigBee is still in its infancy and devices from different manufacturers may not be compatible. The range for an XBee Pro indoors is up to 300 feet while line of site, outdoor communication is up to a mile. (XBee Manual
The XBee requires a 3.3 voltage regulator and the chip is designed to be mounted in specific sockets (See figure) (Note: These sockets don't fit in a standard bread board!)
For the pin locations, see page 7 of XBee Manual or the figure to the right.
For PIC to computer interface a program such as X-CTU needs to be used, X-CTU can be downloaded from X-CTU Site.