Multi Xbee question?

Ravenkallen

I have been using two Xbees(series 1, transparent mode) for awhile now and one thing that i always wanted to do was have multiple xbees talk at the same time... So, lets just say i had two Xbees operating in normal serial mode and they both transmitted at the same time, what would happen? I know the fancier ones have collision detection and clear to send signals, but do those functions work on a simple Xbee series 1? I ask this because i am planning on installing a outdoor sensor array(that will use a Xbee) and i wanted to have the ability to use multiple Xbees in the same area for my other projects(Like my robot). I was thinking i could arrange them like a star network, where the hub initiates all of the communication to prevent any data collisions, but that would not be as robust as a system that is capable of transmitting on its own initiative.... The answer is probably really obvious, but it has eluded me..

Tracy Allen

Are you using XBee series 1, with 802.15.4 firmware? They are smart enough to avoid collisions and to move the data through to the receiver, even if several of them transmit randomly and that happens more or less simultaneously.

The parameter that you have to watch out for is the packetization timeout, "RO". All the bytes that are loaded into the XBee within that time frame will be transmitted as one packet and will come through in one piece at the receiver. If the RO setting is too short, the data or string may come through in pieces. The default setting is 3 character widths, only 3 milliseconds at 9600 baud, and that is often too short for the BASIC Stamp.

You need some way to identify the origin of each packet. In transparent mode, your program will have to add that to each message.

$WMc%

What you need is WiFi 802.11

Ravenkallen

Yes!! That is a relief... Now i can go buy a couple more of them. Thanks for the quick reply and the tip:)

This is the kind i bought..
http://www.parallax.com/StoreSearchResults/tabid/768/txtSearch/xbee/List/0/SortField/4/ProductID/639/Default.aspx

Martin Hebel

If you haven't yet, read through the Getting Started manual, it describes a lot of what you talking about and issues involved (and how the XBee takes care of it).
http://www.parallax.com/Store/Accessories/CommunicationRF/tabid/161/ProductID/718/List/0/Default.aspx?SortField=ProductName,ProductName

-Martin