SparkFun Forums

[Cannibal]

Hi there,

I've used series 1 Xbee modules to do serial cable replacement tasks, but now I have an application where I want to have one base node and two or more remote nodes.

The type of data handling I want to have is to have the centre/master xbee able to send out broadcast data to all nodes, and have the nodes respond back when they can.

Is there a canned solution for this type of topology using Xbee? The range is short so while I am considering ANT, I had a good experience with XBEE, and power isn't a big deal for the master or the nodes.

Thanks in advance, and sorry for the lazyness.

[waltr]

This is doable with 802.15.4. You may wish to consider API command mode for the 'central' node as then the sender's address is part of the data 'Frame' so it can determine from which node the data came from.
You can also send a Broadcast message to all of the nodes or use a nodes address in the data 'Frame' to send to only one node. Note that nodes do not ACK a broadcast message so there can not be any retries.

[stevech]

Elaborating on Waltr's comments
I do star by not using a PAN coordinator nor association messages, etc.
Use the XBee API mode interface to the serial port. Your code wraps data in the well documented Digi API packets that begin with 0x7E. And gets response packets saying transmit done with success, and new packet received from what MAC address and at what signal strength.

So this is peer to peer. Like 802.11's ad-hoc mode. Any node can talk to any other node using the 64 bit IEEE MAC address that's in every XBee.
You can decide that one XBee is the hub of the star and design all others to talk only to that node. It's still peer to peer but by policy, all nodes talk to one, if you wish. You can have the central hub node send a periodic broadcast (not a beacon) to advertise "I'm here". That way, other nodes can discover it and its MAC address. And there could be several such advertising nodes. Some or all of these kind of nodes can gateway to a PC or WAN.

So with this, every XBee is a full function device. Uses 64 bit addressing, no PAN coordinator, disable association, and so on.
It's often more reliable as the chatty messages for association aren't needed, and this is important with weak signals.

Optionally, nodes can relay/retransmit.

the idea is to keep it simple. No mesh protocol like ZigBee and no PAN coordinator or short 16 bit addresses which are DHCP-like.