Zigbee, Atmel and I2C

[jameske]

I2C (Solved) and Atmel, Zigbee

Greetings everyone,
I am wanting to a wireless project and have been searching around for wireless transcievers with a range that will cover atleast 2km easily. Now thats when I tripped over the wireless section of the atmel website! While assessing the modules their, I have thought of something worth noting for this project;

my project involves an I2C bus with 7-bit addressing to communicate between all the devices, however I have come up with an issue. I can use up to 112 addresses to personalise each device which is fine for the average project, but my project requires 5 to 6 networks of 20 devices minimum which means there is not enough addresses. Thats were I wondering, do the Zigbee and Atmel wireless modules (ATZB-900-B0 is the one I'm looking at) use spread spectrum to reduce interference and allow two transmitters in the transcievers to operate at once? I'm thinking that this may be a way to solve my issue of addressing. Otherwise is there another way to over comne this problem without using 10-bit addressing (ie. some way of software addressing)?

Sorry about the long winded question,

Thanks,
James

 

[3v0]

My Zigbee experience is with microchip but I think it will be helpful

Zigbee is built on top of a mesh network. I expect it is the mesh nework you want and not the actualy Zigbee stuff which is an application profile and the software to support it. Zigbee has a huge footprint for a micro controller.

In theory mesh networks can operate in a beacon mode where only one radio is allowed to XMIT. You need to determine if the Atmel or any other radio module will function in this mode.

These mesh networks are designed around the idea that most of the time the modes will be silent. The standard thing where packets are acked works well even with unstructured radio use.

MicroChip lets you use either the Zigbee or the MiWi (mesh but not ZigBee) with the same radios.

EE-Times: **broken link removed**.

The MiWi stack is somewhere between 1/5 and 1/10 the size of a Zigbee stack. It is possible that Atmel has a similar protocol. If not maybe think about using the MicroChip and MiWi.

With ZigBee/MiWi rather complex packets are used. The short address uses 16 bit. Bit 15-7 id the coordinator with bits 6-0 zero. The coordinators children share the upper bits with the coordinator with unique address via bits 6-0.

 

[jameske]

Thanks 3v0, I'd rather a star topology in the sense that each device will communicate back to a base station, this allows me to have one device to control the whole network.

So what I am trying fix is represented in the pictures.

In the first one, you could say that
1. the two networks are running on different channels so the devices don't get confused
2. or there is a way to get more id's/addresses with I2C so I don't have to repeat some due to running out of them.

The second image shows what the network looks like when the cross over.

I hope this isn't too confusing

James

 

[jameske]

Wrong Spot for this post, sorry

 

[3v0]

Zigbee/MiWi can be setup as a star topology. The network coordinator is at the center. But that may limit you to 7 address bits. Not sure you can check the datasheet I linked to the previous post. You really need to study this as it is much more complex then I2C SPI etc !

PAN: Personal Area network
PAN Coordinator: Node that manages the network. In the case of a star network it is the hub. Limited to 127 connections.
Coordinator: Node that is allowed to have 127 additional connections.

I think you want one PAN coordinator with 20 coordinators in a star. Each of the 20 coordinators acting as a star subnet with up to 127 additional nodes. In you second diagram each of the node 4's would share the high order address bits of its coordinator so there would be no conflict.

I am not sure where I2C comes into this. I suppose if you have a uC with I2C you could send it a radio packet with and I2C address and data. Not sure what the point of talking about I2C is in this context.

 

[jameske]

Yes I see what you mean about I2C, I'm going to use UART instead now.

So to get it straight in my mind, is the network configuration set up in the hardware (Xbee board for example) using Zigbee and the UART interface is used to get data out onto the network and back in to the connected microcontroller?

 

[3v0]

You need to be more specific about what you want to do. What part of this is radio and what part is hard wired.

The network is a network of micro controllers connected to radios. The XBee is a prepackaged virsion of this that can be setup as point to point or zigbee.

If you use most anything but XBee you will have a micro controller attached to a radio module. On each micro controller you will have the network stack and your application.

 

[jameske]

I realise that I have not really thought of this network too much in depth and so I have not explained myself very clearly. In the pictures the black lines represent the way the network traffic will follow using addressing.

Each device will receive all the data that is transmitted but it is the device that is addressed that will pay attention to the instructions or contents of the data.

So from the 'wireless hardware' point of view I guess you could say that it will be like point-to-mulitpoint or similar to the mesh, so that each device can contact each other, however, the network traffic will be set up to be like a star network where all the devices will have to talk to a base station to talk to something else.

 

[3v0]

Try reading this. https://ww1.microchip.com/downloads/en/AppNotes/AN1066%20-%20MiWi%20App%20Note.pdf

When you have a handle on it you will be better able to formulate questions or even answer them.

Unless you do that there is not much I can tell you that will make sense.

 

[jameske]

Thanks 3v0, and sorry for the confusion.

James

 

[3v0]

There is nothing to be sorry about. I would love to have someone else interested/working on these Personal Area Networks. Dig in ! I will he happy to answer any question you have when working your way through it.

The document is microchip but as I understand it the addressing is common not only to zigbee and miwi but maybe other 802.11 communication too.