RF Modules (Zigbee)

[Chris Barron]

Although mentioned in another thread, I thought it might save a few people some money if, when they're looking for a simple RF data link, they consider the Telegesis ETRX2 modules.

These use a self healing mesh networking topology so you can introduce as many nodes as you wish to your network and once created by you the network manages itself.

These particular modules have inbuilt digital I/O and A/D, so,
using a simple remote temperature logger as an example, we can do away with the remote host processor completely and replace the RF Module+PIC combination with a single ETRX2.

Sending the following command to the distant ETRX2 from the main coordinator (and data sink) makes the remote send back data relevant to the I/O pins and the A/D

ATREMS:<address>,XX?

Where <address> can be the remote node’s EUI64, NodeID or address table index and <XX> is the register number relating to the data.

All commands are in the AT format so communicating via PICBasic and a PIC is made easy.

My units cost £11.90 each and I suppose if you were making a simple 2-node network then you might be able to beat that price (especially if you are operating in simplex mode), but I feel the ETRX2 are more reliable and less noise prone than other RF modules I have used before. The units have a feature where they can actively search for the quietest channel, and data transmission can be monitored and the creation of ACK and NACK messages is automatic, which means that we can have some reassurance that a message was delivered.

I don't work for Telegesis, but recently have tried several Zigbee modules and development kits and this was by far the easiest way to go
http://www.telegesis.com/products/test_page_1.htm

The full list of commands is on the document download page in a document called "R3xx command list"

[Normnet]

These use a self healing mesh networking topology so you can introduce as many nodes as you wish to your network and once created by you the network manages itself.

Is the mesh in hardware or is it code with a C or Basic example?

Norm

[Chris Barron]

Is the mesh in hardware or is it code with a C or Basic example?

Norm

Norm,
these particular modules are based on the Ember EM250 chips, which have the Zigbee stack built in, written in C code.

you could, if yoiu wanted, blow away all signs of the Zigbeee software and use the devices as ordinary IEEE 802.15.4 compatible radio modules, IE just use the hardware and lay your own software on top. Ember provide the required development tools to do that, as do (I think) Telegesis, who will help you out with any special versions of firmware you might require.

Once I started to play I realised that it might be fun to try to implement something similar in PicBasic for use with the vanilla 433MHz (etc) modules. The software stack needn't be too large. Microchip offer two stacks for their hardware, one if them is Zigbee 2006, the other is their own protocol called 'MiWi', which is a 'star and cluster' topology capable of sending messages between nodes which are a couple of hops away from each other.
The Microchip stacks are written in C and are free to download from the Microchip website, and may provide some ideas. MiWi is a significantly smaller protocol than Zigbee, and can be implemented in a smaller pic than is required for Zigbee

Chris

[Chris Barron]

I've just been reading an online newsletter (Free to subscribe to if anyone wants to stay up to date)
http://www.embedded.com/217400339?cid=NL_embedded
....which poiints out that the Zigbee Alliance is planning further integration of internet standards into the Zigbee protocol. This would mean that you ought to be able to connect anything to the internet using wireless (plus a gateway too, of course)

[Ioannis]

Nice one. Thanks Chris.

Ioannis

[lester]

If your building a ZIGBEE or any other wireless network at 2.4ghz, a major consideration is through put of data and integrity of the wireless link.

Its a good idea to use a spectrum analyser to ensure that your locality is clear of potential killer interferance such as baby monitoring devices, leaky microwave ovens, wire less video camera's and wireless alarm modules, all of which can cripple zigbee or 802.11 network performance

Take a look at www.wi-spy.co.uk

Here is a little video that explains the project range

for home users there is a low cost option: http://www.crownhill.co.uk/product.php?prod=2139

Seriously worth the money, even we cleared up a rougue 2.4ghz signal radiating intermittantly accross the band, without wi-spy we'd probably never have found nit......even though we have a 30K GBP Agilent spectrum analyser sitting in the workshop, wi-spy is just so convienient.