Cheap Zigbee modules
Mitch Davis
I was looking through Farnell's latest flyer, and I saw these:
http://au.farnell.com/jsp/search/productdetail.jsp?sku=163020201
It's a Zigbee-capable SPI-interfaced 2.4GHz wireless transceiver with
onboard PCB antenna. Source code for the Zigbee stack is a free
download from Microchip. And only $13.75 each!
Are these useful?
Mitch.
Jonathan Oxer
> http://au.farnell.com/jsp/search/productdetail.jsp?sku=163020201
...
> Are these useful?
Probably not for interop with XBee modules, which implement ZigBee on
top of the 802.15.4-defined physical and MAC layers. Those Farnell
modules provide the low-level data transport, but don't implement the
ZigBee protocol that sits on top of it.
Could be interesting to if you want to build something from
(semi-)scratch, but you'd have to build / borrow / steal a networking
stack to sit on top.
Cheers :-)
--
Jonathan Oxer
Ph +61 4 3851 6600
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Jonathan Oxer
> On Thu, 2010-02-04 at 13:12 +1100, Mitch Davis wrote:
>
> > http://au.farnell.com/jsp/search/productdetail.jsp?sku=163020201
> ZigBee protocol that sits on top of it.
Hmm, correcting myself and admitting that I didn't fully appreciate
Mitch's comment about the stack being available, it seems that maybe
these *could* interop with XBee modules.
That would be really, really nice. It would take some work to get the
firmware going though.
andyg (@geekscape)
On Feb 4, 1:32 pm, Jonathan Oxer <j...@oxer.com.au> wrote:
> Hmm, correcting myself and admitting that I didn't fully appreciate
> Mitch's comment about the stack being available, it seems that maybe
> these *could* interop with XBee modules.
Digi (nee MaxStream) XBee hardware is called "XBee" or "XBee Pro".
There is a different usage of the phrase "ZigBee Pro", which denotes
the protocol specification also known as "ZigBee 2007/Pro" (see
http://www.daintree.net/resources/spec-matrix.php). My understanding
is that interoperability between manufacturers really only starts to
become viable with the ZigBee 2007/Pro standard and not earlier
implementations of the protocol. Of course, this is all sitting on
top of 802.15.4, which should be fairly interoperable ... but, doesn't
provide mesh-networking, security, etc.
The XBee Series 2 modules (also known as 2.5) come with Digi ZigBee
firmware called "ZNet 2.5" by default. This is prior to ZigBee Pro.
But, it is a simple matter to download the ZigBee Pro firmware using
their X-CTU tool (see "XBP-24" in the pull-down menu, rather than
"ZNet"). This is what I've recommended when playing with ZigBee with
Aiko and the Pebble and Series 2 modules.
The Xbee Series 1 modules come with Digi firmware that implements an
earlier "XB" protocol ... and only provides a small amount of
functionality above the base 802.15.4 standard. There are two
advantages of Series 1 (which may or may not matter to you) ... (1)
Series 1 modules just work with each other, directly out of the box,
no configuration or firmware changes required to get a point-to-point
virtual serial connection going at 9,600 baud (but, you'll need to
play with it, if you need anything else) ... and (2) you can get
higher power 60 mW and also 900 MHz versions of Series 1. Currently,
it appears that Series 2 only comes in 2.4 GHz.
Digi Series 1 and Series 2 are said to be incompatible (regardless or
the firmware you install). Also, beware that many web pages talking
about Digi XBee modules fail to indicate whether they are talking
about Series 1 or Series 2. If they say it just worked out of the
box, then they are probably talking about Series 1. If it looks more
complicated and involved to get things going, e.g. downloading
Coordinator firmware, then they are probably talking about Series 2.
Okay ... this is just within the same manufacturer's hardware /
firmware offering !
So, my guess is that achieving interoperability between MicroChip and
some other vendor, say Digi ... will be quite some fun :)
You could attempt it at the lower level of 802.15.4 first ...
basically just get the radio and some simple packets flowing back and
forth.
Then, aim to get the ZigBee Pro stacks on each ZigBee module working
together.
I'd suggest that you'd probably want to get two MicroChip modules
talking to each other first and two Digi modules (Series 2, with
ZigBee Pro) talking to each other first ... before then attempting to
get a MicroChip module talking to a Digi module. And, you probably
need to be pretty handy with a protocol analyzer that works at radio
frequencies (or call a friend).
Also, the ZigBee Alliance (http://www.zigbee.org) claims to be
open ... but, there are various levels of membership ... so, don't be
surprised if you have to pay to get hold of these "open standards" to
use them commercially ... and if you don't use them commercially, then
the current ZigBee license conflicts with the GPL :( ... see
http://en.wikipedia.org/wiki/ZigBee#Licensing (arrrghh !)
So, it'll be interesting to hear about anyone's experiences with these
MicroChip ZigBee modules. But, I'm not sure that it will be as simple
as saving $13 in hardware costs per module ... and just expecting that
it'll all interoperate with other vendors (without putting in quite
some effort).
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
As an aside, regarding Aiko and the use of ZigBee as the underlying
network.
Currently, Aiko relies upon the ZigBee network (operating as either
peer-to-peer, broadcast, star topology or mesh-network) to deliver
messages (as s-expressions) over a virtual serial connection (provided
by Digi XBee modules running in "AT" mode ... not taking advantage of
the "API" mode yet, but will do in the future).
To a large extent, this looks exactly like the USB serial
connection ... with two exceptions ... (1) more than one Arduino (just
like a party line) ... and (2) it is potentially less reliable, due to
interference, drop-out, etc.
So, Aiko adds "node names" and a simple check of whether messages are
destined for this node or not. In the gateway, there is also a module
for passing message between the USB connection and the ZigBee
network. Underneath, you can configure the ZigBee network physical
and logical topology to suit your needs.
The Aiko-Gateway can then consolidate and route messages between Aiko-
Nodes that are running on ... USB, ZigBee, Ethernet and WiFi ... using
the node names. Pretty simple, but good enough for the number of
Arduinos we've good running on a given network. It'll get more
sophisticated as required.
In the context of the original post ... this Aiko layer was added to
abstract away from all the different networking / connection
possibilities we have with various Arduino environments ... including
just dealing with the differences between Digi Series 1 and Series 2
modules !
cheers andyg (@geekscape)