more on Zigbee

At 12:48 PM 6/1/2005, Steve Hassenplug wrote:
> On Wed, June 1, 2005 12:29 pm, Bruce Boyes said:
> > Bluetooth is actually very poor for embedded or robotic applications. It's
> > a power hog
>
> You mean compaired to other comm devices, or compaired to a couple 
> motors?  I'd
> think if you have a moble robot, the motors are going to use much more 
> power than
> anything else, right?

Good question. I was comparting BT to other RF systems. But you won't 
typically run your motors at 100% load all the time, either. So typically 
on a Lego bot, motors will be the main power users. Add  BT to a Lego Bot 
and the battery life will drop significantly.

> >From what I just read, you can transmit much more data with BT.  Isn't 
> that better?

BT raw data rate is about 700 kbits vs 125-250 kbits for Zigbee. So if you 
want to stream audio, BT is better. For smaller amounts of time critical 
data - like sensor and motor control, Zigbee is better.

BUT BT can only support 7 nodes in a network. Not much good for robot 
swarms. Zigbee supports 255 or more. Plus Zigbee has 5X the range of BT.

> > Zigbee is much newer
>
> And, to me, that's a problem.  This is the first time I've heard of 
> Zigbee.  I know
> I can go out and get a BT card for my laptop.  Or, I can connect with my 
> PDA.  Is
> that same hardware available for ZB?  Where will ZB be in a year?  In five 
> years?

That fact that this list hadn't heard of Zigbee was my main reason for posting.

See the devices available from places like Mouser. Zigbee is less mature 
right now.

Crossbow supports Zigbee embedded nodes, which you can buy today. They do 
not support BT. There are reasons for that: battery life, node count, etc.

What about sensors? Show me a BT environmental sensor....
Here are Zigbee sensors available today:
http://www.xbow.com/Products/productsdetails.aspx?sid=101

> It seems to me that LEGO is NOT a technology company.  They don't design 
> or develop
> new technology.  They make toys.  Toys that use existing technology.
>
> Seven or eight years after the RCX came out, is it still cutting edge 
> technology?
> No.  In fact, I don't think it ever was.  But, it's still very cool.
>
> I think LEGO has to leave it to people like you, Gabe, and John Barnes, to 
> create
> cutting edge stuff.  They need to stick to solid, proven technology.

I partly agree: Lego is a toy company whose Mindstorm market is 
unsupervised 10-year olds, and to keep cost down they need to use "mature" 
technology.

But I also disagree: Few of those unsupervised 10-year olds are on this 
list, and few of us on this list want to bear the same constraints as that 
unsupervised 10-year old.

Maybe I misunderstood - I thought the context of the discussion of BT was 
related to alternate, more advanced controllers for use with Lego motors 
and sensors. These systems would not need to suffer the same constraints as 
Lego's toy products. I doubt Lego makes their design decisions based on the 
interests of this group...

Lego could afford to add BT but could not do that with a low cost 8-bit 
micro like the RCX now uses, and BT is really not the best solution for a 
toy (name one BT toy today). Proprietary, lower cost and lower power 
technology would probably be better from Lego's point of view.

But for those of us making Lego add-ons or alternatives, BT IMHO is a dead 
horse. BT has had zero impact in the embedded control space. Zigbee is the 
way to go. Zigbee is an IEEE standard - 802.15.4 - so that reflects some 
maturity already.

Yes, few people have heard of Zigbee now. Few now have heard of UWB 
either... But about a year before it changed the world, the same could be 
said about the internet. My point is just that Zigbee is already in use in 
industry but it's not in the public eye like BT.

I doubt Zigbee will be installed in phones and PCs. 802.11 will continue to 
dominate there. But 802.11 is also a power hog and not suitable for long 
battery life embedded systems (my Tungsten C being a case in point).

Zigbee appears to be poised to make a great contribution in home 
automation, industrial control and sensing, and other real-time, 
power-sensitive applications.

But the bottom line is I don't have any axe to grind. My purpose in 
emailing was to let people know that Zigbee is a much better RF system for 
new robot and embedded control designs:

http://www.computerweekly.com/Article132791.htm
http://www.embedded.com/showArticle.jhtml?articleID=160911675
http://www.techworld.com/mobility/news/index.cfm?NewsID=3733

The battery life chart on this page is especially interesting:
http://www.atmel.com/products/zigbee/


Regards

Bruce


> Steve

------- WWW.SYSTRONIX.COM ----------
  Real embedded Java and much more
+1-801-534-1017  Salt Lake City, USA