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Low Power Ethernet Hubs?
mike.851 asks: "I'm an engineer working in the embedded systems field. For the past few years, I've been using RS-232 to interconnect various modules into the embedded systems that I build. Lately, I've found that RS-232 simply isn't flexible enough for my growing needs. I need to switch to something else, and I don't think that USB is really an option for me. I've been looking into embedded ethernet as an alternative. I've found several great low-power platforms for hardware development including several of the uClinux kits as well as products from Rabbitsemiconductor. However, I'm having trouble finding ethernet hubs that meet my power requirements (my goal is 2W or better for the hub). So far I've found Ctrlink and W-linx, and I've considered replacing the power supplies in commodity hubs with switching regulators. Does anyone have experience with these products? Does anyone know of other low-power hubs? Thanks."
What about FireWire faster than fast ethernet and is peerless. Apple just released a reference driver.
You could always take a step back in time and use 10base-2. Yeah, coaxial cable sucks and you're limited to 10 Mbps.
Also, I have no idea if any embedded ethernet controllers support BNC connectors, but this would allow to you take one device out of the power consumption equation.
Starting references: here and here.
Ethernet is designed for relatively long distances, and has high power requirements to support those distances. I've worked building embedded systems that used lower power trancievers on the backplane and on each board to save power. Obviously if you do something like this you won't be standards compliant anymore, but if you're only talking to your own devices it could work for you. If not, there are high speed serial interfaces availble on telecom chips that you could use. Search google for HDLC and you'll find exactly what you're looking for.
I ran into a similar perdicament last year where I needed a low power ethernet switch/hub to connect two wireless units on a tower where the cable lengths to the ground were too long.
We ended up using industrial ethernet switches from Sixnet. The price wasn't _too_ bad, I seem to recall $500 for a 5 port switch. Their site is: here
Taking a look at the specifications located here they have units in the 2W Range.
I hope this helps. BTW, we've had no problems with the unit, even after a lightning strike that nuked two of the connected radios.
SIG: HUP
While Ethernet is one option, it might be a poor fit for your needs.
Some of the things you left out were the ability to survive in harsh environments, dirty power tolerance, price considerations, distance, etc.
There are a number of other bus systems that have made a few trade offs in these areas vs. total speed. Many of them are derived from work for the aerospace and automotive markets.
A few systems you might consider are:
LIN - very very low cost, but probably not fast enough for you.
CAN - up to 1 mb/Sec, lots of low cost off the shelf parts available, developed mostly by Bosch.
Flexray - faster yet, parts are more expensive, but it is faster
MOST - very fast, but targeted at moving multi-media data.
TTCAN - a modification of CAN for real time.
Most of these will support power on connects/disconnects, and are very fault tolerent.
Places to go:
www.flexray.com
www.can.bosch.com
www.ami-c.org/downloads1.htm
These are automotive focused (I'm NOT a "Car guy"), but that is because the industry is very cost aware and very big into reliability. What they tend to use is 10 year old technology that has been beat to death, has all the bugs worked out, has bunches of development tools, and all the hard parts (chips, in this case) are commodity items.
----- Lotus Super 7 - A real car.
Have you considered PoE-based solutions? Here's one from 3Com, the NJ100 Network Jack (and a review of it by Tom's Hardware). While the NJ100 is not intended for use inside a closed box, using one of these would allow you to route power along with data between the various modules in one of your systems.
Stay away from 100Mb ethernet- by design, if you have a 100MB link, there is a continuous stream of a pseudo-random code being transmitted by each side, which means, basically, 40mW per port, no matter the activity. 10Mb uses much less frequent link test pulses. You can also go in and remove the LEDs, which are probably unnecessary in your application. If you really want to go hard-core, you can hack your way into the part using the MDIO interface (Similar to I2C) and disable unused ports individually.
The Altima AC205 is an "ultra low power" part that may be used in the hub you want. It is 100Mb, but to use the power hungry 100Mb mode, both sides have to be 100Mb.
The same I2C protocol used in PCs for environmental monitoring and whatnot is useful for embedded too. You can string several devices on a two-wire bus, you get 2Mbps of speed (I think, it's been a while), and I've seen embeeded systems boards as well as devices like lcd display units that support this protocol for generic communication. There's also the I2C-variant "SMBus", not really sure what the difference is between the two.
11*43+456^2
If you reall only need the equivalent of an RS232 connection, then you may only need a crossover cable. Similarly, it may be cheaper to provide two or three ethernet trancievers and crossover cables to the associated units, than it would be to pay for a third-party low-power hub.
Free Software: Like love, it grows best when given away.
But, if that's the case, then every transformer on the planet is using "wireless power". You see, you're making the definition broader than most EEs would agree with, but my whole point was that it is shortsighted to say that the only power is that which we have already gotten into our wires. Everybody already knows about what you're saying, and you add nothing to the discussion.
I should have just left it at that, but you corrected me, and your comment was based on a poor reading of my comment. It's just annoying when people do that. Have a nice day.
They who would give up an essential liberty for temporary security, deserve neither liberty or security
And when we play Quake 3, I'll hang on to the lightning gun, and you can just have the gauntlet.
I think you're pissed that your version of wireless power has wires, while mine doesn't. You seem to believe that electrical power is the only kind of power, but I still bet you'd run to the storm cellar during a tornado! I guess you could say that I accelerated into slashdot with my Mega-Cool low User ID, and yes, hanging around here that long might have a lasting impact on my brain functionality. Duh! Oh well, at least you got in within the first 200000 users!They who would give up an essential liberty for temporary security, deserve neither liberty or security
Sure, my UID is not the lowest, but at the least I've made an effort to contribute in a positive manner along with my smart-ass remarks.
SIG: HUP