Slashdot Mirror
Low-powerered Ethernet Hard Drive?
WotPeed asks: "The company I work for builds extremely sensitive electric and magnetic field sensors. The project I'm just starting needs to use a hard drive to store the digitized data for long-term measurements (no more than 20GB). Unfortunately the hard drive has to be external to the sensor because it generates too much magnetic interference (hard drive needs to be at least 20 feet away). I'm therefore building an ethernet link into the sensor so that it can connect to a remote hard drive. Wireless is an option for a later revision but we're going with wired ethernet at first to keep things simple. There are plenty of network attached storage devices out there but they all assume they will be used in an office environment, and therefore consume a LOT of power. I'm looking for an ethernet hard drive that consumes less than 10W (this system will be used outdoors and runs on 12V batteries). Does Slashdot have any suggestions before I roll my own? I don't need any of the fancy features found in most NAS solutions...I just want a hard drive I can FTP to."
I imagine that MicroDrives consume very little power due to their small size and the fact that they can be powered by a PCMCIA slot.
I'm sure the hard drives used in many MP3 players such as iPods also consume very little power. . .
I'd think you'd have to roll your own. That said, it shouldn't be too hard to do. Just take a laptop drive, interface it to a microcontroller (search Google and you can find code and such to interface PICs, Amtels, HC11s, and others to HDs). Add ethernet (either a ethernet chip, you can find info on interfacing those with the same microcontrollers) or just use a reliable ISA card (3c509s are very well documented) and connect that to the microcontroller (also easy to do).
Comment forecast: Bits of genius surrounded by a sea of mediocrity.
The slowest Seagate 20GB drive i found consumes 24 watts. You'll still need an interface - cpu, memory, network... /." help. If it's a power availability problem - spacecraft maybe?... you're not looking for a COTS solution... there would be none. If it's a power DENSITY problem... consolidate all the drive needs in a server away from the environment you're measuring.
You're talking about NAS. So far, as you note, that's always been an office thing. They're made with ready power and heat dissipation taken for granted. I can't imagine a company with a real need for such a specialized requirement (as in, you're about the only case it's ever been needed) needing "ask
Incidentally, just so you don't embarrass yourself in front of your boss... wireless, at least in the most-commonly used sense, uses both electric and magnetic fields, most commonly at 2.4 or 5 GHz. Hell, conventional ethernet is something like DC-UHF, but mostly contained in the cable... perhaps something optical might be better-suited to your needs?
Frankly, I think I'd take the DC outputs of the sensors and route them as the center conductors of good-quality coax, and bring them all to a bank of A/D converters somewhere away from the environment being measured.... can you give some kind of detail about the environment?
Anyway, when you roll your own, you'll have to use something like a Hitachi microdrive. The 1GB drive consumes 8-1/4 watts on write. Maybe a transmeta-based motherboard won't break the rest of the budget.
I'd be glad to work on it. I need a job.
I'm interfacing MMCs (could just as well be SD cards in non-secure mode) via SPI to a microcontroller right now for data logging....if ~128-512Mb is sufficient for your application, this is an excellent alternative to rotating storage.
-psy
Of course, you'd need to add USB capabilities to your sensor(s) and you wouldn't really FTP to the drive (I don't believe), but this would be a fairly cheap and modular way to solve your problem.
But, if you do roll your own HDD that can be dropped into any network with just a Cat5 connection, let us know! ;)
"1984" was ment to be a warning, not a guidebook. You hear that Kim Jong-il!? BushCo?!
You might consider using compact flash or a similar medium instead of a HDD. That'll be low power. Otherwise, you might power the device over some of the spare pairs in the ethernet cable. Some telco stuff is implemented that way.
Assembly is the reverse of disassembly.
Assuming it is average and you are doing long term measurements, the average data rate must be pretty low (relative to hard disk transfer rates). So, I would add RAM to the sensor end controller and cache information there until you hit lets say 80% cache full, then fire up the hard disk and do the writes.
I would use USB 1.1 for the link, controllers are easy to find and cheap, the power requirements are much lower then ethernet+microcontroller+drive interface.
If your power requirements are peak, then put a lion battery on the hard disk end, charge it from the USB power and operate the drive from that.
If cost it not a huge issue, you might consider 10 2GB compactflash cards. That would eliminate the need to implement the remote data link.
If you're power sensitive, perhaps ethernet isn't the best technology for you. Ethernet is designed for long distances, and is hardly low power relative to other interconnects. If it's in the budget, maybe you should consider optical fibre channel. Then you would have essentially the power requirements of the disk and the tranciever. Another option would be firewire. It's lower power than ethernet and it has the added benefit of being able to power the drive over the interconnect cable.
Ever heard of Near-End-Atenuation? No? Its the electo-magnetic interferance suffered by telecomm gear when lots a wires draw near each other at the switch. Well, thats the snow-ball effect. No single rain-drop thinks it is the cause of the flood! Anyways, if this sensor gear is so sensitive, then ethernet might be too noisy, electro-magneticly speaking! I would sugest a fiber-optic linkage with a low-powered led that is significantly less noisy, in relative terms comparied to a wire. In an ideal situation the sesor would be away from the data collectors anyways. Oh, and BTW - wireless would in theory trip the sensor too! Seems as if optics is the only real true solution, in my mind anyways. ;)
It isn't a lie if you belive it.
If EM interference is an issue, your cabling may cause a problem too... They're a bit pricier, but what about a FibreChannel drive? You've got an optical data path -- no EM interference. Yeah, the adapters cost more, but consider the overall cost for the lab, and the potential EM worries avoided.
Fascism starts when the efficiency of the government becomes more important than the rights of the people.
Sure, but once you specify FTP you then need TCP, which means you need IP, and an FTP server, and a filesystem, and Ethernet, and ... you've just specified a NAS.
But the problem didn't require a NAS. Your problem was "too much interference so need the hard drive 20 feet away". You could solve this problem with Fibre Channel.
Investigate an external disk enclosure with fibre channel and a DC power supply. I know Sun was selling these just 2 months ago for desktop external disks.
There are plenty of bus-powered USB drives for use with laptops. That's the lowest-powered external drive you are likely going to find.
Don't bother with Ethernet-attached storage; those are not usually designed with low power in mind.
The personal server is not an actual product. Just an interesting concept.
what about the terrapin mine at thinkgeek its got ethernet and USB. Seems ver flexible. only 10gigs though but you maybe able to drop a 20 or bigger into with minor hacking...
You bit bang it with a mircocontroller.
There are 4 boxes to use in the defense of liberty: soap, ballot, jury, ammo. Use in that order. Starting now.
just continuing on with another posters idea of using firewire, why not use an apple iPod. It comes with its own built-in battery and add on batteries are on the way for the new models. Apple states a 10 hour battery life (although it will probably be less if you have to spin the drive all the time).
As for the distance factor I use a six foot firewire cable with my iPod but I have seen 10 foot cables before, as for 20 foot ??? they might be possible but you might have to build them yourself. I get the impression you know you way around electronics so this shouldn't be a problem. I would check to see what the cable lenght limit is on firewire first though.