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Portable Hubs? 103

Posted by Cliff from the "portable"-means-not-being-dependent-on-a-wall-wort dept.
Nahdude asks: "A friend of mine and I tend to have frequent mini-LAN parties in odd places like diners or parks with our laptops. We've been using a crossover cable with no problems, but recently we've attracted some attention from friends, and even some strangers, who want in on the action. So I've looked (without success) for a portable networking solution. Has anyone found and had luck with a battery powered network hub? Keeping in mind that wireless, although neat, will probably be a bit difficult because the expense of mobile wireless cards could be out of range of a lot of the people interested (we had 15 people last week in a bar, woot, but only 2 player games with crossovers because they wouldn't let us plug in a hub)." I haven't seen many of these now, but maybe if someone plants the idea in people's heads we'll see these several years from now...
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Portable Hubs? More

Portable Hubs?

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  • the more I really want of these!

    How difficult would it be to coble together some form of power delivery device that one could carry in a backpack. Total wait of the entire contraption (hub + power device/battery) should not exceed 30lbs (I'm being generous).

    Bonus points will be given for: integrated solutions, solutions under 15 pounds, solutions under 5 pounds, solutions with integrated firewall and/or 802.11b support and grand mal bonus points for something that's recharge-able.

    First person to market wins my undying loyalty, gratitude and all the beer, soda and junk food I can provide on my meager salary.

    • Re:The more I think on it... (Score:5, Insightful)

      by Captain Pedantic ( 531610 ) on Friday September 13, 2002 @08:46AM (#4250513) Homepage
      Nothing personal Cliff, but shouldn't their be a "Google Filter" for postings to Ask /.?

      For example, this [kan.org] is the device you're looking for.

      How did I find it? Like this [google.com]. Note the search words; battery powered ethernet hub. Ok, so its a hub, not a switch, but still!

      Ask /. is probably the most interesting part of the site (apart from trolltalk of course) but you also get some of the lamest submissions!
      • BTw did you check out the w-linx solution, even better. (It can be powered over ps/2 or usb whoho!)
      • This is the reason I hate it when people just up and throw out "Use Google", when the truth is, I did use the bloody thing and came up empty: and I'm usually good with keywords, except my '"battery power" hubs' (note the quotes) pulled out only a pair (which wasn't what I was looking for), while your 'battery powered ethernet hubs' pulled out a flush.

        The moral of this posting: Don't think someone DIDN'T check Google because you found something they didn't. This too is one of the primary reasons I do Ask Slashdot.

        PS - Thanks for finding the right keyword set for this, I'll be digging around on my own, this weekend, to see if I can find something that suits me.

        PPS - Re: lame submissions -- Yes, I do get my fair share of those. I've tried to let readers see the kind of stuff that I get that DOESN'T hit the pages every April 1st, but I have to give up that practice for something more original this next year because people hate it when I do that. (I wonder if I should start doing this on Halloween instead as a "trick" instead of the usual "treat".... nah.... I don't look good in digital tomato...)

        • Google Answers [google.com] might be more appropriate when you can't get google to cough up something. It isn't free (US$2.50), but there is a money-back guarantee on the answer. Note though that browsing previous questions and answers is free.

          Of course, if you are truely desperate, you could always contact the Sacred Knights of Cyberspace [hamster.org]. Between Ask Jeeves and Google Answers, there's not much call for us anymore, but back in the day I'd get questions. Usually from kids needing help with finding information for their school assignments.

          Ah, the old days... When the 'net, while not exactly innocent, was still at least collectively naive.
        • Re: lame submissions -- Yes, I do get my fair share of those. I've tried to let readers see the kind of stuff that I get that DOESN'T hit the pages every April 1st, but I have to give up that practice for something more original this next year because people hate it when I do that. (I wonder if I should start doing this on Halloween instead as a "trick" instead of the usual "treat".... nah.... I don't look good in digital tomato...)
          Why don't you just add another section to slashdot?

          The reject of the day section or something, where incredibly lame submissions that (if possible) have some comedic value get sloughed off into. [That way it wouldn't make it to FP, but would be around for people who are into gauging that sort of thing.

      • How did I find it? Like this [google.com]. Note the search words; battery powered ethernet hub.

        In the future, do you believe submissions to Ask Slashdot should include a list of Google queries that failed to produce anything relevant?

    • An APC 600 will be plenty... rechargeable, under 30lb, and just plug in that 5 port LinkSys switch.

      Only problem is finding a way to stop that irritating alarm that UPS's have.

      Regardless, this gives you a backpack-portable solution to multi-user networking.

      To get your wireless solution, then use a wireless hub + cat5 switch combo device.

      gus

  • Googled (Score:4, Informative)

    by Anonymous Coward on Friday September 13, 2002 @08:29AM (#4250461)
    http://www.w-linx.com.tw/products/network/mini-hub s.htm [w-linx.com.tw]
    • Ok just for the uninformed, this is a ethernet hub, powered by either sucking power form a usb, or from ps/2 through a splitter cable for the keyboard. (The ps/2 cable appears to be sold extra)
      Lowest price I've seen is http://www.mypccity.com/proddetail.asp?linenumber= 819#1
      for 39.99
      49.99 most other places, though its hard to find, couldn't find on pricewatch, but google for SW-005CM
      gave me a few hits.
  • You could just set everything up as an Ad-Hoc wireless network, you don't need a hub.
  • Get a 12 volt battery and an inverter (that's a 12 volt DC to 120 volt AC converter) and then plug it in!

    Or, more simply, I just checked out my Netgear MR314 (wireless router, but has 4 wired ethernet ports). It has a DC 12 volt power supply on it (rated at 1.2 amps), so in principle you can run it off a (car?) battery directly. Car batteries come in different sizes, are rated at ~60-200 ampere hours, so you can size your battery on portability basis and on how long you want it to last.

    If you do use a car battery, check the voltage before you connect it, 12.5 volts or so should be OK, but car batteries are only around 12 volts, I've seen them go as high as 13.5 volts (particularly while charging), that could fry your router. So you could connect it up to your car, but it might not be a good idea to leave the engine running in that case.

    • Yeah, anyone is going to carry an inverter, the hub, the hub's AC->DC converter, and, of course, the CAR BATTERY THAT WEIGHS 30 POUNDS, all along with a laptop case.

      Seriously, somebody else posted a link to a genuine battery-powered hub. You should check that out. You should also get your head checked out :)
      • You should also get your head checked out :)
        Not his head, his back. :) If he thinks that a car battery solution is an answer to powering a portable hum, then he's either the new Andre the Giant, or he's got serious back problems.
      • I just checked maplins- a 12 volt 6 ampere hour lead-acid battery weighs 1.6 kg. Heavy, but not outrageous. That would last 4 hours or more, which is plenty. And there's plenty lighter than that.

        You're off by a factor of 15 with your weight.

        A car battery on the other hand is good for a week-long party.

      • Seriously, somebody else posted a link to a genuine battery-powered hub. You should check that out.

        Yeah, I did. You're a total spanner. They took a standard hub and connected a battery to it, just like I was suggesting. It's a smaller one, and so it doesn't last as long. But if you'd actually read my posting, you'd note that I only gave a car battery as an example. You're a total div, you know that?

  • The wall wart of my 5 ports Linksys 10/100 switch gives 7.5VDC at a maximum of 700mA, which is about 5W of power. I'd have to check with a multimeter or use one of the DC power supplies at school, but under normal usage I'm sure it's way lower than that maximum. Even with a 12Ah 12V battery, plus a voltage regulator, you'd still have enough juice to outrun the laptops.

    That's something just thought about: your laptops will drain faster than the hub. So even a smaller battery than the 12Ah I mentionned would do the trick. Pick a rechargeable battery if you don't wan't to throw away too much metal in the trash.

    The only thing you'll need to do is a small package to transform the 12V to 7.5 (7808 or even a small transformer), and wire it to the right DC plug for the hub, and there you go!

    • The only thing you'll need to do is a small package to transform the 12V to 7.5 (7808 or even a small transformer), and wire it to the right DC plug for the hub, and there you go!

      See, this is one of my pet peeves: people talking authoritatively about stuff they have no concept of.

      Well, I'll give you a half point, you did say 7808 which is an 8-volt regulator. But...a small transformer? That's right off the scale. Transformers don't work on DC.

      The regulator is definitely the best way to go, and you'll need a battery voltage that's decently higher than required supply. The reason is that your battery voltage will drop as the hub runs, and I'm not sure how low it will go before the hub quits working. So, don't pick up five 1.5V nickel-metal-hydride AA's to get 7.5 volts.

      A small 12V gel cell battery would be ideal. Put everything into a project box and add a charger, and you've got a solution.

      • That's right off the scale. Transformers don't work on DC.

        My knowledge about transformers is, I confess, rather limited. That's why I put the 7808 before in my list of possible solutions.

        Of course, thinking more about it, since it's DC there's not change in the voltage in the input coil, so no current is inducted in the core of the transformer. No core current, no voltage at the output coil. So yes, the transformer was a very bad idea, unless you want to drain the battery rather quickly :)

        Thank you for pointing out the obvious.

        Another point against 5 1.5V AA batteries is that the energy they have is somewhat limited. So not only their output voltage will drop, but even if they keep their output voltage somehow they won't be able to power the hub (or anything else) for as long as your gel cell battery.

        Bonus question: why do they need 7.5V? I've handled a couple hubs/switches (5 to 8 ports, 10 or 10/100Mbps), and they all need 7.5V. Normal chips need 5V or lower. Is it to drive the Ethernet signals?

  • If it says (eg) 9VDC, then get 6 D-size and tape and a connector (cut it off the power pac if you have to). Schweet. If it needs AC ge a DC to AC module from Tandy or somewhere and your christmas (for a few hours at least)

  • I've used one for a digital readout system before and it lasted for about 8 hours. I'm sure that APC [apcc.com] would have something small that you could plug in and charge, then plug your hub in wherever you wanted to use it.

    • One of the problems with using a UPS (notwithstanding the "heavy" issue) in this setup (in my experience with APC anyways) is that they will not power on without being plugged in first.

      I have seen some that work otherwise, but my suggestion would be to get something a little "easier" on the weight requirement. I believe Radio Shack has "D" size Nickel-Metal Hydride (sp?) batteries that are 4-6 AH. Select the right amount of batteries, grab a battery holder while you're at it (as well as a plug if you don't want to castrate the original power supply), hook it all together, and you've got a cheap, rechargeable portable solution.

      Oh -- you will have one more cost -- you'll need a charger for the batteries as well. Maybe it's not the cheapest solution, but it will definitely be lighter than a UPS.
    • Yea, but doens't the thing usually beep to tell you it's no longer getting power? I don't think what ever place he is in would be that happy if they were all sitting there playing and had some box making some high pitched beeping noise constantly :)
  • Keeping in mind that wireless, although neat, will probably be a bit difficult because the expense of mobile wireless cards could be out of range of a lot of the people interested

    So these people dropped $1000 or more on a laptop but can't afford a $50 WiFi card?

    Is this a joke?

    • I'd call it around $75, but that's a good question. But then again, I'm not interested in buying one even though my school is slowly going wireless, too.
  • Sorry, I don't have a link.
    I saw it in a shop (in Rome, Italy) last year: a small 5-port (with 6th connector also, which is 5th port but crossed over) which would run off a 5v DC power supply or a little pass-thru PS/2 adaptor which would suck the power off the port.

    I know PS/2 only gives very little power, but evidently it was enough.

    I don't know by how much it would shorten a laptop's battery life, but heck, that was a nice, and Tiny! thing to carry along.

  • Have you tried to search for an USB- or PS/2-powered hub ? They may cost a few bucks more than a standard wall-plugged hub, but they do not need a separate battery, they just slowly suck out your Laptop battery.

    (Please note: I do not think of USB Hubs, but USB powered Ethernet hubs.)

    Tux2000

  • Good old Hubby. (Score:4, Informative)

    by SoftwareTechie ( 244191 ) on Friday September 13, 2002 @09:16AM (#4250634)
    Try this [dlink.com] hub. It is powered from a standard keyboard socket and they can be cascaded together.

    -----------------------
    • I see nowhere in any product description of this fact???
      • >>I see nowhere in any product description of this fact???

        That is true, but I have a Hubby. Checking the web site again I find the de906 kit [dlink.com]. On that page it says:

        "Includes [...] two keyboard power cables for hub [...]"

        and

        "For hub features, see DE-805TP/C", which is the product for the original link i provided. They could have made that information a little more straight forward to find!

  • Wireless expensive? Give me a break! (Score:4, Insightful)

    by uradu ( 10768 ) on Friday September 13, 2002 @09:17AM (#4250638)
    You can pick up a basic 802.11b card for $30 [yahoo.com], so price is a flimsy excuse. If they can't afford $30, maybe your friends should play battleships on paper instead? Or maybe they can't afford that fancy paper either?
  • Don't know too much about it, but, check out Power Over Ethernet (POE) [google.ca]. Runs things like hubs by delivering electricity over cat5.

    You need a special "injector", to get power into the cable, though.. might be able to find a battery operated injector.

    Worth a check, at least.

    S
  • I might get laughed out for this, but what about usb networking? Aren't usb hubs powered off the same 5V that feeds devices?

    Also, what kind of bar are you in that you start an impromptu lan game, and *15* people have laptops and want to join. I want to move to whatever utopia you inhabit.
  • Shouldn't there be bassive hubs that require no electricity?

  • How about coax? (Score:3, Informative)

    by (trb001) ( 224998 ) on Friday September 13, 2002 @09:48AM (#4250793) Homepage
    When I was in college, we used to do the same basic thing but none of us had a hub. The solution we found was to get combo ethernet cards that had rj-45 connectors as well as coax connectors (I think that's what they're called). But a few lengths of coax along with t-connectors and terminators and there's no need for a hub. Works great and is (relatively) portable, just throw all the cables and connectors in a bag.

    --trb
    • Coax just means "Coaxial" i.e. the conductors have the same center, which is to say that the conductors form concentric circles. This applies to a lot of different cables and connectors. For example most home audio uses non-coaxial (independent axis?) cable with a coaxial "RCA" type connector. The connector used by thinnet is called BNC, British Naval Connector.

      An additional piece of related off-topic info is that connector sex is determined by the innermost conductor. So a thinnet cable has a male plug and the card has a female jack, though it might appear to be the opposite if you don't look closely.

      That "other" connector on combo cards is not a joystick port, it is an AUI connector which can be used in conjunction with vampire clips (which are exactly what they sound like, they clip through the insulation on a cable to provide a drop) to connect to thicknet.

      Interestingly enough, this same topology is still the basis for Ethernet networking, but the thicknet bus became a thinnet bus became the interior wiring of the hub. Everything related to computers shrinks!

      -Peter
      • And after AUI there was (for a brief time) AAUI, which stood for Apple AUI [hardwarebook.net]. This was a 14 pin mini connector (I forget the connector type) that came on Quadras and the first few generations of PPCs. You could then get either a 10base-2 (thinnet/BNC) or 10base-T (RJ45) transceiver to connect to it.

        Regular AUI Transcivers were a pain in the rear because they were bulky (they used to stick out of the back of a machine 3-4 inches!), and unless you physically screwed them to the network card they would always fall off when someone moved the table. AAUI connectors had this cool built-in clipping mechanism that held them tight, and the transceivers had a short "tail" so that they could dangle down under the table.

        The other nice thing about the AAUI 10b2 transceivers was that they were self-terminating, meaning you didn't need a terminator (a little resister thingy, not a killer robot) if you were at the end of the chain. Then the Web got big, more consumer machines started coming with Ethernet standard, and RJ45 won the battle. Simple wiring is better for home users at the expense of needing an extra device (a hub) to conenct multiple (more than 2) devices.

    • 10 Base 2, I believe it is called. Haven't seen a lot of new NIC's with those attachments...

      • I've seen very cheap converters though (10Base2-10BaseT). I had tons of these laying around but I think they went out in the scrap heap years ago :-/.
  • "we had 15 people last week in a bar, woot, but only 2 player games with crossovers because they wouldn't let us plug in a hub" OK, I agree multiplayer games are **way cool** and I play them every chance I get...but in a bar ??? WTF??? Tell me I'm not the only one who finds this odd...offensive even.
  • Use a battery to power the hub. Essentially, you could probably get a mini switch or hub powerted by 9V, 12V, 24V etc.

    Then link batteries of any value, + to - to + to - and so on.

    Link batteries of any type until you've got the correct voltage.

    Then strip open a power cable that you can slott into the DC input and connect one wire to + and one to -.

    Voila ;)
    • One minor problem with this: If the device wasn't designed to be run off of batteries, then it is expecting a continuous supply of the proper voltage. When the batteries run low, you will be feeding under-voltage to the device, and it may not have circuitry to shut itself down in this instance. Therefore, you may end up frying your hub. If you use a battery pack, make sure you wire up a circuit that cuts off power when voltage drops below an acceptable level.
      • Ahh true! I'm sorry I didn't think of that. One quick hack though, is to make several sets of batteries in series - For 12V, for instance, connect a 9V battery and 2x1,5V batteries... Make several circuits like that and connect them in parallel :) Then the batteries will at least last much longer. Of course if you can carry a car battery it would be even better ;)
  • It might be worth looking into BNC networking, the cables are heavier and less flexable but it is entirely passive. For a small ad-hoc network the low bandwidth and maintenance issues can be overcome. Older PCMCIA cards should be realtively easy to find, I have one in a box somewhere myself and there is one on ebay [ebay.com] or there are converters [milestek.com].

  • Dlink (Score:1)

    by shave ( 16748 )
    Check out http://www.dlink.com/products/hubs/de805/ [dlink.com]. Small 5 port hub, but it can be powered off of your PS/2 port with a little bit of work(see http://www.aitech.com/support/aig2install.htm [aitech.com]) for an example.
  • Maybe the bar across the street would.
    I never ask if im plugging in somenting small and non dangerous, like my cellphone charger or laptop, and noone has ever had a problem with it. It also helps that i generally go to places im at regulary, and i always tip well. Wen i usually drop 30 buks an evening, and a pretty good tip on top of that, i dont think thryre going to worry about the 25 cents of electricty im getting.

  • Solutions, wireless, etc etc. (Score:4, Informative)

    by Andy Dodd ( 701 ) <atd7&cornell,edu> on Friday September 13, 2002 @11:22AM (#4251265) Homepage
    For one:

    Price is a useless excuse for not going wireless. If you search, you can get WLAN cards for $30 on sale these days. And as many pointed out, if you plunked down $1000-2000 for a laptop, you can afford a WLAN card even if it's $100.

    That said, for another year or two, strangers are less likely to have WLAN cards. (But this is changing VERY quickly... It's getting to the point that having a laptop without getting a WLAN card is just plain silly.)

    So your two solutions are:
    PS/2-powered hub. Good if you have a decent mobo, but some laptops don't quite meet the PS/2 power supply spec... And there's no way to tell w/o risking damage to the mobo. Also, it'll drain your battery.

    Homebrew battery-powered hub. IMO this is the way to go. There were a few links to a 9V powered one. Note that trying to find the smallest hub might not give you the one with the lowest power consumption. Also, 9V batteries have VERY low capacity compared to AA/AAA batteries. 4 AA rechargeables will cost you about as much (or less than) a 9V rechargeable and last much longer. I think most 9V rechargeables are 15 mAh rated, "cheap" Walmart AAs will be 1200-1300 mAh. Sears has the best deal on NiMhs I've seen - 1500 mAh units, $10 for 4. I have tons of DieHards now. :) Getting back the 9V vs. AA, a 9v 150 mAh battery is approxibately equivalent to a 4.5v 300 mAh battery. 4 AAs gives you 4.2v at 1200-1500 mAh or more, which is 4x or more the capacity at the same price.

    4.2V will be a bit iffy with a 5V hub, but it'll be easier to charge than having more than 4 batteries. Plus the more rechargeables you have in series, the more likely you are to have problems with cell imbalances. With a step-up regulator (not expensive if you're comfortable with homebrewing some elctronics - Maxim sells some great switching regulator ICs at http://www.maxim-ic.com/), you can power 9V hubs from 4 AAs.

    Don't discharge the battery pack below an average of 1 volt/cell (4.0 volts total) - Any lower and you risk a cell reversal, which will kill the cell for sure and possibly damage other cells in the pack. (Not as much of an issue if each battery is individually removable - it matters more for packs of cells.)
    • I agree on the wireless point. In fact, you might be able to make a few bucks on the deal if you went and bought 5 cheap cards and sold them at the bar to people for a little profit. You can probably get these cards even cheaper from Ebay.
  • ...and then buy a sealed lead-acid 12 volt battery and charger, and pick up the proper plug at Rat Shack.

    There are places that'll sell you this whole thing for cheap. I power my Tascam portable DAT deck with something similar; the battery set with charger cost me about $200, but you can make one yourself (as long as you have the charger) for probably $50.

    - A.P.
  • Run it off a small lead acid battery... There are many small ones that would outlast your laptop batteries (which I'm assuming your not plugging in your laptops since you want a battery powered hub).
  • Looking at the cheapy $40 hub (they go for much less these days) I see that it has a wall wart attached to it. DC, 7.5v.

    So, what you do is you get yourself a hub with a wall wart. Ditch the wart. Wire up a bunch of batteries (five in series, then more in parallel if you need more run time) and plug it into the hub.

    If you are truly '733+, then get a plastic box from someone, and hack things together so that the batteries and hub fit in one box.

  • It's harder to find theses days, but you could also make one if you wanted.

    A Passive hub, which uses no power, as opposed to an Active hub, which you asked about.

    You aren't reaching your 150meter limit on 10bT cables, so there should be no problem.

    ~DW
  • setup an AP in your car guess you could use AD-HOC.
    you and your friend with WIFI cards (maybe a few extras too) and game on... perhaps hack a batterie powered AP. Many small hubs only take 5-9 volts DC.

  • Bar (Score:2)

    by jbolden ( 176878 )
    we had 15 people last week in a bar, woot, but only 2 player games with crossovers because they wouldn't let us plug in a hub

    You guy obviously don't drink enough. A group of 15 regulars who are going to show up en mass and stay for hours, and on a weekday. Heck I'd figure they'd let you plug in your own rack of routers.

  • use a crossover-y cable and route
  • I have run a linksys workgroup switch from a
    12 V ( 13-14 ) car system with Radio Shack's
    12 volt to ?? voltage selector system.

    A small 12 volt ( think alarm system battery )
    would work as well- Duration for a small ( D cell )
    pack might be a problem but the 8x3x6 inch motorcycle/alarm batteries will last -

    Party On
    rcb

  • This is not rocket science.... (Score:3, Informative)

    by adolf ( 21054 ) <flodadolf@gmail.com> on Friday September 13, 2002 @07:05PM (#4254455) Journal
    Nearly any cheap hub you can find today will be running on 5VDC internally.

    Even expensive hubs, like the (older) 10/100 Kingston rackmount that I have here runs at 5VDC internally, despite its direct connection to 120VAC. Even the fan is 5VDC. (and, yes, that did take some time to find a replacement for, but the bearings in the new Sunon are doing justfine, thanks.)

    The wall-wart they come with will deliver a stiff 5 volts, or 7.5 volts, or 12 volts, or whatever. First thing that happens inside of the hub is that it goes through a regulator to bring things down to 5VDC, and this regulator cares not about what the voltage is (within reasonable limits), as long as it is >=5VDC.

    [note: some hubs may have low-voltage AC power supplies. avoid these unless you feel like modding them to bypass the internal AC -> DC conversion.]

    So. What you need is a way to get 5 volts in a portable fashion. Something like this keyboard power tap [compgeeks.com] would make a smooth way to do it.

    All you'd need, given the above, is a durable-looking portable hub and a length of wire with appropriate connectors. You've already got the former, and RadioShack will provide the latter. Or, just cut and splice your existing wire into the adapter. There's a thousand ways to go about it, and they're all sensical and easy.

    If you suspect that your laptop won't supply sufficient power from its keyboard port to power a hub, as some posters have suggested might be a problem, look to Ebay for an all-in-one kit labeled as a "USB Cell Phone Charger."

    USB supplies - you guessed it - 5VDC. Current is spec'd to be something like 500 milliamps, or 2.5 Watts, so you might get pinched if your hub is inefficient about its power draw. (If in doubt, have one of your technologically-inclined LAN-buddy friends measure it.)

    If you feel like it, grab one of those USB cables you've got in a drawer, and hack it into a power supply for a hub.

    I've got a tiny 4-port 10baseT Netgear hub here with what I'd like to say is the same connector as my Nokia cell phone, FWIW. They've probably also got 6- or 8-port versions that are the same. (it's also small, lightweight, and made of steel - great for throwing into a backpack.)

    Else, run it from its own battery supply. Feed it with 6 D cells in series, and it'll outlive any laptop which happens to be connected.

    Other people have suggested sources for seriously low-power ethernet hubs, so I'll skip that research.

    Just don't make the project any harder than it needs to be. You've probably, between you and a few friends, already got everything you need to make it work.
    • I've done what you've said with a variety of hardware - notebooks, all sorts of test equipment, etc. You -must- use a in-line fuse if you are powering something off a battery source that isn't going to have one internally. If there is a short, the battery can easily source enough current to cause a fire hazard. An in-line fuse will run you a few bucks.

      I definately think the way to go is just get the smallest hub you can find (d-link has a great one) and then put batteries on it. Just don't forget that fuse. One thing companies do to protect their equipment is use a reverse-connected diode on the power supply pins. If for some reason you ever hooked something up backwards, for example, that diode can draw enough current to vaporize of a battery. With a in-line fuse, you'd just blow that. Most electronics are fine with a .5A or 1A fuse.

      The optimal solution is to go wireless, but this requires a little more long term planning on the part of all your friends.

      • I did fail to mention a fuse. You are correct as to their importance - justabout any battery is capable of supplying relatively dangerous amounts of current, and having one's backpack catch fire would probably be somewhat less than fun.

        The diode is another good idea, as long as there's a fuse between it and the battery.

        I have a pretty nice 2.4GHz Uniden cordless phone here, which I somehow managed to reverse the battery polarity on. The smell of burnt components was instantaneous.

        Upon further investigation, it had a diode across the battery, but no fuse. The first thing that happened was that it blackened the diode, and then vaporized the PCB which connected it. As the latter occured, any potential that the diode had for saving the device was quickly eliminated, as the other traces from the battery remained intact.

        Talk about bad engineering...
  • I have a project battery sealed lead acid battery i bought from radio shack. You can use a 12 volt charger for it from the same shop. The thing about lead acid batteries, you can charge them any time you want unlike nicads alkies and such. Your only worry is overcharging to the point of overheating causes leakage and leaving uncharged for too long will cause crystals to build up on the terminal rods.

    The battery I own is simply a 5Ah battery I use it to test 12 volt dc lighting before I incorprate them into my car as well as for emergency lighting . One bright neon will light a room or porch just fine and if you choose the right colors, it wont attract bugs.

    Anyways to get along, i would suggest getting 2 of these batteries or look at lawn mower batteries although some larger batteries dont nessecarily have larger run time but have higher amperage for cranking power. Watch your Ah ratings. If i remember things correctly a 4 Ah battery will last 4 hours with a continuous 1 amp draw (typical alarm circut backup battery) and will last longer with less than amp draw.

    Btw, I would advise using a fuse to protect your gear. One lose wire can cause a lot of heat really quick! If you create a wire harness be sure the side for the power source (the battery side) is a female acceptor type plug to protect the terminals within the plug from connecting with any old piece of metal thereby causing a short during travel and a subsequent boom or fire.

    DRACO-
  • Most laptops have IR built in, which lets you set up a network and gives you up to 4Mbps. If it's not built in, you can get a small and cheap USB dongle.

    Bluetooth is another choice: tiny USB dongles and standardized. Up to 1Mbps. The software isn't quite as mature yet, but it's getting there.

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