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Constructing A Low-Power 2U Wireless Rack-Box

Posted by timothy on from the every-household-needs-one dept.

adelayde writes "Recently we decided to build ourselves a custom rack-mountable box that we could use as a web and DNS caching proxy and which would offer flexible wireless networking facilities and have an uniterruptible power supply. The result was a 2U rack-box with dual wireless networks built upon a low-power Via EPIA MiniITX motherboard. The box has two wireless networks built in with external antenna connectors, locking switches on the front to avoid tampering, a battery to give at least 20 mins of autonomous operation, a low wattage power supply and most importantly lots of blue LEDs :)"

7 of 127 comments (clear)

  1. Ummm... Priorities? by pla · · Score: 4, Informative

    ...and most importantly lots of blue LEDs

    You may have meant that as a joke, but blue LEDs suck quite a lot more power than red or green ones.

    When you care about power consumption, rather than coolness, come back and ask again.

    1. Re:Ummm... Priorities? by adelayde · · Score: 4, Informative

      Please correct me if I'm wrong but as all the LEDs used had the same voltage and current ratings, it would mean that they draw the same power. Isn't the difference in the intensity? For example for the LEDs used in this project, they are:

      Red: 3700cd/m2
      Green: 40900cd/m2
      Yellow: 15500cd/m2
      White: 29650cd/m2
      Blue: 4480cd/m2

      Blue being quite a lot less bright, though somehow strangely alluring and the power consumption I think the same.

      In the end even if they do draw a little more, surely it's not that much compared with the draw of the other components? The wireless cards for example seem to draw quite a lot. As what we were looking for was autonomy in the event of a brown-out (or someone tripping over the extension cable), the battery did the job and I don't think having a blue LED or two adversly affected things.

      The comment was a bit of humour on as usual a rather dry subject.

    2. Re:Ummm... Priorities? by tap · · Score: 5, Informative
      This is doubly wrong.

      First of all, the human eye isn't the most sentitive to blue light, it much more sentitive to green. You can see the human eye's response curve here and a breakdown of color vs wavelength.

      Secondly, the lumen or candela rating already takes this into account. At the peak of photopic vision, 555 nm (green), there are 683 lumens per watt. If you had one watt of blue light, it would only be about 100 lumens, because the human eye is less sensitive to that wavelength.

      In other words, one watt of green light appears brighter than one watt of blue light, because humans are more sensitive to that color. One lumen of green light is just as bright as one lumen on blue light, because the lumen measurement takes this into account. That's the whole point of lumens, they are watts times luminous efficacy for human vision.

  2. Mirror linked on page by Anonymous Coward · · Score: 4, Informative

    http://mirror.us.psand.net/plinth/

  3. Would you like to explain that?? by the_rajah · · Score: 5, Informative

    I'm a college degreed Electrical Engineer with over 30 years of experience, including teaching electronics at the college level for three years. That regulator circuit looks quite familiar. As long as the heatsink is sufficient for the heat dissipation in the LM317, there should be no problem. Since this is powering only the wireless bridge, the current drain at 7 volts should be modest and it only needs to drop 5 volts across the regulator IC. The total power dissipation spread across both of the 1/2 watt resistors is only 85 milliwatts so no trouble there either.

    If you are referring to the capacitor voltage ratings, the only requirement there is that the voltage rating of the cap be more than the voltage actually applied to it. For example a 35 volt cap is just fine with 6 volts across it. It could even be a 1,000 volt rated cap with no ill effects.

    "Do the Right Thing. It will gratify some people and astound the rest." - Mark Twain

    --


    "Do the Right Thing. It will gratify some people and astound the rest." - Mark Twain
  4. "Low power"??? by darrylo · · Score: 4, Informative

    I'm curious as to what their definition of "low power" is. Low, compared to a power-sucking P4 or Athlon, maybe, but probably not very low by low power standards.

    I've just set up a similar system as an home file server (no wireless, though, and I've added a cheap DVDROM drive), and my box is sucking up around 55-60W, idle. That's measured via an actual wattmeter connected to the power cord, and not by multiplying V*A.

    On second thought, maybe a soekris board and a 2.5" disk drive might have been a better solution (less RAM and CPU, which would probably be fine for an home fileserver, but the power usage would probably be in the 10-20W range).

  5. Re:Asking for a /. by batkiwi · · Score: 4, Informative

    AHEM:
    http://www.archive.org/web/freecache.php
    a nd
    http://www.archive.org/about/faqs.php

    Freecache only stores files > 5 megs, and ONLY stores what you tell it to. Linking freecache-style to an index page will only cache that index (IF it's >5megs), not the whole site.

    What is it with all the useless freecache links lately?