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Constructing A Low-Power 2U Wireless Rack-Box
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 :)"
Let's see how long she lasts ...
Looking at the pics on the page, it looks like they could have easily built the thing inside a 1U chasis of they used the proper power supply and heatsink. All of the other parts should fit within 1U.
That being said, they could have simply used an ultraportable laptop with the screen unplugged and unnecessary parts removed/disabled.
You'd be amazed as to how little there really is inside a laptop. Think about it -- the drives and batteries take up about 75% of the chasis. Leave about another 10% for the power supply and heatsinking, and you've got a REALLY small PCB.
If space, not power, was their main concern, they could have also used one of the Shuttle cube boxes. They pack an incredibly strong punch for their size, and are usually on par with their desktop equivilants. Hell... they've even got an opteron box. The performance on the EPIA boards is horrific. What were they thinking designing a processor without a FPU? That being said, they're pretty cool because they're small, low-power, and widely availible (which laptop MBs strangely aren't). Still, they're pretty expensive considering that you're getting a PC which would have been considered pretty slow 4 years ago.
-- If you try to fail and succeed, which have you done? - Uli's moose
A lot of people have been use Mini-ITX for HTPCs. The one thing you're going to need to do though is get a hardware based capture card. Not a cheap ATI PCI-TV or anything like that.
Also I believe the new VIA's have a special chip on them to help with the decoding, so you should be good there.
If you can live with only 2 PCI cards, go for it (You can always use USB Tuners as well). They do make very quiet systems.
A lot of people will use them as clients and have a server with the actual tuners in them though. Just another idea to toss out there.
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
Personally, I found their antenna designs much more interesting.
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.