After seeing the "Computer Desk". I became inspired. I am wanting to attack a desk that my mother has. Since this will not be my computer, I am wanting this to be a safe, and quiet machine for her. Any suggestions would be welcome.

Some of the things I am concerned about are:
1) Heat issuse. Since this is a wood desk I was thinking of using something like "FlameStop" to reduce the fire risk. I am also looking at some of the damping material that also are fire resistant.

2)ESD issues. From when I was studing for the A+, I learnd that the ground from the power supply when pluged in can act as the ground for the computer. What I wondering is if having things pluged in is enough or if I need to make sure that there is a metal contact from everything to the power supply.

3)Are there any sort of "Compliances" that need to be meet? This one is for my mother, but she already has a friend that wants one too. I don't want this to come back and bite me later. I know that with some things you can call them something else to get around some of this. For example if you create a wooden truck and call it a craft item it doesn't have to meet all the standards as a Toy would.

Thanks for the help

Phyllis

Welcome to SPCR!

What "Computer Desk" are you talking about? I gather it has something to do with a desk that serves as a built-in computer case, but i'm not quite sure. Perhaps you could provide a link to something similar?

From an ESD/grounding standpoint, it is a good idea to have every device in the computer connected to some sort of chassis ground, and a full metal enclosure is good for minimizing the emission and effects of EM interference.

On something like a motherboard, having a large metal plate behind it is probably important, as it acts as a "ground plane" (an electrical engineering concept) that reduces interference and crosstalk. Improper grounding and shielding could possibly result in stability issues.

As far as a fire hazard goes, nothing in a normal system should ever get hotter than about 70 celsius, far lower than the temperature needed to ignite even something as flammable as sawdust.

If you really want to integrate a computer into a desk, the most practical way would just be to use a normal computer case and build the desk to hold the case in an efficient way, keeping pathways clear for airflow, cabling, and optical drive access.

You do not have to worry about any of the three.

Fire? I have two computers made of cardboard, and I'm not the only one. Cardboard will ignite at MUCH lower temperatures than wood, and even then there's no serious risk.

Electrostatic discharge? The only place where there is a significant rick of shock is within the PSU. As long as you use a standard ATX power supply and leave it enclosed, the PSU will NOT be a shock risk.

Grounding? No problem. There is no requirement for a metal case or any grounding beyond the copious ground wires built into the internal connectors.

Electromagnetic interference? Look at the popularity of cases with side windows. These don't block EM waves. Enough said.

Compliances? This is something which you may have to worry about if you wanted to mass market your product. Otherwise, pretty much anything goes.

Or, if you really wanted to, go out and buy some sheet metal and line the enclosure for the computer.

This would allow a "ground" as long as you connected all pieces together, using a wire or maybe a small weld, and also would help tremendously with EMI/RFI. However, remember that these systems are usually grounded by an acting body, here in the US its the FCC... if you cause a lot of interference and you aren't using the items how they are legally required... they *can* come find you and either tell you to turn it off, or if you have caused any kind of gross interference they can legally come after you.

Its very rare indeed... but its still possible. Just something to think about.

The desks that I was refering to were:

Rusty's Quiet In-Desk PC
http://www.silentpcreview.com/article44-page1.html

and Doug's Quiet Wood Case
http://www.silentpcreview.com/article237-page1.html

I noticed that in both of these they used metal compoents from a case, but they were not touching.

As to a gounding plate. I am very fimilar with electircal engineering terms since I do have a BS in EE. But, If you have your bord set off from the plate (and for a quiet pc I have seen use of plastic off sets) and the spots where the screws are attched to the off sets are issolated from any part of the circuit board how would that ground your board? If the board it's self conducted then you would always have a short wouldn't you? Second, what is gounding the plate. In general you need to have a natural ground to be trully grounded.

Sorry if any of that sounded badly, that was not my intention. I am just way too anial and want to make sure I have covered most of the bases before I start.

Again Thanks For the help
Phyllis

The board grounds through the PSU I believe.

I would highly recommend AGAINST putting a metal plate behind the motherboard, unless you're comfortable with metal fabrication and precisely mounting the standoffs. Otherwise, the slightest amount of bending risks shorting out the motherboard as electrical contacts touch the metal plate. It simply isn't necessary, and it complicates your design.

There's supposed to be at least one metal standoff, which grounds the board through the metal bolt. However, there are ground wires in the PSU connector to the motherboard which provides all the grounding you really need.



If a piece of metal contacts the bottom of the board, then you will short circuit the motherboard and it won't function. If you're lucky, it won't be damaged in the process.

The metal plate behind a motherboard is typically grounded through the rest of the computer case, ultimately in contact with the metal case of the PSU. Inside the PSU, there's something connecting its metal case with the internal ground. Once upon a time, this ground may have been important. Nowadays, it isn't.

Thank you to all of you. You all have been very helpful. Now to get up the nerve to cut apart an antique desk.

Phyllis

From a practical standpoint, I found having the metal plate under the mobo to make things much easier. I just scavenged the mobo tray and the backplane from a junked old case. Having those parts premade saves a lot of trouble in trying to fabricate the precise locations for standoffs, connectors, pci slot covers, etc.

But yes, as others have said, as long as the PSU is grounded, and everything else is connected to the PSU, you're fine from a catastrophic failure point of view. Some people with non-metalic enclosures have reported interference with nearby ham radio's or cordless phones, but it seems to be rare and minor.

Um, I'm not an engineer, but I would have to say that statement is grossly wrong.

Imagine a hot line in the PSU touching the case.

No ground = anything touching the case is now hot. The user goes to turn on the computer, and lawsuits fly.

With a ground = the PSU, if its designed correctly, will shut itself off. If not, worst case scenario is that the electrical circuit will shut itself off.

I would say that the ground is a very important piece of the circuit. It wouldn't be there if it wasn't. Look at any high current draw device... most now have ground plugs to prevent this kind of thing. Especially where the user is in direct contact with the outside of the case of the device.

Yeah, if you have a junked ATX case scavenging parts from it is definitely easier than building your own. I personally don't have the heart to junk an ATX case just to make another case.

I just remembered that my main workstation was a de facto computer desk computer for quite some time. That was simply a matter of having my computer components sitting on a couple desk shelves.

I solve the problem of backplane connectors simply by removing them. Thus, there are no "pokey" bits extending below the plane of the motherboard. As it was, I could have left the backplane connectors on, because my motherboard was sitting on top of a cardboard box (within which was the hard drive).

My idea for mounting a motherboard on wood is pretty simple--instead of using bolts, mount the motherboard using wood screws. No standoffs are needed, since wood is insulative.

I have a "trick" to firmly attach the ATX backplane to the ATX motherboard (instead of attached to the case), which greatly simplifies the problem of fabricating a nice back side to the case. With an all-in-one motherboard using on board VGA, there doesn't need to be any expansion cards to worry about...

<duplicate post>