Friday, August 24, 2012

Computer I/O shield Experiment

I recently came across a large pile of new in the box computer parts at a garage sale ("at pennies on the dollar", said I to my suffering wife). I ended up with a processor (Core 2 Duo, 2.2Ghz), 120 GB hard drive, 4 GB DDR2 ram, Antec case w/ power supply, all of which were hypnotically commanding me to make a complete PC.
So I looked around online for a cheap Socket 775 motherboard and bought one from Geeks.com. It was refurbished and I didn’t notice that the description stated “Cables, I/O shield and Driver discs are not included.”. The I/O shield serves several functions, blocking off excess airflow, grounding the I/O ports and most importantly, shielding RF noise (these are all the fodder for much debate on computer forums). This last become apparent as a buzz on the audio line when I hooked the PC up to the kitchen TV.
Small detour: Did you know that most flat panel LCD and plasma displays usually have standard PC VGA inputs? Yup, they are all waiting expectantly to be hooked up to a computer. You can watch online content (Youtube, Hulu, Netflix, etc) as well as streaming audio from your network or the internet. In most cases all you need at a VGA cable and a 1/8” audio cable. (leaving aside the subject of HDMI which has vexed me of late on our living room TV).
So I figured I would attempt to make an I/O shield. I have come across this problem (missing I/O shield) several times before so I figured that what I learned from the experience would probably pay off later on. I did learn several things, most importantly to not buy motherboards without the I/O shield. (Mom, I/O means “input / output”.)
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I took a picture of the back of the case. That curve to the motherboard is not a camera artifact, the motherboard is warped. What did I expect for $20?
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I cropped and tried to get the sides parallel in Paint.net
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I brought the picture into Rhino and scaled it to suit the ATX standard (6.25” x 1.75” +/- .008”) for the I/O shield hole. Then I drew some boxes around the various components.
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I generated the toolpaths in MadCam (an excellent CAM plugin for Rhino, which was generously donated to yours truly by the fine folks at MadCam.
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Beginning the milling operations on the Taig CNC mill.
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Almost done.
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Attached to “sprues”.
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Cut free and cleaned up. I spent some time deburring.
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It didn’t quite fit in spite of being within the specifications. So I filed the edges a bit and got it into place. So my second lesson learned is to reduce the edge dimension by .004” on all sides. Still within specifications but with some wiggle room.
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Not quite what I was expecting…Seems that I miscalculated or otherwise managed to locate the cutouts slightly to the right of where they should have been. This is with the motherboard shifted left as far as possible. I said it was an experiment…My third lesson is to take some other reference measurements, which I thought I could avoid by working from the picture.
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But the USB cable fits in the connector so all is good. I may remove it and file the openings slightly larger on the left side, or I may just leave it. Maybe I’ll make a new one later.
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So there it is. Hooked it back up in the kitchen and there is now an absence of buzz on the audio output.
UPDATE: I decided to try again with better results, link to post.

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