I'm using an ARM board called the Pandaboard as a media station which works fine, but it doesn't look that good in a living room (despite the fact that I partly share Benders excitement of naked electronics). I thought I would just make my own box, since at the time nothing was available to buy. I did not quite realize the amount of effort needed. However, after putting my sweat and blood into it (literally, as we shall see), in the end I can say that I'm pretty satisfied.
I wanted the following features for my box:
- As small as possible
- Have space for a hard drive
- Have all buttons, LEDs and connectors available
- Look like something you want to put in a living room
I decided to make the box out of wood, partly because it lets through the wireless interfaces and partly because it's easy to work with ('easier' that is). I must admit that the nice look of wood also made a difference.
I knew I needed to be very exact in measurements (sub mm) to get a decent result. Therefore I decided to make a complete model in Sketchup. At the same time I could play with different solutions and see if it looked ok.
Anybody who also has a Pandaboard and wants to do something similar, or simply want to use the model of the board to know exact positions of all the connectors, can find the drawing here.
The sides of the box are made out of solid wood, and the top of film faced plywood. I chose it because I liked the contrast of the dark brown and the beige wood. To make precise cuts I borrowed a Japanese saw from my father. I must say that it's a huge difference compared to conventional saws. Your eyes and steady hands are the limits rather than the tool. For most of the holes I used a drill press (also owned by my father).
There are two LEDs on the Pandaboard, and with the software build I'm using, one is showing the processor activity in a heart-beat fashion, and the other, usage of the SD-card. Obviously I want to see them also after encapsulating the board, so I made two small holes in the front panel. To lead the light I needed some transparent glass or plastic. I looked around to see if that was something you can buy of the shelf, but found nothing. Instead I got a piece of thick plastic from one of my girlfriend's makeup jars and started making one myself.
The light should be directed in 90° so I made an angle of 45° in the plastic, and made it as shiny as possible with a fine file and some leather. 45° will be enough to give total internal reflection, assuming a refraction index of 1.5 of the plastic. To fit the pieces in the front panel holes, I filed them round at one end, and made them small enough to just barely fit in the holes (that way they will stay in place without glue). I also made sure to matte the visible surface with sand paper. My idea is that the light then will get diffused at the surface, and be equally visible from any angle.
I noticed that a lot of light leaked over from the LED close by, so I put some electric tape on the sides. Works quite well! (see the last picture of this blog post to get an idea).
I put the hard drive under the board, and to make the box as small as possible I needed to modify the usb cable to be angled. The first one I made didn't work because the cable was for usb 1.1 only (doh!).
Since I permanently use the hard drive and need one USB slot for a wireless keyboard, it felt like a good idea to add some slots. Fortunately the Pandaboard has two slots on the PCB which just needs a connector. Even more fortunately, the double slot connector I bought could be placed directly on the PCB! Might be of interest to anybody else who simply wants to add two USB slots. Make sure the pinning of the board (find the manual here) corresponds with the pinning of the USB connector. In my case, the pitch was slightly different for the holes and the pins, but not enough to be a problem. Also make sure to isolate the bottom of the connector! Otherwise you're likely to cause a shortcut somewhere. I used electrical tape and pressed the pins through.
Perhaps the most delicate part was to put all the wooden pieces together. Even though I made an effort to be precise when cutting them, there were small variations. In the end the best way was to fasten all four sides in a position that looked good (as seen in the picture below), and glue them on one by one.
I extended the buttons of the board in the simplest way I could come up with: two holes, two screws. To make it look better I polished away the slots on the heads of the screws, and made a thin indent in the wood. I wouldn't say it's impossible to do it with a normal drill, but it's a huge help to use a drill press.
After using the box for a while I noticed that it became pretty hot inside, despite the air holes on the lid and on the bottom. I had a small computer fan laying around which I thought would work. It was rated at 12 Volts, and the Pandaboard works with 5 Volts. That turned out to be only good, however. The air flow doesn't need to be immense, and by running it at the lower voltage it's much quieter.
I used two of the holes in expansion connector A for ground and 5 Volts.
As a final touch, I decided to give the box a name. I first experimented with using the brown top layer of the film faced plywood. This is where the blood comes in... I used a Stanley knife to try to peel off the top layer of a piece of the plywood. It slipped, and ended up in my hand.
I had apparently cut one of the tendons in my thumb, so the doctor had to find both ends of it and attach them together. Months of rehabilitation waited. You could at least have hoped that the idea was good, but when I some weeks later took courage to try again, it turned out the wood was too brittle for letters of the size I wanted. Instead I used a piece of fake leather from a sweater label. I used my friend the Stanley knife to cut the letters out, and a belt hole puncher to make the holes.
And here it is, in its rightful place:
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