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HOT Raspberry Pi DIY Mini Desktop PC Build
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Date: May 20, 2013
Section:Gadgets
Author: Michael Altavilla
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Introduction and Project Scope
We recently set out to design a mini desktop computer with the wildly popular Raspberry Pi single board computer. The Raspberry Pi is a Linux-driven, ARM processor-based micro computer that is known for its low cost and small size. People use the device for a variety of projects, from micro-servers to low cost media players. Basically, our goal was to turn what is currently one of the cheapest bare-bones computer boards  into a fully enclosed mini desktop computer that could be taken anywhere without the need for cabling or setup. One of the high level goals of this project was also to learn about programming with Linux and get a good feel for it with the Debian distribution.

Raspberry Pi Model B Rev 2.0 with 512MB of RAM and 10/100 Ethernet

The Raspberry Pi desktop was an easy project to imagine, but keeping cost to a minimum and educating ourselves on the technology ended up being more time consuming than we initially projected.  Here's a quick list of components we used for our build.

Supply List:

The first step in realizing our design goals involved learning a little about the Raspberry Pi. We started by taking a week and doing some research about how most of the programming works and many of the common commands used in LXTerminal (code receiver and programming window). We then took our 16 GB SD card and downloaded the Debian Linux image to it (a very popular Linux distro that runs well on the Raspberry Pi); using a Win32 Disk Imager as host compiling software. A good tutorial for loading the OS onto an SD card can be found here; and the OS itself can be found on the Raspberry Pi website.


Our choice of plastic enclosure, or "project box"

After a successful load of the Operating System (OS) we plugged in our settings and used the code “StartX” to run the desktop interface. A standard computer monitor was suitable for working out all of the bugs on the big screen. After we were sure we had our OS running properly, we started to work on making it a portable system.


Step one was to use a high speed milling bit to cut ports in the plastic side walls of the enclosure, so that we could have access to the Raspberry Pi's USB, Ethernet and power ports.


The ports are placed up flush against the sidewall

The enclosure we picked was a four piece enclosure that has removable sides. This gave us the ability to remove each panel and mill in our ports, making the job a whole lot easier. Once that was done, we used a hot glue gun to seal off around the ports, create a tighter fit and get rid of the gaps between the ports themselves and the side of the enclosure.


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Constructing The HOT Raspberry Pi
Next, we wired in our main power switch for the Raspberry Pi itself using a rocker on/off switch. We cut a hole in the opposite side of our case and inserted the switch. It is glued down from the inside for a neat and sturdy fit. The cable used is a micro-USB cable that runs to our 5 volt battery that is placed inside of the enclosure. The wire was spliced half way down the cord and connected to a single-pole, single-throw switch. After solder was applied to each lead, hot glue is used as an sealant to make the bond more durable. The battery pack is located on the opposite side and opposite corner of the Raspberry Pi, on the top of the enclosure.


The Micro-USB runs through the switch and directly to the board which is mounted with standoffs.

Next, to mount the board itself down we used stand-offs that fit in the pre-drilled holes in the PCB. Hot glue again was used for a strong adhesion with the standoffs to the base of the enclosure, but the screws that mount into the standoffs still gave us access to remove the board when we please.


Shown is the finished power supply with the bare mono-jack

Now that we had the computer in place, we started to focus more on the display aspect of the project. We ended up deciding on a 7-inch LCD display that is often sold as a reverse backup camera display for vehicles.  It's a full color display with 480x234 resolution - one word, "inexpensive." We then had to decide on which AC adapter was best suited for our display.  From there, we stripped the end connector off (our display didn't come with a power supply), and then took a 3.5mm mono-jack and mono-port and soldered the jack to the stripped end of the power supply. We then drilled a hole in the back of our enclosure that was the diameter of the port and mounted that down. After that, we soldered our cathode and anode off of the port and did the same with the power supply.





The next step was to connect our display by splitting the power cables and rewiring the male RCA cable. A female composite video connection was soldered directly off of the PCB to conserve room to help make running the display's input RCA connector easier to connect.



Once we were done testing, we drilled a hole in the top of the case so that the power cord could run to the mono-jack that we previously installed and so that our RCA cables could pass through to the board. We trimmed down the cable, getting rid of at least 3 feet. This cable was too long because the wire itself was made to run through a car to reach a car battery as a power source. A piece of perforated circuit board holds all 16 of the small individual wires that were inside of the main cable we cut down. The board is shown wrapped in electrical tape here.  It wasn't a simple splice, so we had to improvise a bit.

The last steps included cleaning up all of the loose cables with zip ties and Velcro, trying to make everything fit. We pushed the cable for the display through the hole into the top and mounted the display down with the provided adhesive pads. Then, we screwed everything together, and our project was complete.



Challenges:

Over the course of the project there were many issues we ran into. The major problem was setting up the internal power supply. Every time the supply needed to turn on, it required a button to be pushed. This meant we had to open the computer every time we wanted to use it. To solve this issue we rewired and jumped a small push button to the back of the case.


Also, we ran into the issue of running out of storage capacity while compiling software and games onto the SD card, ruining our first OS and rendering a 4GB SD card useless. We solved this by upgrading to a 16GB SD card and re-installing the Linux image to it. Lastly, as noted, the absurdly long cord of the display, which took up too much room to contain in our small chassis, was solved by manufacturing a perforated board connector on each end.  All told, these were relatively minor hiccups in the grand scheme of things.
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HOT Raspberry Pi Gaming Action
The first piece of software we tried with our new custom mini-computer was the classic first person shooter 'Quake 3' for a little game play. This involved compiling the game to play on Linux which meant grabbing Linux targeted source code through a Dropbox like service we found. This link shows the lines of code used to install Quake, installing the necessary Linux packages, and building a Quake directory.


Raspberry Pi running Quake 3

We also downloaded the popular game Minecraft with a few simple lines of code. This meant simply downloading a user made version of the game and dumping it into a directory via LXTerminal. The team behind the Minecraft Pi edition has created a website for their version on the game here.


Minecraft Pi Edition running on the Raspberry Pi
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Observations and Conclusion

Overall, we were happy with the way our little rainy day project came together. One thing we discovered was that once a Linux image is transferred to an SD card, the partition isn't easily removable even through the Linux operating system. We also tried using the "diskpart" tool under Windows, but experienced an error there as well. Some solution might exist, but we were unable to find a definitive one. Also notable was that the Raspberry Pi is easily able to run off 5V at 1Amp with a variety of accessories attached. In addition, surprisingly, our LCD display ran off 10V comfortably, which was partially blind luck, because the manufacturer doesn’t openly specify what voltage or current to power the display with. All told, from a power consumption standpoint, our portable HOT Raspberry Pi still just sips power.

That said, of course the Raspberry Pi can also be overclocked (to around 1GHz core, 500MHz RAM, 275MHz graphics) to its highest setting for Quake and the like, and still not go over its thermal limitations, given proper airflow.  As you'll note, we have a small heatsink mounted to the main processor on board, which did help moderate temps nicely. 

Though this little machine isn't going to break any land-speed records or give IBM's Watson a run for its money, our efforts with the Raspberry Pi were spent out of the love of technology and creativity.  There are a number of practical uses you could imagine with a little machine like this, especially as a field device for quick monitoring and diagnostic functions, but we just had fun building our own <HOT> Raspberry Pi.



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