The Raspberry Pi is a $ 25 credit-card sized computer that has taken the geek world by storm. It’s a joy for tinkerers because it allows the introduction of some serious computing power into junkyard projects. It means that we can now do water droplet photography on the cheap or even build a budget supercomputer.

I received my own Raspberry Pi fresh from the oven a few weeks ago from RS India. I was mesmerized by the beauty of the board and the infinite possibilities that lay before me. But before I could start to work on the Pi controlled thermonuclear reactor of my dreams, I knew I had to find a secure place to put the board in. A quick search on ebay led me to the RPi_Shop. They stock a range of cases but the Stripped Acrylic Case caught my fancy. It’s reasonably priced and comes with a free RCA cable to sweeten the deal.

The guys at the RPi_Shop are very professional and I enjoyed their proactive and responsive service. The case was shipped to me the very same day I purchased it and was sitting on my desk ready to sheath my precious Pi the next – making me one very happy customer.

The case consists of multiple layers of acrylic 9 layers of acrylic which when put together form one solid shell for the Pi. I would recommend buying this case over snap-in model . It just feels a lot more rigid and looks an order of magnitude better. The craftsmanship was excellent with no visible defects in the acrylic. The laser cut raspberry pattern on top and the alternating black layers gives it a really classy look.

Assembly was a simple procedure. One simply needs to stack layers 0 to 2 onto each other, place the raspberry Pi face up on it, stack the rest of the layers on top and fasten the assembly with the 4 provided nut-bolts. Make sure to just hand-tighten it. Putting too much stress on the acrylic is not a good idea. The case fits the board like a rather pretty glove and leaves all the important I/O ports unobstructed. Unfortunately the insulating acrylic can’t act as a heat sink but the laser cut pattern allows for sufficient ventilation.

Overall I am happy to have picked up a very reasonably priced and well-built case for my Pi. If you want a case that’s a little more upcale consider this one. Makes me wish banks were a lot easier to steal from. Well maybe we can come up with a Pi powered bank robbing robot.

A regulated 5 volt DC supply is essential for powering micro-controller and TTL based circuits. The output of most wall-warts and adapters is to rippled and impure for use in digital circuits. Lets build an inexpensive power supply using some discrete components and a fixed voltage regulator IC.

You will need:

• a step down transformer [12V]
• four silicon diodes [1N4007]
• a resistor [47Ω]
• capacitors [2 x 220µF, 10µF and 100µF]
• three terminal voltage regulator IC [LM7805]
• a small general propose PCB, some wires, and a suitable output port (I use a
• audio connector).

The circuit of the supply is as given below:

Fig: Circuit Diagram, click to expand.

A Picture of all components you will need, a resistor, capacitors, a regulator and diodes:

Fig: Components, click to enlarge.

The circuit consists of three main blocks, the rectifier, filter and regulator. The rectifier is used to transform the mains AC voltage to a suitable DC voltage. The output of the rectifier is however an impure DC signal so we use a filter to clean the signal and finally a regulator to deliver precisely 5 volts, irrespective of the load connected to the output.

Rectifier

It consists of a transformer and a diode bridge. The diodes are standard silicon 1N4007 diodes. We have chosen a 12V transformer because the regulator IC needs at-least 7.5V of input voltage to function properly.

Filter

We use a pi-filter here. The two 220µF capacitors and resistor form the filter. Pi-filters are great for light load applications like digital circuits. Be sure to check the polarity of the capacitors before connecting them. The resistor shown above is one rated to dissipate up-to 5W of power across it. You may use smaller 3W resistors, but availability may be an issue. Don't use the tiny 0.25 W or 0.5W ones though.

Regulator

The voltage is regulated by three terminal voltage regulator IC – LM7805. This regulator provides stable 5V DC output against large fluctuations in input voltage and load. It also has internal protection circuits which 'brownout' the device when overloaded. To decide the pin-outs, hold the regulator with its face towards you and legs pointing upward, the pin to the right is the input, middle pin is ground and left most pin is output.

Construction Tips

• The transformer can be made to snugly fit onto the PCB by bending the screw mounts under and around the board as shown in the picture below.
  
  
• A 6.3mm or 3.5mm female mono TRS connector (tip, ring, sleeve), also known as an 'audio jack' serves as a great output port. The power can then be delivered via standard audio cables.
• Since the power resistors is quite large, solder it vertically to save space on the board.
• Mount the entire board on thermocol when finished to prevent accidental short circuits.

The finished circuit fits neatly into a 2” by 1.5” PCB, excluding the output jack and plug. You can also include a small switch at the out-put for easy operation. The IC can be heatsink-ed on multiple layers of aluminum foil to dissipate the heat, or if you are enclosing this in a metal box, pin the IC to the sides of the box. This is not entirely necessary though.



Fig: The finished circuit, click to enlarge



Fig: 5.03 V, click to enlarge

Links:

TRS connector: http://bit.ly/1ropoc
LM7805 data-sheet: http://bit.ly/15iCku

Questions and suggestions are welcome, please use the comment form below.

Update: You can grab the Eagle CAD project files, including PCB layout here: http://www.mediafire.com/?mqjiwcneyy4

Note: If you have any question, please feel free to contact me.