Introduction
For those of you who don't know, the Sheeva Plug is a tiny computer in the shape of a wall wart power supply made by Marvell. It has a 1.2 GHZ ARM processor, 512MB of RAM, and 512MB of storage. It doesn't come with an easy method of attaching it to a screen and has no on/off button showing that it is intended to do server work and be on 24/7. The development kit which is available through Global Scale Technologies, comes with the Sheeva Plug and everything else you need to work with one. The plug comes with a slim, limited version of Ubuntu on it and is already set up for SSH. You can however easily change the operating system, which I intend to show in a future article.
What I intend to do with it is have it always running in my car. Issue is, the Sheeva Plug is designed to run on 120 volts AC and cars use anywhere from 10 volts to 14 volts DC. Looking at a schematic of the Sheeva before I bought it showed that the components inside are really running off of 5 volts DC and are getting converted. That makes life easier.
My first step was to open it and look inside at what I was working with.
On the left side, is the "bottom" half of the plug which has all the real computer parts. On the right is the AC-DC converter. I took out a multimeter and tested the wires and it shows that there are two 5 volt rails coming out of the converter. Easy.
The next step in the process is to cut off that connector so we can use it for our own purposes. It makes life easier if you cut the red and black to be the same length, I cut mine different sizes accidentally. Strip the coating off the wires and combine two red wires and two black wires. The DC-DC regulator we're using only has one 5 volt rail so the wires need to be combined.
Now we get to start actually putting it together. Here you'll need a soldering iron, solder, a lighter/torch, some heat shrink, and a 12 volt to 5 volt DC-DC regulator capable of handling 15 watts. You can probably get away with a regulator with less wattage if you plan on using self-powered USB devices with the plug, or no USB devices at all. For a torch/solder iron I highly reccommend this guy which I found at lowes for 30 bucks rather than a typical electric soldering iron which takes forever to heat up and doesn't do much good for heat shrink.
The regulator I'm using is the Carnetix PNX-P5V. The instructions following are specific to the P5V but should be easily adaptable to any other regulator.
The output side of the P5V is easy to work with. Carnetix gives you a positive and negative cable which is already stripped and ready to go. Put some heat shrink on each, and attach the black to the black wires on the connector and the red to the red. Since we're using this in an automotive environment where heat is a problem and movement is too, it's a good idea to use solder and heat shrink instead of just electrical tape as it will last much longer. Once you're done soldering, shrink the shrink and it's done.
The input side is a little more complicated. The P5V is designed to work with another power supply from Carnetix, however we're using it as a stand-alone always-on unit. On the input side we have a black wire on its own, two red wires hooked up to a connector, and a black and green wire hooked up to a connector. The black is our negative the two red wires can be combined and used as a single positive wire. The green wire is our "turn on" signal which can also be connected to the red wires so that whenever power is available, it is on. Grab some 16 AWG or thicker wire and make the connections. This positive wire should look ike this:
Solder it and heat shrink it and your input side will be all set.
You can now rip out the old AC - DC converter and external power connector. The connector has a couple of screws on it. Just unscrew them and wiggle it until it comes out. The converter is kind of just clipped in there.
You can put your regulator wherever you want, but I chose to put mine in the space where the old converter used to be and ran the input cables through the hole from the old power connector.
I then realized that it's possible something might tug on the wires and rip them off of the regulator which could cause some serious problems, so I took a piece of scrap metal and drilled two holes in it and screwed it down to the holes where the connector used to be mounted. I then took a cable tie and wrapped it around the metal and the wires so that you can't rip the wires out.
Now connect the power connector the the plug's main board.
Now close the plug up and screw it back together. Heres my finished product:
Now you can connect it to a 12 volt power source like a battery and it should power up and operate:
If you tap the screw in the back you'll feel that it's very hot. I measured that temperature with a thermometer:
It's about 110 degrees Fahrenheit. The regulator is fine up to 130 degrees though so it should be fine. If you are planning in drawing
over an amp total (more than 5 watts), Carnetix reccommends you get some sort of a heat sink. Since my Sheeva Plug is going in a car
I'm going to one-up that reccommendation and put some fans in the plug.
As for power consumption, I measured a draw of .318 amps at 12.6 volts which is just over 4 watts. Very efficient.
And that's about it. Feel free to email questions to paulfurtado91@gmail.com.
