I have been interested in wearable computing for a while. Until the RaspberryPi was released, there was no affordable and compact option for the computer part of a wearable computer. My original setup used a laptop in a backpack, but that is a little too big to be practical. I have seen a lot of arduino based wearable electronics, but they are not exactly what I have been looking for - a full power desktop computer that you can carry around at your side and use while walking, standing, sitting, or doing anything else.

As a linux guy for many years, the RaspberryPi is the perfect solution to my problem, and I'm already comfortable with the OS. Before you begin, make sure you read through my instructions. I have updated several sections through the past few months.

Just so you guys know, this is my first instructable after being a lurker here for almost seven years. I'm excited. So, let's begin!

Update March 2013: I am now using a new (3D printed!) case. Significant updates to the battery pack made as well. The new case prevents the Pi from being totally enclosed, and marginally decreases the form factor.

Update September 2013: Added a new video demonstration. Check it out!

Step 1: Materials

Here's a complete list of everything that I used, where I bought it, and how much it cost me:

Battery Recharger (came with 4xAA batteries) - $35 at Radioshack
6 xAA Recahrgeable Batteries - $7 at Radioshack
RaspberryPi Model B - $45 including shipping
Soft Cellular Phone Case - $5 at 5 and below.
USB Battery Pack - MintyBoost Kit - $20 - https://www.adafruit.com/products/14
2xAA battery holders - $5
Vuzix Wrap 920 Video Glasses - $200 on Amazon - http://www.amazon.com/Vuzix-329T30011-Corp-Wrap-920/dp/B002SUCMUG/
Mouse/Keyboard - $37 on Amazon - http://www.amazon.com/VisionTek-Candyboard-Mini-Keyboard-Touchpad/dp/B007VMCBN4/
RCA Coupler - $4 at Radioshack
Micro-USB Cable - Already had
Wireless Adapter - $15 - www.amazon.com/Edimax-EW-7811Un-Wireless-Adapter-Wizard/dp/B005CLMJLU
SD Card - $9 at Microcenter

TOTAL COST: $382

As with any project, you will need some basic household tools. And some bits of wire. As for the cost, you should expect to spend around $400 for everything you need. Fortunately, half of the cost goes into the video glasses. Otherwise, a laptop would be a better option. Keep in mind that the computer part is $35 (without shipping)

Step 2: RaspberryPi Configuration

So you have a RaspberryPi. I'm not going to cover software installation and basic setup, because there are already some great tutorials out there. Here are some helpful links for that step:

http://www.raspberrypi.org/downloads
http://elinux.org/RPi_Easy_SD_Card_Setup

I recommend Raspbian, simply because I'm a Debian fan, and Raspbian is Debian, but optimized for the Pi. If you already have a preferred distribution, great. Use that.

One thing that I do not like about the Pi is the lack of a heatsink over the CPU. I don't care what anyone says about passive cooling, something about a CPU without a heatsink on it really, REALLY bugs me. So go ahead and slap a tiny heatsink on your Pi's CPU. I used a RAM heatsink from a pack of a bunch of them that I got at Microcenter. This is ironic, since the Pi's RAM is on top of the CPU. Anyway.... some folks are putting heatsinks on other chips, which isn't a bad idea. I just happen to be bothered by the exposed CPU. Plus, the heatsink does get hot during operation. So it's definitely doing something.

I then connected the WiFi dongle and my keyboard's wireless dongle to the Pi, and put it in the cell phone case. I rested the Pi on a part of an anti-static bag, just to avoid shorting anything out.

NEW 11 March 2013: I'm now using a 3D printed case for it. The cell phone case offers the same features, but this printed case is a part of my transition to a slimmer and even more portable version I'm cooking up for the future. This case is simply thing 33694 from Thingiverse. with a belt clip, thing 39983, hot-glued to the bottom.

I have also swapped out the blue aluminum heatsink for a copper one, but that's not necessarily any better than the aluminum one since the Pi only produces negligible heat.

Step 3: Keyboard and Mouse

I bought one of the more affordable miniature keyboard/mouse combos. I also have a different model with the touchpad on the right side, but I had some problems with that one. It did not always play nicely with my Pi, and the touchpad on the side hindered my typing.

This keyboard is really nice for a few reasons. One is the size. It's small enough to carry around in your pocket. It also has a backlight, and is rechargeable. Did I mention the battery is replaceable? That's not something you see in portable electronics these days.

Anyway, make sure you plug the receiver into your Pi, and charge the keyboard for a few hours before using it for the first time.

Step 4: Power

My power system depends on AA batteries. Since I do not want to spend countless dollars on batteries, I got six rechargeable batteries and a recharger. This is pretty simple.

If you get a MintyBoost as I did, you need to make a simple modification to use it on your RaspberryPi. The Pi requires more power than just 2xAA batteries alone can provide. All I did was wire two 2xAA battery packs in parallel before connecting them to the MintyBoost. I don't have an altoids gum case (yet), so I simply dropped the exposed battery pack and minty boost into an anti-static bag. Connect a micro-USB cable to the MintyBoost. Your portable Pi power system is now complete.

I have not done any tests as to how long the battery pack will actually last, but I speculate that it is within the laptop/netbook battery life range. Of course, you can use as much or as little power as you want. It all depends on how much you're willing to carry around with you. This setup is meant to be super-portable.

Having 4 batteries is CRITICAL. I can't stress this enough. Two batteries will run your RaspberryPi, but it is not enough power to power the keyboard/trackpad and WiFi dongle.

Step 5: RaspberryPi Configuration

11 March 2013:

I've slightly improved the battery pack. More Altoids, and more power. And a power switch now! Yay! I managed to stuff the minty boost, a power switch, and four rechargeable batteries into a standard altoids container. I used two 2xAA batter packs, wired in parallel to achieve the proper voltage. It's very similar to the last system, but much cleaner looking. You'll also notice that I have now been tying the battery pack to the Pi case - planning ahead as the battery pack shrinks, as I want to keep the device in as small of a one-piece unit I can manage.

Step 6: Monitor

I used the Vuzix Wrap 920 video glasses as a monitor. They have a 640x480 resolution on each screen, which is pretty good considering the price. It's a big price to pay if it were a full size monitor, but for video glasses, this is the best resolution I could find for the price. Vuzix makes a better pair, the Wrap 1200, which sports twin 852x480px displays, but they cost a lot more ($500 on Amazon, more from Vuzix).

As far as setup goes, connect the glasses to the control box they come with, and plug the RCA adapter the glasses come with into the control box as well. Then connect the "Video" plug on the RCA adapter to the RCA coupler, and plug the other end of the RCA coupler into the Pi. Don't use an RCA cable for this connection. It works, but the coupler is much, much shorter. I also found that this coupler is extremely snug-fitting. I did loosen it up a little bit, but it is still a tight fit, unlikely to come loose while carrying the computer around.

Some people have been asking about what the display actually looks like. I was actually curious myself before buying these glasses. When I tried to photograph them, I realized quickly just how difficult it is to take a picture of such a tiny screen, behind a lens. I posted the best picture I could get. Viewed on my computer screen I could make out words in the image. I don't think it's as easy when viewing the picture from Instructables. You could try downloading it if it's difficult. I assure you it's easier to read when wearing the glasses.

Step 7: Wearing the Computer

This is fairly straightforward, but varies depending on the pants that you wear. I got a cell phone case that clips onto my belt, so the first thing I do is put it on my belt. Then, I put the battery pack in my pocket, and connect the microUSB cable to the Pi. The extra bits of the microUSB cable can be shoved into your pocket. I put the video glasses control box in a separate pocket since I have two (I'm wearing cargo pants).

The glasses you can wear when you use the computer. When not in use, I hang the glasses on the collar of my shirt. You could also get another belt case for them, or put them in a pocket. Or just not wear this computer when it's not in use.

Step 8: Conclusion

I have begun testing this device, and the results seem promising. First, a few things I will note:
-People around you do not know what you are wearing. If you are in a school setting like me, this may lead to a lot of questions and such, but overall, I have found that most people tend to react positively once they realize that you're wearing a computer, not a failed fashion statement.
-You cannot easily see directly in front of you, but you can see around you. My next version will have a camera system for AR/VR.

Now for a review of the mobile computer system after some testing:
-I am able to browse the web, type documents, and <nerd moment> remotely connect to my web server </nerd moment> on the go with this setup. It's a polished system. I have also tried taking notes on it, which works fairly well so long as people around you know what you are doing.
-The video glasses I have support a duplex mode where they display the left side of the screen on the left screen, and the right side of the screen on the right side. Since your eyes are used to seeing the same thing, this is not easy to look at. Some of my friends that I showed my wearable computer to noted that they could see both sides of the screen next to each other. However, since I already got used to viewing the two screens as one, I cannot do the same. I have yet to try extensively.

A few drawbacks I will note:
-The RaspberryPi is slow. It's not extremely slow on Raspbian, but it cannot handle much. I am able to check my emails (through gmail) if I'm desperate, but it cannot handle something that power hungry. I also cannot play videos through VLC at all. If you have better success, please let me know!
-Typing on this keyboard is still different than a desktop keyboard. It's not quite a phone keyboard, or a tablet either. It feels like a desktop keyboard when I type, but I cannot attain the same speed.
-(SOLVED) I do not have a power switch. When I find a suitable case for my battery pack, I will add a switch. Until then, I've been unplugging the Pi when I turn it off. This is a minor inconvenience.

And, while I'm at it.... the next version will have:
-A significantly slimmer profile
-Extended battery life
-Lighter and easier to carry around
-Anything else you can suggest. I'm open to new ideas.

Well, there you have it. Let me know what you think. Is this the way of the future? Or is this too much human/computer integration? Either way, I think it's pretty cool.