The Tummy PC: A Practical Wearable Computer (How to Make Your Own)
© 2005-2009 by John M. Smart

(This article may be excerpted or reproduced in its entirety for noncommercial purposes.)

Tummy PC 1.0 (1998-2005): NEC MobilePro HPC
Ultraportable PC (2006-2009): Sony VAIO TX Series
Tummy PC 2.0 (2010): Largescreen iPhone w/ Keyboard, Ported to a MobilePro Body?

The Tummy PC is my name for a lightweight, wearable personal computer worn at the waist like a "tummy pack," with a near full-sized touch typable keyboard and fabric covering the case when closed, so it looks unobtrusive. This is a very, very productive and useful form factor that I hope to see much more of in coming years.

Tummy PC 1.0 (1998-2005): NEC MobilePro HPC

My Tummy PC Version 1.0 was a 1.8 lb, J-class clamshell handheld personal computer (HPC) made by NEC. I began wearing it in 1998, with the debut of the MobilePro 750. When the clamshell is open, the HPC screen sits out about 4" from the waistline of the wearer (see picture right), for comfortable touchscreen navigation. The 95% size keyboard is comfortable for fast touch typing. When closed, the fabric case cover makes the HPC look like a tummy pack (second picture below). My case cover includes a pouch for a second battery, which is always helpful on the road.

This article tells you how to make your own Tummy PC using NEC MobilePro HPC (picture left). This was an amazingly useful notetaking machine for the seven years I used it, and it was a very sad day when NEC stopped producing them in 2004. The MobilePro 900C was the last and best of the bunch.

I'm really looking forward to someone hacking the iPhone into this amazing form factor. An iPhone-based Tummy PC could be the world's first truly useful and practical mass-market (my solution is home-grown) wearable computer. Can we expect this in 2010?

The "instant on" feature of the MobilePro allows your Tummy PC to be on and ready as soon as you open it on your belt. NEC's elegant, near-full sized keyboard allows you to easily type 50-80 words a minute either sitting or standing, fast enough to catch all but the most rapid conversations verbatim. The touchscreen gives you an intuitive interface for your HPC apps, and adding a Socket CF Wi-Fi Card allows you to waist-browse the web. For more on the NEC MobilePro visit Rich Hawley's great MobilePro 900C compatibility site. You might also look at other HPC sites, like John Ottini's HPC Factor. The best place for help from other MobilePro users and experts is probably PocketPC's NEC MobilePro Forum.

By 2004, the only company still making J-class (HPC) wearables was NEC. They outlasted HP's Journada, a less advanced entry in this class. HPCs may still be sold in Japan, but are now defunct in the US. This is a shame, as NEC did a good business selling them to vertical markets including salespeople and health care workers. They ran only Windows CE, but clearly it is just a matter of time until someone ports OS X and Windows XP into this form factor.

Because I write a lot and like to review and prioritize my agenda, I would guess my TummyPC roughly doubled my note-taking productivity over the seven years I used it, primarily because the HPC is instant-on and always accessible when I'm wearing it. If you wear a belt, I find it best to wear the buckle to one side (picture right) or go beltless. With either of the two mounting options below you will find you can safely run (for planes, to class, etc.) while wearing your HPC (with cellphone clips mounted to the back). You won't even need to take your Tummy PC off when you drive, as you can strap your seatbelt right under it. Thus it is a true wearable computer. For everyone's safety, please don't use it while you drive!

Because of the Mobile Pro's energy-efficient solid state design (no hard drive), with fresh regular-size MC-BA9 batteries (available at places like for about $15 each) you'll get 5.5 hours of use out of each (or as little as 3.5 if you are constantly using Wi-Fi), for seven to eleven hours of cord-free use. I recommend keeping an extra AC adapter in your car and one in your backpack for emergency recharges. After several months of daily use your batteries start to degrade in performance. Buy two replacement batteries on eBay every eight months (put it in your calendar) and you'll always be powered up.

Professionals who are mobile much of the day can greatly benefit from a Tummy PC. So can students, who will find this an ideal notetaker. Finally I'd recommend it for writers, who will find it very easy to input interesting thoughts wherever and whenever they occur. This is much better than speaking it into a voice recorder, as you can edit and reorganize your thoughts as they happen.

Would you like to make your own wearable HPC? Just follow the three step directions at the bottom of this article.

Ultraportable PC (2005-2009): Sony VAIO TX Series

In 2005 Sony introduced a full-featured ultraportable laptop, the VAIO VGN-TX17GP. At 2.7 pounds and with a small form factor (10.7” wide x 7.7" deep x 1.12” high) it isn't wearable like the NEC HPC, but it runs Windows XP and is a full featured laptop with a DVD burner. When this machine came out I decided to move to it while waiting for another great J-class HPC like my Tummy PC. I've been waiting five years, but hopefully it won't be that much longer.

Besides serious miniaturization, the TX's major innovation is its screen. It has a wide, high resolution, 11.1" WXGA (1366x768) LCD display, and most interestingly, white organic LED (the "light source of the future") as a next generation backlight, instead of the typical CCFLs (cold cathode flourescent lamps). This makes the screen bright (though nothing like OLED, which is coming) and amazingly thin and light, and more than twice as energy efficient as the CCFL technology. The efficient screen significantly increases the battery life of the laptop, giving it a real-world four to five hours (six to nine if you buy the extended battery).

Once you've made this portability investment you'll want something like the Verizon BroadbandAccess Cellular Modem Card to give you broadband access to the web wherever you can get a cell signal. The cellular broadband even works in a car driving at 60 miles an hour (with you as passenger, I hope). That makes it either Star Trek technology or the minimum requirement for 21st century living, depending on your attitude with regard to these things. Sony has a reputation for being overly aggressive with their digital rights management tools (eg., their recent rootkit fiasco). But if you believe they will ultimately play fair when challenged, as I do, you may be willing to support their innovation by buying their products.

I currently carry my TX-17 in a small backpack when I leave the house, so I'm using it as an ultraportable rather than a wearable. Using it in sleep mode makes it more accessible, but still nothing like an "instant on" device. Pulling it from my backpack it will boot up from sleep 5-10 seconds after you open the lid and touch any key, so it is still usable for catching quick notes (though in practice I scribble on paper again, as this is still a very significant delay). It sleeps automatically 15 seconds after you close the lid. Again, this is a major downgrade from the wearable accessibility of my HPC, so I'm looking forward to someone bringing back my Tummy PC, the instant-on HPC form factor, wearable at the waist. It is now 2009, and I've been waiting five years. Fortunately, I can see a hack that will solve this problem Real Soon Now (read on!).

Tummy PC 2.0 (2010?): Largescreen iPhone w/ Keyboard, Stuffed into a MobilePro Body!

The iPhone's multi-touch user experience is without parallel, but until it has both an external keyboard, and a double width screen, large enough to read regular-sized web pages without shrinking them from native resolution, it will not be a general purpose notetaking, web browsing, and computing machine.

People have talked about creating a keyboard for it for some time now via Bluetooth, but the iPhone software doesn't provide users that freedom yet. There isn't even a solution to plug a keyboard directly into the machine using the external port, which would be better for our purposes, as there would be no Bluetooth power overhead.

Fortunately, folks have been asking for the external keyboard for years now, and someone will eventually deliver it. Couple that with the knowledge that Apple is finally going to make a larger multi-touch screen, the Apple Tablet in 2010, capable of reading regular-sized web pages, e-books, and the like, and it's clear that we will finally be able to cobble together our beloved HPC again.

Once the Apple Tablet comes out, assuming an external keyboard option can be hacked by then, all we need to do is hire a good local maker to start with an old NEC MobilePro 900c body, swap the tablet in as the replacement screen, throw away the motherboard under the excellent MobilePro keyboard and reuse that space for spare battery.

We will then have an amazing HPC back in the US market (albeit a custom built one) six years after its demise!

As the futurist in me would say: The more things change, the more some things stay the same. :)

Dreams for the Future

I am sure that a lot more people would buy and wear Tummy PCs if they were very light and thin, and came from the factory with clips for easy wearing at the waist, and if they included a few more obviously valuable features (integrated cellphone, i-Pod, camera, 3G EV-DO modem, games, etc.).

After seven years wearing one as a pioneer (1998-2005) I am convinced that having a good, lightweight near full-sized keyboard at the waist is a tremendous asset for some people, particularly students, writers, and certain professionals. Keyboards remain useful even with advanced voice recognition, as they allow you to do two things at once (write and speak, or write and think about what you want to speak). Keyboards will go away only when human fingers go away, so there's a large, unserved market here.

There's also room for some more miniaturization and engineering, which would allow Tummy PCs to be worn even by petite individuals who would find them too big and heavy today. I'm sure that the 1.8 pound HPC form factor I wore for seven years could shrink to one-quarter the size and one-third the weight in coming years. Now that would be a truly mass-market wearable!

How do you get a Tummy PC down below the size of the MobilePro? You can start by using a keyboard and screen that interleaves in on itself as the cover is closed. Keyboard and screen size are now the only limiting factors on the size of the Tummy PC at your waist. The best example I've seen of this to date is IBM's "butterfly keyboard" for their 1995 ThinkPad 701 notebook computers. When you open the cover of a butterfly, the keyboard springs out from interleaved to a flat configuration almost two inches wider than in the closed position (note the keyboard overhang in the butterfly picture at right), and it is quite stable to type on. IBM engineer John Karidis, who developed the butterfly, tells me it can be cheaply licensed to any wearable PC maker, so the opportunity is there. A dual fold multi-touch screen would also be very nice, allowing the user to work with half-sized screen for data entry at the waist, but with an extra half that folds out when you want to browse the web or do other full screen work.

Now imagine a Tummy PC which is the full size of the MobilePro HPC when it is fully unfolded, but when folded, is one-quarter its size, because both the keyboard and the screen fold once and interleave once as it closes, and unfold and uninterleave when it opens. Your Tummy PC could do either under voice control, in just a few seconds.

This, essentially, is a belt buckle that turns into a Tummy PC, in an instant. Think I'm dreaming? Someone will eventually deliver this, because human fingers like to type, and typing at the waist is a natural and very efficient ergonomic, one I used for seven years. When that happens, the Tummy PC 3.0 will be born.

In the meantime, we can predict the obvious, and do our best to speed its arrival. Good luck!

Tummy PC 1.0 Directions

1. Purchase your own MobilePro HPC ($100-500)

If you are on a restricted budget, MobilePro 780's or 790's are quite cheap nowadays ($100 on eBay, $15 for one extra battery). This will work fine for some, but if you can afford it I recommend the MobilePro 900C ($300-500, $30 for batteries) which has several time-saving innovations. The four best new features are:

• A USB1.1 slot, which allows you to rapidly move files from your Tummy PC to your other computers and back using a keychain flash drive (a $20 Iomega 64MB micro mini flash drive, smaller than a door key, is what I use) instead of using the slow serial port and sync software, which is your only transfer option on the older models.

• A coin cell backup battery holder. It is a dirtly little secret that MobilePro backup batteries typically die after about 18 months of extended daily use, and this was the Achilles heel of older units. When your backup battery dies all the info on your unit vanishes, and you have to go back to your last backup (a month old? a year?) and start over. With the 700 series you must hand solder the replacement backup battery yourself, or pay NEC to do it (a long time without your machine). With the 900 series, you just snap a new one in. I recommend doing so every January (put it in the calendar) and you should never run into a data loss problem, even after years of use.

• The 900 has integrated flash ROM for doing automated onboard backups, which prevents you from losing all your data just in case your backup battery does fail. Automated backup using NEC's supplied bUseful utility is quite simple.

• A new OS, Microsoft CE .NET 4.2, comes in the 900C, and it is a big upgrade from the old HPC 2000 OS on the 900 and 700's, and runs on a faster processor. There's also a double size extended battery available, but at 1.8 lbs and with its existing size, a standard Tummy PC (with an extra battery in your pouch) is probably at the upper edge of comfortable all day wearability, for most people. I don't think I'd want anything heavier.

The only shortcoming of the 900C, from my perspective, is the passive matrix color screen, which is faint in daylight and near impossible to read in direct sunlight.

2. Choose a Mounting System So You Can Wear it at Your Waist

After spending several days thinking about this problem in 1998, I decided to mount four cell phone clips on the back of my MobilePro. I've never thought of anything better than this simple hack, and if you come up with a better solution let me know. I mount two in vertical orientation so I can clip the unit to my pants or belt, and two others horizontally as as additional "legs" to make a sturdy four leg "table" out of the device when resting on a flat surface (see picture below).

The best clips I've found are TCC Industries "Clip Kt2's" ( The double stick adhesive is very strong. Buy at least six clips, because if you use your Tummy PC a lot you may break one of the two that you clip to your waist on occasion, and then you'll need to put a new one on (you can pry the broken clip off the unit with two jeweler's screwdrivers wedged underneath, or replace the top half of the clip without prying off the bottom, depending on which part of the clip hinge breaks). If I could find these in metal that would be ideal, as they would never break. Unfortunately plastic is all I've found, so once or twice a year one of them breaks and I have to fix it.

Before placing your clips on the MobilePro, carefully peel off the four grey rubber footpads from the MobilePro (slip an Exacto blade or jeweler's screwdriver under the pads and pry them off). Then use the alcohol wipes to clean off the unit before you put on the clips, as below (no need to be perfect, just get the alignment roughly similar to the picture).

Next, stick the grey rubber footpads on the phone clips near their top edge, after roughing up the clip surface with some light sandpaper and wiping it down. Your MobilePro will now stand up nicely for touch typing on a table when you aren't wearing it.

Those who don't care about aesthetics will now be able to clip a silver colored Tummy PC to their waist, and can use it blissfully unaware of the strange looks of passersby. Carry the extra battery in your pocket and you are good to go for the entire day.


3. Take the Unit to an Upholsterer to Cover the Top Half of Your MobilePro Case With Fabric

If you care about looking unobtrusive, you'll probably want pay a local upholsterer to make a fabric cover for your Tummy PC that includes a pouch to store your extra battery.

You might also consider spray painting the silver sides of your MobilePro black, or taking it to an auto detailer who will do this for you for a small fee. If you are going to paint it yourself be sure to use masking tape on things you don't want painted.

Ask your local upholsterer or auto detailer to put some fabric (I use black nylon) on the MobilePro that covers the top of the case. See the picture at the top of this article to see the solution I chose, which is a piece of fabric that wraps around the case cover and juts out a half inch above the screen at the top, so it covers the top of the unit when closed, protecting it from spills, etc.

I'd suggest your case cover include a pouch to hold your second battery. Make the pouch large enough to slide the second battery in and out easily. I have found the ideal dimensions for the cover are 9.5" wide by 6.5" high, and 7.75" wide by 3.375" high for the front pouch. Radius the bottom corners of the cover, but not the top. The cover will wrap around the "front/top" of your MobilePro (the side that has the cover latch) when you are wearing it.

When the cover is made, your upholsterer will need to make a small hole in it for the cover latch. This is really the only tricky part. One way to do this is by adding some fresh whiteout to the cover latch, test wrapping the cover, and lifting it off. On the underside of the nylon you'll see the whiteout impression, which shows you where to cut an appropriate sized hole in the cover for the latch. Now glue your cover onto the MobilePro using something like 3M's Super 77 spray adhesive.

Congratulations! You now have an upholstered Tummy PC. When closed, it will look and feel like a fanny pack, very unobtrusive. If you aren't particularly petite, you'll find it easy to wear all day long.


Feedback? Edits? Omissions? Feel free to email me at johnsmart{at}accelerating{dot}org. Good luck and happy computing!