This handheld, portable keyboard design was my undergraduate thesis project. The goal was to design a device that provided quick and easy data input for mobile computers such as cell phones and PDAs. The ideal design would allow the device to be quickly accessed and used while walking down the street, riding the bus or during a conversation.
There is currently a variety of options for users to interface with their mobile devices, but the commonly adopted ones are either much slower and more difficult than a traditional QWERTY keyboard (such as phone pads or stylus-based entry) or aren't usable while on-the-go (such as fold out QWERTY keyboards for palm pilots).
One existing solution to these issues is the Twiddler
by Handykey. This is a handheld keyboard with three rows of four buttons on one face, and another set of buttons on the back for the thumb. However, there are few issues with this device that prevent it from being widely adopted. The size of the device prevents it from being conveniently portable. It's impossible to store in a normal pocket, so it must either always remain strapped to the user's hand, or stored in a bag or backpack. People are unlikely to be willing to carry around a big device in their hand all day (both because of the inconvenience and the looks they would get), and keeping it stored in a backpack prevents it from being easily accessed. Lastly, the Twiddler can sometimes be uncomfortable to use, and doesn't take advantage of any existing typing skills.
In the process of designing a solution, I made many models and semi-complete prototypes (some of which can be seen below). For the most recent design, a final, functional prototype was made from a combination of 3d-printed parts, machined aluminum and ABS as well as a variety of electronic components.
The important features of this design are twofold. First, the device has a mechanical component that allows it to lock into a folded position. While folded the device can be stored in one's pocket or can remain relatively hidden in the palm of the hand. Another important feature is the construction and layout of the four finger keys. Each key has three switches (back, center and front) which can be pressed in five different combinations. Each set of three switches is controlled by one finger at one interface point (much like a scrollwheel that can be clicked, rolled forward, or rolled backward). The "back, center, front" action of each key can be used to mimic the three-row layout of the QWERTY keyboard. To access the set of keys normally controlled by the other hand, the device employs a "mirroring" system like those used in Half-QWERTY keyboards.
Other features implemented in the prototype include separate angle adjustability for each key and a wireless PC interface.
A more complete description can be viewed at this website: www.AlexMekelburg.com/keyboard/
(still under construction).
You can also download a PDF of the Thesis document