This page demonstrate how a sequenced chording keyboard on a mobile device might work. The numeric keyboard keys 1 through 5 represent five buttons on a mobile device, each of which can be operated by a separate finger or thumb as the device is held in one hand. By depressing different keys in different combinations, the user can select a character to be entered into an input field. This scheme is known as a chording keyboard.
With the classic chording keyboard, the order of key depressions is not significant, and consequently a five key device can only encode (2^5 - 1) = 31 different characters, which falls way short of what a PC keyboard can do. But in this simulation, the sequence in which the keys are depressed is taken into account. This allows us to distinguish 324 different sequences, if we include truncated sequences. Each of these can potentially encode a different character, giving us more combinations than we need to drive a PC. Taking sequence into account may seem a complex idea, but regular PC keyboard users are already very familiar with the fact that Ctrl-C copies, while C-Ctrl doesn't; and that Ctrl-Alt-Del freshens their OS, whereas Del-Alt-Ctrl doesn't. See my blog for a full description.
The mobile mockup above responds to the keyboard's numeric keys 1 through 5 only. The current interpretation of these keys is shown below the screen, headed by the word Keys. As you press keys, the interepretation changes. If your keyboard won't allow you to hold down more than 2 or 3 keys at a time (like mine), you may release any key but the last one that you depressed without having any effect on the process. When you do release the last key that you depressed, its option is taken and entered into the screen as an input character. Alternatively, if you depress a key that has only one option, this option will be taken immediately. Once the last pressed key is released, all others must be released before you can proceed with the next character. By way of example, to spell "a cat" press (and then release) 1, 5, 123, 1, and 31.
As you depress keys, the background colour of the simulated mobile screen changes to let you know where you are in the process of encoding a character. It starts pale green, turns pale yellow while you are part-way through a key sequence, turns pale pink if you click an unassigned key (but does not lose its place), and turns back to pale green once you have selected a character and it has been entered into the simulated screen. With a real mobile device, the key labels would appear next to the physical buttons that you click on the device, which would make it easier to use than this demo.
© Trevor Turton (http://turton.co.za) 2008