Two-Thumb Keypad Chording

Updates:
The paper has now been presented at MobileHCI 2009. It received a Best Paper Nomination. Also, it received some press here.

My Keynote '09 Slides.

When designing a text entry system for mobile phone keypads, a designer needs to overcome the ambiguity that arises from mapping the 26 letters of the roman alphabet to only 12 keys (0–9, *, #). I created a novel two-thumb chording system for text entry on a standard 12-key mobile phone keypad and a performance model based on Fitts’ Law for an expert user. The model provides a behavioral description of the user and predicts a text entry rate of 55.02 wpm.

Our method consists entirely of one and two-key chords using only the standard 12 keys found on mobile phone keypads. Keys 2–9 are used as character keys while the *, 0, # and 1 keys are used as chording keys. By pressing any of the character keys alone the user enters the first letter displayed on the key. Simultaneously pressing a character key in combination with the * key allows the user to enter the second letter displayed on the key, pressing a character key with the 0 key enters the third character and pressing a character key with # key enters the fourth character in the case of “s” and “z”. The space character is entered by pressing the # key alone. The table below shows the keymap for generating all of the letters and the space character. Numbers are entered by using the 1 key as a chording key to select the numeral on the key. By pressing 1 alone, the user enters 1. By pressing 1 in combination with any other number, the user enters that number. Capitalizing a letter is performed by first pressing the 0 key alone and then entering the character. Rapidly pressing 0 twice allows the user to enter caps-lock mode, pressing 0 again once reverts to the previous mode. Common symbols can be accessed by pressing the # key and character keys other than 7 or 9.

Character Key	None	*	0	#	1
	Chording Key
None				Space	1
2	a	b	c		2
3	d	e	f		3
4	g	h	i		4
5	j	k	l		5
6	m	n	o		6
7	p	q	r	s	7
8	t	u	v		8
9	w	x	y	z	9

The Motorola Razr keypad was used as the model a 12-key phone keypad

Two-Thumb Keypad Chording

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