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4/8/2010

Navigation Controls or D-pad

The navigation control set consists of a four–way directional control that allows the user to navigate the device user interface in the up, down, left or right directions, and an action control that acts or selects on the current highlighted item in focus. The navigation control area of the device is used more than any other area or set of keys and so it is essential that these controls function consistently, with acceptable force–to–fire (FTF), tactility and with no inadvertent actuations.

Isolating Action from Navigation

You should avoid combining directional buttons with action or select buttons under common keycaps since this can greatly increase the likelihood of inadvertent actuations during navigation. Successful designs for navigation separate the navigation keys from the action key.

Two examples of implementations of combined navigation would be:

  • D-pads where directional navigation and action button are not differentiated through individual key caps, surface breaks, or parting lines.

  • Navigation barrels that tilt for side–to–side (left/right) navigation, and roll up/down some number of limited degrees for up/down navigation. In this case the action is accomplished with a push exactly in the center but often leads to inadvertent actuation of left or right navigation buttons.

Numeric Keypad or 12 Key

Location and Size

As device displays become larger, such as for candy bar forms, and as overall device size shrinks, the numeric keypad layout tends to be pushed ever further downward on the device. As the keypad moves downward the overall size of the keypad becomes smaller, and the keypad gets closer to the lower end of the device. The human finger cannot actuate keys that get smaller than a certain size and tactility. The variables of placement on device, tactility, and size make it difficult to create hard guidelines however. Performing usability studies is encouraged to identify and separate usable vs. unusable and desirable vs. undesirable designs.

As the keypad moves to the lower part of the device, thumb displacement, which is the common method for one handed key actuation, becomes greater and less desirable. This leads to the device being moved further out of the hand to accommodate the lower keypad, which increases the potential for a less secure device grip and dropping the device.

Sometimes these tendencies are unavoidable due to the trends with increasing screen sizes and decreasing device sizes but anything that can be done to minimize this is encouraged.

In the Dark Dialing and Tactility

Tactile indicators should assist users with no–look dialing, lead the fingers to a known home key, and enable dialing without looking, relative to a known location. Numeric keypads should include tactile indicators to indicate the center or home key. Typically the tactile indictor on a numeric keypad is the 5key, and it is tactilely identified by a small bump, or bumps, on or around the key.

Send, End, Home, Back and Soft Keys

When applicable, these keys are primary, high–use keys. Their placement and identification should reflect this; they should be easy to actuate without actuating neighboring keys, and their legends should be highly legible.

  • Send and End

    Many users are accustomed to the de-facto industry standard which is a left-right arrangement of the Send key and End key respectively, and so these keys should be arranged this way as much as possible.

  • Soft Keys

    Soft keys should visually map to their UI counterparts as closely as possible, and should not be arranged with other keys in any way that confuses them with other keys or functions. Where possible, the soft keys should be placed directly adjacent to the display, to further identify their connection to the interface. In situations or forms where this is not possible, such as in clamshell forms, where the keypad and the display are physically separated, visually connecting the soft keys to their UI counterparts is highly recommended. At a basic level, this can be done through alignment and etched connecting lines on the surfaces.

Note:
Beginning with Windows Mobile 6.5.3, soft keys are replaced by touchable tiles on Windows Mobile Professional phones.
  • Home and Back Keys

    When these keys are arranged in a horizontal fashion, Homeshould be on the left, and Backshould be on the right. This arrangement is consistent with almost all Windows Mobile devices on the market.

  • Dedicated HW buttons

    Dedicated hardware buttons are external buttons dedicated to specific, usually non–customizable (by the end user) functions. Two examples are the camera button or voice record/command button. Dedicated hardware buttons should be accessible and usable, while at the same time not likely to be actuated by accident, such as while being held, or while being carried in a pocket or bag.

Alphabetic Keyboards

Regional/Localized Layout

The layout of keys in an alphabetic keyboard should reflect the region in which the device is sold. For example, a QWERTY arrangement for the U.S., AZERTY arrangement for France, QWERTZ arrangement for Germany.
Identifying Keys

Alphabetic keyboards have the highest density of keys for any area on a mobile device. A key high density can make key search and identification challenging. To provide a great user experience, you should consider correctly balancing key size, pitch, profile, color, contrast and legend designs. This challenge has many variables and you should consider industrial and interaction design principles when developing these keyboards.

Key legends should be easily legible, with high contrast against the field color of the key. Alternate key character legends accessed through the Shift, Fn, or Ctrlkeys or other modifier keys should be presented as secondary in hierarchy to the primary key character, and should remain legible. For modifier keys other than Shift, a distinct graphic connection should be made between the modifier key and its modified characters. An example is a modifier key character sharing the same color with its modified characters.

For use of the keyboard in low-light conditions, backlighting is extremely helpful. Care should be taken not to make backlighting too intense, and to determine an optimal backlight through usability research.
Key Size, Pitch (Spacing) and Profile

Designs for alphabetic keyboards vary greatly and the most apparent variables are key size, key pitch and key profile. User impressions and preferences vary widely around these. The one goal that must be clear is discreet key actuation, which is the ability to hit one key at one time, must be reliable and consistent. Key and key layout designs that cannot be actuated without accidentally hitting their neighbors are unacceptable. Designs should be subjected to usability and user preference studies to determine and refine proposed designs.

The equation whose variables are key size, pitch and profile controls usability. For small keys, for instance, profile (key height and shape) or pitch (center–to–center distance) generally should be increased. As usual, usability testing to determine optimal designs is highly encouraged and strongly suggested.

Key FTF (Force–to–Fire)

Key FTF may vary by large percentages across different manufacturers and even across the same keyboard. Switches used in mobile device keyboards can have a large production variation. The variation depends on the switch type whether it is dome, snap, etc. Care should be taken to account for these production variations when specifying the desired FTF. Users expect the force required by keyboard keys to be high enough to prevent inadvertent actuations, yet soft enough to be easy to use. The amount of this ease is variable and it should be established by solid usability methodology with typical target users of the product.

Switch vs. Key Cap Placement on the printed circuit board (PCB)

Extreme care should be taken in the manufacturing process, as well as in any prototyping process where units are intended for usability or user preference feedback, to align switches to the centers of the keys that actuate them. This is especially true for mechanical designs that employ dome switches, where even slight misalignments with their key caps result in poor or no switch tactility.

See Also