Category: Hardware

Adapted Computer Keyboard

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PROTOTYPEPURPOSE: To design a customized computer keyboard for an individual who is legally blind and has fine motor skill disabilities. Initial tests included two visual and two motor skill tests to determine the consumer’s abilities so the keyboard would meet all specified needs. The final design included keys that were large enough and spaced so the consumer would be able to identify and depress only one key at a time. The size of the lettering was also increased to accommodate the consumer’s visual disabilities. The total number of keys was reduced to 49 from the standard 104: the numbers 0-9, letters A-Z, and six punctuation keys: Return, Space, Backspace, Shift, Caps-lock, a key to start the e-mail application, and a key to start an Internet browser. The consumer requested that the keys be arranged in alphabetical order. Key size, spacing, and layout were determined based on tests of the consumer’s mobility and reach, ability to depress keys of certain sizes and spacing, and ability to read letters of different sizes, stroke widths, and color patterns. The team also determined that the consumer typically depresses a key for approximately three seconds for a keystroke and requires a concave key surface to prevent fingers from sliding off the keys. The curvature of the keyboard was modified to match the consumer’s reach patterns. The switching mechanism used in the keyboard design is a flexible printed circuit board (PCB). This mechanism uses three Mylar or Kapton sheets. The bottom sheet is connected to the short slot in the encoder, and the top sheet is connected to the long slot in the encoder. The middle sheet is used as a spacer sheet with strategically placed holes. When a key is depressed it pushes down a rubber dome, which then makes contact with a particular node on the first sheet, and finally makes contact with another node through the spacer sheet, thus closing the circuit. The flexible PCB design was done in AutoCAD to ensure the nodes lined up exactly with the locations of the centers of each key. An existing fully-functional keyboard encoder was used and the new keyboard layout was programmed using Microsoft’s Keyboard Layout Creator. The keys and keyboard frame were manufactured from delrin, chosen for its high strength to resist frame deflection and its low coefficient of friction to resist key binding. The keyboard frame was made with extra internal supports to stiffen the structure in case the consumer hits the frame instead of the keys. The keys were made using a CNC machine, and were designed with a flat surface to prevent them from spinning in place. The user has been given a detailed user’ manual that includes installation instructions as well as key identification for keys with non-alphanumeric symbols. The total cost of the project was approximately $550. TITLE: Adapted Computer Keyboard. JOURNAL: NSF 2006 Engineering Senior Design Projects to Aid Persons with Disabilities. REF: Chapter 9: pp. 106-107. PAGES: 3 with cover. 2006.


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