Optics: image projectors – Miscellaneous
Patent
1989-08-28
1991-07-30
Haroian, Harry N.
Optics: image projectors
Miscellaneous
353DIG3, 353DIG5, 353 44, 434365, G09B 1900
Patent
active
050355023
ABSTRACT:
A hand-held calculator has a transparent window carrying a liquid crystal display as well as transparent number and function key locations such that when placed on an overhead projector, the calculator can be used to demonstrate to a classroom of students all operations performed in a sequence of mathematical operations. The plastic casing of the calculator has one or more small holes passing through the casing at corners. Another feature of the calculator is an improved keyboard of relatively small domain size for each key, with a spacer grid on the back surface of the keyboard membrane panel overlay element, effective to provide pressure isolation of an active key from adjacent keys and also to prevent other pressures on the keyboard from causing mistaken entries. A further feature of the calculator is a protrusion or foot at each corner of the back of the calculator casing. Finally, the calculator in a preferred embodiment has a plurality of different background colors for different groups of the transparent function keys.
REFERENCES:
patent: 4154007 (1979-05-01), Judd
patent: 4290708 (1981-09-01), Siwula
patent: 4632529 (1986-12-01), Levin
patent: 4652101 (1987-03-01), Grunwald
patent: 4810860 (1989-03-01), Sekine
patent: 4836786 (1989-06-01), Wong
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