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This article describes a scheme for finger detection on the screen, permitting convenient use of a keyboard in conjunction with a screen menu.
English (United States)
This text was extracted from a PDF file.
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Finger Detection On Display Devices
This article describes a scheme for finger detection on the screen, permitting
convenient use of a keyboard in conjunction with a screen menu.
The frame of the display screen is fitted with a row of lights along the top,
shining down. There is a corresponding row of light sensitive devices along the
bottom, with lenses arranged so that each light lights one sensor. Similarly,
lights on the left of the frame light sensors on the right. The sensors are
connected via a control box to the other terminal/computer lines. When a finger
is placed on the screen at the intersection of two beams, the position of the finger
The detection may be used to interrupt the computer, to modify a displayed
field (cf delayed pen action) or to position the cursor.
It is possible to break two parallel beams at once, given an ambiguous
position. A finger may brush past other beams on the way to the right position.
As an enhancement the control box does not register a position until it has been
unambiguously held for a period of time 1/4 second). Twelve vertical and twelve
horizontal beams are used giving 144 detectable places. Alternatively a very
large number of beams could be used, with software/firmware resolution of