US 4,893,120 AGranted

Touch panel using modulated light

AssigneeDigital Electronics Corporation

InventorsRoger W. Doering, Colin F. McManus

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Abstract

A touch panel system using modulated light beams to enable the system to detect when one or more of the light beams are blocked even in bright ambient light conditions. The system has a "touch sensitive" display surface with a defined perimeter. Surrounding the display surface are a multiplicity of light emitting elements and light receiving elements. These elements are located so that the light paths defined by selected pairs of light emitting and light receiving elements cross the display surface and define a grid of intersecting light paths. A scanning circuit sequentially enables selected pairs of the light emitting and light receiving elements, modulating the amplitude of the light emitted in accordance with a predetermined pattern. A filter generates a blocked path signal if the currently enabled light receiving element is not generating an output signal modulated in accordance with the predetermined pattern. Finally a computer is used to determine if an object is adjacent to the display surface and the location of the object, by determining if the filter is generating at least two blocked path signals corresponding to light paths which intersect each other within the perimeter of the display surface. A failure detection circuit for testing the LEDs and phototransistors, by checking for blocked LED/phototransistor pairs. When a blocked pair is found the phototransistor of the blocked pair is paired with an LED near the blocked LED and the block LED is paired with a photo-transistor near the blocked LED to determine if they have failed.

Claims9

Dependent claims

A touch panel, comprising:

a display surface having a defined perimeter;
a multiplicity of light emitting elements and light receiving elements;
said elements located so that the light paths defined by selected pairs of light emitting and light receiving elements cross said display surface and define a grid of intersecting light paths thereon;
said light receiving elements including means for generating an output signal corresponding to the amplitude of the light received thereby;
scanning means for sequentially enabling selected pairs of said light emitting and light receiving elements;
modulation means for modulating the amplitude of the light emitted by the currently enabled light emitting element at a frequency of at least 10 kilohertz in accordance with a predetermined pattern;
filter means for generating a blocked path signal if the currently enabled light receiving means is not generating an output signal modulated in accordance with said predetermined pattern;
and
computer means, responsive to signals from said filter means, for determining if an object is adjacent to said display surface and the location of said object, including means for determining if said filter means is generating at least two blocked path signals corresponding to light paths which intersect each other within the perimeter of said display surface;
including component failure detection means, including means for testing a selected light emitting element, said testing means including means for:
enabling said selected light emitting element and a light receiving element across said display surface from said light emitting element, and testing for the presence of a blocked path signal;
enabling the same light receiving element and a second light emitting element which is located near said selected light emitting element, and testing for the presence of a blocked path signal;
and
denoting the detection of a component failure if a blocked path signal is detected when said selected light emitting element is enabled, but no blocked path signal is detected when said second light emitting element is enabled.

11 more elements

A touch panel, comprising:

a display surface having a defined perimeter;
a multiplicity of light emitting elements and light receiving elements;
said elements located so that the light paths defined by selected pairs of light emitting and light receiving elements cross said display surface and define a grid of intersecting light paths thereon;
said light receiving elements including means for generating an output signal corresponding to the amplitude of the light received thereby;
scanning means for sequentially enabling selected pairs of said light emitting and light receiving elements;
modulation means for modulating the amplitude of the light emitted by the currently enabled light emitting element in accordance with a predetermined pattern;
filter means for generating a blocked path signal if the currently enabled light receiving means is not generating an output signal modulated in accordance with said predetermined pattern;
computer means, responsive to signals from said filter means, for determining if an object is adjacent to said display surface and the location of said object, including means for determining if said filter means is generating at least two blocked path signals corresponding to light paths which intersect each other within the perimeter of said display surface;
and component failure detection means for testing the operability of a selected one of said elements by performing the steps of:
enabling said selected element and a complementary element across said display surface from said selected element, and testing for the presence of a blocked path signal;
enabling the same complementary element and a second element of the same type as said selected element and which is located near said selected element, and testing for the presence of a blocked path signal;
and
denoting the detection of a component failure if a blocked path signal is detected when said selected element is enabled, but no blocked path signal is detected when said second element is enabled.

10 more elements

Dependencies are inferred from the claim text.