Touch input device having digital ambient light sampling
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United States of America Patent
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Jul 24, 1990
Issued Date -
N/A
app pub date -
Dec 6, 1988
filing date -
Jun 18, 1984
priority date (Note) -
Expired
status (Latency Note)
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Abstract
A touch input device which continuously samples and digitally stores ambient light readings and compares these with previously stored readings is taught. Briefly stated, a phototransistor is turned on before, during and after an LED emitter energization. An ambient value is calculated which is subtracted from the value obtained during LED firing so as to develop a signal indicative of the presence or absence of the LED pulse, irrespective of ambient light fluctuations. The ambient level is stored for comparison purposes during the next sampling of the associated phototransistor.
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