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Liquid Crystal Watch

IP.com Disclosure Number: IPCOM000078773D
Original Publication Date: 1973-Mar-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Edmonds, HD: AUTHOR [+2]

Abstract

Liquid-crystal display devices scatter light when a voltage is applied, and in this way provide a suitable contrast ratio between an activated element and an off element. One of the biggest problems with liquid crystals is their relatively short life, which decreases with increasing applied voltage. The lifetime of liquid-crystal materials, as presently driven, is barely adequate for use in electronic watches. To increase material lifetime, the present system utilizes the fact that the contrast ratio increases with increasing ambient light for a particular applied voltage.

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Liquid Crystal Watch

Liquid-crystal display devices scatter light when a voltage is applied, and in this way provide a suitable contrast ratio between an activated element and an off element. One of the biggest problems with liquid crystals is their relatively short life, which decreases with increasing applied voltage. The lifetime of liquid- crystal materials, as presently driven, is barely adequate for use in electronic watches. To increase material lifetime, the present system utilizes the fact that the contrast ratio increases with increasing ambient light for a particular applied voltage.

A photosensitive detector 12 is incorporated on the face 11 of watch 10 to monitor the ambient light level. The output of photodetector 12 then controls how much voltage is applied to the liquid-crystal elements 14 to yield a good contrast ratio. When the watch is viewed in bright ambient surroundings, the photodetector signal is high and, therefore, the voltage applied by driver 20 to the liquid-crystal elements 14 is decreased. When the ambient light level is low, the signal from detector 12 is low, and the voltage applied to elements 14 through driver 20 is increased to keep the contrast ratio constant.

The main advantage of this circuit is to apply a lower voltage to the liquid crystal, where the higher voltage is not required in high-ambient light surroundings, as is the case for most of the time When a watch is being read. Thus, the lifetime of the liquid crystal is...