GB2269686A

GB2269686A - Time piece display.

Info

Publication number: GB2269686A
Application number: GB9214608A
Authority: GB
Inventors: Siu Fan Kwan
Original assignee: Nat Electronics & Watch Compan
Current assignee: Nat Electronics & Watch Compan
Priority date: 1992-07-09
Filing date: 1992-07-09
Publication date: 1994-02-16
Also published as: GB9214608D0

Abstract

A time piece is disclosed which includes a liquid crystal display 2, 3, 4 and an array of light emitting diodes 7, 8, 9 which is disposed behind the display in the viewing direction. Preferably the liquid crystal display is negatively biased so that the light emitting diodes when actuated radiate light through the display to give the impression that the display 3 is itself formed from light emitting diodes. The liquid crystal display is arranged to be permanently actuated to provide a constant display of time and the light emitting diodes have a separate power supply, so that use thereof does not unnecessarily exhaust the power supply for the time display. <IMAGE>

Description

A TIME PIECE This invention relates to a time piece, in particular a time piece which utilizes a liquid crystal time display.

Liquid crystal time displays have been used in time pieces for many years but have the disadvantage that they do not emit light themselves and thus are only viewable in the dark if an auxiliary light is fitted. It has been known to provide such a light at the side of the display, light being transmitted through the display in a lateral direction to provide some illumination. However, it is a disadvantage of such a technique that the lighting of the display is poor and the display is still difficult to read.

According to the invention there is provided a time piece comprising a liquid crystal time display, a light source disposed behind the display for emitting light through the display in the viewing direction, power supply means connected to the display to provide a continuous display time and connected to the light source and; a switch for selectively actuating the light source.

In the invention as claimed, as the light source is disposed behind the display and transmits light through the display in the viewing direction, the illumination of the display is considerably enhanced. Preferably, the light source is comprised by a plurality of light emitting diodes which illuminate the display with a red colour and, preferably, the display is negatively biased, so that the background to the numerals indicating the time is opaque whereas the numerals themselves ves are transparent. This variation has the added advantage that the numerals are more clearly indicated and the display resembles a light emitting diode display, even though the display is of liquid crystal construction.

Furthermore, the power supply means is preferably provided by two independent power supplies, one connected to the light source to provide the continuous display of time and the other connected selectively via the switch to the light source.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is an exploded perspective view of an embodiment of a time piece according to the invention; Figure 2 is a schematic view of the light emitting diode array and conventional driver circuitry; and Figure 3 is a schematic view of conventional LCD display control circuitry.

With reference to the drawings an embodiment of the invention is shown which includes a casing 1 in which an LCD display and driver circuitry 2-4 is disposed comprising a LCD-display 3, together with driver circuitry as shown in more detail in figure 3 sandwiched between first and second polarizers 2 and 4.

Behind the LCD display, an array of light emitting diodes 7, provided on a circuit board 8, together with a driver circuit 9 is provided. The array of light emitting diode 7 is of similar shape to the LCD display 3 and a diffuser 5 is provided between the LCD display and light emitting diodes to diffuse the light therefrom.

The LED array 7 and LCD display 3 are each provided with separate and independent battery power supplies V1 and V2 as shown in figures 2 and 3 so that use of the light emitting diodes does not exhaust the power supply for the time display.

A driving circuit for the light emitting diode 7, labelled 10 in figure 2 is of standard construction and a switch S1 is provided for selectively actuating the driving circuit to illuminate the light emitting diodes 7.

The driving circuit 12 for the LCD display 3 is of standard construction and include a crystal 14 and biasing capacitors C1, C2, together with switches for adjusting the time etc S2, S3. The power supply V2 is permanently connected to the circuit 12 so that a continuing display of time is provided.

Preferably, the LCD display is negatively biased, so that the numerals showing the time appear clear to the eye, with the surrounding background being opaque. With such an arrangement, when the light emitting diode 7 are actuated by depression of switch S1, the light therefrom shines through the transparent numeral-forming regions thus giving the impression that the time display itself is formed from light emitting diodes. Alternatively, the display may be positively biased as is normally used, although the LED effect would not be produced.

In use, the liquid crystal time display 3 continuously shows a display of time, which is readable when the ambient light is sufficient. When such light is insufficient, a user may depress switch S1 thus actuating the LEDs 7 which will shine through the display in the viewing direction illuminating the numerals and thus indicating the time.

While an embodiment of the invention has been described, this is not to be construed as limitative. For example, although the light source has been shown as an array of light emitting diodes, any other suitable light source, with, for example, a colour filter if necessary or desired, may be used. If a colour filter is employed, this may advantageously be combined with the diffuser 5.

Claims

1. A time piece comprising: a liquid crystal time display, a light source disposed behind the display for emitting light through the display in the viewing direction, power supply means connected to the display to provide a continuous display of time and connected to the light source and; a switch for selectively actuating the light source.

2. A time piece as claimed in claim 1 wherein the light source comprises at least one light emitting diode.

3. A time piece ashclaimed in claim 1 wherein the light source comprises a plurality of light emitting diodes.

4. A time piece as claimed in claim 3 wherein the light emitting diodes are arranged in an array corresponding to the shape of the liquid crystal time display.

5. A time piece as claimed in any one of claims 1 to 4 further comprising a diffuser disposed between the display and the light source.

6. A ime piece as claimed in any one of claims 1 to 4 wherein the power supply means comprises a first power supply connected to the display and a second power supply connected to the light source, the first and second power supplies being independent.

7. A time piece as claimed in claim 6 wherein the first and second power supplies are formed from batteries.

8. A time piece as claimed in any one of claims 1 to 4 wherein the liquid crystal display is negatively biased.

9. A time piece as claimed in any one of claims 1 to 4 wherein the liquid crystal display is positively biased.

10. A time piece substantially as hereinbefore described with reference to the accompanying drawings.