US3715881A - Display control device for timepieces - Google Patents

Abstract

The display is controlled by a device supplied by the same battery as the timing base of the timepiece. The signals produced by the timing base are then sent to a voltage elevating device through an amplifier. Afterwards they are rectified, hacked and pulsed to a liquid crystal cell having an electrooptic effect and displaying the time indications.

Description

one-woe: SR 1 x s s V Y k j. u mted States j 1 3,715,881 Girard 1 Feb. 13, 1973 DISPLAY CONTROL DEVICE FOR [56] References Cited TIMEPIECES UNITED STATES PATENTS [75] Inventor! PierreGiral'dBienneSwitzerland 3,664,116 1972 Emersonetal. ..58/50R 3,613,351 10/1971 Walton ..58/23 BA [73] Assgnee' r ggr g gfi i s xgzz fifi 3,630,015 12/1971 Lehovec ..S8/5O R [22] Filed: May 11, 1971 Primary Examiner-Richard B. Wilkinson Assistant Examiner-Edith C. Simmons Jackmon [21 1 App! 142,309 Attorney-Stevens, Davis, Miller & Mosher Foreign Application Priority Data [571 ABSTRACT The display is controlled by a device supplied by the May 11, 1970 Switzerland ..6974/ Same battery as the timing base of the timepiece The signals produced by the timing base are then sent to a [52] "58/50 58/23 350/l60 LC voltage elevating device through an amplifier. After- [51] litt- Cl. ..G04b 19/30 wards they are rectified hacked and pulsed to a liquid [58] new of Search 58/23, 23 A, 23 50 R; crystal cell having an electrooptic effect and display- 350/ ing the time indications.

8 Claims, 2 Drawing Figures l l J I 2 3 3 3 Ub Ub I 1 1 l r-9 mi ie 16 oous'rms CIRCUIT 4 B lO AMPLlFlER- ADAPTER DECODER 11 l 7 I F Y DISPLAY CONTROL DEVICE FOR TIMEPIECES BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to display control devices for timepieces and in particular to control devices for display means comprising a liquid crystal cell having a modified light transmitting behavior upon applying an electric field thereto.

2. Description of the Prior Art For some time those skilled in the art have known that it is possible to use liquid crystals in the manufacture of static elements for displaying ,either a digital or an analogic time indication in timepieces, especially in electronic timepieces. The liquid crystals used for that purpose are in the form of thin layers sandwiched between a pair of plates carrying electrodes. Normally, i.e. in the absence of an electric field, the liquid crystal layer is as transparent as water. This layer becomes, on the contrary, opaque as soon as an electric field is applied thereto. This behavior enables cells to be made for displaying either a digital or an analogic time indication.

A difficulty has, however, heretofore barred the use of liquid crystal cells in timepieces of small size, especially in Wristwatches or in pocket-watches. Since these timepieces have to operate autonomously, their source of electric power usually consists of a DC battery having a relatively low voltage. This lowvoltage may very well drive a timing base such as a quartz or another electronic oscillating device, but if such a low voltage had to be applied to liquid crystal cells so as to modify their optical behavior, the liquid layer would have to be made extremely thin. Reliable cells displaying, moreover, a time indication of the aesthetic quality required with watches would be difficult and delicate to manufacture.

A voltage higher than that used for the electronic circuits of the watch could, of course, be resorted to for exciting the liquid crystal cells; the timepiece would merely need be provided with two power sources having different voltages. This solution would, however, involve a noticeable increase in the size of the timepiece.

SUMMARY OF THE INVENTION It is therefore an object of the invention to permit liquid crystal cells to be used for displaying the time indication in autonomous electronic timepieces of small sizes, such as Wristwatches or pocket-watches.

A more particular object of the invention is to provide the timepiece with an electric DC source, a timing base supplied by that source and emitting an oscillatory signal, and a voltage elevating means having an input connected to the timing base and an output connected to the liquid crystal cell.

Further objects of the invention will become apparent in the course of the following description.

BRIEF DESCRIPTION OF THE DRAWING Two embodiments of the display control device according to the invention are represented diagrammati cally and by way of example in the accompanying drawing.-

In the drawing FIG. 1 is a sketch of circuits comprising a'transformer and pertaining to the first embodiment, and

FIG. 2 is a wiring diagram of a voltage elevating circuit belonging to the second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 the liquid crystal which displays the time indication is diagrammatically represented by its electronic equivalent, i.e., a load resistance (RL). The different possible structures of such a display device will not be described in detail herein. Quite generally, a liquid crystal cell comprises a thin liquid crystal layer sandwiched between two solid plates, for instance, glass plates. Thin metallic blades forming electrodes are provided on the surfaces of these glass plates coming in contact with the liquid crystal. These metallic blades may have various shapes and be variously arranged; they are individually connected to a decoder 10 in such manner as to permit an analogic or digital time indication to be displayed. Several embodiments of display devices of this kind are disclosed in my copending application Ser. No. 142,141 filed on the same date and entitled: Time display device for timepieces".

The electronic device controlling the display is supplied by a DC source having a low voltage such as, for instance, one or more batteries 1 connected in series. It comprises a timing base 2 which includes an oscillatory member driven by the battery 1 and emitting an electric signal oscillating at a relatively high frequency. The timing base may comprise, for instance, a quartz like oscillator 2 of FIG. 1. This timing base is connected to one stage of a frequency divider 3, which reduces the signal frequency to values proper for the control of the application of a voltage to cells RL. As shown in FIG. 1 one stage of the frequency divider is connected through an amplifier 4 to a transformer 5 elevating the voltage. The secondary of transformer 5 has a peak voltage substantially higher than the input voltage. The frequency of this transformer is chosen as high as possible so that it can be made with a very small number of windings. It operates according to the formula: I

Np number of the primary windings Ep primary voltage f frequency B induction S sectional area of the core.

Iff is very high (for instance, kHz), this transformer can be made with a core having a very small sectional area, because its power is itself very small. Its primary and secondary coils can also have a small number of windings. A transformer of that type canbe wound on a ferrite torus.

The output signal of this transformer is rectified by means of a rectifying circuit 6 connected to the output of transformer 5. The output voltage of the rectifier, which is substantially constant, is then clipped by a transistor 7, the base of which is connected to the input of the last stage of divider 3. Transistor 7 thus produces pulses having a frequency of 16 Hz in the disclosed embodiment. An adapter 8 is connected between the frequency divider and the base of transistor 7. The voltage applied to the liquid crystal cell is pulsed at a frequency corresponding to the input of the last divider stage and it is high enough to produce a well noticeable contrast within the nematic liquid of cells RL. Since the electric current flows through the nematic liquid only during half the time the cell operates, the device disclosed saves the energy of battery 1, thus increasing its life time.

The adjusting circuit 9 of the timepiece controls the decorder 10 directly connected to the liquid crystal cells RL.

The use of a high frequency also permits the replacement of transformer 5 by another voltage elevating device. Instead of miniaturizing a transformer as indicated hereabove, it is possible to use a voltage elevating device comprising cascaded circuits, which are composed of diodes and capacitors, each stage of this device doubling the voltage.

FIG. 2 shows such a circuit which is used for merely doubling the voltage. This circuit need not be disclosed in detail, because it is well known to those skilled in the art. It is accordingly possible to elevate the primary voltage v applied to the input a, b and to obtain at the output c, d a voltage being approximately twice as high as the input voltage. A second cascaded circuit will again double the voltage so that the voltage v at the output e, d is four times the voltage v and twice the voltage v With a very high frequency and small energy requisites the diodes D and the condensors C of the voltage elevating device may be integrated in a single circuit element. As disclosed with respect to the embodiment of FIG. 1 the voltage thus obtained can then be rectified and either directly applied to the liquid crystal or be pulsed, or even converted into an alternating voltage by means of an electronic switch. Such an electronic switch could also be integrated, because the consumption does not exceed some microwatts.

The advantage of such a voltage elevating device thus resides in the possibility of realizing the same within a very small space by integrating. Its mounting in a wristwatch does accordingly not raise any problem of location. If the transformer disclosed with reference to FIG. 1 allows providing a voltage elevating device having a substantially broader scale of adapting possibilities than a device which merely doubles the voltage, it has also the drawback that it cannot be reduced in sizes to the same extent as an integrated circuit.

It appears from the above-standing disclosure that the same power source may supply the electronic circuits of the timing base and of the frequency divider at a relatively low voltage, while the liquid crystal cells are excited at a substantially higher voltage. The layers of liquid crystal may thus have a substantial thickness and accordingly ensure a good display of the time indication.

Still further modifications within the scope of the appended claims will appear to be obvious to those skilled in the art.

I claim:

1. In a timepiece, in combination,

as display means of the time indication a liquid crystal cell having a modified light transmitting behavior upon applying an electric field thereto, an electric DC source,

a timing base supplied by said source and emitting an oscillatory signal, voltage elevating means having an input connected to said timing base and an output connected to said cell.

2. In the timepiece of claim 1, said voltage elevating means consisting of a transformer.

3. The timepiece of claim 1, further comprising a rectifier connected between the output of said voltage elevating means and said cell.

4. The timepiece of claim 1, further comprising hacking means connected to the output of said voltage elevating means and adapted for converting the output signal to a pulsed or alternating voltage.

5. In the timepiece of claim 4, the timing base including a multistage frequency divider, said voltage elevating means being connected to one stage of said divider, and the output signal of said timing base controlling the application of the pulsed or alternating voltage to said cell.

6. In the timepiece of claim 5, said one stage of the divider to which said voltage elevating means are connected having a first frequency, a further stage of said divider having a second frequency lower than said first frequency, said further stage of the divider having an output emitting a signal controlling said hacking means.

7. In the timepiece of claim 1, said voltage elevating means comprising cascaded electronic circuits, each stage of said cascaded circuits having an output voltage substantially twice as high as its input voltage.

8. In the timepiece of claim 7, said voltage elevating means being constituted by an integrated circuit.

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Claims (8)

1. In a timepiece, in combination, as display means of the time indication a liquid crystal cell having a modified light transmitting behavior upon applying an electric field thereto, an electric DC source, a timing base supplied by said source and emitting an oscillatory signal, voltage elevating means having an input connected to said timing base and an output connected to said cell.

1. In a timepiece, in combination, as display means of the time indication a liquid crystal cell having a modified light transmitting behavior upon applying an electric field thereto, an electric DC source, a timing base supplied by said source and emitting an oscillatory signal, voltage elevating means having an input connected to said timing base and an output connected to said cell.

2. In the timepiece of claim 1, said voltage elevating means consisting of a transformer.

3. The timepiece of claim 1, further comprising a rectifier connected between the output of said voltage elevating means and said cell.

4. The timepiece of claim 1, further comprising hacking means connected to the output of said voltage elevating means and adapted for converting the output signal to a pulsed or alternating voltage.

5. In the timepiece of claim 4, the timing base including a multistage frequency divider, said voltage elevating means being connected to one stage of said divider, and the output signal of said timing base controlling the application of the pulsed or alternating voltage to said cell.

6. In the timepiece of claim 5, said one stage of the divider to which said voltage elevating means are connected having a first frequency, a further stage of said divider having a second frequency lower than said first frequency, said further stage of the divider having an output emitting a signal controlling said hacking means.

7. In the timepiece of claim 1, said voltage elevating means comprising cascaded electronic circuits, each stage of said cascaded circuits having an output voltage substantially twice as high as its input voltage.

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