US3701249A

US3701249A - Solid state timepiece with liquid crystal display

Info

Publication number: US3701249A
Application number: US123672A
Authority: US
Inventors: John M Bergey; Eric L Blouch; Richard S Walton
Original assignee: Hamilton Watch Co
Current assignee: Hamilton Watch Co
Priority date: 1971-03-12
Filing date: 1971-03-12
Publication date: 1972-10-31
Anticipated expiration: 1989-10-31
Also published as: FR2128761B1; FR2128761A1; JPS5328461Y2; GB1358707A; CH363072A4; DE2210454B2; JPS4716465U; DE2210454A1; CA931768A

Abstract

Disclosed is a solid state wristwatch having an improved liquid crystal time display. Solid state time-keeping components are continuously energized from a low voltage battery while the display is energized only on demand from a separate high voltage battery. The direction of current flow through the liquid crystals is reversed during display to improve display life. A highly polished mirror surface is provided on the outside of the back plate of the thin glass sandwich where it is not in contact with the liquid crystal material.

Description

355M334 SR 1 #,f/\

KR DQ70192 t w United Statt [151 3,701,249 Bergey et al. Oct. 31, 1972 [54] SOLID STATE TIMEPIECE WITH 3,576,099 4/1971 Walton ..58/23 R LIQUID CRYSTAL DISPLAY 3,505,804 4/ 1970 Hofstein ..58/50 R X [72] Inventors: 3 r' B T Primary ExaminerRichard B. Wilkinson ouc an c M a Assistant Examiner-Edith C. Simmons Jackmon ton, Lancaster, all of Pa. An0mey Le Blane & Shut [73] Assignee: Hamilton Watch Company, Lancaster Pa [22] Filed; Mal-ch 2 197 Disclosed is a solid state wristwatch having an im-.

proved liquid crystal time-display. Solid state trme- PP 123,672 keeping components are continuously energized from a low voltage battery while the display is energized only on demand from a separate high voltage battery. [52] CL "58/50 58/23 The direction of current flow through the liquid 51 I t Cl G04) 19/30, crystals is reversed during display to improve display I'l- I A mirror Surface is Provided on [58] held of Search "58/23 23 50 235/92 the outside of the back plate of the thin glass sandwich 350/160 R; 340/166 where it is not in contact with the liquid crystal material. [56] References Cited 19 Claims, '7 Drawing Figures UNITED STATES PATENTS 3,654,606 4/1972 Marlowe ..340/l66 79 76 t Li 1i 5 8O 20' T: 70 r 69 m POLARITY LIQUID CRYSTAL 72 W REVERSER A v DISPLAY L l 26 30 l l 34 it 68-:\ I

FREQ FREQ. DISPLAY STD CONV. ACTUATOR i 74 v l l l 3 7 0 .1 2 49 tin-1N 58/50?! PATENTED um 31 m2 SHEET 1 BF 2 FIG. 3

INVENTORS JOHN M. BERGEY ERIC L BLOUCH RICHARD S. WALTON zffldw 1 38 i; 1% Fr 19;?

ATTORNEYS PATENTED nm 3 1 m2 SHEET 2 0F 2 LIQUID CRYSTAL DISPLAY FIG. 5

FIG. 7

POLARITY REVERSER LOW VOLTAGE INVENTORS'.

JOHN M. BERGEY ERIC L. BLOUCH RICHARD S WALTON BY 5544M v Jzih ATTORNEYS.

3 7 O 1 249 1 2 SOLID STATE TIMEPIECE WITH LIQUID packaged in a conventional-sized wristwatch chassis or CRYSTAL DISPLAY case. A tiny quartz slab is precisely cut to predeter- This invention relates to a solid state timepiece and more particularly to an electric watch which employs no moving parts. In the present invention, a frequency standard in the form of a high frequency crystal controlled oscillator acts through solid state electronic circuit dividers and drivers to power in timed sequence the elements of an electro-optic display. Low power consumption and small size and weight are achieved through the use of complementary MOS circuits to produce what is in essence a miniaturized fixed program computer.

In the present invention, the electro-optic display takes the form of a matrix of liquid crystals which when energized disperse light to give a visual indication of time. Important features of the present invention include an improved liquid crystal display in which the display is energized either on demand or continuously. In addition, current is reversed to the electrodes of the liquid crystals to improve their operation and life. The

liquid crystal display is operated from a separate high voltage power supply and the outside surface of the back glass of the liquid crystal display is provided with a highly polished mirror surface to improve contrast ratios in the display.

In recent years, considerable effort has been directed toward the development of a wristwatch which does not employ an electromechanical oscillator as the master time reference. In many instances, these constructions have utilized a crystal controlled high frequency oscillator as a frequency standard in conjunction with frequency conversion circuitry to produce a drive signal at a suitable timekeeping rate. However, difficulties have been encountered in arriving at an oscillator-frequency converter combination having not only the required frequency stability, but also sufficiently low power disspiation and small size to be practical for use in a battery-powered wristwatch.

In order to overcome these and other problems, there is disclosed in assignees copending US. application Ser. No. 768,076, filed Oct. 16, 1968, now US. Pat. No. 3,5 60,998, a crystal controlled oscillator type watch construction using lower power complementary MOS circuits. In assignees US. Pat. application Ser. No. 794,551, filed Jan. 28, 1969, now abandoned and application Ser. No. 824,148, now Pat. No. 3,576,099 filed May 13, 1969, there are disclosed watches of this type incorporating a liquid crystal display. Finally, assignees US. Pat. application Ser. No. 818,228, filed Apr. 22, 1969, now Pat. No. 3,576,099, discloses a watch construction in which the optical display takes the form of a plurality of light-emitting diodes which are intermittently energized on demand at the option of the wearer of the watch.

The present invention is directed to a new and improved watch construction of the same general type as disclosed in the aforementioned copending applications, as well as in assignees copending application Ser. No. 35,196, filed May 6, 1970, and one which utilizes no moving parts to perform the timekeeping function. The watch of the present invention consists of only three major components, namely, a quartz crystal time base, a miniature digital time computer, and an optical time display. These micro-miniature components are mined dimensions so that it vibrates at 32,768 Hz when properly stimulated by pulses from an electronic oscillator. The high frequency from the crystal time base is divided down to one pulse per second by utilizing a multi-stage, integrated circuit binary counter. The time computer module counts the input pulse train, encodes it into binary form, and then decodes and processes the results so as to provide the appropriate signals at display stations.

Situated on the front of the watch adjacent the display is a pushbutton demand switch which when pressed instantly activates the appropriate visual display stations. Minutes,hours, and seconds are programmed to display with a touch of the demand switch. The seconds continue to count as long as the wearer interrogates the computer module. Computation of the precise time is continuous and completely independent of whether or not it is displayed.

Incorporated in the watch case are a pair of batteries (or a single battery and appropriate circuits for providing both high and low voltage), namely, a high voltage battery for actuating the liquid crystal display and a low voltage battery for continuously operating the timekeeping portions of the watch. The high voltage power source is connected to the liquid crystal .display through a polarity reverser so that the current through the liquid crystal display is reversed at a rate between 10 Hz and 500 Hz. Also, in order to improve apparent contrast ratios, a highly polished mirror surface is deposited on the outside or inside of the back glass of the liquid crystal display structure to improve the display and enhance its life.

It is therefore one object of the present invention to provide an improved electronic wristwatch.

Another object of the present invention is to provide a wristwatch which utilizes no moving parts for performing the timing function.

Another object of the present invention is to provide a completely solid state electronic wristwatch in which the display is in the form of a plurality of liquid crystal segments.

Another object of the present invention is to provide an improved solid state wristwatch incorporating a separate high voltage power supply for actuating the liquid crystal display.

Another object of the present invention is to provide a solid state wristwatch having a liquid crystal display in which the timekeeping portions of the watch are continuously energized from a low voltage power supply and the liquid crystal display is energized continuously from a separate high voltage power supply.

Another object of the present invention is to provide a solid state wristwatch having a liquid crystal display in which the polarity of the DC voltage applied across the electrodes of the liquid crystals is alternately reversed.

Another object of the present invention is to provide a solid state wristwatch in which a highly polished mirror surface is provided on the outside of the back glass of the liquid crystal display to improve apparent contrast ratios and lengthen the life of the display.

These and further objects and advantages of the invention will be more apparent upon reference to the following specification, claims, and appended drawings, wherein:

FIG. 1 is a perspective view showing a wristwatch constructed in accordance with the present invention;

FIG. 2 is a block diagram illustrating the major components of the wristwatch of FIG. 1;

FIG. 3 shows a bar segment display usable in the wristwatch of FIG. 1;

FIG. 4 is a partial cross section through the bar segment display of FIG. 3;

FIG. 5 is a circuit diagram showing the manner in which the components of FIG. 2 are connected to the separate power supplies of the watch;

FIG. 6 is a more detailed circuit diagram showing the operation of the polarity reverser for reversing the polarity of the voltage applied to the liquid crystal segments; and

FIG. 7 is a diagram showing the output of the flipflop of FIG. 6.

Referring to the drawings, the novel watch of the present invention is generally indicated at 10in FIG. 1. The'watch is constructed to fit into a watch case 12 of approximately the size of a conventional mans wristwatch. The case 12 is shown connected to a \vristwatch strap 14 and includes a display window 16 through which the time is displayed in digital form and a pushbutton 18 for operating a demand switch through which the display is activated.

In normal operation, time is continuously being kept but is not displayed through the window 16. That is, no time indication is visible through the window and this is the normal condition which prevails in order to conserve battery energy in the watch. However, even though the time isnot displayed through the window 16, it is understood that the watch 10 continuously keeps accuratev time and is capable of accurately displaying this time at any instant. When the wearer desires to ascertain the correct time, he depresses pushbutton 18 with his finger and the correct time immediately is displayed giving the correct time reading at 10:10:59, namely, 10 minutes and 59 seconds after 10 oclock, as indicated at 20. The hours, minutes and seconds, i.e., 10:10:59, are displayed through the window 16 for a predetermined length of time, preferably one and one-quarter seconds, irrespective of whether or not pushbutton 18 remains depressed. The exact time of the display is chosen to give the wearer adequate time to consult the display to determine the hour, minute and second of the time. Should the minutes change during the time of display, this change is indicated immediately by advancement of the minute reading to the next number, i.e., 11, as the watch is being read. The advancing seconds cycling from 0 to 59 continue to be visible through window 16 until the pushbutton 18 is released. It is understood that it is also possible, if desired, to display hours, minutes, and seconds simultaneously for as long as the demand button is depressed.

FIG. 2 is a simplified block diagram of the electrical circuitry for the watch of FIG. 1. The circuit comprises a time base or frequency standard 26 including a crystal to provide a very accurate frequency such that the frequency standard or oscillator oscillates at 32,768 Hz. This relatively high frequency is supplied by lead 28 to a frequency converter 30 in the form of a divider which divides down the frequency from the standard so that the output from the converter 30 appearing on lead 32 is at a frequency of 1 Hz. This signal is applied to a display actuator 34 which, in turn, drives the display 20 of the watch by way of electrical lead 36.

The details of the frequency standard 26, frequency converter 30, and display actuator 34 will not be described in any great length since they are in all respects identical to those shown and described in assignees copending application Ser. No. 35,136, filed May 6, 1970, the disclosure of which is incorporated herein by reference.

Briefly, these components are made of complementary MOS transistors and are formed as integrated circuits so as to require minimum power for operation and so as to withstand the reduction in size necessary for incorporation in a conventional size man s wristwatch.

While the watch of FIGS. 1 and 2 is illustrated as employing a 27-dot matrix of liquid crystals for each display number, this need not be the case and the display may take the form of a seven-bar segment as illustrated in FIG. 3. FIG. 3 shows seven

liquid crystal segments

38, 40 42, 44, 46, 48, and 50 of elongated shape and arranged so that by energizing an appropriate combination of the bar segments, any of the numbers 0 through 9 may be displayed. In certain applications, the sevenbarsegment display of FIG. 3 is preferred in that it requires less energy forthe optical display than the 27- dot matrix. shown in FIG. 1,

FIG. 4 is a partial cross section showing a portion of two adjacent bar segments of the display, such as the uppermost segment 38 and the adjacent segment 48 of FIG. 3. It is understood that the remaining bar segments for that display number and the bar segments of each of the other display numbers (and the colon dots) are similarly constructed. The bar segment display, which is labeled 20' to distinguish from the dot display 20 of FIG. 1, comprises a front substantially transparent plate 52, preferably formed of glass, and a rear plate formed of glass, as indicated at 54.

The glass plates 52- and 54 are spaced one from the other by suitable spacers (not shown) and a liquid crystal substance 56, described below, is disposed between and preferably coextensive with

plates

52 and 54. A reflective layer 66, described below, is applied to the back surface of plate 54. The frontsurface of the rear glass plate 54 and the rear surface of the front glass 52 are coated with a transparent electrode material, indicated at 58 and 58, respectively, with portions of the surface uncoated. The

electrodes

60 and 62 form the bar segments. For example, coating 58 may be applied over the entire front surface of rear plate 54 with the electrode material subsequently etched away to define electrodes for each sement of the seven-bar segments (and the colon dots), as well as to electrically insulate the electrode pairs from one another. As illustrated in FIG. 4, two

adjacent electrodes

60 and 62 are shown with the etch of the electrode material at 61. Bar segment 38 is the liquid crystal material 56 between electrode 60 and layer 58 and bar segment 48 is the liquid crystal material between electrode 62 and the directly opposite portion of conductive layer 58'. Each of the bar segements of each display numeral is similarly formed by electrode pairs across the liquid crystal material. Light passes through the front plate 52, as indicated by the arrows at 64, to make the display visible, which light may be either ambient light or light from a suitable source mounted on the watch.

As noted above, the liquid crystal substance 56 is disposed between

glass plates

52 and 54. The term liquid crystal is used to mean a substance whose rheological behavior is similar to that of fluids but whose optical behavior is similar to the crystalline state over a given temperature range. These substances exhibit mesomorphic behavior and of the three states of mesomorphic behavior, the nematic state exhibits the electromagnetic optic effect utilized in the present digital time display. A preferred nematic liquid crystal having the required properties is p-azoxyanizole. This material exhibits the desired mesomorphic behavior within the desired temperature range for watches and it is characteristic of this liquid crystal under these temperature conditions, that with no electric or magnetic field applied, it is substantially transparent. However, when a field, either electric or magnetic, is applied, the liquid crystal becomes turbulent and scatters light, the effect of which is to reflect light which appears white. An additional characteristic of the liquid crystal is the fact that the greater the incident light on the energized liquid crystal, the greater the reflectivity, brightness, and hence contrast with the surrounding environment.

It is gnderstood that when the portions of the liquid crystal 56 disposed between the electrodes of the bar segments remain in an unenergized state, the reflective background of the rear plate 54 is seen through the front transparent plate 52 and the transparent liquid crystal. Accordingly, in viewing the display window 16, the reflective dark-appearing background afforded by rear plate 54 is seen through the transparent electrode material 58 and 58 (essentially the entire display face)and through the portions of the liquid crystal lying between the electrodes of the unenergized bar segments. However, the electrodes which are energized through the display actuator 34 of FIG. 2, energize the liquid crystals between them such that incident light is scattered. This incident light which is reflected appears white against the dark surrounding background. In this way, the energized liquid crystal bar segments provide a readily readable and clearly distinguishable time display in digital form, the digits being formed by the selectively energized liquid crystal bar segments which appear white by scattering incident light and which contrast with the dark background of the rear plate 54. Moreover, the greater the incident light, the greater the contrast. This effect is enhanced by the reflective mirror 66 which reflects light coming through window 16 back through the now opaque liquid crystal material of an energized segment. The reason that the mirror is so effective in enhancing the appearance of a segment is because energized liquid material scatters the light best in a forward direction. Therefore, light coming from within the display is scattered most effectively.

Reduction of a liquid crystal sandwich display cell for use in a conventionally sized wristwatch has several practical production shortcomings using present day technology. Two major problems relate to the relatively short life of nematic liquid crystals and the comparatively high operating voltage required for effective dynamic scattering to take place. The present invention incorporates several features helping to overcome these problems. For example, in order to improve ap parent contrast ratios, it has been the practice to deposit a highly polished mirror surface, such as an aluminum film, on the inside of the back glass structure. A problem with this construction has been that some liquid crystal material tends to eventually attack the mirrored surface and produce an undesirable bubblelike appearance. Another shortcoming is that the surface must typically have very thin yet visible electrode isolation lines in order to prevent shorting. It is a feature of the present invention that the mirrored surface, i.e., the aluminum film, is deposited, as indicated at 66 in FIG. 4, on the outside surface of the back glass rather than the inside surface. This eliminates both the previously discussed problems of bubble-like appearance and electrode isolation lines. The added parallax is practically insignificant provided the thickness of back glass 54 does not exceed about 0.040 inch. In addition, this technique permits the display to appear visibly brighter because of the increase in the light gathering ability of the newly positioned mirrored surface.

As previously pointed out, the watch of the present invention incorporates a display demand switch operated by pushbutton 18 of FIG. 1. This substantially increases the life of the liquid crystal, as well as the power supply, by several orders of magnitude since, based upon past experience, the operate to no-operate ratio becomes quite small (on the order of 0.05 percent) when the demand technique is employed. In addition, it has been found that AC operation improves the life of theliquid crystal material on the order of four or five times of DC operation. While DC operation is preferred to AC conversion in a wristwatch, it is possible to approximate the beneficial effects of AC operation regarding the transient ions in the liquid crystal material by incorporating current reversal. That is, the

display still sees a DC voltage but the direction of the 1 electrical field between anode and cathode is reversed periodically when a segment is energized.

A further feature of the present invention resides in the fact that it has been found that by reducing the thickness of the liquid crystal material by placing the glass (or other sandwich material) in closer proximity, it is possible to reduce the operating voltage and dynamic scattering mode decay times for the liquid crystal. However, although larger voltage reductions are possible by reducing material thickness, when the material thickness is reduced below about 0.001 inch, the practical problems of glass flatness, display cell sealing, and material uniformity becomes significant. In order to meet these problems with the limited power supply energy available in the small space of a wristwatch, the present invention provides an arrangement in which the watch is powered by two separate batteries or power supplies. Specifically, a low voltage, high capacity battery is continuously connected to the frequency standard (crystal oscillator) 26, the frequency converter (divider) 30, and the display actuator 34. A separate high voltage battery is provided and connected only on demand to energize the liquid crystal display.

The power supply circuit incorporating separate batteries is generally illustrated in FIG. 5. In that figure,

the frequency standard 26, frequency converter 30, and display actuator 34 are shown as continuously connected across a low voltage battery 68. By way of example only, battery 68 may take the form of a conventional 1.5 volt high capacity silver oxide cell. The battery is illustrated as connected to the timekeeping component of the watch, generally indicated at 70, by way of terminal 72 and grounded terminal 74. Terminal 74 may be grounded to the watch case in a conventional manner.

FIG. 5, which is a simplified circuit diagram of the watch construction, also shows a manually operated demand switch 76 which is normally open but which is closed when the pushbutton 18 of FIG. 1 is manually depressed. Switch 76' reopens when the pushbutton 18 is released. This switch is illustrated as connecting terminal 70 of a high voltage source 78 to the liquid crystal display 20' by way of a polarity reverser 80. By way of example only, high voltage source 78 may take the form of a solid state battery of approximately 30 volts potential at l mamp/hr and is included for the sole purpose of operating the liquid crystal display. An alternative high voltage source can be provided by up converting the low voltage source.

FIG. 6 is a more detailed circuit diagram showing the battery connections and the polarity reverser 80 of FIG. 5. A portion of the display actuator 34 is shown at the righthand end of FIG. 6 and a portion of the divider 30 is shown at the left side of FIG. 6. Actuator 34 supplies the timing signals for the liquid crystal display and a display polarity reversing signal is derived from an intermediate stage of the frequency converter or divider 30. In the preferred embodiment, the display is disconnected by the low voltage demand switches, such as switch 76A in FIG. 6, connected to divider 30, and switches 76B, connected to actuator 34. These switches in FIG. 6 replace the high voltage switch 76 of FIG. and make it possible to effect disconnection of the display without the necessity for interrupting the high voltage from battery 78.

In FIG. 6, a pair of decoder drivers in the display ac tuator 34 produce timing signal outputs at 82 and 84. The decoder drivers operate at low voltage and are connected to the low voltage lead 69 from low voltage battery 68. In the preferred embodiment, they each take the form of a complementary pair of P and N- channel MOS transistors. The driver outputs are connected through switches 76B and the respective resistors 86 and 88 to respective pairs of switching transistors, such as

transistors

91 and 93 for liquid crystal display segment 38 and transistors 91' and 93' for liquid crystal display segment 40. Connected across the respective transistors are

bypass rectifier diodes

95, 97, 95 and 97. The transistor bases are connected to the driver outputs through

rectifier diodes

90A, 92A, 90B and 92B.

A polarity reversing signal at a frequency preferably between about 10 Hz and 500 Hz is taken from an intermediate stage of divider 30 and applied through switch 76A and resistor 106 to the base of a transistor 107. This transistor has its output connected to a high voltage flip-flop 81 having

outputs

103 and 105,1abeled Q and 6, respectively, for applying the high voltage potential of battery 78 through the respective liquid crystal segments, such as the

segments

38 and 40, illustrated in FIG. 6. The output stages of high voltage flipflop 81 are shown in more detail in FIG. 7 as comprising a first pair of

complementary MOS transistors

117 and 118 and a second pair of complementary MOS transistors 12] and 123.

The driver outputs 82 and 84 are connected by resistors 86 and 88 to the blocking

diodes

90A, 92A, 90B, and 92B of the control circuits 99 and 101. It is understood that identical control circuits are provided for each segment of the display,only two

segments

38 and 40 being illustrated in FIG. 6 for the sake of simplicity. Control circuit 99 is illustrated as controlling the current flow through segment 38 and control circuit 101 controls the current flow through segment 40.

In order to activate segment 38, output 82 must be positive. This allowed base current to flow in either

transistor

91 or 93, depending upon the state of the flip-flop 81. Assuming the Q output 103 is and the 6 output 105 is at ground, the base current will flow through diode 92A and turn on transistor 93. With transistor 93 on and transistor 95 ofi, current will flow from the Q output 103 through bypass diode 95, through liquid crystal segment 38, through transistor 93, and back to ground through 6 105. With the outputs of flip-flop 81 in opposite states and output 82 from the driver in a positive state, the current flow through the liquid crystal segment 38 is reversed. Base current for transistor 91 flows through blocking diode 90A tu rning on transistor 91. This causes current flow from Q 105 through bypass diode 97, through liquid crystal segment 38, through transistor 91, and back to ground at Q 103.

The state of flip-flop 81, which is operated at high voltage and provides the high voltage to the liquid crystal segments through

outputs

103 and 105, is controlled through the voltage transistor 107, by the output through switch 76A from the frequency divider 30. Since transistor 107 is a current amplifier, it is independent of voltage and can be used to go from the low voltage of the divider 30 to the high voltage of the flip-flop 81. Current in the base-emitter circuit of transistor 107 causes current to flow in the collector-emitter circuit and this causes a voltage drop across load resistor 1 13. As a result, the input to the flip-flop 81 changes and this changes the state of the

outputs

103 and 105.

FIG. 7 shows these outputs in detail. The output devices are P and N-channel MOS transistors in complementary symmetry configuration. This means that when the P-channel transistor is on, the N-channel transistor is off. For example, when Q at 103 is high, the P-channel transistor 117 is on and provides a low resistance path to positive voltage and almost infinite resistance to negative voltage.

Transistors

121 and 123 make up a similar complementary pair but because the output of this pair is connected to the input of pair 1 17 and 119, the output Oat 105 is out of phase with the output at Q 103. Therefore, transistor 123 provides a low resistance path to negative voltage for Q at 105. It can be seen that a control Qrcuit such as circuit 99 connected between Q and Q is essentially connected between positive and negative voltage and when the state of the flip-flop 81 changes, the polarity of this voltage changes.

It is apparent from the above that the present invention provides an improved solid state watch with no moving parts and especially a solid state watch of this type having an improved liquid crystal display. Important features of the present invention include a demand display arrangement which not only reduces the drain on the small battery or batteries available in a wristwatch case, but also,because of the very small operate to not-operate ratio when the demand technique is employed, substantially increases the life of the liquid crystal material forming a part of the display. An additional feature of the present invention is a current reversal circuit so that the direction of current flow through the liquid crystal is reversed. The current reversal additionally contributes to substantially increased life for the liquid crystal material. In certain instances, the current reversal improves liquid crystal life to a point where the demand switch is not necessary.

An additional feature of the present invention resides in the provision of a high voltage battery which is only periodically energized to actuate the liquid crystal display and a separate low voltage, high capacity battery which is continuously connected to the timekeeping components of the circuit so that time is continuously kept. Such an arrangement complements the varying requirements of the liquid crystal display which, while made as thin as practical, nevertheless requires relatively high voltage energization and the low power continuous operation desirable for the watch timekeeping components. Finally, increased life and enhanced appearance is provided for the liquid crystal display by providing a highly polished mirror surface, such as an aluminum film, on the outside of the back glass of the display so as to avoid the problem of attack by the liquid crystal material and eliminate the previous undesirable electrode isolation lines.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

l. A timekeeping device having sufficiently small size for use as a wristwatch comprising an electrical timing source, an optical time display, a time computer coupling said timing source to said time display, a power source, and a polarity reverser coupling said power source to said time display.

2. A device according to claim 1 wherein said time display is a liquid crystal display.

3. A device according to claim 2 including a second power source coupled to said timing source and said time computer.

4. A device according to claim 3 including means for continuously coupling said second power source to said timing source and said time computer.

5. A device according to claim 1 wherein said timing source comprises a crystal oscillator.

6. A device according to claim 1 wherein said time computer comprises a frequency divider and optical display decoder and driver.

7. A device according to claim 1 wherein said polarity reverser is coupled to said timing source whereby the current flow through said display may be continually reversed.

8. A device according to claim 1 wherein said display comprises a liquid crystal sandwich construction including a 1i uid crgstal material sandwiched between space ron and ack plates, and a layer of highly polished mirror surface material on said back plate.

9. A device according to claim 8 wherein said layer comprises an aluminum film.

10. A timekeeping device having sufficiently small size for use as a wristwatch comprising a high frequency electrical timing source, a liquid crystal time display, a digital time computer coupling said timing source to said liquid crystal display, a first low voltage power source continuously coupled to said time computer, a second high voltage power source, and a demand switch coupling said high voltage power source to said liquid crystal display whereby said display is only actuated on demand.

11. A device according to claim 10 wherein said low voltage power source comprises a high capacity silver oxide cell.

12'. A device according to claim ll-wherein said high voltage power source comprises a solid state battery.

13. A device according to claim 12 wherein said battery produces from 9 to 30 volts at about 1 milliampere hours minimum.

14. A device according to claim 10 including a polarity reverser coupling said liquid crystal display to said time computer whereby the potential across said display is continually reversed.

15. In an electronic wristwatch, a timing source, a liquid crystal display, a high voltage battery, a time computer coupled to said timing source and a demand switch coupling said battery to said display whereby said display is energized only on demand, and including a polarity reverser coupling said display to said time computer.

16. Apparatus according to claim 15 wherein said reverser comprises a plurality of of solid state bidirectional gates coupled to said display.

17. Apparatus according to claim 16 wherein said display comprises a plurality of liquid crystal elements arranged to form a decimal digital display.

18. Apparatus according to claim 17 wherein said elements comprise liquid crystal bar segments.

19. Apparatus according to claim 18 including a separate gate for each of said segments, and a flip-flop coupling said time computer to said gates.

Patent No. 3 701,249

Dated October 31 1972 Inventor(s) John M. Bergey, Eric L. Blouch and Richard S W a l j: on

It is certified that error appears in the zzmwc-idcmtifi 0d patent and that said Letters Patent are hereby corrected as shown below;

In Column 1, line 46, "lower" should read --low-- In Column 4, line 20, Mo 42," should read "40, 42,,

In Column -6, line 26, "no -operate" should read --not-operate--.

'In Column 7, lines 2 3, "component" should read- -components-.

In Column 10, line 45 Claim 16, "of of" should read --of--.

Signed and sealed this 15th day of May 1973 (SEAL) Attest:

EDWARD M.FLETCI:IER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

Claims

1. A timekeeping device having sufficiently small size for use as a wristwatch comprising an electrical timing source, an optical time display, a time computer coupling said timing source to said time display, a power source, and a polarity reverser coupling said power source to said time display.

8. A device according to claim 1 wherein said display comprises a liquid crystal sandwich construction including a liquid crystal material sandwiched between spaced front and back plates, and a layer of highly polished mirror surface material on said back plate.

9. A device according to claim 8 wherein said layer comprises an aluminum film.

12. A device according to claim 11 wherein said high voltage power source comprises a solid state battery.