FIELD OF THE INVENTION

The present invention relates to wearable devices, and particularly to wearable timepieces and watches.

BACKGROUND OF THE INVENTION

A watch is a portable timepiece intended to be carried or worn by a per- son. It is designed to keep a consistent movement despite the motions caused by the person's activities. A wristwatch is designed to be worn around the wrist, at- tached by a watch strap or other type of bracelet, including metal bands, leather straps or any other kind of bracelet A pocket watch is designed for a person to carry in a pocket, often attached to a chain.

The most common function of the watch is to show the time of day. So called smart watches or "smartwatches", are wearable electronic devices with a number of features packed into the simple design of a watch, typically a wristwatch. Unlike conventional wristwatches though, the smart watches do a lot more than tell time. Smart watches are essentially small computers that typically include a processor, some memory, an ability to execute application software, a user inter- face, such as a display and user input means, and a wireless communication capa- bility. Smart watches may offer accessibility to several applications and features that give users the ability to perform a number of tasks from the comfort of their wrists. Smart watches can be stand-alone or purpose-specific devices. They can ei- ther work by themselves or work in conjunction with smart phones. Typical fea- tures found in smart watches may include: Alerts /notifications, media manage- ment, applications, messaging capabilities, mobile calls, health and fitness tracking, GPS (Global Positioning System) capabilities, etc. Smart watches are a beneficial asset to individuals who desire to keep regular tabs on their health and vital organs, as they can be effectively utilized in monitoring the users' health and bodily func- tions. A smart watch can monitor its wearer's heart rate and act as a pedometer to keep track of physical activity, as well as other health-related functions. Moreover, smart watches equipped with a variety of sensors, such as an accelerometer, heart rate monitor, and GPS can be utilized as wrist worn safety devices for the elderly, cognitively impaired as well as lone worker adults, for example.

Traditionally, watches have displayed the time in analog form, with a numbered dial upon which are mounted at least a rotating hour hand and a longer, rotating minute hand and arranged to indicate the time by pointing to the relevant numbers on the dial. Many analog watches also incorporate a third hand that shows the current second of the current minute. All three hands are normally mechanical, physically rotating on the dial, although a few watches have been produced with "hands" simulated on a digital display. A digital watch indicates the time by way of digits on a digital, usually LCD, display that changes with the changing time. An "ana-digi" smart watch or hybrid smart watch is an analogue watch with mechani- cal hands but also with features of a smartwatch hidden under the under tradi- tional faces, possibly alongside a digital LCD display. As used herein, the term "an- alog smart watch" refers to any smart watch having mechanical hands for indicat- ing time, with or without an additional digital display. Analog smart watches with mechanical hands have remained popular, as many people find it easier to read than digital display under all conditions due to clearly marked digits, easily visible hands, large watch dials, etc. Analog display of the time is preferred in more subtle and arguably more classy watches, such as those sold as jewelry or collectibles, and in these watches, the range of different styles of hands, numbers, and other aspects of the analog dial is very broad. The analog smart watches have the advantage of much longer battery life, because power-consuming digital screens are avoided, smaller in size, or powered-on only seldom.

Examples of analog smart watches are disclosed in

US2019/0064746A1, US2019/02044790A1, US2021/0003972A1,

US10459570B2, and W02019209587A1.

Analog smart watches with mechanical hands have a small knob, called the crown, that the end user can use to manually adjust the time. Alternatively push-buttons, a touch screen display or other type of user interfaces can be used to make the adjustment or calibration of time. These manual actions would then move the hands incrementally, and consequently, moving the hands to their correct po- sitions is up to the end user. This however requires the user to be capable of such observing an error in the display of the hands and attending the required manual user actions. Regarding the intended user group of analog smart watches in safety and health care applications, such as elderly and cognitively impaired people, this is not always the case, and it is essential that the hand calibration process is auto- mated and as robust to errors as possible. Also many capable users often find it convenient and desirable to have an automatic calibration feature in their analog watches. There may also be "drifting" of the time indicated by the mechanical hands from the correct time due to inaccuracy or failure of a hand rotating mechanism, for example.

To automatically calibrate the time indicated by mechanical hands a smart watch has to determine the present positions of watch hands. Convention- ally, watch hand positioning is based on optical measurements. A typical imple- mentation uses an optical sensor (typically infrared (IR) sensor) based on an opti- cal transceiver, where the portion of transmitted light reflected back from a reflec- tive surface, in this case, the watch hands, is measured. Considering the use case of a wrist worn device, where such optical sensor is susceptible to constantly chang- ing ambient circumstances, which are not always easy to predict These changes in ambient environment can look positively like the expected signal of a watch hand passing over the optical sensor. This aforementioned condition can lead to false positive readings and false positioning of the hands, which in turn, lead to wrong time being shown to the end user. Certainly, this is not desirable and such, more robust solution is needed.

US20210157279A1 discloses a time correction method of an analog smart watch using wireless communication between a smart phone and the smart watch having no hand position sensor. US10663925B discloses a hybrid smart watch having an indicator (watch hand) sensor and an arrangement for automatic adjustment of time.

BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention is to provide an analog smart watch having an improved automatic watch hand calibration.

The objects of the invention are achieved by an analog smart watch ac- cording to claim 1. The preferred embodiments of the invention are disclosed in the dependent claims.

An aspect of the invention is an analog smart watch, comprising a housing, a support frame provided within the housing, a watch dial provided above the support frame, at least one watch hand provided above the watch dial and attached to a central drive shaft extending below the support frame, a watch hand actuation apparatus provided below the support frame within the housing and attached to the central drive shaft and configured to rotate the at least one watch hand, a watch hand position sensing means configured to provide a position signal, a processor system provided on a circuit board below the support frame within the housing and coupled operably to the watch hand position sensing means, the watch hand actuation apparatus, and a memory, the processor system being configured to determine a position of the at least one watch hand responsive to the position signal and to control the watch hand actuation apparatus to cali- brate the position of the at least one watch hand, wherein the watch hand position sensing means comprises an oscillator circuit having a sensing inductor and a capacitor and configured to oscillate at a preset resonant frequency, wherein the sensing inductor is a single-layer or multi- layer planar spiral sensing inductor provided in the watch dial or in the support frame or therebetween, the planar spiral sensing inductor having an axis of sym- metry substantially parallel to a radial direction of the watch dial at a predeter- mined watch hand position and substantially perpendicular to a direction of rota- tion of the at least one watch hand.

In an embodiment, the single-layer or multilayer planar spiral sensing inductor comprises an open central area aligned with the axis of symmetry.

In an embodiment, the multilayer planar spiral sensing inductor com- prises two or more spiral coil layers in series connection.

In an embodiment, the multilayer planar spiral sensing inductor com- prises two or more spiral coil layers with aligned axes of symmetry.

In an embodiment, the part of the oscillator comprising the resistor and the capacitor of the oscillator is provided on or under the bottom surface of the support frame and electrically connected to the single-layer or multilayer planar spiral sensing inductor of the oscillator through the support frame.

In an embodiment, the single-layer or multilayer planar spiral sensing inductor is provided on a rigid, non-rigid or flexible substrate or circuit board in- stalled between the watch dial and the support frame, optionally attached to the bottom surface of the watch dial or to the top surface of the support frame.

In an embodiment, the oscillator circuit comprising the single-layer or multilayer planar spiral sensing inductor, the resistor and the capacitor is pro- vided on a rigid, non-rigid or flexible substrate or circuit board, and at least the part of the substrate comprising the single-layer or multilayer planar spiral inductor is installed between the watch dial and the support frame, optionally attached to the bottom surface of the watch dial or to the top surface of the support frame.

In an embodiment, the part of the non-rigid or flexible substrate comprising the single-layer or multilayer planar spiral inductor is installed be- tween the watch dial and the support frame, and wherein the part of the non-rigid or flexible substrate or circuit board comprising the resistor and capacitor of the oscillator is bent to extend under the support frame, preferably extending parallel to the bottom surface of the support frame, and optionally attached to the bottom surface.

In an embodiment, at least the single-layer or multilayer planar spiral sensing inductor, is a printed electronics inductor in the watch dial and/or in the support frame, preferably on the bottom surface of the watch dial and/or on the top surface of the support frame, and wherein optionally also the resistor and the capacitor of the oscillator are printed electronics components.

In an embodiment, the single-layer planar spiral sensing inductor is a Laser Direct Structuring (LDS) inductor on the top surface of the support frame.

In an embodiment, the capacitor of the LC oscillator, and optionally a series resistor of oscillator, is/are provided adjacent to the single-layer or multi- layer planar spiral sensing inductor in the watch dial or in the support frame or therebetween.

In an embodiment, the watch hand position sensing means further comprises an excitation signal source coupled operably to feed the LC oscillator with an excitation signal at the resonant frequency of the LC oscillator, and a detec- tor circuit coupled operably to the oscillator circuit to detect a change in the reso- nance frequency of the LC oscillator caused by the at least one watch arm passing over the single-layer or multilayer planar spiral sensing inductor, the detected change being largest when the at least one watch arm is aligned with the symmetry axis of the single-layer or multilayer planar spiral sensing inductor.

In an embodiment, the excitation signal source is the processor system, and the excitation signal preferably is a square-wave signal.

In an embodiment, the detector circuit comprises an envelope detector outputting the position signal representing the amplitude of resonance frequency of the LC oscillator.

1 In an embodiment, the watch hand position sensing means further comprises an analog-digital (A/D) converter coupled to receive the position signal position signal, and wherein the A/D-converter preferably is integrated into the processor system. BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail by means of preferred embodiments with reference to the attached [drawings, i which Figure 1A is a top view of an analog smart watch according to an em- bodiment of the present invention;

Figure IB is an exploded perspective view of an analog smart watch ac- cording to an embodiment of the present invention;

Figure 1C is an exploded perspective view showing in more detail a watch dial and a support frame of an analog smart watch according to an embodi- ment of the present invention;

Figure 2 is a functional block diagram of an analog smart watch accord- ing to an embodiment of the present invention;

Figure 3 is a cross-sectional partial side view of an analog smart watch according to an embodiment of the present invention;

Figures 4A and 4B are top and bottom views of a series-connected two- layer planar coil according to an embodiment of the present invention;

Fig. 5A and SB are top and bottom views of a support frame having a planar coil installed according to an embodiment of the present invention;

Figure 6 is an exploded perspective view showing in more detail a watch dial and a support frame having a planar coil installed according to an embodiment of the present invention;

Figures 7 A and 7B are top and bottom views of a series-connected two- layer planar coil according to another embodiment of the present invention;

Figure 8 is a schematic diagram of an oscillator circuit of a watch hand position sensor according to another embodiment of the present invention;

Figure 9A is schematic diagram of a watch hand position sensor and an envelope detector according to an embodiment of the present invention;

Figure 9B is a block diagram illustrating connection of a watch hand po- sition sensor and an envelope detector to a microcontroller unit MCU according to an embodiment of the present invention;

Figures 10A, 10B and 10C illustrate rotation of a mechanical watch hand over a planar coil of a watch hand position sensor, and Figure 10D illustrates an example of a resulting envelope of a measured oscillator output signal;

Figures Fig. 11A and 11C are top and bottom views of a support frame having a planar LDS coil manufactured on it according to an embodiment of the present invention; Figure 11B is an exploded perspective view showing in more detail a watch dial and a support frame having a planar LDS coil manufactured on it accord- ing to an embodiment of the present invention; and

Figure 12 is an enlarged top view of an LDS coil according to an embod- iment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present invention relates to analog smart watches, particularly to wristwatches. As used herein, the term "analog smart watch" refers to any smart watch having mechanical hands for indicating time, with or without an additional digital display.

Referring to Figures 1A, IB, 1C, and 3, an exemplary structure of an an- alog smart watch 10 according to an embodiment of the invention is described. The smart watch 10 comprises a housing or case 11 which may accommodate a (re- chargeable) battery 21 as a power source and a circuit board 19, often referred to as a mother board, carrying the electronic circuitry needed for the smart features of the smart watch 1, as well as a watch hand actuator mechanism 30. The housing may further accommodate a speaker 23 and a microphone 24, or other audio in- put/output devices. The housing 11 is preferably made of metal but may alterna- tively be made of plastic. Above the mother board 19 there may be provided a sup- port frame 20 fixed within the housing 11, e.g. by means of screws, to cover and protect the electronic circuitry on the mother board 19 and to provide support to a watch dial 13 installed on the top surface of the frame 20. Two or more mechan- ical watch hands, such as an hour hand 14 and a minute hand 15, are arranged above and parallel to the top surface of the watch dial 13. The watch hands 14 and 15 are mechanically connected to the watch hand actuator mechanism 30, typically rotating coaxial shafts thereof, extending in an axial direction (perpendicular to the top surface of the watch dial 13) through a central opening 131 in the watch dial 13 and an opening 210 in the frame 20. The watch actuator mechanism 30 is ar- ranged to rotate the watch hand 14 and 15 independently of each other to point to a desired radial (angular) direction and a desired time in hours and minutes. The peripheral area of the watch dial 13 or dial ring may be provided with indices 132, such as digits 1 to 12. The analog smart watch may optionally be provided with a digital or graphical display unit 17, such as an LCD display, to display further infor- mation in addition to the analog indication of time by the mechanical watch hands. Display unit 17 may be installed on the motherboard 19. The support frame 12 may be provided with an opening 210 and the watch dial 13 may be provided with an opening or window 130, respectively, for the display unit 17 so that the top surface of the display unit 17 is visible to the user. The top surface of display unit may be parallel with the watch dial 13. A transparent protective cover 13, often called a crystal or lense, may be provided above the watch dial 13 and the watch hands 14 and 15. The crystal 13 may be fixed to the housing 11 by a bezel ring 12 installed to surround the crystal. The bezel ring 12 may be either fixed or rotating. A crown 16 may installed to the side of the watch housing 11 for operating the watch. A strap 25 can be fixed to the housing 11.

It shall be appreciated that the examples of structure of the smart clock are given only to facilitate the description of exemplary embodiments of the inven- tion. The inventive watch hand position sensing according to the present invention can be applied in various types smart clocks within the scope of the attached claims.

Referring to a functional block diagram, the smart watch 10 is illus- trated as including a processor 29 and a memory 27. The processor 29 provides processing functionality for the smart watch 10 and can comprise a micro-control- ler or other processing system, and internal or external memory for storing data and other information accessed or generated by the smart watch 100. The proces- sor 29 can execute one or more software programs (e.g., an operating system (OS), a user interface (UI), applications, etc.) that implement the techniques and func- tionalities described herein. The processor 29 may be configured to control and interact with various functional units of the smart watch 10, such as one or more of a watch hand actuator mechanism 300, wireless communication unit(s) or mod- ule(s) 33, a display unit 17, such as an LCD display, a user input/output (I/O) de- vices 31 (e.g. a crown 16, a speaker 23, a microphone 24, a touch screen, etc.), and one or more sensors 32, such as an accelerometer, heart rate monitor, and GPS. The software program(s) executed by the processor 29 may utilize obtained sensor data to monitor the user's health and bodily functions, to keep track of the user's physical activity, and monitoring the user's safety, such as a geographical position (GPS) and falls (accelerometer) of the elderly, cognitively impaired user as well as lone worker adults, for example. It should be appreciated that embodiments of the invention are not limited to or necessarily require any other sensors than the watch hand positioning (sensor) 400.

The wireless communication unit(s) 33 performs wireless communica- tion with a communication network or another wireless user device, such as a smart phone, and enables two-way data and/or speech communication. The communication unit(s) 33 may be capable of utilizing a variety of different types of networks such as a cellular network; a mobile data network; a wireless intranet, WiFi network, a satellite network, etc. To this end, the wireless communication unit(s) 33 is coupled to an antenna or antennas 34 installed in the smart phone. The implementation of the antenna 33 in the smart watch may be challenging due to the small size of the watch, especially if the housing or case 11 of the smart watch is made of metal. Then it may be necessary to install the antenna in the upper part of the phone. In an embodiment of the invention a bezel ring 12 is configured to act as an antenna 34. It should be appreciated that embodiments of the invention are not limited to any implementation of a wireless communication, and do not neces- sarily require any communication unit at all, particularly in the case an automatic internal synchronization of position of the watch hands to the internal time is per- formed.

The watch hand actuator mechanism 300 may rotate any of the watch arms 14 and 15, either clockwise or counterclockwise, in response to a watch arm control from the processor 29. The watch hand actuator mechanism 300 may in- clude one or more micro-stepper motors or another actuation mechanism 30 dis- posed on a mother board 19. It should be appreciated that embodiments of the in- vention are not limited to any implementation of an actuation mechanism for per- forming the watch hand rotation.

The watch hand positioning (sensor) 400 provides a position signal rep- resenting the present positions of the mechanical watch hands 14 and 15, The pro- cessor 29 determines the present positions of watch hands based on the position signal, compares they to a correct time of date or the corresponding positions, and controls the watch hand actuator mechanism to mechanically rotate the mechani- cal watch hands to the desired positions. The correct time of date may be received from an external source by means of the wireless communication unit 33, for ex- ample.

As discussed above, the watch hand positioning is conventionally based on optical measurements. A typical implementation uses an optical sensor (typi- cally infrared (IR) sensor) based on an op-tical transceiver, where the portion of transmitted light reflected back from a reflective surface, in this case, the watch hands, is measured. Considering the use case of a wrist worn device, where such optical sensor is susceptible to constantly changing ambient circumstances, which are not always easy to predict These changes in ambient environment can look positively like the expected signal of a watch hand passing over the optical sensor. This condition can lead to false positive readings and false positioning of the hands, which in turn, lead to wrong time being shown to the end user. Certainly, this is not desirable and such, more robust solution is needed.

The optical sensor conventionally used for calibration requires an opti- cally clear area or opening to be pierced into the watch dial for the sensor light to pass through. This design is non-ideal from the aesthetic perspective. It is also chal- lenging to align the optical sensor installed on a mother board and the opening in the watch dial 13, and a possible opening in the support frame 20.

From the design point of view, it is important criteria that watch hand position sensing would not be evidently visible to the end user. This means moving away from the conventional optical sensing to allow for a more visually pleasing watch dial design. This design criteria also means that the sensor needs to be lo- cated under the watch dial, which houses some issues depending on the sensor type selected.

Considering for the application, watch hand sensing, where the space, most of all, is limited and no large sensing structure can be used. One limiting factor regarding the mechanics of the device is the effective surface area for the sensor. Because of the internal structure of the smart watch, the maximum usable area is limited, for example up to 14 mm in width and up to 16 mm in length (radial direc- tion), for watch sizes up to 48 mm (an outer diameter of the watch case), The avail- able usable area decreases with the decreasing case diameter of the watch, the available being approximately 8 mm * 7 mm for a women's watch size 24 mm (case diameter), for example.

In addition, the thickness of the sensing structure shall be minimal. The thickness of a watch normally refers to the width between the case back and the top of the crystal. A general rule is, as the diameter of the case increases or de- creases, the thickness does as well. Typically, the thickness of the watch is in a range of from 6 mm to 15mm. The available useable thickness for the sensing struc- ture may be 0.1 mm to 0.4 mm, for example

In addition to the limitations resulting from the mechanical design of a watch there is yet another limitation with considerable effects on the sensing ele- ment design. This limitation is the surface area of the mechanical watch hands as well as the material build-up. For simplicity, the watch hands will be considered as quadrilaterals. A typical hour hand of wristwatch can be simplified to be a quadri- lateral with the width of 0.8 mm and length of 10 mm, this will result in area of 8 mm2 material that can be sensed (for a watch sizes about 45-48 mm in a case diameter). Similarly, a typical minute hand can be simplified to be a quadrilateral with the width of 0.6 mm and length of 13.5 mm. This in turn, results in 6,135 mm2 of area which can be sensed. These extremely small areas imply a serious problem to many types of sensors. The sizes of watch hands decrease and the sensing prob- lems increase with decreasing watch size (case diameter).

According to embodiments of the invention, a substitute for non-optical sensing would be inductive sensing. A rule of thumb exists for inductive sensors, here the area to be sensed should be three times larger than the sensors diameter. Obviously, this houses a problem with design of the sensing element insomuch as the condition will be near impossible to fulfil.

The inventors have observed that, for the watch hand position sensing in a smart watch, it is sufficient to simply sense the presence of material, and there- fore meeting these rule of thumb criteria is not necessarily imperative.

According to embodiments of the invention, a change generated by a watch hand passing over an inductive sensor is detected. The benefits of detecting the generated change will be discussed below.

According to embodiments of the invention, the watch hand position sensing 400 comprises an LC oscillator circuit 80 having a sensing inductor L and a capacitor C and configured to oscillate at a preset resonant frequency ft), as illus- trated in Figures 4A-4B, 7A-7B, 8, 9A, 11A-11C, and 12. The benefits of implement- ing a sensor in form of the oscillator will be discussed below.

According to embodiments of the invention, the sensing inductor L is a single-layer or multilayer planar spiral sensing inductor 40 provided under the watch dial 13 or on the support frame 20 or therebetween, as illustrated in Figures 3, 5A, 6, 7 A, 7B. Planar inductor or coil is named for the parts of the coil being pri- marily on the same plane (i.e., nearly flat). The planar inductor takes up less space than other inductors and thus is suited for the watch hand position sensing appli- cation with size restrictions. The planar inductor or coil can be fabricated on both rigid and non-rigid surfaces, which means the planar inductor can be integrated onto printed circuit board (PCBs) as well as flex circuits. Planar inductors and coils can also be batch fabricated, which results in a more cost-effective manufacturing process.

According to embodiments of the invention, the sensing inductor L is a multilayer planar spiral sensing inductor 40 comprising two or more spiral coil lay- ers 401 and 402 in series connection as illustrated in Figures 4A-4B and 7A-7B. A multilayer planar inductor may comprise two or more serially connected sandwich planar inductors, i.e. micro planar coils with an isolating layer therebetween. The series connected multilayer planar coils have a multiple total inductance as com- pared to an inductance of a single-layer planar coil when an excitation signal cur- rent is applied to coils, while the required area of the multi-layer planar inductance does not increase from the area of the single-layer with increasing number of lay- ers, and an increase in the thickness of the multilayer inductance is very small with increasing number of layers. Thus, the multilayer planar inductor enables a suffi- cient inductance for the watch hand position sensing application while still meeting the size restrictions.

In the example embodiment of Figures 4A and 4B, a two-layer planar spiral sensing inductor 40 of a rectangular shape is shown in a top view and in a bottom view, respectively. The rectangular planar sensing inductor 40 is elongated such that the length of the inductor 4 in the direction parallel to a watch hand to be sensed is longer than the width in the direction perpendicular to the watch hand. In Fig.4A, a first spiral coil layer 401 is shown on the top surface of a substrate 410. In Fig. 4B, a second spiral coil layer 402 is shown on the bottom surface of the sub- strate 410. The outer diameter of each of the spiral coil layers 401 and 402 in the width direction is Dout, and the inner diameter of each of the spiral coil layers 401 and 402 in the width direction is Din. The inner dimension Din is preferably about equal to the width of the watch hand or greater. The first coil layer 401 and the second coil layer 402 are series connected by a through-connection 403. The end of the second coil layer 402 is connected to a contact track 405 on the top surface by a through-connection 404. The end of the first coil layer 401 is connected to a contact track 406 on the top surface. The contact tracks 405 and 406 may be con- figured to be connected to the circuitry on the mother board 19 by connection means, such as spring contacts 190 illustrated in Fig. 3. In the example shown, the extension 40A of the substrate 410 may comprise a capacitor C and a resistor R of the oscillator 80. In Figures 7A and 7B, another two-layer planar spiral sensing in- ductor 40 of a rectangular square shape is shown in a top view and in a bottom view, respectively. Apart from the square shape, the inductor 40 may be similar to that shown in Figs. 4A and 4B.

According to embodiments of the invention the planar spiral sensing in- ductor 40 has an axis of symmetry substantially parallel to a radial direction of the watch dial 13 at a predetermined watch hand position and substantially perpen- dicular to a direction of rotation of the watch hand 14 and 15, as illustrated in Fig- ures 5A, 6, 10A, 11 A, and 11B. According to embodiments of the invention, the single-layer or multi- layer planar spiral sensing inductor 40 comprises an open central area aligned with the axis of symmetry. The width of the central open area may be defined by an inner diameter Din of the spiral sensing inductor, as illustrated in Figures 4A, 4B, 7a, 7B, and 12.

According to embodiments of the invention the multilayer planar spiral sensing inductor 40 comprises two or more spiral coil layers 401 and 402 with aligned axes of symmetry as illustrated in Figures 4A, 4B, 7a, and 7B.

According to embodiments of the invention the single-layer or multi- layer planar spiral sensing inductor 40 is provided on a rigid, non-rigid or flexible substrate or circuit board 410, as illustrated in Figures 4A, 4B, 7a, and 7B. Accord- ing to embodiments of the invention the substrate 410 is installed between the watch dial 13 and the support frame 20, optionally attached to the bottom surface of the watch dial 13 or to the top surface of the support frame 20.

According to embodiments of the invention, the part 40A of the oscilla- tor 80 comprising the resistor R and the capacitor C of the oscillator 80 is provided on or under the bottom surface of the support frame 20 and electrically connected to the single-layer or multilayer planar spiral sensing inductor 40 of the oscillator through the support frame 20, as illustrated in Figures 3, 5A-5B, 6, and 11A-11C.

According to embodiments of the invention the oscillator circuit or sen- sor 80 comprising the single-layer or multilayer planar spiral sensing inductor 40, the resistor R and the capacitor C is provided on the same rigid, non-rigid or flexible substrate or circuit board 410, as illustrated in Figures 4A, 4B, 7a, and 7B. Accord- ing to embodiments of the invention at least the part of the substrate 410 compris- ing the single-layer or multilayer planar spiral inductor 40 is installed between the watch dial 13 and the support frame 20, optionally attached to the bottom surface of the watch dial 13 or to the top surface of the support frame 20.

According to embodiment of the invention, the part of the non-rigid or flexible substrate 410 comprising the single-layer or multilayer planar spiral in- ductor 40 is installed between the watch dial 13 and the support frame 20, and the part 40a of the non-rigid or flexible substrate or circuit board 410 comprising the resistor R and capacitor C of the oscillator 80 is bent to extend under the support frame 20, preferably extending parallel to the bottom surface of the support frame 20, and optionally attached to the bottom surface, as illustrated in Figures 3, and 5A-5C.

According to embodiments of the invention, the single-layer planar spiral sensing inductor 40 is a Laser Direct Structuring (LDS) inductor on the top surface of the support frame 20 as illustrated in Figures 11A-11B and 12. Laser Direct Structuring (LDS) process uses a thermoplastic material, doped with a (non- conductive) metallic inorganic compound activated by means of laser. A suitable material may be PC+GF30%, for example. The basic component, such the support frame 20, can be single-component injection molded. A laser then writes the course of the later circuit trace on the plastic substrate, such as the support frame 20. Where the laser beam hits the plastic substrate the metal additive forms a micro- rough track. The metal particles of this track form the nuclei for the subsequent metallization. In an electroless bath of conductive material, such as copper Cu, nickel Ni or gold Au, the conductor path layers arise precisely on these tracks. Suc- cessively layers of can be raised can be raised in this way. High line precision of down to 80 pm or below is possible, which may allow higher number of coil turns and higher inductance in a single-layer planar coil without requiring more surface area compared with a single-layer planar coil implemented by flex circuits, for ex- ample. Thus, the LDS planar inductor is well suited for the watch hand position sensing application with size restrictions. However, due to the narrow track width the flux of the magnetic field on the area of the watch hand 14 or 15 as compared to the flux of the magnetic field in a multilayer planar coil implemented by flex cir- cuits, for example which results in smaller detected change in the position sensing when the watch hand passes by. A further challenge regarding the planar LDS coil is the high inherent resistance of the LDS coil. Therefore, a separate resistance R in series with the LDS may be omitted, as illustrated in Figure 11C. In the example illustrated in Figures 11A-11B and 12, the single-layer planar LDS inductor 40 may have the following values: number of turns is 10, the width of conductor track 402 is 100 pm, and the distance between the conductor tracks 402 of neighbouring turn is 100 pm. The thickness of the conductive track 402 may in range of 5-10 pm for Cu, 3-5 pm for Ni, and 0.05-0.07 pm for Au.

In embodiments of the invention, the conductive tracks 405 and 406 re- quired for the capacitor C and resistor R of the oscillator 80 are provided by the LDS process on the bottom surface of the support frame 20, as illustrated in Figures 11A-11C and 12. The LDS tracks on the bottom surface may be connected to the LDS coil 40 on the top surface of the support frame 20 by means of through con- nections 407 and 408, for example.

According to embodiments of the invention, at least the single-layer or multilayer planar spiral sensing inductor 40, is a printed electronics inductor in the watch dial 13 and/or in the support frame 20, preferably on the bottom surface of the watch dial 13 and/or on the top surface of the support frame 20. In embodi- ments according to the invention, optionally also the resistor R and the capacitor C of the oscillator 80 are printed electronics components. When using Printed Elec- tronics method, conductive traces are printed onto the surface of the substrate, such as the watch dial 13 or the support frame 20. A direct deposition without plat- ing is possible. Aerosol jet, inkjet, or screen printing may be used. High line preci- sion of down to 10 μm is possible, which may allow higher number of coil turns and higher inductance in a planar coil without requiring more surface area. Thus, the printed electronics planar inductor is well suited for the watch hand position sens- ing application with size restrictions. However, in a similar manner as for the LDS inductor, due to the narrow track width the flux of the magnetic field on the area of the watch hand 14 or 15 as compared to the flux of the magnetic field in a multi- layer planar coil implemented by flex circuits, for example which results in smaller detected change in the position sensing when the watch hand passes by. In printed electronics, the thickness of circuitry can be tightly controlled, and complex cir- cuitry is possible as conductive traces, isolation layers, dielectrics, and other mate- rials can be deposited in multiple layers, Thus, also multilayer planar inductors ac- cording to embodiments can be implemented with printed electronics so that the magnetic flux can be increased. A further challenge regarding the printed electron- ics coil may be the high inherent resistance of the LDS coil.

In inductive sensing, electromagnetic properties of a coil and material to be sensed will be used. In the following, basics of inductance and how it can be used in sensing metallic materials will be covered.

A magnetic field will react with conductive materials providing the ob- servable change. It is important to note that the material to be sensed will need to be conductive in order to be sensed inductively.

The following formula known as Faraday's law of induction shows that electromotive force, or voltage is generated by a changing magnetic field

The formula (1) applies for any piece of conductive material, but for a coil consisting of multiple turns of same material the formula can be presented in a more convenient form

The formula (2) above states that the generated voltage V, depends on the rate of change of the magnetic field B, cross sectional area of the coil A and finally the number of turns in the coil N. Gathering from the information above, ways to use the electromagnetic properties of a coil can be observed.

Since magnetic field strength is dependent on the distance to the source, a change in voltage can be observed simply by moving the sensor coil away from the source, thus producing a change in the magnetic flux B. Another com- monly used method is to present conductive material to the changing magnetic field which induces alternating currents in the material generating its own electro- magnetic fields that react with the existing changing field. Here a change in induced voltage to a coil can be observed. This type of sensor is called an eddy current sen- sor.

The dielectric properties of the medium between the sensor and the object will not have effect on the operation of the sensor. Considering the intended use case of watch hand sensor, this property is especially desirable since the mate- rial of the watch dial 13 will not matter, as long as it is not conductive in the eyes of the sensor itself.

According to embodiments of the invention, the watch hand position sensing 400 comprises an oscillator circuit 80 having a sensing inductor L and a capacitor C and configured to oscillate at a preset resonant frequency ft).

According to embodiments of the invention, a sensor may use a simple parallel LC tank oscillator 80 to detect the watch hands 14 and 15. Here, the sensor would consist of a sensing coil L and a capacitor C needed for the LC oscillator 80. In addition to the coil L and capacitor C there may be a series resistor R that acts as part of a voltage divider circuit as well as a current limiter for the system. Basic structure of an LC oscillator is illustrated in Figure 8. A known excitation signal In will be supplied to the LC oscillator at the resonating frequency of the oscillator circuit, resulting in amplified sinusoidal waveform of the same frequency. This re- sulting signal Out can then be measured. By moving a conductive object close to the sensing coil 40 , the changing magnetic field generated by the sensing coil 40 will induce eddy currents to the object creating an opposing magnetic field. This results in decrease of the inductance thus changing the resonant frequency of the LC circuit 80 further affecting the output amplitude of the LC oscillator 80.

The resonant frequency ft) of the LC oscillator 80 can be calculated by the following formula Impedance of the LC tank can be calculated with the following formula

Inspecting the system further it can be seen that the LC oscillator 80 and the input resistor R form a voltage divider. From formula (4), the impedance ZLC goes towards infinity at the resonant frequency ft) of the system and gets smaller further away from the ft). The higher the impedance of the LC part of the voltage divider, the higher the amplitude of the system output Out Thus, a sensing arrange- ment based on LC oscillator 80 is well suited for a watch hand position sensing in a smart watch, since a small change in the inductance of the coil 40 will result in large change in the sensor output Out

A benefit of this type of a measurement system is that the circuit does not need convoluted circuitry to be used. In an embodiment, the system input In can be supplied from a pin of a microcontroller unit and the output Out can be read by an analog-to-digital converter ADC already existing in the microcontroller.

Given the amplitude response of the sensor, the LC system may be tuned so that the resonant frequency ft) will be achieved by the sensor in a free space. The mechanic watch hand 14 or 15 will then move over the sensing coil 40 and cause a change in the inductance of the sensing coil 40 which will shift the resonant fre- quency of the LC oscillator 80 resulting in a change in the amplitude of the output signal Out The largest change will be achieved this way. The LC oscillator 80 may also be tuned to the resonant frequency ft) when the mechanical watch hand 14 or 15 is on top of the coil, but this would require retuning the sensor for every type of watch hand used.

Due to the physical limitations the main limiting factors for the sensing coil 40 will be the surface area available. In addition, the thickness of the sensing coil 40 shall be minimal.

In embodiments of the invention, the manufacturing method of the pla- nar coil sensor may be chosen to be a multilayer flexible PCB. With a 2 -layer flexible PCB one can achieve a final thickness down to at least 0.1 mm. The thickness de- pends on the capabilities of the manufacturer. The multilayer planar coil structure will increase the number of turns of the inductor leading to increased inductance of the sensing coil 40, enabling to achieving a larger change in a sensed amplitude at the output of the oscillator 80.

The optimum shape of the sensor coil 81 for a passing object is rectan- gular. In embodiments of invention, the inner diameter for the coil 81 shall be chosen so that the whole of the watch hand fits in the magnetic field generated by the current flowing in the sensing coil 81. In embodiments of the invention, a sen- sor coil layout is designed so that it contains the maximum number of turns in the space that is available mechanically. Therefore, it is preferable to choose the track width and clearance (a distance between neighbouring tracks) to be smallest avail- able. In the examples illustrated in Figures 4A-4B or 7A-7B, both the track width and clearance have been chosen to be 0.15 mm.

Example configuration. Now using the mechanical dimensions of the sensor inductor 40, inductance of the sensing coil 40 can be estimated using the following formula (5)

The value is not an exact representation of the coil impedance but can be considered acceptable for modelling the watch hand positioning. In order to estimate the sensor performance, the series and parallel resistance of the sensing coil need to be evaluated as well. Using the formula (6) below the inherent series resistance Rs of the sensing coil 40 can be estimated. Where ft) is the resonant frequency, p relative resistivity, w trace width in inches and d trace height in inches. Here the unit for Rs is resistance /inch, and therefore this needs to be multiplied with the length of the conductor to get the total series resistance of the coil 40 at the resonant frequency ft). The series re- sistance Rs of the coil 40 can then be used to calculate the equivalent resistance of the LC tank at the resonant frequency ft), which largely defines the amplitude of the output signal Out The equivalent resistance can be calculated with the following formula (7)

In embodiment of the invention, the watch hand position sensing means 400 further comprises an excitation signal source coupled operably to feed the LC oscillator with an excitation signal at the resonant frequency of the LC oscil- lator 80, and a detector circuit 81 coupled operably to the oscillator circuit 80 to detect a change in the resonance frequency of the LC oscillator 80 caused by the watch arm 14 or 15 passing over the single-layer or multilayer planar spiral sens- ing inductor 40, the detected change being largest when the at least one watch arm 14 or 15 is aligned with the symmetry axis of the single-layer or multilayer planar spiral sensing inductor 40.

In embodiments of the invention, the detector circuit comprises an en- velope detector 81 outputting the position signal Out representing the amplitude of resonance frequency of the LC oscillator 80.

In embodiments of the invention, the system input In can be supplied from an output pin of a microcontroller unit 29 and the output Out can be read by an analog-to-digital converter ADC already existing in the microcontroller unit 29. Therefore, as illustrated in Figure 9B, the watch hand position sensing 400 may consist of only three parts, the MCU 29, the LC sensor 80 and the envelope detector 81. Having the MCU 29 selected to be the excitation signal source as well as the measurement device allows to save layout space and to cut down on component count

In embodiments of the invention, the watch hand positioning operates as follows: a square wave signal In is generated by the MCU 29 at the resonant fre- quency fo of the LC sensor 80. This will provoke the LC sensor 80 to oscillate at the resonant frequency ft). As described above, the maximum amplitude of the LC sen- sor 80 can be measured in the resonant frequency ft). By introducing conductive material (the watch hand 14 or 15) close to the sensing coil 40, the inductance of the sensing coil 40 will decrease leading to a change in the amplitude over the LC sensor 80. This will essentially generate an amplitude modulated signal where, de- pending on the resonant frequency fo, the rate of change of the signal Out can be too high for the MCU ADC to measure. To mitigate this issue the amplitude modu- lated signal may be fed through the envelope detector 81 which will smooth the signal and modulate it into a form that can be easily measured and processed with the MCU ADC.

An exemplary configuration of an envelope detector 81 is illustrated in Figure 9A. The resistor R1 acts as a current limiting resistor as well as a part of a voltage divider in combination with the LC oscillator 80. Diode DI is a signal diode with low forward voltage which, together with the RC low pass filter formed by a a capacitor C2 and resistor R2, form the envelope detector 81. Values of the capacitor C2 and the resistor R2 are preferably selected so that the resonant frequency ft) of the LC sensor 80 will be heavily attenuated, while the amplitude modulated signal caused by the passing watch hand 14 or 15 will not be affected. Since the modula- tion frequency of the passing watch hand will be in the range of 1 Hz or lower, and the carrier frequency (the resonant frequency fO) in the range of hundreds of kil- ohertz's it is sufficient to only consider attenuating the carrier frequency.

After initial calculations above, an overview of the systems components can be presented. Here one must note that the component selection will surely change in the realised setup due to the factual coil inductance as well as parasitic capacitances introduced by the mechanics. However, the logic behind the selection remains the same. In the example case, the value of resistor R1 may be selected to be 300 ohms. The value of resistor R1 comply to the current supplying limitations of the MCU IO pins along with supplying sufficient current for the LC tank oscilla- tion. In the example, the LC oscillator 80 may be supplied with 10 mA of peak cur- rent which will sustain the oscillation. Supplying a higher current would increase the output amplitude of the LC oscillator 80 and using a lower current would in turn lower the output amplitude.

Selection of the Cl tank capacitor depends mainly on the inductance of the coil 40 and the desired operation frequency. When using the theoretical induct- ance value of the coil found in the calculations above, the selected capacitor value used in the simulations may be 68 nF, because it is readily available and it sets the oscillation frequency ft) in the desired range of hundreds of kilohertz. Using com- ponent values stated above the resonance frequency of oscillator 80 will be set to 775 kHz, which is close to what can be easily generated by the MCU. The diode D1 can be any small signal diode with a low voltage drop, the lower the forward volt- age of the diode the higher the output signal will be. As stated, earlier the selection values of the capacitor C2 and the resistor R2 is not critical as long as the 775 kHz excitation frequency is sufficiently attenuated This can be achieved, for example, by selecting t = RC which is smaller than the period of signal frequency and larger than the period of excitation frequency. In the example, values of 120 nF and 5 kohm were used for the capacitor C2 and the resistor R2, respectively. The high value of the resistor R2 was selected in order to have high amplitude output signal for the MCU ADC.

The material of the watch hands 14 and 15 may have effect on the di- rection of change in inductance of the coil 40. When a watch hand of a conductive material is passed over the sensing coil 40, the inductance of coil 40 will decrease. However, if there is ferromagnetic material in the watch hand passing over the sensing coil 40, the inductance of coil 40 will increase instead of decreasing. For example, a watch hand made of aluminium may be treated with nickel surface fin- ish. Nickel Ni and most of its alloys are ferromagnetic. Fortunately, the direction of the change does not matter in a watch hand positioning, as the sensor is as sensitive to the increase in inductance as well as to the decrease, and the passing watch hand will be detected in both cases.

A watch hand position sensing according to a embodiment of the inven- tion was simulated in MultisimLive circuit simulator. Components with values as described above with reference to Figure 9 A were used. Rotation of the watch hand 14 or 15 over a sensing coil 40 was simulated as illustrated in Figures 10A-10C. A clock voltage source was used to simulate the MCU generated excitation signal In, with the amplitude of 3V and the operating frequency of 775 kHz. In Figure 10D, a signal amplitude at the node of the LC oscillator 80 (the grey area 100) and at the output of the envelope detector 81(the solid line 101) with time are depicted. The system was then started at time 0, and it can be seen that roughly 0.3 ms delay is required for the sensor 80 and the detector output Out to stabilize before the meas- urements can be made. The inductance of the coil was then changed to simulate a watch hand passing over. The first dip 102 in amplitude of the output signal is caused by simulating a passing hour hand 14 by changing the coil inductance by 8 nH. The inductance of the coil 40 was then changed back to the default value of 0.62 uH, causing the amplitude of the output signal to return to normal. The sensor 80 was then let to stabilize for a while, and the next dip 103 in the amplitude of the output signal was caused by simulating a passing minute hand 15 by changing the coil inductance by 15 nH after which the inductance was changed back to the de- fault value of 0.62 uH. As can be seen from Figure 10D, the amplitude of the output signal will change noticeably despite the relatively small change of 1.3% in the in- ductance of the coil 40. In reality, the change may not be expected to be as smooth as in the simulation, but the change is expected to be symmetrical, nevertheless. From the symmetrical output signal the centre point will indicate the hands posi- tion being directly on top of the sensing coil 40. The amplitude of the output signal will also determine which of the two hands has passed over the sensing coil.

In an embodiment, the measurement procedure may be performed un- der control of the MCU 29 as follows. The measurement procedure may be started occasionally, upon receiving external time synchronization, or in response to the user's input, for example. At the start of the measurement cycle the excitation sig- nal is fed to the oscillator 80, after which a sufficient time delay is preferably im- plemented so that the oscillator 80 has time to stabilize. After the output of the oscillator 80 has stabilized to its maximum value, the watch hands 14 and 15 may be moved one at time over the sensing coil 40 so that a change in the sensor output Out is provided, corresponding to the watch hand passing over the sensing coil 40. This change in the sensor output Out may be monitored with an ADC built into the MCU or with an external ADC component The MCU 29 is configured to determine the position of the watch hands 14 and 15 based on the data provided by the meas- urement procedure.

The invention and its embodiments are not limited to the examples de- scribed above but may vary within the scope of the claims.