HK1066877B - Portable electronic device including capacitive water detection means and method of implementation - Google Patents

Description

Portable electronic device including capacitive water detection device and implementation method

Technical Field

The invention relates to a portable electronic device comprising means for supplying power to an electronic circuit, in particular comprising a data processing unit, the electronic circuit being housed in an assembly formed by a glass-enclosed casing, the portable electronic device further comprising a pressure sensor, and water presence detection means capable of generating an electrical signal to be sent to the data processing unit, the detection means comprising at least one capacitive sensor, in particular comprising a capacitor, one plate of which is formed by an electrode placed on an inner region of the casing-glass assembly, the capacitance of which can be modified when an external medium, located in direct contact with an outer region of the casing-glass assembly opposite said electrode, undergoes a change in properties, for example when said outer region is in contact with water.

The invention also relates to a method for implementing a water presence detection device in a device of this type.

Background

The state of the art for electronic devices of this type has been described.

Japanese utility model No.60-183896, published 6.12.1985, discloses an electronic device equipped with a device for measuring and displaying the depth of immersion in water, including in particular a pressure sensor. Since the operation of the pressure sensor involves high power consumption, the device is provided with means for detecting the presence of water to control the supply of power to the pressure sensor so that the supply of power can be interrupted when the person carrying the device is not in the water. Thus, the proposed solution consists in using a capacitive sensor comprising transparent electrodes placed on the inner surface of the glass. The capacitive sensor causes a capacitance to appear when water comes into contact with the glass, causing a change in the reference signal through the electronic processing unit. Thus, the pressure sensor is only energized when water is detected in contact with the glass of the device.

It should first be noted that a number of devices are known which implement ohmic type devices for detecting the presence of water. These detection devices, although generally having a reasonable power consumption, have a significant drawback in that they require a more or less complex structure. In particular, a small hole must be made in the housing of the device, which creates a water resistance problem. For this reason, the applicant has sought to improve capacitive detection systems which do not require a specific aperture in the casing of the device.

However, the technical solution proposed in the aforementioned japanese utility model has a number of drawbacks. In particular, a main switch is provided to control the supply of power to the pressure sensor, which works in conjunction with means for detecting the presence of water. The water presence detection means functions in some way as a secondary switch. A direct consequence of the presence of the main switch is that it is not possible (and in some cases useful, as explained below) to make a pressure measurement when the device is not immersed in water. Furthermore, the main switch is arranged to be positioned such that the water presence detection means is always powered by the clock signal. Thus, since the test for the presence of water is always carried out, these detection devices waste energy for a long time and the function of the secondary switch of the device to cut off the power supply to the pressure sensor is downstream of the detection device.

It should also be noted that the proposed solution does not take into account the fact that said structure of the capacitive sensor has stray capacitances, which necessitates the choice of forming a higher capacitance value on the glass of the device in order to enable the detection device to operate effectively. As a result, another disadvantage occurs in that the detection means consumes high power due to the high capacitance value. Given that the stray capacitance will vary with the environmental conditions to which the device is subjected, and in particular with temperature, the capacitance value chosen will have to be higher. Similarly, since the presence of water is detected by detecting changes in the reference signal, and since the amplitude of these changes varies with the value of the capacitance present due to the presence of water, the value of said capacitance must be sufficient to enable the amplitude of the changes to be detected by the electronic processing circuit.

In addition, the stray capacitance value may fluctuate over a long period of time, which may lead to malfunction of the detection device, in particular because the measurements taken are absolute rather than relative.

Disclosure of Invention

A first object of the present invention is to overcome the above-mentioned drawbacks of the prior art by providing a device comprising capacitive means for detecting the presence of water, having a low power consumption and an enhanced long-term reliability under various environmental conditions.

The invention therefore provides a portable electronic device of the aforementioned type, characterized in that the pressure sensor operates in at least two power supply modes, a first referred to as surface mode and a second referred to as dive mode, in which the detection means are periodically activated to measure a quantity representative of the capacitance of the capacitor, the detection means further comprising means for comparing at least two consecutive measurements of said quantity and generating an electrical signal in response to a variation between said two consecutive measurements of said quantity being greater than a predetermined value, to activate the dive power supply mode.

In a preferred embodiment, a plurality of capacitive sensors are provided, regularly distributed on the glass of the device, measuring a quantity representative of the capacitance of each sensor at each powering cycle of the detection device, in order to limit the inadvertent triggering of the dive powering mode that can occur on a single sensor. The detection means are then configured to: the dive powering mode is triggered when a variation of part, preferably at least half or even all, of the measured quantity is greater than a predetermined value. Such a configuration allows in fact to analyze a greater part of the total surface of the glass, preventing for example the person carrying the device from activating the power supply of the pressure sensor immediately upon putting his finger on the glass.

Alternatively, a single electrode may be placed on the inner surface of the glass, covering substantially the entire surface of the glass. A trigger threshold may then be provided to correspond to a predetermined value for the covered glass portion such that the capacitance of the capacitive capacitor is a function of the covered surface. For example, it can be decided arbitrarily that the device is considered to be immersed in water in the case where the value of the measured quantity corresponds to half the total area of the glass covered. Thus, in contrast to the operation of the above-described main embodiment, the change in the measured quantity of two consecutive measurements must exceed a new predetermined value, which is higher than the value of the aforementioned predetermined threshold value, in order to activate the dive powering mode.

Preferably, the water presence detection device according to the invention is realized as a diving computer type device or a wristwatch type device incorporating diving specific functions. In the latter case, it is desirable that the pressure measurement is performed periodically even when the user is not in a diving state. These measurements can be taken into account in the calculation of an algorithm implemented in the watch to improve the accuracy of the determination of the diving parameters.

Furthermore, an additional use of the capacitive sensors is foreseen when the device is not immersed in water, i.e. they may also fulfill the function of a manual control element.

The invention also relates to a method for implementing a water presence detection device as described above.

Drawings

The invention may be better understood with the following description of various embodiments with reference to the following drawings.

FIG. 1 is a schematic cross-sectional view of a preferred embodiment of an apparatus according to the present invention;

FIG. 2 is a simplified electronic diagram of an embodiment of a water presence detection device;

fig. 3 shows a block diagram of an exemplary embodiment of the device according to the present invention, when the water presence detection device comprises a plurality of capacitive sensors.

Detailed Description

Fig. 1 shows a schematic cross-sectional view of an electronic device 1, represented in the form of a non-limiting watch-type device, comprising a housing 2 and a glass 3. The electronic circuit 4 is placed inside the housing 2. According to a known configuration of the prior art, a conductive electrode 5, preferably transparent, is placed on the inner surface 6 of the glass 3 of the device 1. Wires 7 connect the electrodes 5 to the electronic circuit 4. A battery or other electronic power source 8 is also disposed in the housing 2 and is connected by a lead 9 to the positive terminal of the electronic circuit 4.

The electrode 5 forms one plate 20 of a capacitive sensor (shown in figure 2), the other plate 21 of which is formed by the water-covered glass 3 when the device 1 is immersed in water. The water can establish an electrical connection (shown in dotted lines in fig. 1) between the housing 2 and the glass 3 of the device 1, which has the effect of returning the potential at the outer surface of the glass 3 to the ground 11 of the electronic circuit 4 if the housing 2 is connected to the negative terminal of the electronic circuit 4 and to the battery 8.

The device 1 further comprises a pressure sensor 12 of conventional type, housed in the casing 2 and connected to the electronic circuit 4 by wires 13.

Fig. 2 shows a non-limiting example of a preferred embodiment of an electronic circuit 22 for detecting the presence of water, used in the device 1 of fig. 1, which generates an electrical control signal in response to the activation of the capacitive sensor 20. The detection circuit 22 is connected to a frequency detector DF, which is in turn connected to a data processing unit (shown in fig. 3) which manages the operation of the pressure sensor 12, as described below.

The detection circuit 22 comprises a capacitive sensor 20, a stray capacitance Cp being present due to the structure between the electrode 5 and the casing 2 of the device 1. This stray capacitance is represented in fig. 2 by capacitor 23. Capacitive sensor 20 and capacitor 23 are connected in parallel between ground 11 and the inverting input of operational amplifier 24.

The detection circuit 22 further comprises resistors 25, 26 and 27, all connected in series between the output of the amplifier 24 and ground 11. The non-inverting input of amplifier 24 is connected to the junction between resistors 26 and 27. In this configuration, amplifier 24 and resistors 25, 26 and 27 form a schmitt trigger that provides a signal at its output 28, i.e., the junction between resistors 25 and 26, that has a high logic level or a low logic level as a function of the relative values of the voltages at the inverting and non-inverting inputs of amplifier 24. Two zener diodes 29 and 30 mounted head-to-tail are connected between output 28 and ground 11 to stabilize the voltages defining these logic levels, respectively.

The detection circuit 22 further comprises a resistor 31 connected between the output 28 and the inverting input of the amplifier 24. The resistor 31 and the capacitive sensor 20 and the capacitor 23 form part of a low-pass filter, integrating the voltage at the output of the schmitt trigger. The plate potentials of capacitors 20 and 23 are applied to the inverting input of amplifier 24. As a result, the detection circuit 22 operates like a voltage-to-frequency converter, in other words, as a voltage-controlled oscillator.

In the embodiment shown in fig. 2, the voltage-to-frequency converter is designed in the form of an unstable multivibrator, since it creates a periodic signal with two quasi-stable states and free oscillation at the same time. But it can also be designed in the form of any periodic signal generator, in particular in the form of a voltage-controlled oscillator as described before. The structure shown in fig. 2 is particularly advantageous because it is simple to manufacture and because no high-precision electronic components are required.

The oscillation period T of the detection circuit 22 is expressed by the following relation:

T＝2.R₃₁.C_tot.In(1+(2.R₂₆)/R₂₇)

in the formula R₃₁、R₂₆And R₂₇The values of the resistors 31, 26 and 27, C_totIs the total capacitance between the inverting input of amplifier 24 and ground 11. It can be seen that the oscillation frequency of the output signal of the detection circuit and the total capacitance C_totIs proportional, the capacitance of the capacitive sensor and the stray capacitance together determine the value of the oscillation frequency of the detection circuit 22.

Thus, the oscillation frequency of the voltage-to-frequency converter varies with the presence or absence of water on the outer surface of the glass 3. When the device 1 is not immersed in water, the plates 21 of the capacitive sensor 20 are not present in the circuit shown in figure 2. The total capacitance is now equal to the stray capacitance Cp between electrode 5 and ground 11. The oscillation frequency of the output signal of the detection circuit 22 is then proportional to the inverse of the stray capacitance Cp.

But when the device 1 is immersed in water, the plate 21 is formed, so that the capacitive sensor has a capacitance Cd and acts in practice on the detection circuit 22. In these cases, the total capacitance C_totEqual to the sum of the capacitances Cd and Cp.

In this way, the data required in the output signal of the detection circuit 22 is included in its frequency in a known manner, which can be recovered using simply designed digital means. For example, a pulse counter that is turned on in a fixed duty cycle may be implemented. The number of pulses received in this fixed period directly represents the frequency, i.e. the presence or absence of water in contact with the glass 3. Those skilled in the art will be aware of the current state of the art and will not have particular difficulty in implementing these devices or equivalent devices.

Fig. 3 shows in block diagram form a preferred embodiment of the complete set of electronic circuits of the device 1 according to the invention. Only those elements that are directly related to the present invention are shown in this figure.

In fig. 3, the glass 3 of the device 1 is shown, which is structured with a capacitive sensor 6 on its inner surface, which shows electrodes 5a to 5 f. Of course, the following description of this particular embodiment also enables the person skilled in the art to realize a simplified solution using a single sensor, the general operating principle being the same.

Each of the 6 electrodes 5a to 5f is connected via a conductive path 101 to a multiplexer circuit 100 of conventional type, the output of the multiplexer circuit 100 being connected to the input of a detection circuit 22 of the type shown in fig. 2. The output of the detection circuit 22 is connected to a data processing unit 102, which, as mentioned above, can also send instructions to control the detection circuit 22.

The data processing unit 102 is powered by the battery 8 of the device 1. The processing unit 102 is connected to the pressure sensor 12, which pressure sensor 12 can in turn generate an electrical signal of analog type which is sent to an analog-to-digital converter 103, which analog-to-digital converter 103 is itself connected to the processing unit 102 to send digital data thereto. The processing unit 102 further comprises an electrical connection to a control circuit 104 of a display device (not shown), and two memory areas 105 and 106. It can be seen from fig. 3 that each memory area 105 and 106 is shown with 6 different addresses, the respective functions of which are explained below.

The electronic circuitry of the device 1 further has a time base (not shown), provided for example by a quartz resonator, which time base sends a clock signal to the processing unit 102, which time base may be directly integrated in the processing unit or arranged elsewhere in the electronic circuitry of the device 1 than the processing unit.

On the basis of the above-described structure, the following preferred method is proposed for realizing the apparatus for detecting the presence of water according to the present invention.

The device 1 comprises at least two operating modes, preferably a specific power supply mode and a specific display mode corresponding to each operating mode. A first mode of operation, which may be referred to as surface mode, is activated when the device 1 is not immersed in water, and a second mode of operation, which may be referred to as diving mode, is activated when water is detected in contact with the device 1.

In the surface mode of operation, the means for measuring the current time and its display may be provided by conventional means, for example. Moreover, as mentioned above, the powering of the pressure sensor 12 in this operating mode preferably enables periodic measurements of the ambient pressure at predetermined periods (of values of about 30 minutes to 1 hour). The pressure measurements are stored in a dedicated memory (not shown) and may be used later during diving. Indeed, if the device 1 according to the invention is made in the form of a diving computer, the decompression algorithm is stored in a specific memory of the electronic circuit, in particular for calculating the decompression parameters during a dive ascent. The memory may be arranged directly in the processing unit 102. The accuracy of the calculated decompression parameter can be improved by taking into account the fact that in the calculation of the decompression algorithm the historical values of the ambient pressure experienced by the person wearing the watch before diving.

Of course, the value of the power supply period of the pressure sensor 12 in surface mode can be chosen by the person skilled in the art according to the characteristics of the battery 8 used, the required accuracy of the decompression parameters and the required independence of operation.

Furthermore, still on the basis of the clock signal, the data processing unit 102 periodically activates the water presence detection means 20, 22, 100 to determine whether the device 1 is immersed in water. To this end, the detection circuit 22 successively measures, through the multiplexer 100, the capacitance of each capacitive sensor associated with the electrodes 5a to 5f, forming a first series of measured values S1. The measured quantity is preferably converted into a frequency in the manner previously shown in fig. 2 and then stored in the first memory area 105 of the memory areas 105, 106. Thus, each address of memory region 105 receives a value associated with a given capacitive sensor 20.

After the next powering cycle of the detection device, typically 2 to 30 seconds, preferably about 10 seconds, the detection circuit 22 makes a second series of measurements S2 of the capacitance of each capacitive sensor 20 through the multiplexer 100. A second series of measured values S2 is stored in the second memory area 106, each address of the second memory area receiving a value associated with a given capacitive sensor.

After storing the second series of measured values S2, the data processing unit 102 reads the contents of the memories 105 and 106 in turn. In each readout step, the processing unit reads out the content in each memory area 105 and 106, respectively, in the address associated with the same capacitive sensor 20, in order to calculate the variation that the frequency associated with said given capacitive sensor 20 may undergo between the two series of measured values S1 and S2. It is then proposed that the rate of change associated with this frequency be calculated by the processing unit 102, obtaining a quantity that can later be compared with other values, in particular a reference value predetermined by the device designer, typically around 10%. These operations are performed in sequence for all memory addresses to calculate the frequency change associated with each of the 6 capacitive sensors. Each value found for each rate of change is compared to a reference value, which defines a trigger threshold.

The next series of frequency measurements made during the next power cycle is stored in the first memory area 105, replacing the first series of measurements and comparing them to the second series, and so on.

In this way, the storage of each new series of measured values is always performed, the new series replacing the older series originally stored in the corresponding memory area. As a result, a comparison is always made between the new series of measured values and the previous series of measured values, the two series being separated in time by one detection device supply cycle.

A criterion is proposed to confirm, from the measurements made, the presence or absence of water as a function of the number or proportion of capacitive sensors 20 whose associated frequency variation has exceeded the reference value between two successive series of measurement values.

For example, it may be provided that the confirmation that water is in contact with the device 1 is performed when the frequency group respectively associated with the capacitive sensor 20 has breached the triggering threshold.

It may also be provided, however, that according to a preferred variant, the presence of water is confirmed when part, for example at least half (but not all), of the measuring frequency has changed, so as to breach the trigger threshold.

In fact, when the device is immersed in water, all quantities respectively associated with the capacitive sensors generally vary by more than a predetermined trigger threshold, unless, for example, a user inadvertently touches one of the capacitive sensors during a series of measurements made immediately prior to immersion. In this case, one capacitive sensor has a capacitance value corresponding to the activated state when the series of measurements before immersion is stored, and all capacitive sensors have an activated state when the series of measurements after immersion of the storage device is next. In this way, the rate of change respectively associated with the capacitive sensors and calculated from these series of measured values has a value higher than the trigger threshold predetermined for all capacitive sensors, except for the one that was activated before the immersion.

In this case, the measurement of one capacitive sensor does not breach the detection threshold, and if the stored confirmation of the presence of water corresponds to the simultaneous activation of all capacitive sensors, the presence of water cannot be confirmed. Defining a more flexible validation criterion, such as validating the presence of water when at least half of the capacitive sensors have been activated, makes the detection of the presence of water more reliable.

Furthermore, as mentioned above, given that the capacitance of a capacitive sensor may fluctuate slowly over time due to changes in ambient conditions, the calculation method for comparing successive measured values used in the present invention may avoid calculation errors resulting from these fluctuations.

When the trigger threshold is simultaneously breached, i.e. by all or a portion of the capacitive sensors 20 in the same series of measurements (depending on the validation criterion used), the data processing unit 102 changes the power mode of the pressure sensor 12. The submersible power mode is initiated when the frequency of ambient pressure measurements made by the pressure sensor 12 is much higher than in the surface power mode. It may be mentioned, for example, that the frequency of the ambient pressure measurement is approximately one measurement per second, or even more than one measurement per second.

The ambient pressure measurement is sent to the data processing unit 102 via the analog-to-digital converter 103 or is utilized by the processing unit 102 directly according to a depressurization algorithm or is used by an additional integrated circuit (not shown) connected to the processing unit according to a depressurization algorithm. Using these calculations, the decompression parameters can be defined in a known manner and by way of non-limiting example, advantageously for a person wearing a watch when diving. A signal is generated by the processing unit 102 or additional integrated circuit and sent to the display device control circuitry 104 to specifically display the depth of the dive in progress and various pressure reduction parameters. These decompression parameters may include, for example, the time left to continue diving before the decompression phase at the time of ascent that the person wearing the device must perform, or data regarding any decompression phase that needs to be observed at the time of ascent.

The man skilled in the art will find, among the various calculations performed by the decompression algorithm, a compromise between improved accuracy due to the high frequency of pressure measurements and the limited energy consumption of the pressure sensor to maintain a reasonable autonomy of the device 1 without particular difficulties.

It is of course also possible to realize a very simple device 1, which indicates mainly or exclusively the (quasi) instantaneous depth to the user from the time the water presence detection device according to the invention detects flooding.

Preferably, the water presence detection means is also powered at the same power frequency as in the surface mode when the apparatus 1 is in the dive power mode. The capacitance value of each capacitive sensor does not vary much between two successive series of measurements as long as the device 1 remains in the immersed state.

However, when the device 1 is taken out of the water, each value undergoes a new significant change, which is detected by the data processing unit 102 via the circuit 22 detecting the presence of water, the measured values being stored in turn in the memory areas 105 and 106. If a change is detected that breaches the trigger threshold and occurs in a direction opposite to that occurring upon entry into the water, either all capacitive sensors are simultaneously or on some of the capacitive sensors, depending on the validation criteria used, the data processing unit 102 will be caused to stop the submersible power mode and initiate the surface power mode.

Since the method of detecting the absence of water is based on the same principle as the above-described method of detecting the presence of water, it will not be described in detail.

It should be noted that the above description of fig. 3 still applies if the means for detecting the presence of water comprise only one capacitive sensor 20. The electronic circuit 4 of the device 1 may be constructed identically or may be simplified so that only the necessary components remain. In this case, multiplexer 100 may be omitted and memories 105 and 106 may be simplified to include only one memory address per memory. The operation of the electronic circuit 4 thus simplified is similar to that described above, i.e. based on the principle of continuously comparing measured values.

In another embodiment with a single capacitive sensor, the surface area of the respective electrodes may be substantially equal to the area of the inner surface of the glass. In this case, the validation criterion for detecting the presence of water may be adjusted as a function of a certain proportion of the surface area of the cover glass. In this way, the threshold value of the change in capacitance value can be predefined, for example corresponding to 50% of the surface area of the cover glass, whereby the data processing unit considers the electronic device to be in contact with water.

Further, it should be noted that the number of memory regions and their operating modes described herein are not limiting. Instead, more than two storage areas may be provided, so that the measurement values of the latest series can be compared with the measurement values of the first few series, instead of only the last series. It is possible to store the series of measurements alternately with three of the four memory areas without going beyond the scope of the embodiment just described.

Likewise, a variant can also be provided, for example, in which there are four memory areas which behave as a shift register, i.e. the new series of measured values is still stored in the first memory area, while the contents of memory area or row i are stored in memory area i + 1. This is how the content of the last memory area (fourth in this example), i.e. the one corresponding to the earliest series of measured values, is deleted and replaced by the content of the third memory area, which is replaced by the content of the second memory area, which itself is replaced by the content of the first memory area. In this way, the processing unit can be programmed to compare the new series of measurements with the first three series of measurements simultaneously, thereby increasing the reliability of the detection of the presence of water.

The person skilled in the art does not encounter any particular difficulty in achieving the number of memory areas best suited to their specific situation and operation, so that an optimum compromise between the space occupied by the memory areas in the electronic circuit and the reliability of the detection of the presence of water can be found.

An advantageous alternative of the embodiment, in which the means for detecting the presence of water comprise a plurality of capacitive sensors 20, consists in providing the capacitive sensors 20 with an additional function of a manual control element.

At this time, the following configuration and operation are proposed, which is a preferable mode but not restrictive.

The device comprises a manual control element 107 of a conventional type, for example a push button, which, when activated, enables a specific command in the processing unit 102. The device further comprises an additional memory area 108 comprising at least one memory address per capacitive sensor 20, e.g. 6 memory addresses as shown in fig. 3.

The invention also proposes that a mode of operation, or a function, is associated with each capacitive sensor and is activated in response to the action of the user placing a finger on one of the electrodes 5a to 5f on the corresponding capacitive sensor. To this end, the electronic circuit may comprise a unit 109 for controlling additional functions respectively associated with the capacitive sensors.

The function of the control element of the known capacitive sensor is not always active, the obvious reason for this being the power consumption and the prevention of the function respectively associated with the capacitive sensor from being unintentionally activated.

Therefore, the data processing unit 102 is configured to activate the manual control element function of the capacitive sensor 20 in response to the user action detected by the control element 107.

For this purpose, and in order to reliably detect the placement of a user's finger on one of the capacitive sensors, the data processing unit 102 activates the detection means 20, 22, 100 in response to the motion detected on the control element 107, measuring in turn, by means of the multiplexer 100, the capacitance of each capacitive sensor associated with the electrodes 5a to 5 f. The first series of measurements thus obtained is stored in the memory area 108, forming a reference series, which eliminates the above-mentioned problem of fluctuations in the capacitance value of the sensor 20 over time.

A new series of measurements is continuously taken during a predetermined period, preferably about 20 seconds, during which the detection means are continuously powered. At the same time, each measurement associated with a given capacitive sensor 20, as described above, is compared to a corresponding reference value in the memory area 108.

As mentioned above, the comparison method used is preferably based on calculating the rate of change between the reference measurement and each new measurement. When the rate of change calculated for a capacitive sensor 20 at the time of measurement exceeds the above-mentioned predetermined threshold value, the exceeding value is interpreted by the data processing unit 102 as a command to start the function associated with the relevant capacitive sensor. The associated function is initiated either directly by the processing unit 102 or, if applicable, by the additional function control unit 109. Further, the adjusted electrical signal is sent to the display device control circuit 104 to display data regarding the new function that is activated. The functions that can be implemented in the present device are of any known conventional type, including chronograph, alarm, time zone change or even thermometer, compass or altimeter functions, the list of which is not exhaustive or limiting.

As mentioned above, after a predetermined period of about 20 seconds, the processing unit 102 interrupts the continuous supply of power to the detection means 20, 22, 100 if no measurement quantity in the continuous series of measurements breaches the trigger threshold at least once.

According to the specific work described above, it is preferable to have the function of the detection means 20, 22, 100 to simultaneously ensure that they detect the presence of water in contact with the device according to the invention.

Thus, the data processing unit 102 continues to calculate, based on the clock signal, a time interval corresponding to the above-defined period of the periodic supply of power to the detection means 20, 22, 100. Moreover, if necessary, i.e. in particular in the case where the power supply cycle of the detection means is fixed for less than 20 seconds, the processing unit 102 commands the alternate storage in the memory areas 105 and 106 of the series of measurements which substantially occur at the end of each interval. Also, the rate of change of the measurement from each capacitive sensor is calculated using two successive series of measurements, and the dive fix mode is initiated in response to all or some of the capacitive sensors simultaneously breaching a predetermined change threshold, as previously described.

Preferably, the operation of the capacitive sensor 20 as a manual control element is immediately interrupted upon detection of water contact with the device. Furthermore, if a specific additional function control unit 109 is provided, this element is also deactivated when the presence of water is detected.

It should be noted that there may be different schemes as far as the criterion for verifying the presence of water is chosen, which are of course included in the context of the present invention. For example, if the detection means comprises a plurality of capacitive sensors, an additional step may be provided to process the frequency measurements made before the rate of change calculation is made. This additional processing step can be implemented in the form of calculating the mean value of the measured values obtained in a series of measurements for all capacitive sensors, calculating two mean values respectively for two consecutive series of measured values, then comparing them with each other by means of corresponding rate of change calculations, as previously described.

In this way, the criterion for verifying the presence of water may be defined with respect to a rate of change calculation of the average frequency respectively associated with the capacitive sensors 20. In this case, it is clear that the more capacitive sensors the device comprises, the more reliable the detection of the presence of water.

Alternatively, the above-described first embodiment may also be accomplished by adding a filter function to the data processing unit 102 based on the calculation of the rate of change of frequency for each capacitive sensor. Indeed, it can be provided that if, in a given series of measurements, only one capacitive sensor 20 is activated by an inadvertent touch or use of its control element function, the processing unit replaces in one of the memory areas 105, 106, in a storage step, a new value of its associated frequency with the frequency value stored in the previous series of measurements.

In this case, the above-described criterion of verifying the presence of water based on the simultaneous activation of all the capacitive sensors is applicable without the reliability problem of detecting the presence of water.

Of course, those skilled in the art will have no difficulty adopting other comparison means equivalent to those described above, without departing from the scope of the present invention.

Moreover, the foregoing description is intended to illustrate specific embodiments in a non-limiting manner, and the invention, for example, is not limited to the number or positioning of capacitive sensors. In particular, it is possible to place the capacitive sensor in the centre of the glass of the device, or even at least one or all of the capacitive sensors in suitably different areas of the assembly consisting of the casing and the glass of the device according to the invention.

Claims (20)

1. Portable electronic device (1) comprising power supply means (8) for supplying power to an electronic circuit (4) comprising a data processing unit (102), said electronic circuit (4) being housed in an assembly formed by a casing (2) closed by a glass (3), said portable electronic device further comprising a pressure sensor (12) and detection means (20, 22, 100) for detecting the presence of water, said detection means being able to generate an electric signal to be sent to said data processing unit (102), said detection means comprising at least one capacitive sensor (20) comprising a capacitor, one plate of which is formed by an electrode (5) placed on an internal region of the casing-glass assembly and which undergoes a change in property when an external medium placed in direct contact with an external region of the casing-glass assembly opposite said electrode (5), -the capacitance (Cd) of said capacitor is variable in response thereto, characterized in that said pressure sensor (12) operates in at least two power supply modes, a first referred to as surface mode and a second referred to as dive mode, -said detection means (20, 22, 100) are periodically activated to measure a quantity representative of the capacitance value of said capacitor, -said electronic circuit (4) further comprises comparison means (102, 105, 106) for comparing at least two consecutive measurements of said quantity and generating an electric signal to activate said dive power supply mode in response to a change in said capacitance between two consecutive measurements of said quantity being greater than a predetermined value.

2. Portable electronic device according to claim 1, wherein the electrode (5) is transparent and placed on the inner face of the glass (3), characterized in that the surface area of the electrode is substantially equal to the surface area of the inner face of the glass, and that the predetermined value corresponds to the change in the measured quantity between a preceding external medium not in contact with the glass and a subsequent external medium in contact with the glass (3) at a surface area representing a predetermined part of the surface area of the electrode (5).

3. Portable electronic device (1) comprising power supply means (8) for supplying power to an electronic circuit (4) comprising a data processing unit (102), said electronic circuit (4) being housed in an assembly formed by a casing (2) closed by a glass (3), said portable electronic device further comprising a pressure sensor (12) and detection means (20, 22, 100) for detecting the presence of water, said detection means being able to generate an electrical signal to be sent to said data processing unit (102), characterized in that said pressure sensor (12) is able to operate in at least two power supply modes, a first called surface mode and a second called dive mode, in which the detection means for detecting the presence of water comprise at least a first capacitive sensor and a second capacitive sensor (20), each comprising a capacitor, one of whose plates is formed by an electrode (5) placed on an inner region of the casing-glass assembly, and the capacitance (Cd) of said capacitor can be changed when a change in the property of an external medium located in contact with the external area of the housing-glass assembly directly opposite said electrode (5) occurs, said detection means (20, 22, 100) being periodically activated to measure a first and a second quantity respectively representing the capacitance value of said first capacitive sensor and the capacitance value of said second capacitive sensor, said electronic circuit (4) further comprising means for comparing at least two consecutive measurements of said first quantity and said second quantity respectively and generating an electric signal to activate said submersible power mode when the change in said first and second quantities between two consecutive measurements is simultaneously greater than a predetermined value.

4. A portable electronic device as claimed in claim 3, wherein said detection means comprise at least three of said capacitive sensors (20), characterized in that said at least three capacitive sensors are substantially regularly placed at a position close to the periphery of said glass (3), and said detection means (20, 22, 100) generate said signal to start the dive powering mode if half of said quantities respectively associated with said at least three capacitive sensors (20) simultaneously vary by a respective value greater than said predetermined value between two consecutive measurements.

5. A portable electronic device according to claim 3, characterized in that said electronic circuit (4) comprises multiplexing means (100) for making a measurement of each capacitive sensor (20) at each activation cycle of said detection means (20, 22, 100) to form a series of measured values of said quantity respectively associated with said respective capacitive sensor, two consecutive series of measured values being alternately stored in the first and second memory area (105, 106) so as to calculate, after each series of measurements, a respective variation of each of said quantities between the last series of measured values and the previous series of measured values.

6. Portable electronic device according to claim 4, characterized in that said electronic circuit (4) comprises multiplexing means (100) for making one measurement for each capacitive sensor (20) at each activation cycle of said detection means (20, 22, 100) to form a series of measurements of said quantity respectively associated with said respective capacitive sensor, two consecutive series of measurements being alternately stored in the first and second memory area (105, 106) so as to calculate, after each series of measurements, the respective variation of each of said quantities between the last series of measurements and the previous series of measurements.

7. A portable electronic device according to claim 3, characterized in that said electronic circuit (4) comprises multiplexing means (100) for making a measurement for each capacitive sensor (20) at each activation cycle of said detection means (20, 22, 100) to form a series of measurement values of said quantity respectively associated with said respective capacitive sensor, said data processing unit (102) being able to calculate an average value of said series of measurement values respectively associated with said capacitive sensors (20), said average values being respectively and alternately stored in first and second memory areas (105, 106) so as to calculate, after each series of measurements, a respective variation of each of said average values between the last series of measurement values and the previous series of measurement values, said predetermined value being defined with respect to the average value of the series of measurement values.

8. Portable electronic device according to claim 4, characterized in that said electronic circuit (4) comprises multiplexing means (100) for making one measurement for each capacitive sensor (20) at each activation cycle of said detection means (20, 22, 100) to form a series of measurement values of said quantity respectively associated with said respective capacitive sensor, said data processing unit (102) being able to respectively calculate an average value of said series of measurement values respectively associated with said capacitive sensor (20), said average values being respectively and alternately stored in a first and a second memory area (105, 106) in order to calculate, after each series of measurements, a respective variation of each said average value between the last series of measurement values and the previous series of measurement values, said predetermined value being defined with respect to the average value of a series of measurement values.

9. A portable electronic device according to claim 1, characterized in that said portable electronic device (1) comprises at least one control element (107), said electrodes (5) being transparent and placed on the inner face of said glass (3), at least one of said capacitive sensors (20) being also capable of ensuring an additional control element function in said surface mode in response to an action on said control element (107).

10. A portable electronic device according to claim 3, characterized in that said portable electronic device (1) comprises at least one control element (107), said electrodes (5) being transparent and placed on the inner face of said glass (3), at least one of said capacitive sensors (20) being also capable of ensuring an additional control element function in said surface mode in response to an action on said control element (107).

11. Portable electronic device according to claim 1, characterized in that said detection means particularly comprise additional means (24 to 27, 31) for converting a first electrical signal into a second periodic electrical signal, wherein the amplitude of said first electrical signal depends on the capacitance value of said capacitor and the frequency of said second periodic electrical signal depends on said capacitance and corresponds to said measured quantity.

12. A portable electronic device according to claim 3, characterized in that said detection means particularly comprise additional means (24 to 27, 31) for converting a first electrical signal into a second periodic electrical signal, wherein the amplitude of said first electrical signal depends on the capacitance value of said capacitor and the frequency of said second periodic electrical signal depends on said capacitance and corresponds to said measured quantity.

13. A portable electronic device as claimed in claim 1, characterized in that the pressure sensor (12) measures the ambient pressure periodically in the surface-powered mode and in real time in the dive mode.

14. A portable electronic device according to claim 3, characterized in that the pressure sensor (12) measures the ambient pressure periodically in the surface-powered mode and in real time in the dive mode.

15. Method for detecting the presence of water in contact with a portable electronic device (1), said electronic device (1) comprising power supply means (8) for supplying power to an electronic circuit (4) comprising in particular a data processing unit (102), said electronic circuit (4) being housed in an assembly formed by a casing (2) enclosed by a glass (3), said electronic device (1) further comprising a pressure sensor (12) operating in at least two power supply modes, a first called surface mode and a second called dive mode, said electronic device (1) further comprising detection means (20, 22, 100) for detecting the presence of water, able to generate an electric signal to be sent to said data processing unit (102), said detection means for detecting the presence of water comprising at least one capacitive sensor (20) comprising a capacitor, one of its plates (21) is formed by an electrode (5) placed on the internal region of the envelope-glass assembly and the capacitance (Cd) of said capacitor can be changed when a change in the properties of an external medium located in contact with the external region of the envelope-glass assembly directly opposite said electrode (5) occurs, said detection means (20, 22, 100) being activated periodically to measure a quantity representative of the value of the capacitance of said capacitor, said method comprising the following periodic steps:

a) measuring the value of the quantity;

b) calculating the change between its new value and the previous value at each new measurement of said quantity;

c) starting said submersible powering mode if said variation calculated in step b) has a value higher than a predetermined value, otherwise starting from step a) again during the next period.

16. A method as claimed in claim 15, characterized in that said electronic circuit (4) comprises at least two memory areas (105, 106) for storing, at each power supply cycle of said detection means (20, 22, 100), a measured value representative of a quantity of capacitance of said capacitor, said memory areas (105, 106) being used alternately from one cycle to the next in order to calculate, after each new measurement of said quantity, a change of said new value with respect to said previous value.

17. A method as claimed in claim 16, said detection means comprising n of said capacitive sensors (20), n being at least equal to 2, each of said storage areas (105, 106) comprising at least n memory addresses, characterized in that said method comprises the steps of:

a) measuring the value of said quantity of each of said n capacitive sensors during a power cycle of said detection device (20, 22, 100) to form a series of n measured values;

b) -calculating, at each new series of measurements, each variation between a new value of said quantity associated with each of said capacitive sensors (20) and the respective previous value;

c) initiating said start-dive powering mode if at least half of said n variations calculated in step b) simultaneously have respective values higher than a predetermined value, otherwise starting from step a) again during the next period.

18. The method according to claim 16, said detection means comprising n of said capacitive sensors (20), n being at least equal to 2, characterized in that it comprises the steps of:

a) measuring the value of said quantity of each of said n capacitive sensors during a power cycle of said detection device (20, 22, 100) to form a series of n measured values;

b) calculating an average of the n measurements obtained at each new series of measurements;

c) calculating each variation between the new average calculated in step b) and the average corresponding to the previous series of measurements;

d) if the variation calculated in step c) has a value higher than a predetermined value, said submersible power supply mode is activated, otherwise, starting from step a) again during the next period.

19. A method according to claim 17, characterized in that said detection means comprise multiplexing means (100) and means (24 to 27, 31) for converting a first electrical signal into a second electrical signal, wherein the amplitude level of said first electrical signal represents the capacitance value of a capacitor and the frequency of said second electrical signal represents said capacitance value, said measured quantity corresponding to the frequency, by making a series of n measurements with said multiplexing means (100).

20. The method according to claim 15, characterized in that the power supply period of the detection means (20, 22, 100) has a value between 2 and 30 seconds.