Abstract:
The invention concerns a device for indicating the state of watch batteries. Said device comprises, in combination: a circuit for determining ( 34 ) at least a physical characteristic of the cell ( 10 ) which varies when it is nearly discharged, a circuit for metering ( 36 ) the power consumed by the watch, a circuit for assessing ( 40 ) the capacity rating of the battery, connected to the determining ( 34 ) and metering ( 36 ) circuits and designed to process data and select the most relevant information derived either from the determining circuit ( 34 ), or from the metering circuit ( 36 ), means for displaying the state of the battery ( 38,40,42 ), and a circuit controlling ( 39 ) the display means.

Description:
FIELD OF THE INVENTION 
   The invention concerns a device indicating the state of batteries, designed to equip a watch. Such devices are well known to those skilled in the art. 
   BACKGROUND OF THE INVENTION 
   One of them is described in U.S. Pat. No. 5,446,702. It comprises, in a watch, an electronic circuit for assessing the charge of its battery, a device for displaying the date and an independent motor to drive this display device. When the charge falls below a limit value, the electronic circuit gives the order to the motor to drive the display device to a position indicating that the battery is nearly discharged. The information thus given is therefore of the binary type. The person wearing the watch thus has a few days to change its battery. 
   Another device of this type is described in document JP 58061488. This concerns more specifically a watch including means for converting the battery charge into an operating time. This watch comprises a counter and a display. The counter is regularly incremented and its content, which corresponds to the remaining lifetime, is indicated by means of the display. The wearer thus knows the battery&#39;s life expectancy at any time. For such a device to be reliable, a large safety margin must be adopted. This is because the capacity of a battery cannot be measured precisely without discharging it. This capacity varies considerably from one battery to another, notably due to storage conditions. Accordingly, there is no doubt that, in many cases, the battery will be changed when its power reserve could still ensure operation for several weeks, or even several months. If the safety margin is inadequate, it is likewise possible that the reserve may be smaller than that assessed, so that the watch stops before the indicator is at zero, which is even more troublesome. 
   SUMMARY OF THE INVENTION 
   The aim of the present invention is to overcome these drawbacks. This aim is achieved due to the act that the device according to the invention comprises, in combination:
         a determining circuit for determining at least one physical characteristic of the battery, which varies when it is nearly discharged;   a counting circuit for counting the power consumed by said watch;   an assessing circuit for assessing the capacity of the battery, connected to the determining and counting circuits and designed to process data derived from the determining circuit, the counting circuit, or a combination thereof;   means for displaying the state of the battery, said means consisting of a hand and a scale against which said hand moves, said scale comprising a first sector which indicates the quantity of power available in a range between 100% and a non-null value, and a second sector, which indicates that the battery is nearly discharged, and   a controlling circuit for controlling the display means, said controlling circuit being designed so that it brings the hand opposite the first sector exclusively so long as the physical characteristic is greater than a limit value.       

   While the simplest watches comprise merely a motor driving all their moving parts, others, more complex, comprise additional transducers, like an electro-acoustic transducer, activated to indicate, by emitting a sound, a pre-determined time. Such transducers considerably influence the watch&#39;s power consumption. That is why, in a very interesting embodiment in which the device is designed to equip a watch which comprises several electrical components of which at least one serves to activate an additional function at the request of the user, the counting circuit includes a memory in which is stored information relating to this component&#39;s power consumption. The counting circuit is designed to send to the assessing circuit data relating to the power consumed, whenever the additional function, activated on demand, is utilised. 
   It is generally advantageous for the assessing circuit to be designed so that it sends to the controlling circuit the information derived from the counting circuit so long as the information derived from the determining circuit indicates normal operation of the battery. This is because, in most cases, the information derived from the determining circuit varies only when the available power can ensure a few more days&#39; normal operation. By proceeding in this way, the watch indicates, during most of the operating lifetime of its battery, information derived from the counting circuit which is given based on the consumption of the various components, whereas when the battery it is nearly discharged, it is the determining circuit that takes over, so that the information displayed is based on information relating to the state of the battery. 
   In a preferred embodiment, the displaying means comprise a hand. Moreover, the controlling circuit is designed so that, for a given power consumption, the hand&#39;s movement increases as the available power decreases. In this way, the reading can be taken over a large angle when the battery is nearly discharged, which is the most critical period. 
   Preferably, the displaying means comprise, in addition, a scale against which the hand moves. This scale comprises a first sector indicating the available power, ranging between 100% and a non-null value, and a second sector indicating that the battery is nearly discharged. The controlling circuit is designed so that it moves the hand opposite the first sector exclusively so long as the information derived from the counting circuit is considered the most relevant. The controlling circuit is designed so that the hand is moved opposite the second sector when the assessing circuit sends to the controlling circuit an order indicating that the battery is nearly discharged, as soon as the information derived from the determining circuit shows that the physical characteristic of the battery is varying. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other advantages and characteristics of the invention will become clear from the following description, made with reference to the annexed drawings, on which: 
       FIG. 1  represents schematically a watch provided with such a device, and 
       FIG. 2  shows part of the watch dial with the means for displaying the state of the battery. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   The watch schematically represented in  FIG. 1  comprises, conventionally, a battery  10 , an electronic time counting circuit  12 , an electronic alarm circuit  14  and a device for detecting and indicating the state of the battery  16 . The battery  10  powers circuits  12  and  14  and the device  16 , as represented on the drawing by the thick lines. 
   The time counting circuit  12  consists of a time base  18 , generally a quartz crystal and its control circuit, a frequency divider  20  also performing a counter function, and an electromagnetic transducer  22 , formed of a motor and its control circuit. 
   The time base  18  delivers a sinusoidal signal of stable frequency. The divider  20  converts the sinusoidal signal into square pulses and divides the frequency to 1 Hz or less, depending on the motor&#39;s frequency of rotation. The divider  20  also performs a counter function. It is designed to contain information relating to the second, minute and hour of the current time. The 1 Hz signals are applied to the control circuit of the motor, which delivers drive pulses. The motor of the transducer  22  comprises a rotor, driven by these drive pulses, which sets in rotation a gear train, schematically represented in  24 , carrying the hands that provide a display of the current time. 
   The alarm circuit  14  is formed of a comparator  26 , a memory  28 , a control  30  and an electro-acoustic transducer  32 . It is designed to draw the attention of the wearer at a given time, chosen beforehand. The comparator  26  is connected to the dividing circuit  20 , to the memory  28  and to the control  30 . When the contents of the memory  28  and of the counter part of divider  20  are identical, this means that the chosen time is reached. The comparator  26  gives this information to the control  30  which then activates the transducer  32 . 
   The device for detecting and indicating the state of the battery  16  comprises a circuit  34  for determining the state of the battery charge, a circuit  36  for counting the power consumed by the watch components, display means  38 , a circuit  39  controlling the display means, and an assessing circuit  40 . 
   The circuit  34  determines whether the voltage measured on load is or is not less than a limit value which, when it is reached, means that the battery is nearly discharged. It is connected to the terminals of the battery  10  or of a resistance mounted in series at its output, to measure the voltage, in conventional manner. 
   The counting circuit  36  is connected to the divider  20  and the control  30 . It thus knows the time during which the transducer  32  operates and the number of times that the alarm is activated. Note that it is not necessary for the counting circuit  36  to be connected to the transducer  22 , because the latter operates in a regular manner, so that its consumption can be assessed on the basis of information derived from the divider  20 . 
   It is quite clear that if the watch was provided with other functions, e.g. a chronograph, the counting circuit  36  would also be connected to the circuit controlling that function, so as to know the time during which it operates. 
   The counting circuit  36  comprises a memory and a decrementing counter, which have not been represented in the drawing to avoid cluttering it. The memory contains information relating to the foreseeable capacity of the battery and the power consumption of each of the watch components, which will be specified further on. This information is introduced in the factory. 
   The display means  38  are partly represented in FIG.  2 . There one can see a hand  42  and a display scale  44  comprising a first sector  44   a  opposite which are indications relating to the charge, in this case the numbers “100, 50, 20 and 10”, and a second sector  44   b  opposite which the hand  42  is placed when the battery is nearly discharged. 
   The hand  42  is carried by a wheel forming part of a gear train, itself driven by a stepping motor. Neither the motor nor the gear train has been represented in the drawing to avoid cluttering it. 
   The assessing circuit  40  receives information from both the determining circuit  34  and the counting circuit  36 . 
   The watch as defined above comprises, moreover, controlling means making it possible to correct the time displayed and enter the times at which the alarm is to be activated, which have not been represented, because they are well known to those skilled in the art. It operates as follows. 
   The time base  18  delivers an input signal to the divider  20 . The latter sends pulses to the motor  22  which drives the gear train  24 . The divider  20 , in its counter part, contains information relating to the current time, i.e. the minute, hour, day, etc. 
   The controlling means of the watch consist, for example, of a crown wheel or push-buttons, allowing to modify the information displayed by the hands by causing the motor  22  to operate at high speed and, simultaneously, to correct the content of the divider  20 . 
   The controlling means perform, moreover, the modification and activation or deactivation of the alarm circuit  14 . More precisely, the content of the memory  28  can be adjusted, to thus record an alarm time. Moreover, the comparator  26  is operated in such a way that the control  30  is activated when the content of the memory  28  corresponds to the content of the counting part of the divider  20 . The transducer  32  then emits one or more audible alarms informing the wearer, as programmed by him (her). 
   The counting circuit  36  has, in its memory, information relating to the capacity of the battery and the power consumption of the various watch components, as well as the indication of the battery charge. More precisely, the memory contains a value C p  corresponding to the battery charge and two other values T m  and T a , relating to the watch&#39;s power consumption. T m  refers to the watch&#39;s power consumption in normal operation, i.e. that relating to circuit  12 , and T a  to operation of that alarm, i.e. to circuit  14 . 
   For example, with a battery capacity equal to 10 mAh, C p  could be equal to 10,000. T m  and T a  are, then, the time duration necessary for the watch in normal operation and the alarm respectively, to consume 1 μAh, i.e. one ten-thousandth of the total charge. Typically, T m  could be equal to 3 600 seconds, i.e. one hour. This means that the watch&#39;s power consumption is 1 μA. T a  could be equal to 3.6 seconds, the power consumption of the transducer  32  being equal to 1 mA. The information concerning the indication relating to the battery charge concerns the values of the state of the for which the hand should be moved. These values are called skip values in the remainder of the description. 
   When a new battery is installed, the decrementer is initialised at its nominal value. It is decremented by 1 whenever the watch in normal operation has fulfilled its function during a time T m , or when the additional function is activated during a time T a . The state of the decrementer is then compared with the value stored in memory relating to the indication. Whenever the state corresponds to a skip value, the information is transmitted to the assessing circuit  40 . 
   The assessing circuit  40  receives information from both the determining circuit  34  and the counting circuit  36 . So long as the determining circuit  34  informs the assessing circuit  40  that the battery voltage is greater than the limit value, the assessing circuit  40  considers the information derived from the counting circuit  36  relevant. It therefore gives the order to the indicator  38 , and especially its motor, to drive the hand  42  by one step whenever the content of the counting circuit  36  is equal to a threshold value. The number of skip values, typically between 5 and 25, is equal to the number of steps that have to be executed by the motor of the indicator  38  for the hand  42  to pass through the angle corresponding to the sector  44   a.    
   When the hand  42  has reached a position corresponding to the end of the sector  44   a , this means that, for a normal battery, its life expectancy is low, approximately a few days to a few weeks. Below this value, there are no more skip values. 
   The hand  42  enters the second sector  44   b  only when the determining circuit  34  sends to the assessing circuit  26  the information relating to the voltage drop across the terminals of the battery  10 . At that time, whatever the position of the hand  42 , the latter is brought opposite sector  44   b.    
   With such a mode of operation, it is possible that the hand  42  may never reach the boundary of the first sector or, on the contrary, may remain there for a relatively long time. A suitable choice of the value C p  will be able to prevent the skip from being too great at the time when the determining circuit  34  informs the assessing circuit  40  that the battery is nearly discharged. In this way, the user may allow for this battery&#39;s end of life, changing it when he (she) has to leave on a trip, for example, whereas he (she) can wait for the hand to reach the sector  44   b  in normal conditions of life. 
   In the above description, various electronic circuits performing specific functions are mentioned. Needless to say that these functions could be performed by a microprocessor containing a program whose various sequences would perform the functions mentioned above. 
   The device as described can, of course, accept numerous variants. For example, it is possible to provide for a counting circuit  36  with an incrementer rather than a decrementer. It is also possible to provide for a linear scale for displaying the available power. 
   An equivalent solution can be applied to a watch provided with a liquid crystal display, of digital type or by sectors. One could also consider associating with the watch an additional indication when the battery is nearly discharged, e.g. by causing a seconds-hand to limp, by causing a display to flash, etc. It is also possible to interrupt the possible use of certain functions that are heavy power consumers, such as a chronograph, for example.