ELECTRONIC TIMEPIECE

Abstract: An electronic timepiece comprises an oscillator (1) for generating a time base signal, a frequency divider (2) for frequency dividing the time base signal, a pulse synthesising circuit (3) for producing a plurality of control signals in response to a signal from the frequency dividing (2), and a step motor driving circuit (5) for generating and controlling driving pulses for a step motor (10) in response to the control signals of the pulse synthesising circuit (3). A power supply (9) generates, stores and supplies electric energy. A voltage detecting circuit (4) detects a plurality of voltage levels of the power supply (9) and a charge control circuit (6) controls storage and supply of electrical energy in and from the power supply in response to the result of detection of the voltage detecting circuit (4).

Description: This invention relates to electronic timepieces and in particular, although not so restricted, to electronic timepieces with a charging function in which solar cells or generators serve as power sources. There is a demand for a rechargable electronic timepiece which has a primary power source such as a solar cell or a manually operated generator, and a secondary power source such as a plurality of capacitors having different capacitancies. One conventional electronic timepiece of this type has a capacitor with a relatively large capacitance which, when fully charged, is capable of driving the electronic timepiece for several days, a capacitor with a relatively small capacitance which can be instantaneously charged to produce a relatively large voltage but which is capable of driving the electronic timepiece for only several seconds, and a charge control circuit which connects or disconnects the primary power source with the secondary power source by detecting terminal voltages of both capacitors. The operation of the charge control circuit is as follows: (a) In an initial state of charging, the primary power source is disconnected from the relatively large capacitance capacitor and electric current is supplied only to the relatively small capacitance capacitor. (b) As the terminal voltage of the relatively small capacitance capacitor rises above an operational voltage of the electronic timepiece, primary power source is connected to the relatively large capacitance capacitor, and the relatively large capacitance capacitor is electrically charged. The electronic timepiece continues to be powered only by the relatively small capacitance capacitor. (c) As the terminal voltage of the relatively small capacitance capacitor falls near to the minimum operational voltage of the electronic timepiece, the primary power source is disconnected from the relatively large capacitance capacitor again, and only the relatively small capacitance capacitor is electrically charged. (d) The relatively large capacitance capacitor is electrically charged while steps (b) and (C) are repeated. As the terminal voltage of the relatively large capacitance capacitor rises over the operational voltage of the electronic timepiece, both capacitors are connected in parallel with each other, and both are electrically charged to the same terminal voltage. Here, the electronic timepiece is powered by both capacitors. (e) As the terminal voltage of the relatively large capacitance capacitor reaches near the maximum rating voltage thereof, the primary power source is short-circuited, and the charging operation is completed. (f) As the terminal voltage of the relatively large capacitance capacitor decreases near to the minimum operational voltage of the electronic timepiece, the relatively large capacitance capacitor is disconnected from the relatively small capacitance capacitor and only the latter is electrically charged. Thereafter, steps (b) and (c) are repeated. The conventional rechargable electronic timepiece as described above has the following disadvantages. Time intervals for detecting the terminal voltage are the same for the relatively small capacitance capacitor and the relatively large capacitance capacitor. However, there is a tendency to employ capacitors having as small a capacitance as possible in order to shorten the time for initiating operation of the electronic timepiece. Furthermore, recently there has been proposed a primary power source which is capable of rapidly generating electricity, such as a manually operated generator. In this case, if the voltage detecting period is long, the current supply path is not properly switched, and the relatively small capacitance capacitor loses performance, or in the worst case breaks down, due to being charged to a voltage in excess of its maximum rating voltage. Moreover, when a step motor of the electronic timepiece is stopped by an external operation, all the circuits are reset and, in particular, detection of the terminal voltage of the capacitor is not carried out. Therefore, if the charge controlled circuit is stopped when the capacitors are being charged, they become overcharged and may deteriorate or break down. On the other hand, when the charge control circuit is stopped when the capacitors are discharging, operation may not restart even after a reset condition is released. Furthermore, there is no means for warning a user of the electronic timepiece of the necessity of charging in steps (a) and (c). Therefore, it often happens that the electronic timepiece ceases to operate without the user noticing. Moreover, the charge control circuit has a relatively large number of circuit elements since a plurality of voltage levels have to be detected for each capacitor and the same voltage cannot be detected since different voltage driving impedance elements have to be provided for each of the voltages to be detected. Another conventional rechargeable electronic timepiece is disclosed in GB patent publication no. 2158274. This timepiece also involves voltage detection of the charge stored on the capacitor acting as the power source but suffers from the problems enumerated above, in particular that of detecting the voltage quickly enough. According to the present invention there is provided an electronic timepiece comprising: oscillator means for generating a time base signal; frequency dividing means for frequency dividing the time base signal; pulse synthesising circuit means for producing a plurality of control signals in response to a signal from said frequency dividing means; a step motor driving means for generating and controlling driving pulses fora step motor in response to the control signals of said pulse synthesising circuit means; power supply means for generating, storing and supplying electric energy which includes a primary power source for generating electric energy, and a secondary power source for storing said electric energy and comprising a first capacitor having a relatively large capacitance, and a second capacitor having a relatively small capacitance; voltage detecting means for detecting a plurality of voltage levels of said power supply means; and charge control means for controlling storage and supply of electric energy in and from said power supply means in response to the result of detection of said voltage detecting means characterised in that said voltage detecting means comprises a sampling signal selecting circuit for producing sampling signals of different periods depending upon the result of voltage detection, and a plurality of voltage detectors for detecting a plurality of voltage levels of said first capacitor and said second capacitor, respectively. Said sampling signal selecting circuit may be arranged to produce a first sampling signal having a relatively short period when the electronic timepiece is powered by said second capacitor, and produces a second sampling signal having a relatively long period when the electronic timepiece is powered by said first capacitor. Preferably each voltage detector comprises a plurality of switching elements for selecting the voltage to be detected, and a voltage comparator for comparing said selected voltage with a reference voltage. In the preferred embodiment said step motor driving means is arranged to generate driving pulses to effect different manners of movement of a time indicating member in dependence upon the result of voltage detection. Thus said step motor driving means may be arranged to generate a first driving pulse for normal movement of said time indicating member when the electronic timepiece is powered by said first capacitor and to generate a second driving pulse for abnormal movement different from the normal movement of said time indicating member when the electronic timepiece is powered by said second capacitor. Preferably the electronic timepiece is provided with first reset means for resetting, in response to an external operation, said step motor driving means but not said oscillator means and said frequency dividing means and a second reset means for resetting at least said frequency dividing means for a relatively short time after a reset condition of the first reset means has been released. The invention is illustrated, merely by way of example, in the accompanying drawings, in which:- Figure 1 is a block diagram of an electronic timepiece according to the present invention; Figure 2 is a diagram showing the states of a charge control means of the electronic timepiece of Figure 1; Figure 3 is a circuit diagram of a voltage detecting means of the electronic timepiece of Figure 1; Figure 4 is a simple circuit diagram of a sampling signal selecting circuit of the electronic timepiece of Figure 1; Figure 5 is a circuit diagram of first reset means and second reset means of the electronic timepiece of Figure 1; Figure 6 is a timing chart associated with Figure 5; Figure 7 is a circuit diagram of a voltage detector shown in Figure 3; Figure 8 is a timing chart associated with Figure 7; and Figure 9 is a graph showing the relationship between voltage VC1 and movement of time indicating hands in the electronic timepiece according to the present invention. Referring first to Figure 1, there is shown one embodiment of an electronic timepiece according to the present invention. The electronic timepiece has an oscillator 1 which oscillates at, for example, 32768 Hz, a frequency divider 2 which divides the frequency of the output of the oscillator circuit 1, a pulse synthesising circuit 3 which receives suitable signals from the frequency divider 2, a voltage detecting means 4 which receives a sampling signal from the pulse synthesising circuit 3 and which detects the voltage of a plurality of capacitors contained in a power supply means 9. An output of the voltage detecting means 4 is connected to a charge control means 6 and to a step motor driving circuit 5. The charge control means 6 receives the output of the voltage detecting means and controls a switching operation of charge/discharge states of the capacitors. The step motor driving circuit 5 receives an output from the voltage detecting means 4 and an output from the pulse synthesising circuit 3, and sends a driving signal to a step motor 10. The step motor 10 drives a time indicating member 11 such as hours, minutes and seconds hands. A first reset means 8 stops the drive signal from being generated under a reset condition determined by external operation, and a second reset means 7 resets the frequency divider 2 for a short period of time after the reset condition has been released. Figure 2 is a diagram showing the states of the charge control means 6, wherein symbol GEN denotes a generating means such as a solar cell or manually operated generator, C1 denotes an electric double layer capacitor having a relatively large capacitance, for example, 0.33F and C2 denotes a tantalum capacitor having a relatively small capacitance of, for example, 6.8 micro F. Symbols D2 and D3 denote reverse current preventing diodes, and symbol D1 denotes a diode that is contained in the generator means. Symbols S1, S2 and S3 denote switches for changing a loop for electric charge/discharge states. Symbol VC1 denotes a voltage on the capacitor C1, VC2 denotes a voltage on the capacitor C2 and VDD and VSS denote voltages with which the power supply means 9 drives a logic circuit 20 which comprises the circuits of Figure 1. Symbols VSD aid VSB denote anode voltage and cathode voltage respectively of the diode D2. Now, VOP1 is defined as a voltage at which the logic circuit 20 operates, VSTP is defined as a minimum operable voltage of the logic circuit 20, VOP2 is defined as: VSTP < VOP2 < VOP1 and VFUL denotes a maximum rating voltage of the capacitors. In Figure 2, a state (A) shows the state under the condition of VC1 < VOP2 and VC2 < VOP2. In this case, the switches S1, S2 and S3 are all turned off, and electric current generated from the generating means GEN is supplied to the logic circuit 20 through a loop "a". Therefore, the capacitor C2 is electrically charged immediately. In state (A), the voltage VC2 is detected. If VC2 > VOP1, state (A) changes to state (B). In state (B), the switches S1 and S3 are turned off, and the switch S2 is turned on. The generating means GEN and the capacitor C1 are independently connected, and the electric current from the generating means GEN charges the capacitor C1 through a path "b". During this period a voltage VC2 is applied to the logic circuit 20 and a discharge current flows from the capacitor C2 through the path "b". In state (B) the voltage VC2 is detected. If VC2 < VOP2, state (B) returns to state (A). The voltage VC1 is also detected in state (B). If VC1 > VOP1, this state changes to a state (C). As will be explained below in detail, the time indicating hands are moved in the states (A) and (B) in a manner different from normal movement. In state (C) of Figure 2, the switches S1 and S2 are turned on, and the switch S3 is turned off. This is a normally used condition where the capacitors C1 and C2 are connected in parallel with the generating means GEN to supply the logic circuit 20. If VC1 < VSTP, this state returns to state (A). Further, if VC1 > VFUL, this state changes to state (D). In state (D), the switches S1, S2 and S3 are turned on. With the switch S3 turned on, a voltage greater than VFUL is not applied to the capacitor C1 to prevent overcharging. In this case, the voltage of the capacitor C1 is supplied to the logic circuit 20. If the voltage VC1 of the capacitor C1 becomes smaller than VFUL, this state returns to state (C). In states (C) and (D), the time indicating hands are moved normally each second. Figure 3 illustrates the voltage detecting means 4 and the charge control means 6, which enable the charge/discharge states of Figure 2 to be changed. The voltage detecting means 4 consists of a voltage detecting circuit 25 and a control circuit. The charge control means 6 consists of MOS transistors switches S1, S2 and S3. A voltage detecting operation and a switching operation will now be described. A voltage detecting output 27 detects VSTP and VC1. When VC1 < VSTP, the voltage detecting output 27 assumes "L" level, and the output of an inverter 32 assumes "H" level, whereby a latch circuit constituted by NOR gates 33 and 34 is reset, and switches S1 and S2 are turned off in response to the output of inverters 37,38 and inverters 41,42. This operation means that state (C) of Figure 2 is changed to state (A). A voltage detecting output 28 detects VOP2 and VC2. When VC2 < VOP2, the voltage detecting output 27 assumes "L" level, whereby a latch circuit constituted by NOR gates 39 and 40 is reset, and the switch S2 is turned off in response to the output of the inverter 42. This operation means that state (B) of Figure 2 is changed to state (A). In state (C), however, the NOR gate 33 produces an output of "H" level, so the switch S2 is not turned off. A voltage detecting output 29 detects VOP1 and VC2. When VC2 > VOP1, the voltage detecting output 29 assures "H" level, whereby the latch circuit constituted by NOR gates 39 and 40 is set, and the switch S2 is turned on. This operation means that state (A) of Figure 2 is changed to state (B). A voltage detecting output 30 detects VOP1 and VC1. When VC1 > than VOP1, the voltage detecting output 30 assumes "H" level, whereby the latch circuit constituted by NOR gates 33 and 34 is set, and the switch S1 is turned on. This operation means that state (B) shown in Figure 2 is changed to state (C). A voltage detecting output 31 detects VFUL and VC1. When VC1 > VFUL, the voltage detecting output 31 assures "H" level and the output of an inverter 43 assumes "L" level, whereby the switch S3 is turned on. When VC1 < VFUL, on the other hand, the switch S3 is turned off. This operation means that state (C) of Figure 2 is changed to state (D), or vice versa. The voltage detecting circuit 25 comprises five voltage detectors. Sampling signals SP1, SP2, SP3, SP4 and SP5 for these voltage detectors are supplied by the pulse synthesising circuit 3, and a control signal SF selects a frequency of the sampling signals SP2 and SP3 which are used for detecting the voltage VC2 of the capacitor C2. Figure 4 is a simple circuit diagram which shows an example of a sampling signal selecting circuit 12 which is comprised of two AND gates 15,16 which receive the control signal SF and signals of 1Hz and 1KHz sent from the frequency divider 2, and an OR gate 17 which receives outputs of the AND gates 15,16 and which produces the sampling signal SP2 or SP3. Operation of the sampling signal selecting circuit will now be described. First, as electric charge is initiated, the control signal SF assumes "L" level so long as a condition VC2 < VOP1 is maintained. In Figure 4, therefore, the gate 16 is turned on, the gate 15 is turned off, and the sampling signal SP2 or SP3 produced by the sampling signal selecting circuit 12 is such that the signal of 1KHz is selected, and the voltage is detected at a relatively fast period. Then, when VC2 > VOP1 and VC1 > VOP1, the control signal SF assures "H" level. Therefore, the gate 15 is turned on, the gate 16 is turned off, and the sampling signal SP2 or SP3 produced by the sampling signal selecting circuit 12 is such that the signal of 1Hz is selected, and the voltage is detected at a relatively slow period. Namely, in states (A) and (B) (Figure 2) in which capacitor C2 undergoes the charge/discharge operation, i.e. under the condition where VC1 < VOP1, the time interval for detecting the voltage is shortened to detect the voltage in a relatively short time interval. In states (C) and (D) in which the capacitor C1 undergoes the charge/discharge operation, i.e. under the condition of VC1 > VOP1, the same interval for detecting the voltage is increased, such that the voltage is not detected in an unnecessarily short time interval. Figure 5 concretely illustrates the first reset means 8 and the second reset means 7 and Figure 6 is a timing chart illustrating their operation. When the first reset means 8 is reset in response to an external operation, a reset terminal 49 assumes "H" level and data is read through a chattering-preventing circuit which is constituted by flip-flops 53, 54, 55, 56 and 57. As shown in Figure 6, to read the data a minimum time of 7.32 msec and a maximum time of 11.23 msec is required. When the flip-flop 55 produces an output of level "H", the step motor driving circuit 5 is reset to stop the driving signal from being generated. Since the first reset means 8 does not reset the frequency divider 2, the voltage detecting means 4 operates in its ordinary manner. The second reset means 7 produces a one-shot pulse of a width of 0.49 msec after the reset condition is released. As the timing chart of Figure 6 illustrates, the one-shot pulse is produced by a NOR gate 58 after a time of 0.98 msec has elapsed at the longest from release of the reset condition. Using tie one-shot pulse, a frequency dividing stage of the frequency divider 2 subsequent to 512Hz is reset, and the driving signal is produced after about one second has elapsed. In a NAND gate 50, an input RIS is sent from the step motor driving circuit 5, and denotes an inhibition signal for resetting operation when the driving signal is produced. Figure 7 shows a voltage detector for detecting VC2 > VOP1 and VC1 > VOP1 in the voltage detecting circuit 25 in Figure 3. In general, each voltage detector consists of impedance elements which divide the voltage VC1 or VC2 according to each detecting voltage level, and a voltage comparator which compares the divided voltage VDIV with a reference voltage VREF produced by a voltage reference 61. In the case of Figure 7, the voltage VOP1 is compared with voltages VC1 and VC2 so that impedance elements Z1,Z2 and a voltage comparator 60 are used for both voltages VC1 and VC2. Moreover, switching elements TR1 and TR2 which select the voltage VC1 or VC2 to be detected, and AND gates 62,63 which select the output of the voltage comparator 60 are provided. The operation of the voltage comparator of Figure 7 will now be described. The sampling signal SP3 or SP4 produced from the pulse synthesising circuit 3 turns the switching element TR1 or TR2 on, and the terminal voltage VC1 or VC2 to be detected is divided by the impedance elements Z1 and Z2. The resulting divided voltage VDIV is compared by the voltage comparator 60 with the reference voltage VREF, and the compared result is produced as a signal OUT. Upon receipt of the signal OUT, the voltage detecting output 29 or 30 is produced by the AND gate 62 or 63 in accordance with the sampling signal SP3 or SP4. Next, the operation will be described further using the timing chart of Figure 8. The sampling signals SP3 and SP4 are produced maintaining a predetermined period, as required. For instance, these signals are produced as shown in Figure 8. If the sampling signal SP4 assumes "H" level, the switching element TR1 is turned on, and the voltage VC1 to be detected is divided by the impedance elements Z1 and Z2. If the voltage drop through the switching element TR1 is neglected, the divided voltage VDIV is given by, VDIV (SP4) = VC1 x Z1/(Z1 + Z2) Similarly, if the sampling signal SP3 assumes "H" level, the divided voltage VDIV is given by, VDIV(SP3) = VC2 x Z1/(Z1 + Z2) The comparator 60 compares the reference voltage VREF with the divided output VDIV, and produces the result as the signal OUT. Therefore, the condition in which the signal OUT assumes "H" level is given by, VC1 > VREF x (Z1 + Z2)/Z1 VC2 > VREF x (Z1 + Z2)/Z1 Therefore, if the terminal voltages VC1 and VC2 to be detected change as shown in Figure 8, the signal OUT operates in sections T1, T2 and T3 as follows: T1 - The signal OUT does not assume "H" level with sampling signals SP3 or SP4. T2 - The signal OUT does not assume "H" level with the sampling signal SP4 but assumes "H" level with the sampling signal SP3. T3 - The signal OUT assumes "H" level with the sampling signal SP3 and SP4. Figure 9 illustrates the relationship between the voltage VC1 and the movement of the timekeeping hands wherein the charging operation is continued from when the voltage VC1 of the capacitor C1 is zero volts to when it reaches VFUL, and after the moment the charging operation is stopped. The state (A) or state (B) in Figure 2 is established from OV to VOP1; during this period the step motor is driven by the voltage VC2. The seconds hand is moved every two seconds to warn that the electronic timepiece will cease to operate soon if the charging operation is not carried out. As the charging operation is further continued, state (C) is established where the step motor is driven by the voltage VC1, and the seconds hand moves normally every second. As the voltage VC1 reaches VFUL, state (D) is established, and the voltage VC1 is clamped. If the charging operation is stopped at this moment, the voltage VC1 gradually decreases due to discharge of electricity and the seconds hand is moved normally every second until the voltage VC1 falls to VOP2. If the voltage VC1 becomes smaller than VOP2, the seconds hand is moved again every two seconds to warn that the voltage VC1 is low. If the voltage VC1 falls below VSTP, state (A) is resumed. If a charging operation is still not carried out, the electronic timepiece ceases to operate. Although the above embodiment is so designed that the seconds hand is moved every two seconds over a range of the voltage VC1 from OV to VOP1, it is also possible to move the seconds hand in a different manner such as every three seconds to distinguish from the movement of the seconds hand when the voltage VC1 is smaller than VOP2. In an electronic timepiece having only a minutes hand and an hours hand, it is easy to move one of the hands in a manner that the step motor is turned forward and backward every second. In the above described electronic timepiece according to the present invention, the charge control means is provided with a voltage sampling signal selecting circuit, and the period for detecting the voltage on the capacitors is varied depending upon the terminal voltage of the capacitor, so that the relatively small capacitance capacitor is not impressed with a voltage greater than its maximum rating voltage and so that it will not lose performance or break down. Furthermore, providing the first reset means and the second reset means, allows the charge/discharge operation to continue irrespective of the reset condition or non-reset condition, and without requiring any additional element. While the electronic timepiece is powered by the small capacitance capacitor only, the time indicating hands are moved in a manner different from their normal movement thereby indicating that the capacitor is being electrically charged. This helps solve the problem of the electronic timepiece ceasing to operate while the user is unaware of the fact that the capacitor needs to be charged. Thus, the electronic timepiece can be used reliably. Moreover, the voltage detecting circuit employs a reduced number of elements compared to that of conventional electronic timepieces to detect voltage. This allows a decrease in the number of parts of an electronic timepiece or reduction in size of parts, and, hence, a reduction in the size of the electronic timepiece as a whole and a decrease in manufacturing cost.

Claims: An electronic timepiece comprising: oscillator means (1) for generating a time base signal; frequency dividing means (2) for frequency dividing the time base signal; pulse synthesising circuit means (3) for producing a plurality of control signals in response to a signal from said frequency dividing means (2); a step motor driving means (5) for generating and controlling driving pulses for a step motor (10) in response to the control signals of said pulse synthesising circuit means (3); power supply means (9) for generating, storing and supplying electric energy which includes a primary power source for generating electric energy, and a secondary power source (C1,C2) for storing said electric energy and comprising a first capacitor (C1) having a relatively large capacitance, and a second capacitor (C2) having a relatively small capacitance: voltage detecting means (4) for detecting a plurality of voltage levels of said power supply means (9); and charge control means (6) for controlling storage and supply of electric energy in and from said power supply means in response to the result of detection of said voltage detecting means (4) characterised in that said voltage detecting means (4) comprises a sampling signal selecting circuit (12) for producing sampling signals of different periods depending upon the result of voltage detection, and a plurality of voltage detectors (25) for detecting a plurality of voltage levels of said first capacitor (C1) and said second capacitor (C2), respectively. An electronic timepiece as claimed in claim 1 characterised in that said sampling signal selecting circuit (12) is arranged to produce a first sampling signal having a relatively short period when the electronic timepiece is powered by said second capacitor, and produces a second sampling signal having a relatively long period when the electronic timepiece is powered by said first capacitor. An electronic timepiece as claimed in claim 1 or 2 characterised in that each said voltage detector comprises a plurality of switching elements (TR1, TR2) for selecting the voltage to be detected, and a voltage comparator (60) for comparing said selected voltage with a reference voltage (VREF). An electronic timepiece as claimed in any preceding claim characterised in that said step motor driving means (5) is arranged to generate driving pulses to effect different manners of movement of a time indicating member (11) in dependence upon the result of voltage detection. An electronic timepiece as claimed in claim 4 characterised in that said step motor driving means (5) is arranged to generate a first driving pulse for normal movement of said time indicating member (11) when the electronic timepiece is powered by said first capacitor and to generate a second driving pulse for abnormal movement different from the normal movement of said time indicating member (11) when the electronic timepiece is powered by said second capacitor. An electronic timepiece as claimed in any preceding claim characterised by first reset means (8) for resetting, in response to an external operation, said step motor driving means (5) but not said oscillator means (1) and said frequency dividing means (2) and a second reset means (7) for resetting at least said frequency dividing means (2) for a relatively short time after a reset condition of the first reset means has been released.

Inventors: INOUE, YUICHI, MASAKI, HIROYKI, NAKAMURA, CHIAKI, OTAWA, SHUJI
Applicants: SEIKO INSTRUMENTS INC.
Application year: 1987
Main classification: G04C10
IPC codes: G04C10