WRISTWATCH PAGER WITH BATTERY CHARGER
Field of the Invention This invention relates to radio pagers and more particularly to a battery charger for a radio pager.
Description of Prior Art The prior art shows radio pagers that are combined with wristwatches. For example, see U.S. Patent No. 4,713,808 to Gaskill et al. which discloses a wristwatch pager in which the "duty cycle," i.e., the percentage of the total time during which the pager receiver must be turned on, can be reduced to as low as 0.006 percent. This low duty cycle prolongs the life of the battery which powers the pager. While the system shown in the above patent does considerably extend battery life, even a further extension of battery life or a technique for easily recharging the battery in the pager is desireable.
A wide variety of battery charging devices are known. For example, U.S. Patent No. 4,311,952 issued to Mabuchi et al. describes an apparatus for charging a plurality of Ni-Cd batteries simultaneously. Similarly, U.S. Patent No. 4,692,682 discloses a method wherein a Ni-Cd battery may be recharged rapidly. U.S. Patent No. 4,409,536 to Evjen describes a transformer battery charger designed to be mounted directly to a conventional AC wall outlet. Similarly, U.S. Patent No. 4,829,224 to Gandelman et al. discloses a "battery pack" specifically for a cellular telephone that can be connected to either an AC or DC power source. U.S. Patent No. 4,829,226 to Nakamura et al. describes a battery-pack and charger combination that permits charging of different types of batteries.
Many portable devices such as tooth brushes, shavers, flashlights, screw drivers or similar hand tools, have built-in battery charging circuitry. Such devices generally include a transformer-diode bridge combina- tion, some degree of filtering to "smooth out" the resultant DC voltage, and often some regulating circuitry. For example, U.S. Patent No. 4,514,790 to Will discloses a flashlight that for battery-recharging purposes connects directly to an AC wall outlet through a built-in plug. A disadvantage of this type of approach is that the device itself must include all of the battery-charging circuitry, which adds an inconvenient weight.
To avoid excessive weight in battery-powered devices, it is known that one can include in such a device itself the DC connections, which can connect directly to the batteries to be recharged. The AC circuitry, such as a transformer-diode bridge combination and perhaps some filtering and regulating circuitry, can be placed in a separate charger "stand" that will thus provide only a DC charging current, and the device can be inserted into the stand for recharging its batteries when it is not in use.
Other known prior art devices such as a prior art battery powered toothbrush provides a stand which includes a coil which can inductively couple to a specially provided coil in the device, thereby transferring energy to the device which is used to charge the battery in the device.
None of the known devices provide a satisfactory means for charging the battery in a wristwatch pager. In particular, the known devices require substantial circuitry including a coil which is dedicated to the charging circuit. Including this type of device in a wristwatch pager would make the pager too large to conveniently fit on a user's wrist.
Summary of the Invention The present invention provides a method and apparatus for charging the batteries in a wristwatch pager. The present invention is designed to operate with a wristwatch pager that includes an antenna as part of the wristband. The invention includes a "charging stand" onto which the wristwatch pager may be placed to receive the required charging current while still remaining operative. The invention utilizes the pager's antenna to both receive radio signals and to charge the pager's battery. The invention provides battery charging capability while not interfering with the existing higher frequency radio receiving operation. The charging stand allows the pager to remain continually operative.
The invention is described below with reference to the accompanying drawings, which are to be construed as illustrative only and not limiting on the scope of the invention, which is to be construed only from the accompanying claims and equivalents thereof.
Brief Description of the Drawings Fig. 1 is a perspective view of a wristwatch device from the prior art into which the present invention can be incorporated.
Fig. 2 is a diagram of a watch wristband antenna, also from the prior art, and its connection to the circuitry of the watch.
Fig. 3 is a diagram of the preferred embodiment of the present invention in the case of battery-operated devices that include an antenna and a radio-receiving function.
Fig. 4 is a perspective view of a charging stand in ac- cordance with the present invention. Fig. 5A is a perspective view of an alternative embodi- ent of a charging stand according to the present invention.
Fig. 5B is a cross-sectional view of a portion of Fig. 5A taken along the lines 5B that shows an optional concavity that may be included in this charging stand.
Fig. 6 is a perspective view of a device attachable to a flashlight for use with the charging stand of Fig. 6.
Figure 7 is a circuit diagram for a feature that can be added to this invention.
Detailed Description of the Invention It is known that one can transfer electrical power from one device to another by inductive coupling or by electro magnetic radiation. Inductive coupling is usually done at power frequencies (e.g. , 60 Hz) while coupling by electromagnetic radiation is usually done at radio frequencies. Generally inductive coupling is done using a coil and electromagnetic radiation is coupled using an antenna. The present invention combines the functions of and inductive coil and an antenna in a unique manner.
The invention is described herein as applied to a wristwatch pager of the type shown in U.S. Patent No. 4,713,808 to Gaskill et al. The wristwatch pager of Gaskill et al. is shown in Fig. 1. Fig. 1 shows a wristwatch 10 that includes a watch 12 and wristband 14. It should be noted that digital display 16 included in watch 12 has the purpose of displaying the messages received by device 10 when operating as a radio frequency paging receiver. Although time display 18 included in watch 12 is shown as being analog in nature, it could of course be digital as well. The specification of patent 4,713,808 is hereby incorporated herein by reference.
Fig. 2 shows some of the details of construction of wristband 14. As noted in the Gaskill et al. patent, the small size and portable nature of a wristwatch receiver in the form of wristwatch 10 place stringent demands on the receiver's antenna system. As shown in the Gaskill patent, the antenna is placed within wristband 14 it- self.
The reception of an antenna loop contained within wristband 14 is maximized if wristwatch 10 is laid on a table or the like so that the Z axis of coordinate system 20 pointed upward. That fact is significant in the design of a stand onto which wristwatch 10 can be placed for recharging its batteries, while at the same time maintaining operative the receiver circuitry of a pager constructed in the form of wristwatch 10. In the preferred embodiment shown in Fig. 2, loop antenna 22 comprises a strip conductor 24 mounted within the wristband 14 shown externally in Fig 1. In the illustrated embodiment, wristband 14 comprises two sections fastened by a conductive clasp assembly 26. Strip conductor 24 is connected to both elements of clasp assembly 26 so as to form a continuous conductor when the clasp is engaged.
The ends of strip conductor 24 are connected to (e.g. soldered to) wires 42A and 42B which provide differential inputs to the radio receiver in the pager. For the present invention, it is only necessary that the wristband 14 form a loop antenna by appropriate connection to wires 42A and 42B. Pins 32 and sleeve 30 connect the wristband to the case in a conventional manner.
Antenna 22 is shown schematically in Fig. 3, in which nodes 46 and 48 corresponds to the connection of wires 42A and 42B to the radio receiver as previously described. Fig. 3 shows a charging circuit 50, an antenna tuning circuit 52, RF matching circuit 54, and the input of a radio receiver 56.
The charging circuit 50 includes a rechargeable battery 50A, a diode 50B, and a coil 50C. The impedance of coil 50C is chosen so that its impedance is high at RF frequencies and thus at RF frequencies charging circuit 50 acts as an open circuit. However, at low power frequencies (i.e. 60 Hertzs) any energy passes through the coil and it is rectified by diode 50B so that it charges battery 50A. Thus, any low frequency energy that is coupled into antenna 24 is rectified and it is used to charge battery 50A. It is noted that the output Vcc of battery 50A is the source of power for the receiver and for the entire pager and wristwatch.
The antenna tuning circuit 52 includes two conventional varactors 52A and 52B and a control line 52C. This is a prior art antenna tuning circuit. For example see application serial number 07/279,952 file December 5, 1989, the description of which is incorporated herein by reference.
The RF matching circuit 54 includes two capacitors 54A and 54B. The value of these capacitors is chosen so that at radio frequencies they match the input of the radio receiver 56 and at power frequencies they are essentially an open circuit.
The important point to note is that with the circuit of Fig. 3 antenna 22 functions both as a conventional loop antenna and as a charging coil for recharging battery 68. The present invention provides a charging stand 90 upon which wristwatch 10, can be placed for purposes of recharging. Figure 4 shows a charging stand 90 in accordance with the present invention. Stand 90 includes a hollow base 92 through a convenient side or bottom of which is connected power cord 94. Optionally, power cord 94 may include an AC power switch 96 shown in dotted outline. Extending upward from base 92 is a hollow vertical member 98 shaped approximately in the form of a cone that decreases in size in the upward direction, the outer dimension of which is sized to accommodate the inner diameter of wristband 14. To receive recharging of its batteries, a wristwatch 10 is simply dropped over the top of vertical member 98.
To provide the required charging current, power cord 94 extends upward through the inside of vertical member 98 to a height that will approximate that of a wristwatch 10 that has been dropped over the top of vertical member 98, and connects at that height to charging coil 100, which for the purpose of the present invention should have on the order of 100 turns. Charging coil 100 may be mounted within vertical member 98 by any convenient means such as bracket 102. It should be noted that the dimensions of Fig. 4 have been somewhat exaggerated for clarity, and that the distance between charging coil 100 and a watch 10 dropped over the outside of vertical member 98 should be adjusted to provide adequate inductive coupling therebetween, in a manner that will be well known in the art. (The term "adequate inductive coupling" of course means a degree of coupling that will excite sufficient charging current in charging circuit 50 to charge battery 68.)
An alternative charging stand 104 according to the pre- sent invention is shown in Fig. 5. Base 106 likewise has a power cord 108 connected therethrough to its interior. (An optional AC power switch 110 is again shown.) In this case, however, extending above base 106 is a hollow toroidal member 112, within which charging coil 114, of the same nature as charging coil 100 of the embodiment of Fig. 4, is concentrically disposed. Charging of the battery in a watch 10 is accomplished in this case by dropping watch 10 into the cup-like depression 116 located within toroidal member 112. Charging stand 104 may optionally include a microswitch (not shown) that would connect AC power to charging coil 114 upon placing a watch 10 into depression 116.
As shown in Fig. 5B, cup-like depression 116 may op- tionally include a cavity 118 sized to accommodate the outer dimension of a watch case 12, so that when a watch 10 is placed within depression 116, the lateral extension of a watch case 12 (which is typically wider than watch band 14) will not force watch band 14 to lie at an angle relative to the plane of charging coil 114. It will be understood that the lengthwise dimension (not shown) of cavity 118 need only be so long as to accommodate the length of watch case 12.
It should also be noted that the structure of charging stand 104 permits its use with appliances other than the wristwatch type of devices that have been described. To illustrate such a use, Fig. 6 shows a screw-on extension 120 that can be built into the end of a flashlight opposite to the lens and bulb, or into a similar such device such as a power screwdriver. That is, extension 120 essentially comprises a hollow cup-shaped body having a charging coil 122 concentrically disposed therein, and to which the circuitry of Fig. 3 may be connected at nodes 46 and 48 in any convenient manner. (Charging coil 122 thus serves in lieu of antenna 22 of Figs. 2 and 3.) Extension 120 may conveniently include threads 124 for screw-like attachment to a flashlight or similar appliance (not shown) that is suitably threaded for such attachment, or attachment may also be by means of a friction fit. Of course, such larger appliances will be expected to have somewhat different charging re- quirements, so the number of turns in charging coil 122 and the sizes of the circuit components of Fig. 3 would need to be changed accordingly in a manner that will be well known in the art. (The physical size of charging stand 104, however, would likely not need to be changed given that the diameters of many appliances such as flashlights are approximately that of the human wrist and hence of wristband 14 that charging stand 104 has been sized to accommodate.) The batteries of such an appliance can then be charged simply by placing the end thereof to which extension 120 has been attached within depression 116 of charging stand 104.
It is noted that the coil 102 could be wound so that it has a considerable height in the vertical direction. While some flux would be lost with such an embodiment, the invention would still operate and such a coil might be easier to fabricate under some conditions.
An added feature of the invention is shown in Figure 7. Figure 7 shows coil 102 and a second RF coil 102A coaxial therewith. The coil 102A is powered by a a broadband RF amplifier 601. The amplifier 601 receives a signal from an external antenna 602. Antenna 602 could be an external dipole antenna or it could be a connection to a Cable TV system which has FM signals thereon. The object of this embodiment is to provide a means of picking up RF signals with an antenna which supplements the wristband antenna. The wristband antenna would be put over the core 603 which connects coils in charger 990. Thus when the wristwatch pager is put on the charger, it RF receiving capability is enhanced. Having described and illustrated the principles of the invention in terms of specific circuit and charging stand embodiments, it will be obvious to those of ordinary skill in the art that various modifications of those embodiments may be adopted without departing from those principles. Consequently, we claim all such modifications coming within the true spirit and scope of the invention as set forth in the following claims and in the equivalents thereof.