Abstract:
A quasi-passive wake-up function for an electronic device that employs a continuous low power standby mode compares a received signal to a predetermined signal and wakes up the device when the received signal is the same as the predetermined signal. An electronic device having a quasi-passive wakeup function includes a receiver for receiving at least one stimulus signal, a comparator for comparing the received signal to a predetermined signal, and at least one logic gate for waking up the electronic device when the received stimulus signal is the predetermined signal. In one application, identification tags are used to distinguish a unique tagged item from among a plurality of items with a similar appearance. When an interrogation signal is not present, the tags sleep at a very low power level.

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 10/255,557, filed Sep. 26, 2002, now U.S. Pat. No. 7,109,865, issued Sep. 19, 2006, the entire disclosure of which is herein incorporated by reference. 
    
    
     FIELD OF THE TECHNOLOGY 
     The present invention relates to self-powered electronic devices that have a low power shutdown “standby” mode and, in particular, to minimization of the power consumption of such devices. 
     BACKGROUND 
     Identification systems are used to locate both animate and inanimate objects. For example, identification systems can locate vehicles carrying interstate freight, employees within a hospital, and items in retail establishments to guard against theft. Identification systems may also be used to locate sources of information. However, in some ways, the difficulty of locating unique information has increased with modern advances in information technology and related storage devices. Because many forms of modern information storage media have a nondescript appearance, there is an increased need to locate specific files and data from among many objects that have similar, or even identical, appearances. For example, a collection of compact discs (CDs) that contain stored data (e.g., digital photographs) may be searched in order to locate the specific CD that contains a particular digital photograph being sought. If the contents of each CD are clearly indicated on the CD or the CD storage case, the search will likely be successful, but it will also be tedious because each CD must be inspected until the photograph is found. If the CD contents are not identified, the search will become even more lengthy because each CD must be inserted into a computer where the contents of the CD may be read. Many other forms of information storage media present similar difficulties in locating specific stored information. As a result, the search for the media containing a specific document or file may become painstakingly tedious because the field of search is large. 
     The preceding example is directed to a single type of information storage medium, e.g., CDs. However, because more than one type of information storage medium may be suitable for storing a particular type of data, the search for a unique item from among multiple different types of items (e.g., digital audio tapes, floppy disks, DVDs, and miniDVDs) may be required. This multi-medium search presents many of the previously described challenges, particularly when the searcher is not sure which medium contains the unique item that is sought. 
     These challenges are not limited only to electronic storage media, and information storage media generally. For example, the collection of anonymous boxes and crates found in any warehouse are also difficult to distinguish from one another, and determination of their contents is generally difficult without a close individual investigation. 
     Many of today&#39;s identification systems employ “tags” that may be read by an external (and typically wireless) reader. Generally, identification tags fall into one of two categories: passive and active tags. Passive identification tags are powered by a tag sensing system. For example, the tag circuits of some passive tagging systems are powered via a magnetic, electrostatic or RF field broadcast by a tag reader. Active power tags are those tags that include a power supply. Active tags consume a considerable amount of power in order to receive the tag identification signal, in part because of the linear amplifiers typically required in the receivers of these tags. Because, generally, a battery supplies the power for active tags, these tags have relatively short operational lives before either the battery must be replaced or the tag discarded. 
     One method that may be employed to conserve the operational life of active tags or other self-powered electronic devices is to provide the device with a lower power “standby” or “sleep” mode. The inherent problem with such a solution is devising a way to “wake up” the device when it is needed. Existing devices require that the device periodically wake itself up in order to ascertain whether or not it has been called, a requirement that necessarily requires power every time the device wakes up. For example, in U.S. Pat. No. 5,387,993 (Heller et al), a tag is disclosed with a “sleep mode”. The “sleep mode” of Heller is a shutdown period of a predetermined time, after which the tag reactivates itself to perform various tasks [Heller at col. 3, lines 48-57]. The sleep mode of Heller is therefore very power-costly, with the tag spending a fair amount of time awake and using power on a fixed, predetermined schedule, even when no transmissions are being sent out by the transmitter. What has been needed, therefore, is a wake-up function for electronic devices that keeps the device in a low-power standby mode until, and unless, an interrogation or other summoning signal is detected. 
     SUMMARY 
     The present invention is a quasi-passive wake-up function for electronic devices that have, or can be modified to employ, a low power standby mode. The function of the present invention permits the associated electronic device to be maintained in an extremely low-power shutdown mode until, and unless, a stimulus signal is detected. The function of the present invention is therefore extremely power-conserving, waking only when “called” by a transmitter, rather than reactivating at periodic intervals even when not needed. The present invention may be advantageously employed in self-powered devices and any other device where energy efficiency is desired. 
     In one aspect, the present invention is a method for waking up an electronic device, being maintained in a continuous low power shutdown mode, by comparing a received signal to a predetermined unique stimulus signal and waking up the device when the received signal is the same as the predetermined unique stimulus signal. In one embodiment, the present invention further comprises isolating at least one characteristic of the received signal from background signals, determining whether or not the characteristic of the received signal matches a same characteristic of the predetermined unique stimulus signal, and asserting a logic gate to wake up the electronic device when the received signal is the predetermined signal. In one embodiment, the received signal is filtered to isolate the carrier frequency of the received signal for comparison to the carrier frequency of the predetermined signal. 
     In one aspect, the present invention may be employed in a system that facilitates discrimination among similar items by causing the item itself, or a tag associated therewith, to produce—directly or indirectly—an observable signal. Thus, in response to a signal that encodes the identity of the desired item, that item will effectively announce itself in a manner that facilitates its ready location. In one embodiment, an improved approach to locating items is provided by identification tags that respond to an interrogation signal only when the signal containing that tag&#39;s unique identification is received. That response is an observable signal rather than one detectable only by the tag reader. Particular advantages are achieved when the tag is substantially passive, operating in a very low-power “sleep” mode according to the present invention until the signal uniquely associated with that tag is detected. 
     In a further aspect, an identification tag employing the present invention is associated with a specific object having a generic appearance. The tag includes a receiver for receiving an interrogation signal that includes an object identification, a memory for storing a tag identification that uniquely identifies the tag, and a device for emitting an observable signal in response to the interrogation signal when the object identification matches the tag identification. The tag of this embodiment includes a power source that supplies an operating current for the tag. In a version of any of these embodiments, the tag operates in a very low power sleep mode when not processing the interrogation signal. In a particular, a power source supplies an operating current of less than or equal to 500 nanoamps when the tag is in a sleep mode. In this case, the tag “wakes up” from its very low power sleep mode upon detecting the carrier frequency of the interrogation signal, then responds upon finding a particular modulated transmit code. In still another embodiment, the observable signal is audible. In a further embodiment, the observable signal is visible. 
     In another aspect, the present invention is quasi-passive wakeup device for waking up an electronic device being maintained in a continuous low power shutdown mode, comprising a comparator for comparing a received signal to a predetermined stimulus signal and at least one logic gate for waking up the electronic device when the received signal is the predetermined signal. In one embodiment, the device includes a filter for isolating at least one characteristic of the received signal and the comparator compares the isolated characteristic to a same characteristic of the predetermined signal. In another aspect, the present invention is an electronic device having a quasi-passive wakeup function. In one embodiment, the electronic device includes a receiver for receiving at least one stimulus signal, a comparator for comparing the received stimulus signal to a predetermined stimulus signal, at least one logic gate for waking up the electronic device from low power sleep mode when the received stimulus signal is the predetermined stimulus signal, and electronic circuitry, responsive to the operation of the logic gate, for further operation of the electronic device. The device may further include a self-power source that supplies an operating current for the electronic device, which source may be a battery, solar cell, or any other type of self-power source known in the art. In one aspect, the present invention may be advantageously employed in an electronic device that is operable by a remote control device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other aspects, advantages and novel features of the invention will become more apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings wherein: 
         FIG. 1  is a block diagram of an object-locating system in accordance with one application of the invention; 
         FIG. 2  is a schematic diagram of an identification tag in accordance with one aspect of the invention; 
         FIG. 3  is a graph of a photodetector signal and a comparator output in accordance with another aspect of the invention; and 
         FIG. 4  is a graph of the life of an identification tag power source in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  provides a general overview of an object-locating system whereby a single item can be quickly and precisely located from among a plurality of similar items. A searcher can locate the specific item sought by identifying the source of an observable signal  8  emitted by an identification tag  10 . In one embodiment, the identification tag  10  emits the observable signal  8  when it receives a unique interrogation signal  12 . As is described herein, the search protocol provided by the system allows an area to be rapidly scanned without the need to individually inspect each item. 
     Each identification tag  10  is associated with a unique object. In one embodiment, the identification tag  10  is affixed to or otherwise associated with the object. In another embodiment, the tag  10  is affixed to or otherwise associated with an item in close proximity to the object (e.g., a cartridge, a storage container, a physical location, an article of clothing, etc.). The system also includes a transmitter  14  that transmits the interrogation signal  12  in order to locate the object being sought. The interrogation signal  12  may be any signal such as an RF signal, an optical signal (e.g., a light beam), a microwave signal and the like so long as the signal can provide wireless transmission of an object identification. The object identification is information that uniquely identifies one of the tagged items. 
     In one embodiment, the tag  10  includes a receiver  16 , a signal processor  18 , a microprocessor  20 , a read/write interface  24 , a power supply  26 , and one or more transducers  28 . The receiver  16  may comprise any device such as an antenna, a photodetector, a rectenna and the like provided it is capable of wireless reception of the interrogation signal  12 . The received signal is processed by the signal processor  18 , which may comprise one or more digital and/or analog electronic components. For example, the signal processor  18  may provide filtering and signal conditioning to facilitate comparison of the object identification contained in the interrogation signal  12  with the tag identification contained in a memory of microprocessor  20 . Alternatively, the tag identification may be stored in the media itself. For example, the tag identification may be written onto a protected section of an information storage disk, e.g., a CD. 
     In one version, the tag identification is stored within the tag  10  at the time it is manufactured. In another version, the tag identification is written to the microprocessor  20  at a later point in time, for example, when the system is configured for a specific application. In one embodiment, the tag  10  includes a read/write interface  24  that facilitates the writing of the tag identification to the tag  10  and subsequent alteration thereof. In another embodiment, the read/write interface  24  allows the tag identification to be read by another device. It should be understood, however, the read/write interface  24  is not required (e.g., where the tag identification is provided at the time of manufacture or system initialization). In either case, the tag  10  may include an external surface where the stored tag identification is also reproduced visibly for easy reference. The ability to read and write the tag identification to or from memory located in the tag  10  is particularly advantageous when the tag  10  is associated with an object of electronic storage media. For example, at the time information is stored in a unique media object, the media&#39;s object identification can be automatically associated with the tag  10  via read/write interface  24 , thereby identifying the media item where the information is stored. In one version of this embodiment, the read/write interface  24  facilitates physical connection to, e.g., the serial port of a personal computer. Alternatively, the interface  24  may utilize wireless, non-contact communication. For example, the interface  24  may be an optical signal path or an RF signal path. 
     Regardless of whether a read/write interface  24  is used, each unique object is associated with a unique tag identification. This association creates an object identification that may later be used to identify the object from among a plurality of similar items. Additionally, to facilitate future searches, it is advantageous to record an object-identification/tag-identification association in a manner that allows for its later retrieval. In one embodiment, the association is recorded in a computer database. In a version of this embodiment, the association is automatically recorded when information is stored in an object of electronic storage media. 
     In one embodiment, the tag  10  is also equipped with a power supply  26  that supplies power to the tag&#39;s electronic components. In one embodiment, the power supply  26  is a battery. In a version of this embodiment, the power supply  26  is a lithium coin cell. As described in more detail herein, in one embodiment, the tag  10  operates in a substantially passive mode despite the fact that the tag  10  includes a power supply  26 . In particular, the identification tag  10  operates in a low-power shutdown mode until the interrogation signal  12  is detected. In one embodiment, substantially passive operation is achieved, in part, because the tag  10  does not include a linear amplifier. Instead, the tag includes a filter to isolate the carrier frequency of interrogation, and a very low power comparator to detect the frequency and wake up the tag&#39;s microprocessor  20 . The tag  10  desirably draws less than 500 nanoamps when not processing an interrogation signal  12 . Indeed, the tag  10  may draw less than 300 nanoamps or even less than 100 nanoamps. 
     In one embodiment, the tag  10  is comprised of a single integrated circuit. However, the tag  10  need not be a single unit and it is shown in this manner only for reference. Thus, various of the identified system elements may be moved outside the tag  10  provided that the functional objectives are achieved. For example, the transducers  28  may be located in a storage rack adjacent the tagged item. 
     In one embodiment, the transmitter  14  of  FIG. 1  includes a programming port  30 , a message storage device  32 , a message processor  34 , an interrogation signal source  36 , a message entry device  38 , and a power supply  40 . The message storage device  32  stores one or more object identification messages. Additionally, to ease the retrieval of object identification messages, the message storage device  32  (or an external computer in communication with message storage device  32 ) may also store one or more item/message associations in a database. These associations allow a user to simply select the item to be located, and the database then selects the corresponding object identification message. In one embodiment, the transmitter  14  includes a separate memory for storing these item/message associations. The message storage device  32 , which may be a microcontroller incorporated in a circuit card, supplies the object identification message to the message processor  34 , which embeds this in an output signal in a detectable fashion (e.g., by modulating the signal). For example, the object identification message may be embedded in either an AM or a FM signal. With either signal type, the signal includes a carrier frequency with a signal characteristic altered in a manner that encodes the message in the signal. Additionally, regardless of the modulation scheme employed, the message is encoded such that when interrogation signal  12  is demodulated by tag  10 , the message includes the object identification. In a version of the AM embodiment, the message processor  34  comprises an amplitude-modulating driver, e.g., a MOSFET switch, which acts on the message received from the message storage device  32 . 
     The interrogation signal source  36  receives the signal from the message processor  34  and transmits it in a format that is compatible with the tag&#39;s receiver  16 , e.g., an optical signal or a RF signal. To encode the message, message processor  34  causes the interrogation signal source  36  to alter the output intensity or frequency of the interrogation signal  12 . For example, in the optical embodiment, the intensity of the resulting interrogation signal  12  is altered in response to the modulated signal. In one version of this embodiment, the message processor  34  provides an amplitude-modulated 2 kHz signal that is converted to an optical signal by the interrogation signal source  36 . The interrogation signal source  36  may be a laser diode. In another version, the laser diode is a 5 milliwatt red diode laser similar to laser diodes employed in laser pointers. In still another version of this embodiment, the interrogation signal source  36  is an array of bright LEDs. The interrogation signal source  36  may include a lens, e.g., a defocusing lens. The ability to defocus an optical interrogation signal  12  is advantageous because it improves the system&#39;s safety and broadens the search area. Alternatively, the transmitter  14  may include an adjustable lens capable of being adjusted to change the area that is reached by the interrogation signal  12 . The range of the transmitter  14  is desirably at least three meters. 
     Optical interrogation is advantageous, generally, because it provides visual confirmation of the area that is being searched at any moment. Thus, optical interrogation increases the speed and efficiency of the search. Additionally, optical interrogation is compatible with common experience (e.g., scanning a darkened room with a flashlight) so its operation is natural and familiar. 
     The programming port  30  and the message entry device  38  each provide independent (or alternative) means of entering one or more object identifications into the transmitter  14 . In one version, the programming port  30  is a USB port that facilitates the serial transmission of information from a computer or other electronic storage device to the transmitter  14 . Alternatively, in another version, the programming port  30  is a receiver for receiving object identification information that is transmitted to the transmitter  14  via a wireless LAN (e.g., IEEE standard 802.11). In this way, a database of objects and identifiers associated therewith may be stored on an external computer. When the user selects an item of interest, the database supplies the corresponding identifier to the message entry device  38  via the programming port  30 . The user therefore need not maintain any awareness of object identifiers; he or she simply selects the desired item. (As previously described, the database may alternatively be included in memory located within the tag  10 , and the item selection may be entered directly into the tag  10  via the programming port  30 .) 
     Alternatively, the user may identify the desired item directly, using the message entry device  38 . This may be, for example, a keypad or a writing pad integral to a personal digital assistant in which the transmitter  12  is implemented. In still another version, the message entry device  38  includes one or more switches. 
     The system also achieves an energy efficient interrogation scheme because the transmitter  14  can be configured to consume a minimal amount of power. For example, in one embodiment involving optical signals, the total power drawn by the transmitter  14  is less than or equal to 60 milliamps. As a result, the transmitter  14  can be integrated into wireless handheld devices. In one version of this embodiment, noted above, the wireless handheld device is a personal digital assistant. In another version, the wireless handheld device is a cellular phone. 
     The signal processor  18  of the tag  10  includes a circuit (such as a passive filter) that isolates particular characteristics of the interrogation signal (such as its carrier frequency), as detected at the receiver  16 , from background signals. The signal processor is designed to operate at very low power. When the interrogation signal is detected, a logic gate is asserted, which wakes up the microprocessor  20 . The receiver  16  and signal processor  18  of the tag  10  cooperate to condition the object identification code in the received signal (e.g., by demodulation or discrimination). The microprocessor  20  then compares the stored tag identification with the object identification received with the interrogation signal  12 . Upon detection of a match, the microprocessor  20  causes the transducer  28  to emit the observable signal  8 . The observable signal  8  may be either audible, visible, or both. In one version, the transducer  28  comprises one or more light emitting diodes (“LEDs”). In a further version, the transducer  28  comprises a piezoelectric buzzer. A plurality of transducers  28  may be used to increase the amount of information conveyed by the tag  10  upon interrogation. For example, one observable signal  8  may be emitted when the tag  10  receives an object identification that matches the tag identification and a different observable signal  8  may be emitted when the tag  10  receives an object identification that does not match the tag identification. 
     In an alternate embodiment, the tag  10  may be employed to block an otherwise observable signal from view until the object identification matching the identification contained in the tag  10  is received. Upon receipt of the matching identification, the tag  10  allows the signal to be observed. In this case, the observable signal  8  may be emitted from a source external to the tag  10 . For example, in one embodiment, the tag  10  may include a window that under ambient conditions is opaque, and therefore blocks a light source located behind the tag  10 . However, the window becomes transparent when the object identification associated with the tagged item is received, thereby allowing the observable signal  8  to be seen. In one version of this embodiment, the window is a liquid crystal that can be toggled between an opaque state and a transparent state. This version is advantageous because the power consumption of the tag  10  is reduced as a result of the low power requirements of the liquid crystal. 
     Refer now to  FIG. 2 , which illustrates a suitable circuit for a tag  10  incorporated in an identification system utilizing pulse-coded optical interrogation signals. This approach is advantageous for at least two reasons. First, because the ambient optical environment is relatively free of optical signals with sharp edges, pulse-coded optical transmission achieves a relatively high signal-to-noise ratio. As a result, a linear amplifier is not required in the tag  10  circuitry, and a very low-power comparator  56  can be used to wake up the microprocessor  20  upon detection of these pulses. Second, an optical message provides a visible beam that indicates to the searcher the area that is being scanned with the interrogation signal  12 . 
     The illustrated circuit comprises a microprocessor  20 , transducers  28 , a power supply  26 , a receiver  16 , and signal processing circuitry  18 . In the embodiment shown, the receiver  16  is a photodiode and the power supply  26  is a battery, e.g., a lithium coin cell that produces a nominal operating voltage of three volts DC at a nominal capacity of 48 milliamp-hours. The detection and signal processing circuitry  18  includes a high pass filter capacitor  50  connected between the cathode  52  of the receiver  16  and the inverting input  54  of a comparator  56 . The anode  58  of the receiver  16  is connected to ground  59 , and a load resistor  60  is connected in parallel with the receiver  16 . A 15 kΩ resistor  60  results in a large amplitude for the 2 kHz interrogation signal  12  so that the signal  12  is readily sensed by the comparator  56 . A second resistor  62  is connected between the inverting input  54  of the comparator  56  and ground  59 . Additionally, a third resistor  64  is connected between the inverting input  54  and non-inverting input  66  of the comparator  56 . The non-inverting input  66  is also connected to both the comparator&#39;s  56  reference voltage input  68  and hysteresis input  70 . The positive terminal  72  of the power supply  26  is connected to the positive supply voltage terminal  74  of comparator  56 . Both the comparator&#39;s negative supply voltage terminal  76  and ground terminal  77  are connected to ground  59 . The power supply  26  also provides power to the microprocessor  20  and transducers  28 . A second capacitor  78  is connected in parallel with the power supply  26  to remove electrical noise from the output of power supply  26 . The comparator output  80  is connected to the microprocessor  20 . A crystal  82  is also connected to the microprocessor  20 . The crystal  82  provides a clock signal used for timing. In one embodiment, the microprocessor  20  is clocked at 4 MHz and has a 1 MHz instruction cycle. In the embodiment shown, the transducers  28  are LEDs. The anode  84  of each transducer  28  is connected to the positive terminal  72  of the power supply  26 , and the cathode  86  of each transducer  28  is connected to the microprocessor  20  through separate transducer resistors  88 . 
     In one version of this embodiment, the values of the high pass filter capacitor  50  and the third resistor  64  are used to set the time constant of the input filter, and the values of the second resistor  62  and the third resistor  64  are used to set the triggering threshold on the received interrogation signal  12 . The high pass filter prevents the tag  10  from processing optical signals other than those issuing from the transmitter  14 , keeping the microprocessor, which by far dominates the power consumption of the tag electronics, in a very low-power sleep state until the carrier is detected. Thus, the tag  10  will not falsely detect signals generated by either natural light or artificial light, and will not falsely power the processing electronics under these conditions. In one embodiment, the filter time constant is chosen to be much greater than the total period of the interrogation message in order to pass the bits of the interrogation message intact. 
     In one version of the embodiment shown, the comparator  56  is a nano-power comparator that draws approximately 300 nanoamps when the identification tag  10  is not processing the interrogation signal  12 . In this version, the comparator  56  provides a one volt reference which can source or sink up to one milliamp of current. In another version of this embodiment, the tag&#39;s power consumption is further reduced by utilizing a microprocessor  20  that operates on approximately 2.5 volts, and draws approximately 200 nanoamps when the microprocessor  20  is in sleep mode. In a further embodiment, the total power consumption of the identification tag  10  is less than or equal to 100 nanoamps when the tag  10  is not processing an interrogation signal  12 . 
     As a result of these features, substantially passive operation of the identification tag  10  is achieved.  FIG. 3  demonstrates the extended battery life that results therefrom. In this version, the battery life is approximately ten years—essentially the battery&#39;s shelf life. As can be seen from the graph, this capacity translates into a total battery life of approximately eight years when the identification tag  10  is interrogated twenty-five times a month. Thus, in many applications, the life of the tag  10  is greater than the useful life of the tagged item. 
     Because the photodiode is both insensitive to common dynamic light sources (e.g., fluorescent lights) and unaffected by ambient light levels, the identification tag  10  remains in the sleep mode until the interrogation signal  12  is received. When the comparator  56  receives the filtered output from the receiver  16 , the tag  10  awakens and the microprocessor  20  begins to analyze the interrogation signal  12 . The comparator output  80  supplies the coded message to the microprocessor  20 . The microprocessor  20  hence wakes up when a carrier frequency is detected and begins to decode the message to determine the object identification contained therein.  FIG. 4  depicts an example of a receiver output signal  90  and a comparator output signal  92 . In one version of this embodiment, the microprocessor  20  employs a conventional serial decoding scheme to decode the message. The communication protocol may employ an on-off keying on half of the transmitted waveform. In one version of this embodiment, the microprocessor  20  is programmed to decode an eight-bit 2 kHz signal. 
     The identification tag  10  readily synchronizes to the transmission of a 2 kHz signal. In particular, the decoding program synchronizes with the signal by locating a signal transition from zero to one. Once the microprocessor  20  receives the quantity of bits required for a complete object identification, the microprocessor  20  determines if the decoded object identification matches the stored tag identification. Where the message is received serially, the microprocessor  20  rotates each newly-received bit through its buffer and determines the object identification for each new set of bits. In one version, an asynchronous communication protocol is employed. An eight-bit protocol results in thirty-six independent codes, and of these, thirty-five codes are usable because an all zero code is not detected. Further, in another version of this embodiment, a thirty-two bit protocol is employed to provide approximately 70 million independent codes. This approach may also be scaled-up to employ a sixty-four bit or larger protocol. 
     The system achieves a rapid response time. In one embodiment the microprocessor  20  will wake from the sleep mode approximately 18 milliseconds after receipt of the interrogation signal  12 . Once the microprocessor  20  is fully operational, approximately four milliseconds are required to decode the message, thus bringing the total response time to approximately 22 milliseconds. A rapid response time is also achieved with either thirty-two bit or sixty-four bit protocols because only approximately 0.5 milliseconds of additional processing time is required per bit. These results can be further improved by increasing the data rate of the tag  10 . In one embodiment, the microprocessor  20  responds by flashing a green, low-power LED if the transmitted object identification matches the tag identification, and a red LED if the object identification does not match the tag identification. 
     While a preferred embodiment of the present invention is disclosed, many other implementations will occur to one of ordinary skill in the art and are all within the scope of the invention. Further, while the present invention is described in relation to a particular application, it will be clear to one of ordinary skill in the art that the present invention may be advantageously employed for any number of applications in the electronic arts including, but not limited to any self-powered electronic device including, but not limited to, battery- and solar-powered devices, and any electronic device powered by any means that may be remotely activated including, but not limited to, televisions and other audiovisual devices, audio equipment, and automobile remote starters, alarms, and door locks. Use of the present invention in such devices increases the battery life and/or run-time of self-powered devices and decreases the power consumption of any electronic device that employs a “standby” mode by increasing its energy efficiency. 
     Each of the various embodiments described above may further be combined with other described embodiments in order to provide multiple features. Furthermore, while the foregoing describes a number of separate embodiments of the apparatus and method of the present invention, what has been described herein is merely illustrative of the application of the principles of the present invention. Other arrangements, methods, modifications, and substitutions by one of ordinary skill in the art are therefore also considered to be within the scope of the present invention, which is not to be limited except by the claims that follow.