Abstract:
An electronic access control device is disclosed comprising two microprocessors. The first microprocessor receives a wirelessly transmitted that is compared to a stored access code. If those two codes match, the first microprocessor transmits a special communication code to the second microprocessor. The second microprocessor opens the lock if the transmitted communication code matches a stored communication code.

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of co-pending U.S. patent application Ser. No. 10/885,998, filed Jul. 7, 2004, now U.S. Pat. No. 7,482,907 which is a continuation of co-pending U.S. patent application Ser. No. 10/024,945, filed Dec. 19, 2001, now U.S. Pat. No. 6,977,576 which is a continuation of U.S. patent application Ser. No. 08/760,062, filed Dec. 4, 1996, and issued as U.S. Pat. No. 6,359,547, which is a continuation-in-part of U.S. patent application Ser. No. 08/339,555, filed Nov. 15, 1994, and issued as U.S. Pat. No. 5,617,082. 
     This application is also a continuation-in-part of co-pending U.S. patent application Ser. No. 10/329,626, filed Dec. 26, 2002, now U.S. Pat. No. 6,900,720 which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/344,221, filed Dec. 27, 2001. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to access control devices for vending machines, and more particularly to an electronic access control device for a vending machine, or the like, wherein the device is controlled by one or more microprocessors and can be operated by a wireless electronic key. 
     BACKGROUND OF THE INVENTION 
     An electronic access control device, such as an electronic combination lock or an electronic alarm system, allows the user to activate or deactivate the access control without the use of the conventional key and mechanical lock mechanism. With the development of microprocessor integrated circuits, it is becoming common to implement microprocessor-based control circuitry in electronic access control devices. Electronic access control devices are known, for example, from U.S. Pat. No. 5,021,776. In this device, and other common electronic access control devices, a microprocessor is used in combination with a keypad and an electrically programmable read only memory (EPROM). The microprocessor compares the combination entered in the keypad by the operator with the combination stored in the EPROM. If the two combinations match, the microprocessor opens the lock. 
     There are problems associated with previous electronic access control devices. One area of problems concerns the manufacture of the devices, including the difficulty in programming the non-volatile memory, such as the EPROM, for storing the access code and other useful information for the operation of the device. EPROMs, which usually require parallel programming, interrupt the manufacturing process in that they restrict when the manufacturer can program the device. A manufacturer would prefer to program the access code into the EPROM as the last step in the manufacturing process. However, with parallel EPROMs, burning in the code after the device has manufactured is difficult. After the device is soldered together, the manufacturer must contend with integrated circuit pin clips and must worry about interference with other circuitry on the manufactured device. Further, manufacturing, with known electronic access control devices, requires many pin connections which increase manufacturing cost. 
     Related to the problems associated with the pin connections of the microprocessor integrated circuit (IC) is the concern of device reliability and ease of use. When the device contains a significant number of pin connections, the reliability of the device decreases. Further, serial access to the EPROM to determine the electronic access code is easier than parallel access in terms of pin connections. When the user forgets or loses the access code in the EPROM, a locksmith could plug into the device and retrieve the access code serially without breaking into the safe. However, with parallel EPROMs, serial access is not available. 
     One common problem associated with previous electronic locks is their potential vulnerability to tampering. A conventional electronic lock receives an access code via an input device such as a keypad or electronic key reader, verifies the access code, and then energizes a solenoid, relay, motor, or the like to open the lock. This arrangement is vulnerable to tampering because if the control circuit is somehow broken in or removed, one can open the lock by “hot-wiring” the control lines for activating the lock-opening mechanism. 
     Another technically challenging problem is related to the need to provide electrical energy to power the operation of the electronic access control device. For many applications, it is desirable to use a portable or alternative energy source, such as a battery, to power the access control device. A battery, however, has a rather limited amount of electrical energy stored therein. Thus, in many applications it is important to reduce the power consumption of the control circuit and peripheral devices of the access control device to extend the service life of the batteries. 
     For instance, it is typical to use a solenoid-operated lock in an electronic lock. The consumed by the solenoid in opening the lock is quite significant. Thus, the battery can be rapidly drained by the repeated operation of the solenoid. As another example, it is common to include a low-battery detection circuit in an electronic lock to provide a warning signal to the user when the battery voltage falls below a predetermined level. The operation of the low-battery detection circuit, however, also consumes electrical energy and contributes to the draining of the battery. 
     Some electronic locks are provided with electronic keys. When an electronic key is presented to a key reader of an associated electronic lock, it transmits an access code to the electronic lock. By using an electronic key, the user does not have to enter manually the access code by means of a keypad. In certain applications, a remote control unit is used which has a radio transmitter to send the access code to the lock without direct electrical contact with the electronic lock. 
     Although electronic keys are a convenient feature, they have their associated problems. One problem is related to the unauthorized use of the keys. For example, many hotels provide safes equipped with electronic locks in their hotel rooms. Such safes typically allow the hotel guests to set their own access codes. In cases where the hotel guests forget the access codes they set, the hotel management has to send someone with a master key which has a master access code stored therein to open the safes. There is a danger that such a master key may be used for unauthorized opening of other safes in the hotel. 
     Another problem associated with the use of an electronic key or a wireless access code transmitter is that the key or the transmitter may be lost easily, or the user may simply forget to bring the key or transmitter. This problem is especially serious if the electronic access control device does not provide other means, such as a keypad, for entering the access code. 
     Vending machines are widely used in various locations as automated means for selling items such as soft drinks, snacks, etc. Traditional vending machines are equipped with mechanical locks, which can be unlocked with a corresponding mechanical key to open the door of the machine to allow reloading of goods and collection of money. 
     One significant problem with conventional vending machines is the difficulties in managing the distribution and usage of the keys to ensure the security of the locks on the vending machines. The process of collecting money from the vending machines scattered at different places is a very manpower-intensive operation that requires many employees to go into the field with numerous mechanical keys for operating the locks on the vending machines. It requires a considerable amount of attention and efforts to manage and track the distribution of the keys to the field workers to keep the keys secure. 
     Moreover, the mechanical keys and lock cores of vending machines are a point of attack for vandals. The keys can be lost or copied easily, and the stolen or copied keys may then be used by an unauthorized person to access the machines, and it is difficult to discover such misuses and security breaches. Also, a skilled vandal can easily pick or drill-out the lock core tumblers and measure the key cuts of the lock core tumblers to re-produce a like key and compromise the security. In the event a security breach is identified, the mechanical lock cores of the affected vending machines typically have to be manually replaced, which is a time-consuming and very costly process. Furthermore, mechanical keys and locks are devices that cannot be partially limited in operation they operate indefinitely if in use. Also, they do not have the ability to record access operation attempts of their operation. 
     SUMMARY OF THE INVENTION 
     It is a general object of the present invention to develop an electronic access control device which is easier to manufacture and more reliable to operate, and provides improved security to prevent tampering or unauthorized access. 
     It is an object of the present invention to provide an electronic access control device with a non-volatile memory for storing an access code that permits the manufacturer of the device to easily insert the access code into the device and then read out the code for verification. 
     It is an object of the present invention to provide an electronic access control device that provides significantly enhanced security and reduced vulnerability to tampering as compared to previous electronic locks. 
     It is an object of the present invention to develop an electronic access control device which has fewer total components and pin connections for smaller device area and greater reliability. 
     It is another object of the present invention to develop an electronic access control device with a solenoid-operated lock which has reduced power consumption by reducing the power used in operating the solenoid. 
     It is a related object of the present invention to develop an electronic access control device that has an improved low-battery detection circuit which has minimized energy consumption. 
     It is another more specific object of the present invention to provide an electronic access control system with a master key for a plurality of remote electronic locks that effectively prevents the unauthorized use of the master key. 
     The present invention accomplishes these and other objects and overcomes the drawbacks of the prior art. First, there is provided an electronic access control device which reduces the number of pin connections required to manufacture, to read, to program, and to operate the device. The device multiplexes the inputs and outputs of the microprocessor IC so that a single pin can function as an input in one mode and an output in another. The microprocessor determines, based on the mode of operation, whether a pin functions as an input or an output. 
     The electronic access control device of the present invention has a communication port connected to selected pins of the microprocessor IC for accessing the non-volatile memory for storing an access code. Through the communication port, the manufacturer can interact with the microprocessor to store an access code into the non-volatile memory and retrieve the access code for verification. By virtue of the provision of the communication port, the factory-programmed access code can be saved into the non-volatile memory after the control circuitry is completely assembled. 
     In one embodiment, the electronic access control device has a microprocessor IC with a plurality of pins, a keypad for inputting user-entered access codes and a non-volatile memory, such as an EEPROM, external of the microprocessor for storing an access code. At least one of the IC pins is connected to both the keypad and the non-volatile memory for receiving the user-entered code from the keypad and transferring data between the IC and the memory. 
     In accordance with the object of the invention to reduce the vulnerability to tampering, the present invention provides an electronic access control device which has two microprocessors. The first microprocessor is preferably disposed close to the user interface such as a keypad or an electronic key reader. The second microprocessor is preferably disposed close to the lock mechanism and substantially shielded from external access. When the first microprocessor receives a user-entered code, it compares the entered code to a stored access code. If those two codes match, the first microprocessor transmits a special communication code to the second microprocessor. The second IC opens the lock if the transmitted communication code matches a stored communication code. Since the second IC is well protected from external access, the risk of tampering by hard-wiring is significantly reduced. 
     This dual-microprocessor arrangement is advantageously used in a voice activated access control system which has a first microprocessor circuit having speech recognition capability, and a second microprocessor circuit which carries out a commanded operation when receiving a correct communication code from the first microprocessor circuit. The first microprocessor circuit may include a transmitter for wireless transmission of the communication code. 
     The present invention also provides an effective solution to the problem associated with the intensive need for power of the solenoid. In the present invention, the electronic access control device pulses the power to the solenoid so that the overall power consumption in operating the solenoid is lower. Thus, the battery has a longer life and the lock has an increased number of accesses. 
     In accordance with a related aspect of the present invention, the electronic access control device employs a low-battery detection circuit that is turned off and therefore consumes no electrical power when the microprocessor is in the sleep mode. The low-battery detection circuit uses a combination of a voltage divider and a transistor to compare the battery voltage and the regulated voltage for determining whether the battery voltage is low, and uses another transistor in series with the voltage divider to selectively turn the current through the voltage divider on and off. When the current through the voltage divider is off, the low-voltage detection circuit does not consume electrical energy. 
     In the case of an electronic access control system with a master key and a plurality of remote electronic locks, the present invention effectively prevents unauthorized use of the master key. In accordance with the present invention, the master key has a master access code and a number of access stored therein. Each of the remote electronic lock has a key reader to communicating with the master key. When an electronic lock detects in the key a correct master access code and a number of access that is at least one, it opens the associated lock and decrements the number of access in the key by one. 
     In view of the foregoing, the present invention can provide a vending machine with a field-programmable electronic lock. The electronic lock can learn a key code from a corresponding electronic key. Alternatively, the electronic lock can learn that it should be accessed by an electronic switch controlled by a mechanical lock that can be opened with an associated mechanical key. The electronic lock has a learning process activation device that is accessible only when the door of the vending machine is in the open position. Using the learning process activation device, a service person sets the electronic lock in a learning mode, in which the electronic lock receives a key code transmitted from an electronic key, and stores the key code in a non-volatile memory for future access control of the vending machine. In the case where the lock access is to be controlled by the switch-lock combination, during the learning process the electronic lock controller receives an electronic closure signal from the switch. The lock thus learns that it is to open the door of the vending machine in response of the switch signal in lieu of reception of key codes from electronic keys. 
     The key-learning process in accordance with the invention allows electronic locks in vending machines to be easily and inexpensively programmed in the field. Thus, the electronic locks do not have to be manufactured with pre-defined permanent key codes and are not tied to any specific electronic keys for field use. There is no need to replace any physical part of the electronic lock in this key-learning process to learn a new key code and/or replacing an old key code. In contrast, mechanical locks conventionally used on vending machines have lock cores that have to be manufactured for specific keys, and once manufactured the lock cores cannot be changed. If the mechanical key is lost, the entire lock cores have to be replaced. More than one electronic key can possess a given keycode. The electronic lock on a vending machine can allow more than one keycode to be learned into the lock and used to access the lock. 
     The use of the field-programmable electronic locks for vending machines provides an effective way to reduce theft and fraud in terms of unauthorized access to the machines. The electronic keys provide a greater level of key security compared to mechanical keys, as they cannot be copied as easily as conventional mechanical keys. The use of non-contact wireless data communication between the key and the lock prevents breeches of security associated with vandals measuring key cuts, copying keys and picking locks. The use of data encryption in the wireless communications between the key and the lock prevents the key code from being copied by electronic monitoring and eavesdropping. The data transmission between the key and lock may be implemented in the infrared range to provide close-proximity highly directional communication of secure codes to further prevent eavesdropping of the security codes and to prevent accidental unlocking of locks. 
     The use of programmable electronic locks on vending machines and the associated electronic keys also provides advantages in terms of significant reduction in the costs associated with managing the distribution of the keys for unlocking the machines and the monitoring of the usage of the keys. Key IDs in addition to the key codes used in accessing the lock may be used to distinguish keys having the same key codes. Customized access limitations may be programmed by a supervisor into the electronic keys to restrict when and how they can be used to access the vending machines. Each key may also be programmed with a specific list of lock IDs identifying the electronic locks on vending machines that the key is allowed to unlock. 
     In accordance with one aspect of the invention, a history of access attempts may be stored in each of the electronic key and the electronic lock for audit purposes. The key may store the access history each time it is used to access an electronic lock on a vending machine. Likewise, each electronic lock on a vending machine may store audit data regarding the access attempts directed to it. The audit data may be transferred from the electronic lock to the electronic key during an unlocking operation, and the audit data of different vending machines collected by an electronic key can be later downloaded to a computer for analysis. 
     In accordance with another aspect of the invention, the electronic lock may accept more than one type of keys and corresponding key codes. The different key types may be associated with different levels of security of the unlocking operations and the type of data transmitted between the key and lock during the unlocking operations. 
     In accordance with another aspect of the invention, the electronic lock in a vending machine can work in conjunction with an electronic communication device in the vending machine that is in wireless communication with a home base to accomplish many of the same access control, auditing, and additionally some inventory and money settlement processes. 
     These and other features and advantages of the invention will be more readily apparent upon reading the following description of the preferred embodiment of the invention and upon reference to the accompanying drawings wherein: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing an electronic access control device having a keypad; 
         FIG. 2  is a block diagram of the electronic access control device of  FIG. 1 ; 
         FIG. 3  is the schematic of the electronic access control device; 
         FIG. 4  is the flow chart at power-up of the device; 
         FIG. 5  is the flow chart of the device in normal operation; 
         FIG. 6  is a block diagram of a remote access control device; 
         FIG. 7  is a schematic of the input electronics of the remote access control device of  FIG. 6 ; 
         FIG. 8  is a schematic of another embodiment of the electronic control access device which has a non-volatile memory sharing certain pins of a microprocessor with a keypad; 
         FIG. 9  is a functional block diagram showing an embodiment of an electronic access control device having two microprocessors communicating with each other to provide enhanced security of the device; 
         FIGS. 10A and 10B  are schematic views together showing an application of the dual-microprocessor configuration of  FIG. 9  in an electronic combination lock; 
         FIG. 11  is a functional block diagram showing an application of the dual-microprocessor configuration of  FIG. 9  in an ignition control system for a motorcycle; 
         FIG. 12  is a functional block diagram showing an application of the dual-microprocessor configuration of  FIG. 9  in a voice controlled access control device; 
         FIG. 13  is a functional block diagram showing another embodiment of the voice controlled access control device; 
         FIG. 14  is a functional block diagram showing another embodiment of the voice controlled access control device which has a central control station and remote devices; 
         FIG. 15  is a schematic view showing an electronic access control system which has a master key for opening a plurality of remote electronic locks; 
         FIG. 16  is a schematic view of an electronic alarm system for a bicycle which has a remote control unit mounted in a riding helmet and an electronic alarm mounted on the bicycle; 
         FIG. 17  is a schematic view of a vending machine and an electronic key for opening an electronic lock inside the vending machine; 
         FIG. 18  is a perspective view of an electronic lock assembly mounted on a door of a vending machine; 
         FIG. 19  is a block diagram showing electronic circuit components of an electronic lock used in a vending machine; 
         FIG. 20  is a block diagram showing electronic circuit components of an electronic key; 
         FIGS. 21A and 21B  are schematic diagrams showing key codes stored in the memories of an electronic key and an electronic lock, respectively; 
         FIG. 22  is a schematic diagram showing the transmission of data between an electronic lock on a vending machine and an electronic key during a simplified unlocking process; 
         FIG. 23  is a schematic diagram showing communications between an electronic lock on a vending machine and an electronic key during an unlocking process that has higher security than the process in  FIG. 22 ; 
         FIG. 24  is a schematic diagram showing communications between an electronic lock on a vending machine and an electronic key during an unlocking process similar to that  FIG. 23  but with a step of checking the lock ID for access control; 
         FIG. 25  is a schematic diagram showing a computer used to program operational limitations into an electronic key; 
         FIG. 26  is a schematic diagram showing the downloading of audit data from vending machines to an electronic key; and 
         FIG. 27  is a schematic diagram showing an example of audit data uploaded from a vending machine to an electronic key. 
         FIG. 28  is a flowchart showing the key code learning process of an embodiment of the electronic lock; 
         FIG. 29  is a flowchart showing an operation by an embodiment of the electronic key to back up the time and date for restoring the clock of the key in case of a faulty or removed battery; 
         FIG. 30  is a flow chart showing an operation by the electronic key to record the number of power-up of the key to prevent tampering by battery removal; 
         FIG. 31  is a schematic block diagram showing an embodiment of a vending machine that has a communication device that is interfaced to the electronic lock and in wireless communications with a home base for access control and auditing purposes; 
         FIG. 32  is a schematic diagram showing vending machines accessible by an electronic key that has a narrow wireless signal transmission pattern to avoid accidental opening of the vending machines; and, 
         FIG. 33  is a functional block diagram showing an embodiment of an electronic access control device having two microprocessors communicating with each other and wherein the device wirelessly communicates with an electronic key. 
     
    
    
     While the invention is susceptible of various modifications and alternative constructions, certain illustrated embodiments hereof have been shown in the drawings and will be described below. It should be understood, however, that there is no intention to limit the invention to the specific forms disclosed, but, on the contrary, the invention is to cover all modifications, alternative constructions and equivalents falling within the spirit and scope of the invention as defined by the appended claims. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, there is shown in  FIG. 1  an illustrative electronic access control device  10  having a keypad  11 , light emitting diodes (LEDs)  12  and  13 , and a mechanical lever arm  14 . In this illustration, the device is used as a lock for an office safe. The device can also be applied to various applications including locks for vending machines or amusement games. 
     The main components of the electronic access code device are shown in  FIG. 2  which include a keypad  11 , a microprocessor  14 , an access code input and output  15 , an acoustic output (a piezo ceramic bender, Model No. KB1-1541) 16, LEDs  12  and  13 , a voltage regulator (LM2936Z-5.0) 17, a battery  18 , an electromechanical driver output  19 , an oscillator  20 , and a reset circuit  21 . Inputs to the device may take the form of a thumbprint scan, a retinal scan, or a magnetic strip input which may work in conjunction with a keypad or as a sole means of input. Outputs may take the form of an alpha-numeric display which may work in conjunction with an acoustic output or an LED or as a sole means of output. 
     The manufacturers which provide microprocessors applicable to the device include: Micro-Chip (PIC 16C54, PIC 16C57, PIC 16C71, PIC 16C76); Motorola (MC68HC705J1, MC68HC705K1, MC69HC705P6, MC68HC705P8, MC68HC705P9); National Semiconductor (COP 820C); SGS-Thomson (ST 6210); Texas Instruments (370C311); Zilog (Z84C01). 
     A more detailed schematic of the device is shown in  FIG. 3 , highlighting the reduced pin configuration and the serial access to the electrically programmable read only memory (EPROM)  22 . Several of the pins on the microprocessor  14  are multiplexed and perform multiple functions, at times used as inputs and at times used as outputs; thereby, the pin configuration is able to use only 9 pins for the keypad input, the acoustic output, and the EPROM  22  reading and writing. For example, the 12 keypad entries are shown in rows and columns. Each keypad entry in a row is connected to the corresponding pin. For example, keypads “3”, “6”, and “9” are connected to pin R 1 . Each keypad entry in the same column is connected to a corresponding pin as well. For example, keys “3”, “0”, “1”, and “2” are all connected to pin C 3 . 
     The multiplexing of the keypad allows for input of twelve different inputs (“0” through “9”, PROG, and CLR) using a four by three configuration, as shown in  FIG. 4  and  FIG. 5 . In particular, there are four rows and three columns in this configuration. In accordance with another embodiment, a keypad with four different inputs allows for as little as a two by two configuration through multiplexing the inputs. 
     The following example will illustrate the multiplexing with respect to the keypad  11 . Normally, in sleep mode, pins R 1 , R 2 , R 3  and R 4  are waiting for an input. When, for example, the keypad “3” is input, pin R 1 , which keypad “3” is connected to, is triggered signifying to the microprocessor  14  that an interrupt has occurred. The microprocessor  14  then executes an interrupt in the software program and changes one of the four pins (R 1 , R 2 , R 3  and R 4 ) into an output whereby a logic high is sent to the R 1  pin. When a keypad is pressed, it acts as a short circuit; thus, when the microprocessor  14  sends out a logic high, it then senses pins C 1 , C 2  and C 3  to determine exactly which keypad in the row has been pressed. In this case, where keypad “3” is input, C 3  is high. Pressing keypad “3” acts as a short circuit so that when R 1  is sent high, there is a direct electrical connection between pin R 1  and C 3  via keypad “3”. Thus, the microprocessor  14  can determine that keypad “3” was pressed based on R 1  and C 3  both being logic high. 
     Another example of using multiple functions as connected to a single pin is the acoustic output  16 . The acoustic output  16  is connected, via a transistor, to pin C 2 . Pin C 2  is also connected to keypads “CLR”, “4”, “5”, and “6”. When the microprocessor  14  sends an audible signal output, pin C 2  acts as an output. When the microprocessor is sensing the keypad input, C 2  acts as an input. 
     A further example of multiple functions as connected to a single pin is the EPROM  22  sensing function. The EPROM  22 , as shown in  FIG. 3 , is part of the microprocessor  14 . The DATA line (bidirectional in that the line is able to input data to write and output data to read) and CLOCK line of the EPROM  22  are connected to C 1  and C 2 , respectively. Pins C 1  and C 2  are connected to the keypad as well. When the PROGRAM signal is input, C 1  and C 2  function. as inputs when writing to the memory location in the EPROM and function as outputs when reading from the memory location in the EPROM  22 . Through this arrangement, the manufacturer may serially program the device with the access code. The microprocessor  14  uses registers  56  to transmit the incoming serial data into parallel data for the EPROM  22  to input. Further, the end user may read the EPROM  22  access code serially as well. In reading the EPROM  22 , only three pins must be accessed (PROGRAM, DATA, and GROUND). The microprocessor  14  uses registers  56  to transmit the outgoing parallel data from the EPROM  22  to serial form for output. 
     It will be appreciated that by installing a communication port, namely the access code I/O  15 , in the microprocessor-based control circuit, the manufacturer of the device can access the EPROM by interacting with the microprocessor  14  via the communication port. By virtue of this arrangement, the manufacturer can program the access code into the EPROM as the last step in the manufacturing process, i.e., after the control circuit has been fully assembled. Thus, there is no longer the need to use a EPROM that is pre-programmed with access codes, or to attempt to input the access code into the EPROM by means of pin clips or the like during the manufacturing process. This ability to program the EPROM after the completion of the control circuit imparts significant flexibility, efficiency, and reliability to the manufacturing process. 
     The operation of the electronic access code device is shown in flowchart form in  FIG. 4  and  FIG. 5 .  FIG. 4  shows the initialization sequence of the device upon power-up  24 . The microprocessor, which contains an EPROM  22  and a random access memory (RAM)  23 , checks to see if there is an access code stored  25  in the EPROM  22 . The microprocessor  14  performs this operation by checking if a proprietary bit sequence is set, wherein the particular sequence of bits signifies that the EPROM  22  has a stored access code. If the bit sequence is present, the EPROM  22  contains the access code, whereby the microprocessor  14  waits for input from the keypad or waits for an external read signal  26  from the microprocessor  14 . 
     If the bit sequence is not present, the EPROM  22  does not contain the access code in its memory. The microprocessor  14  must then wait for the external program signal  28  which signifies that the access code is being written to the EPROM  22 . The external program signal, as shown in  FIG. 3 , is labeled PROGRAM and is connected to pin  104  and pin IRQ of the microprocessor  14 . In this mode, when the PROGRAM signal is toggled, this signifies that the access code is being burned into the EPROM  22 . The microprocessor  14  then uses the CLOCK and DATA lines to clock in the data thereby reading the access code. Then, the microprocessor  14  stores the access code into memory  30 . The microprocessor  14  subsequently sets the proprietary bit sequence on the EPROM  22  signifying that the EPROM  22  contains the access code. Finally, the microprocessor  14  waits for input from the keypad or waits for an external read signal  26  from the microprocessor  14 . 
     The EPROM  22  can also be used to store features other than the access code. It can be used to determine such things as: (1) the amount of time the solenoid  31  is to be energized upon opening the lock; (2) the number of key presses in the access code; (3) the option of disabling the permanent access code temporarily when a new-access code is stored in RAM  23 ; (4) the device serial number; and (5) the date and time the device was manufactured or put in service. These features allow the manufacturer to deliver to an original equipment manufacturer (OEM) customer a generic electronic lock assembly. The OEM customer may then characterize all the specific lock features at the OEM customer facility. 
     As shown in  FIG. 5 , after the power-up initialization routine, the microprocessor waits for an entry from the keypad  32 . Several functions are available based on the keypad entry. If the program key (PROG key) is first pressed, the operator wishes to input an additional access code  33 . In this mode, the microprocessor  14  inputs the next five numbers from the keypad  34 ,  35 ,  36 ,  37 , and  38 . The comparator  57 , within the microprocessor  14 , compares the two numbers and checks if the input number matches the access code  39  from the EPROM  22  which is stored in RAM  23 . If the two numbers match, this signifies that the operator knows the access code in the EPROM  22  and therefore has clearance to input an additional access code  40 . Thus, the microprocessor accepts the next five numbers from the keypad as the additional access code  41 ,  42 ,  43 ,  44 , and  45 , and stores the new access code  46  in RAM  23 . The operator may then input either the access code from the EPROM  22  or the additional access code to open the lock. The operator may repeat this procedure and place additional access codes into RAM  23 . The additional access codes will be stored in RAM  23  until the power is removed from the microprocessor  14  at which time the RAM  23  memory will be lost. 
     An alternate mode of using the PROG key is to disable the permanent access code in the EPROM  22  temporarily when a new access code is entered into RAM  23 . After the PROG key is hit, the microprocessor  14  inputs the next five numbers  34 ,  35 ,  36 ,  37  and  38 . The comparator  57 , within the microprocessor  14 , compares the input number with the permanent access code  39  from EPROM  22 . If the two numbers match, the microprocessor  14  inputs a second access code  41 ,  42 ,  43 ,  44 ,  45 . In this alternative, when the microprocessor  14  stores in RAM  23  the new access code  46 , it disables access to the permanent access code in RAM  23 . Therefore, until the battery  18  is turned off, the only access code available is the new access code stored in RAM  23 . 
     If an operator enters the PROG key at any time other than at the first keypad entry from sleep mode, the microprocessor will display the error message  47  by sounding the acoustic output  16  through pin C 2  and the LED  13 . 
     If a number from the keypad  11  is first entered while in sleep mode  48 , the microprocessor  14  waits until another four numbers are entered  49 ,  50 ,  51 , and  52 , from the keypad  11 . The microprocessor  14  then compares the number entered from the keypad  11  with the access code  53  stored in RAM  23 . If the numbers match, the microprocessor  14  energizes the solenoid  31  at the output  54 . The microprocessor  14  can also energize a DC motor, an electromechanical relay, or a solid-state relay. If the numbers do not match, the error message is sent  47  by sounding the acoustic output at pin C 2 . 
     If the clear key on the keypad is entered at any time in the operation of the device, the microprocessor  14  waits 5 seconds before going back into sleep mode and waiting for the next keypad entry. 
     One feature of the device is a lockout of keypad operations. If the microprocessor  14  receives three consecutive operations which generate error messages  47 , the microprocessor  14  will disable operation of the device for two minutes. Any attempt to operate the device in the two minute lockout period will generate an error message  47 . 
     An additional feature of the system is a requirement that a digit must be entered within a specified time. Otherwise, the microprocessor  14  will send an error message  47  if there is a five second lapse between keypad entries. 
     A further feature of the system is the modulated voltage across the solenoid  31 . When the correct access code is input  53  from the keypad  11 , the microprocessor  14  energizes the solenoid  31 . The microprocessor  14  must supply sufficient power to the solenoid to unlock the lock (i.e., the solenoid must push the plunger in against the coil to open the lock). This involves two different operations. First, the solenoid  31  must physically push the plunger against the coil. Second, the solenoid  31  must keep the plunger pushed against the coil for the specified time in which to keep the lock unlocked. 
     The first operation (pushing the plunger) is very energy intensive. The solenoid  31  must exert kinetic and potential energy to physically move the plunger against the coil. The second operation (maintaining the position of the plunger) is less energy intensive. The solenoid  31  must exert only potential energy in terms of keeping the plunger compressed against the coil. The device, in order to unlock the lock, supplies the entire battery power necessary for the solenoid  31  to pull the plunger in against the coil. The microprocessor  14  accesses the timer  55 , within the microprocessor  14 , whereby the timer indicates when to reduce the power. Once the plunger is pulled in, the microprocessor  14  modulates the voltage to the solenoid  31 . This reduces the current into the solenoid while the solenoid plunger is held in since the entire DC current is not required to keep the plunger in the closed position relative to the coil. This in turn reduces the total amp-hours of current out of the battery during an access cycle, and the total number of accesses to the device increases. 
     By way of example, the solenoid  31  requires 300 milliamps of current to pull the plunger in. The microprocessor  14  accesses the timer  55 , waiting 0.5 seconds to do that operation. The microprocessor  14  then drops the solenoid current to 150 milliamps. This current is sufficient for the solenoid  31  to keep the plunger flush against the coil. The microprocessor  14  accesses the timer  55  again, waiting for the timer  55  to indicate that three seconds have passed, supplying the lower current to allow the user to open the door. In this manner, the microprocessor  14  uses approximately ½ as much power in the modulated mode. 
       FIG. 6  highlights another aspect of the invention, the remote operation of the electronic access code device using a battery. The device can be integrated with other electronic devices forming a system of electronic locks. At the center of the system is a central control station whereby each of the devices may be accessed. 
     The accessed device is designed for low power consumption so that it may operate on a battery for an extended period of time. The remote access device is normally in a sleep mode. In other words, the device is not in active operation. The remote device can “wake-up” from the low power sleep mode in a variety of ways. One method is for the circuitry in the sleep mode device to sense the incoming signal. When the signal is sent, the remote device resumes normal operation. Another method is for the circuitry in the sleep mode device periodically to resume normal operation and sense if there is an incoming signal. If the incoming signal is sent, the circuitry is able to receive the bitstream data that contains the access code. The circuitry thus remains in a low-power sleep-mode condition for the majority of the time, dissipating low power, while no signal is received. The device may then be powered by a battery. 
     The remote electronic access code device is divided into two parts: the input electronics  60  and the processing electronics  64 . The processing electronics  64  contains a microprocessor, an access code input and output, an acoustic output, light emitting diodes (LED), a voltage regulator, and an electromechanical driver output. Thus, the remote device is similar to the microprocessor in processing the input access code, as shown in  FIG. 1 , except the access code may be input in several ways. In this embodiment, the data stream is input serially into the microprocessor  14  so that a variety of serial inputs may be connected to the input of the microprocessor  14 . For example, the access code may be input using a traditional keypad  11  transmitting data in serial mode. Moreover, the data may be input serially using an electromagnetic signal input from the radio frequency (RF), optical frequency or infrared frequency bands. Thus, the microprocessor  14 , in this configuration, may accept the input from any one of this inputs. 
     The input electronics  60  accepts the code sent from the central control. The method of transmitting the code may take several forms including an electromagnetic signal (such as a RF signal sent by an RF serial bitstream transmitter, or an infrared signal) or a data line (telephone line). 
     When an RF signal is used, the central station transmits a signal via a transmit antenna  63  (transducer that sends radiated electromagnetic fields into space). The radiated waves containing the RF signal contains the bitstream access code which is sent to the input electronics  60 . The input electronics  60  contains the RF wake-up  61  and the RF decode circuitry  62 . In one embodiment, the RF wake-up circuit  61  is ordinarily in a low power sleep-mode. However, for a 10 millisecond period every 1 second, the RF wake-up circuit  61  senses for an RF bitstream signal. If an RF bitstream signal exists, it remains awake and receives the entire RF bitstream signal. The RF wake-up circuit  61  then sends a wake-up enable signal to the RF decode circuit  62 . The RF decode circuit  62 , via the antenna  63 , translates it into a series of bits and then sends the digital bitstream signal to the processing electronics  65  to determine if the digital bitstream signal contains the access code. 
     In another embodiment, the RF wake-up circuit  61  remains in low power sleep mode until it senses the RF signal. The RF signal, in this embodiment, contains a low carrier frequency way and a high frequency RF bitstream superimposed on the low frequency carrier wave. When the RF wake-up circuit  61  senses, via the antenna  66 , that there is a signal tuned to the low frequency carrier Wave, the RF wake-up circuit  61  sends a wake-up enable signal to the RF decode circuit  62 . The RF decode circuit  62  then accepts the RF bitstream access code signal, and translates it into a series of bits for the microprocessor  14 . 
       FIG. 7  shows the schematic of the input electronics  60  wherein the RF wake-up circuit  61  periodically wakes up from a low power sleep mode and senses if there is an incoming RF signal. The RF wake-up circuit  61  consists of two low-power CMOS inverter gates, INV 1  and INV 2 , a CMOS transistor Q 3 , resistors, and a capacitor. The two inverters INV 1  and INV 2  are configured in an oscillator configuration in a ratio of 1 to 100. In other words, the oscillator will switch on for 1/100 of a second. At this time, the CMOS transistor Q 3  will turn on and supply the battery power to the RF decode circuitry  62 . The RF decode circuitry  62  will only draw battery power for 1/100 of the time, and thus the battery will last 100 times longer than if the battery were permanently connected to the RF decode circuitry  62 . 
     The RF decode circuitry  62  consists of two bipolar junction transistors Q 1 , Q 2 , two Operational Amplifiers, OP 1  and OP 2 , and resistors, capacitors, inductors and diodes connected to these components. The RF input signal is referred to as an on-off keying of high frequency bursts for set time frames. In the present invention, the frequency is set at 320 MHz. A burst of frequency is detected by the Q 1  and Q 2  transistors with their circuits tuned to the correct frequency (320 MHz in this example). The RF decode circuitry  62  then senses the data bitstream sent in the form of digital 1 data signal and digital 0 dead band of no frequency. Thus, a train of on and off frequency pulses would be received by the antenna, conditioned and amplified by Q 1  and Q 2  of the RF decode circuitry  62 , and converted to bitstream 1 and 0 digital signals by the two operational amplifier signal conditioners OP 1  and OP 2 . 
     Typically, the operator of the control unit  59  which contains the RF transmitter will enable the RF transmitter with a transmit button  58  to send an RF on-off keying pulse for approximately one second. The RF signal being transmitted is a digital bitstream conditioned to an RF on-off keying signal which takes about two milliseconds in which to transmit one complete signal. The control unit  59  then repeats the signal over and over for the duration that the RF transmitter is enabled. In order for the receiver to detect one complete bitstream from the transmitter, the RF signal only needs to be sampled for two milliseconds during which the transmitter is enabled and transmitting. If the RF transmitter is enabled for one second, the transmitted bitstream signal takes 1/500 of a second to be transmitted and is repeated 500 times over the entire one second. The receiver is enabled for 1/100 of a second every second, and will have the opportunity to sample and detect a signal that is 1/500 of a second in duration, transmitted 500 times over one second. After the 1/100 of a second, the oscillator, formed by INV 1  and INV 2 , will switch Q 3  off, and the battery power to the RF decode circuitry will be shut off. Only the oscillator circuit (INV 1  and INV 2 ) will dissipate battery power at a small rate of less than 100 micro-amps. 
     If less power dissipation by the RF decode circuitry  62  is required, the decode circuitry power duty cycle can be reduced by increasing the oscillator frequency to more than 100 to 1 and thus decreasing the RF decode circuitry  62  sample rate. In order to ensure the RF decode circuitry  62  will be enabled long enough to detect the entire transmitter digital bitstream, the lock CPU would wait for the beginning of the bitstream signal which is received by the RF decode circuitry  62  when the circuitry was enabled and conditioned through OP  1 , and then would send an output enable signal back to Q 3  to override the oscillator and keep the RF decode circuitry  62  enabled with battery power until the lock. CPU has received the correct amount of bitstream data from the transmitter through the decode circuitry. Thereafter, the lock CPU would disable the Q 3  transistor and the RF decode circuitry and let the oscillator go back to its low rate of sampling. 
     The processing electronics  64  remains in sleep-mode low current operation until a valid on-off keying frequency signal is received while the RF decode circuitry is enabled and a digital bitstream signal is sent to the lock microprocessor  65 . Upon transferring the bitstream signal, the microprocessor  14 , within the processing electronics, compares the input code with the access code in the comparator. If correct, the solenoid, DC motor, electromechanical relay, or solid-state relay is activated. After this operation, the microprocessor  14  sends a disable signal to the RF wake-up circuit to assume a low power mode. 
       FIG. 8  shows the schematic of another embodiment of the electronic access control device which also multiplexes the inputs and outputs of the pins of the microprocessor to reduce the number of pins required. The microprocessor  81  used in this embodiment is preferably the MC68HRC705J1A integrated circuit (IC) manufactured by Motorola. As illustrated in  FIG. 8 , the input devices include a keypad  11  and an electronic key reader  82 . 
     In this embodiment, instead of using an EPROM internal of the microprocessor as in the case of the embodiment of  FIG. 3 , an EEPROM  84  external of the microprocessor  81  is used to store the programmed access code as well as other useful information. The EEPROM  84  used in this embodiment is preferably the 93LC46 IC manufactured by Microchip. Alternatively, a FLASH read-write memory, or any other type of suitable memory, may be used. To effectively use the limited number of pins of the microprocessor  81 , the pins are multiplexed such that the keypad  11  and the EEPROM  84  share several communication pins. As illustrated in  FIG. 8 , pins  16  (PA 2 ),  17 (PA 1 ),  18  (PA 0 ) of the microprocessor  81  are connected to pins  4 ,  3 , and  2  of the EEPROM  84 , respectively. These pins of the microprocessor  81  are also connected to the keypad  11  for receiving access codes entered by means of the keypad. Pin  3  (PB 5 ) of the microprocessor  81  is connected to pin  1  of the EEPROM. In this configuration, pins  1 - 4  of the EEPROM  84  are used, respectively, for chip select, data in, data out, and clock. 
     In accordance with an aspect of the present invention, the microprocessor-based control circuit further includes a low-battery detection circuit  68  that does not consume electrical power except when a low-battery detection is in progress. As illustrated in  FIG. 8 , the access control device is powered by a battery pack  70  which includes one or more batteries. The output of battery pack is connected to a voltage regulator  72  which provides a regulated voltage for operating the control circuit. The low-voltage detection circuit  68  includes a voltage divider  74  which has its input end connected to the output of the battery pack  70  (which in the illustrated case is after an isolating diode  71 ). The voltage divider  74  is connected in series with a transistor  76  to ground. The base of the transistor  76  is connected (via a resister  77 ) to pin  6  (PB 2 ) of the microprocessor  81 . When Pin  6  of the microprocessor  81  is set high, the transistor  76  is turned on, thereby allowing current to flow through the voltage divider  74 . When pin  6  is set low, the transistor  76  is turned off, and the current through the voltage divider is cut off. In that case, the output voltage of the voltage divider  74  will be pulled up to that of the battery voltage minus the voltage drop across the diode  71 . 
     The output end of voltage divider  74  is connected to the base of a second transistor  80 . The input end of the transistor  80  is connected to the output of the voltage regulator  72 , while the output end of the transistor  80  is connected to pin  15  (PA 3 ) of the microprocessor  81 . Normally pin  6  of the microprocessor would stay low, and both the transistor  76  and the transistor  80  would be turned off. When a battery voltage test is performed, pin  6  is switched to the high (“1”) state to turn on the transistor  76 , and the state of pin  15  is sensed by the microprocessor  81  to determine the on/off state of the transistor  80 . If the battery voltage is sufficiently high, the output of the voltage divider  74  would be high enough to turn the transistor  80  off. On the other hand, if the battery voltage is low, the output of the voltage divider would be low enough to turn the transistor  80  on, and pin  15  would be switched to the high state. 
     In accordance with an important aspect of the present invention, there is provided an electronic access control device that provides substantially enhanced security and reduced vulnerability to tampering by using two microprocessors.  FIG. 9  shows generally the functional block diagram of such a device. As illustrated in  FIG. 9 , the control device has a first microprocessor  90  and a second microprocessor  92 . The first microprocessor  90  is connected to an input device  94  for receiving a user-entered control signal signifying a demand to operate an electronic device  98 . The second microprocessor  92  controls a driver circuit  96  for energizing the electrical device  98  to effect a desired operation. The electrical device  98  may be, for example, a solenoid, motor, relay, or the like for opening a lock, or, as will be described in greater detail below, the ignition relay of a motorcycle. The first microprocessor  90  may be positioned close to the input device  94 , while the second microprocessor  92  may be located close to the electrical device  98  and is preferably well shielded from external access. The two microprocessors are connected by a two-way communication link  100 . 
     As will be described in greater detail below, the user-entered control signal may be, for example, an access code entered using a keypad or electronic key, the operation of an electronic ignition switch controlled by a mechanical lock, or a voice command entered through a voice sensor such as a microphone. Once a user-entered control signal is received, the first microprocessor  90  determines whether the demand to operate the electrical device  98  should be transmitted to the second microprocessor  92 . If the demand is to be transmitted, the first microprocessor  90  sends a special communication code to the second microprocessor  92  via the communication link  100 . The second microprocessor  92  compares the transmitted communication code with a preset communication code stored in a non-volatile memory  102 . If the transmitted code matches the stored code, the second microprocessor  92  activates the driver circuit  96  to energize the electrical device  98 . 
     It will be appreciated that this dual-microprocessor configuration significantly reduces the vulnerability of the device to tampering. Even if a tamperer may gain access to the first microprocessor, it is intended that the second microprocessor is well shielded and therefore cannot be reached easily. Since the second microprocessor responses only to a correct communication code, the tamperer will not be able to use the trick of “hot-wiring” to activate the driver circuit  96 . 
     Moreover, even if the circuit containing the first microprocessor is somehow replaced by another similar microprocessor circuit for which the correct control signal is already known, that new microprocessor is unlikely to know the communication code specific to the second microprocessor  92 . In this way, the two microprocessors function as two individual gate keepers. Even if the first microprocessor could be somehow bypassed, the second microprocessor would not activate the driver circuit without receiving the correct communication code. 
     The microprocessors can also be programmed to implement the “code-hopping” or “rolling-code” scheme used in some existing electronic access control devices to further improve the security of the device. In such a scheme, the preset code stored in the non-volatile memory  102  is used as a seed, and the communication codes stored in the first and second microprocessors are changed as a function of the number of code transmission according to a predefined algorithm based on the seed code. The changes of the communication codes in the two microprocessors are synchronized so that the they remain in operative relationship. 
       FIGS. 10A and 10B  illustrate an application of the dual-microprocessor configuration in an electronic lock. In this embodiment, the control circuit has two halves connected by a cable. The first half, which is shown in  FIG. 10A , contains a first microprocessor  110 . The second half, shown in  FIG. 10B , contains a second microprocessor  112 . Pin  11  (PA 7 ) of the first microprocessor  110  is connected to pin  18  (PA 0 ) of the second microprocessor  112  via the cable  115  and the mating connectors  114  and  116  to establish a two-way serial communication channel between the two microprocessors. 
     The electronic lock has a keypad  11  and an electronic key reader  82  as input devices which are connected to the first microprocessor  110 . The second microprocessor  112  controls a energizing circuit  118  for energizing a solenoid  120  to open the lock. When the first microprocessor  110  receives an access code via either the keypad  11  or the key reader  82 , it compares the entered access code with an access code stored in its memory. If the entered code matches the stored access code, the first microprocessor  110  transmits a communication code to the second microprocessor  112  via the communication channel described above. The second microprocessor  112  then compares the received communication code with a preset communication code stored in an EEPROM  122 . If the two communication codes match, the second microprocessor  112  activates the energizing circuit  118  to energize the solenoid  120  to open the lock. 
     The correct access code and communication code are preferably stored in the EEPROM  122 . During initial power-up, i.e., when the battery is first attached to the electronic lock, the second microprocessor  112  transmits the access code and the communication code to the first microprocessor  110 , which then stores the codes in its memory (which may be volatile) for subsequent operation. 
     The dual-microprocessor configuration illustrated in  FIG. 9  can also be advantageously used in other types of applications. For example,  FIG. 11  shows an electronic ignition control system for a motorcycle. In this embodiment, the device contains a first microprocessor  126  and a second microprocessor  128  which are connected by a cable  130 . A three-position ignition switch  132  is connected to the first microprocessor  126 , which may be located close to the ignition switch. The second microprocessor  128  is connected to an ignition relay  134  and an accessory relay  138 , and is preferably disposed close to the ignition mechanism of the motorcycle and well protected from external access. 
     In this arrangement, the ignition switch  132  serves as the input device, and the position of the ignition switch is used as the user-entered control signal. The first microprocessor  126  monitors the switch position. When the ignition switch  132  is turned to the “accessory” position  135 , the first microprocessor  126  transmits a communication code together with a switch-position code corresponding to that switch position to the second microprocessor  128 . The second microprocessor  128  compares the transmitted communication code with a preset communication code stored in a non-volatile memory  138  which has been programmed at the factory. If the two codes match, the second microprocessor  128  determines from the switch-position code that the switch is set at the accessory position and closes the accessory relay  136 . 
     Similarly, when the ignition switch  132  is turned to the “ignition” position  133 , the first microprocessor  126  transmits a communication code and a switch-position code corresponding to the ignition position to the second microprocessor  128 . The second microprocessor  128  compares the transmitted communication code with the preset communication code. If the two codes match, the second microprocessor  128  determines from the switch-position code that the switch is set at the ignition position and accordingly closes the ignition relay  134  and the accessory relay  136  to start the engine. 
     It will be appreciated that due to this dual-microprocessor arrangement, this ignition control system cannot be “hot-wired” to start the engine of the motorcycle like conventional motorcycle ignition control systems. This system is also not susceptible to tampering by replacing the assembly of the ignition switch  132  and the first microprocessor  126  with another such assembly for which an ignition key has been obtained. 
       FIGS. 12-14  show another advantageous application of the dual-microprocessor configuration of  FIG. 9  which utilizes speech recognition to control the operation of an electronic access control device. As illustrated in  FIG. 12 , the access control device uses a speech recognition microcomputer integrated circuit (IC)  1200  to process voice commands given by a user. The speech recognition IC  1200  is capable of not only recognizing the commands given but also the voice of the speaker. In other words, the IC is capable of speaker dependent recognition, allowing the user to customize the words to be recognized. Such an IC may be, for example, the RSC-164 microcomputer of Sentry Circuits, Inc. 
     In the embodiment shown in  FIG. 12 , the speech recognition IC  1200  has a microphone  1202  connected thereto for receiving voice commands from a user. In this embodiment, the combination of the voice recognition IC  1200  and the microphone  1202  serves generally the function of the input device  94  of  FIG. 9 . An optional keypad  11  may also be used for entering an access code. After receiving a voice command, the speech recognition IC  1200  analyzes the voice command to recognize the command and the voice pattern of the speaker. If the voice recognition IC  1200  recognizes the voice pattern to be that of an authorized user, it transmits a command code corresponding to the command received to the first microprocessor  190 . The first microprocessor  190  transmits an operation code corresponding to the command and a communication code stored in its memory to the second microprocessor  192  via a bidirectional communication link  180 . The second microprocessor  192  compares the transmitted communication code with a preset communication code which is stored in a non-volatile memory  194 . If the two communication codes match, the second microprocessor  192  activates the driver circuit  196  to energize an electrical device  198  to carry out the operation specified by the operation code. 
       FIG. 13  shows another embodiment of the voice controlled access control device. In this embodiment, the voice recognition IC  1200 , which is a microcomputer in itself, is used to serve the function of the first microprocessor  190  of  FIG. 12 . Upon receiving a voice command through the microphone  1202 , the voice recognition IC  1200  recognizes the command and analyzes the voice pattern of the speaker. If the voice recognition IC  1200  determines that the speaker is an authorized user, it transmits an operation code and a communication code stored in its memory  1201  to the second microprocessor  192 . If the transmitted communication code matches a preset communication code, the second microprocessor  192  executes the command by activating the driver circuit  196 . 
       FIG. 14  shows another embodiment of the voice operated access control device which includes a central control station  1220  and one or more remote devices in the arrangement shown generally in  FIG. 6 . The central control station  1220  may be formed as a hand-held remote control unit which can be conveniently carried and handled by the user. For illustration purposes, two remote devices  1212 A,  1212 B are shown, each of which has its own unique identification code. The identification codes are stored in the memories  1216 A,  1216 B of the microprocessors  1228 A,  1228 B of the respective remote devices. The central control station  1220  has a voice recognition IC  1200  coupled to a microphone  1202  for receiving and recognizing a voice command. If the voice pattern of the speaker matches a voice pattern stored in the voice recognition IC  1200 , the voice recognition IC transmits a command code corresponding to the given command to a central microprocessor  1222 . The command code may contain a code to indicate which remote device is to be contacted. Alternatively, the determination of which remote device is to be contacted may be made by the central microprocessor according to the command code provided by the voice recognition IC  1200 . 
     The central microprocessor contains a memory  1224  which has the identification codes for the remote devices stored therein. After receiving the command code, the central microprocessor  1222  sends out through the transmitter circuit  1226  a bitstream signal which contains the identification code of the remote device to be addressed and an operation code indicating the operation to be performed. In the preferred embodiment, the bitstream signal is transmitted at a radio frequency (RF). Other suitable transmission bands may also be used. 
     The remote devices  1212 A,  1212 B preferably are normally in the sleep mode and can wake up in the ways described in conjunction with  FIG. 6 . In the illustrated embodiment, each remote device has a wake-up circuit  1230 A,  1230 B and a radio frequency decode circuit  1232 A,  1232 B. After receiving the bitstream signal from the central control station  1220 , the radio frequency decode circuit of each remote device converts the received RF signal into a computer-compatible binary code which includes the identification code and the operation code. Each remote device then compares the received identification code with its own identification code. If the codes match, the remote device carries out the specified operation. 
     This voice-activated remote access control system finds many applications in different settings. For example, as illustrated in  FIG. 14 , the remote access control device  1212 A is connected to a file cabinet  1240  and a desk  1242  in an office for locking and unlocking the cabinet drawers and desk drawers. By way of example, when the user gives the voice command “lock desk,” the central control station  1220  receives the command through the microphone  1202 . If the speaker&#39;s voice is recognized, the central control station  1220  sends out a bitstream signal to cause the remote unit  1212 A to operate a lock mechanism  1241  in the desk  1240  to lock the desk drawers. As another example illustrated in  FIG. 14 , the remote device  1212 B is used to control a motor  1243  in a tool chest  1244  to lock and unlock the doors and drawers of the tool chest. 
     In accordance with the object of the present invention to prevent the unauthorized use of electronic keys, there is provided an electronic access control system which has a plurality of remote electronic locks and a master key that has a number of access programmed therein. As illustrated in  FIG. 15 , the access control system includes a master control device  140  for programming a master access code and the desired number of access into the master key  142 . In the illustrated embodiment, the master control device  140  is a personal computer which has an interface device  144 , such as a key reader, for communicating with the master key. The master key  142  contains a non-volatile memory which includes an access code storage  146  for storing the master access code specific to the control system, and a counter  148  for storing the number of access allowed. Also shown in  FIG. 15  is an electronic lock  150  which can be opened by the master key. The electronic lock has a control circuit based on a microprocessor  151  and a key reader  152  for communicating with the master key. When the master key  142  is presented to the key reader  152 , the microprocessor  151  of the electronic lock reads the access code stored in the master key and compares that code to a preset master access code stored in its memory. If the two codes match, the control circuit reads the number of access stored in the master key. If the number of access is one or greater, the microprocessor  151  energizes the solenoid  154  to open the lock  156 . In conjunction with the opening of the lock, the microprocessor  151  of the electronic lock  150  decrements the number of access stored in the counter  148  of the master key by one. Thus, if the number of access in the counter  148  is initially set to one, after the opening of the lock the counter is reduced to zero, and the master key cannot be used to open another lock. 
     In this way, by limiting the number of times the master key  142  can be used to open locks, the unauthorized use of the master key is effectively prevented. For instance, in the setting of a hotel, it is necessary to have a mater key for opening the electronic locks installed in the safes in the hotel rooms. If a hotel guest forgets the access code for the safe in his room, the master key can be programmed with the number of access set to one, and used to open that safe. Since the number of access will be reduced to zero after the lock is opened, the master key cannot be subsequently used to open the safe in another room. The use of the master key is thus strictly controlled. 
     In accordance with another aspect of the invention, there is provided an alarm system for a bicycle or a similar manually powered vehicle. As illustrated in  FIG. 15 , this alarm system includes a remote control  160  mounted in the helmet  162  of the rider of the bicycle  166 , and an electronic alarm  164  mounted on the bicycle. The remote control  160  has a transmitter  168  for the wireless transmission of a communication code and other types of control signals to the alarm  164  on the bicycle, which has a receiver  170  for receiving the transmitted signals. 
     In the preferred embodiment, the remote control  160  has a button  172  which when pushed transmits a control signal including the communication code to the alarm  164  on the bicycle to activate or deactivate the alarm. Alternatively, the helmet may be equipped with a keypad for entering an access code by the user. After receiving the access code, the remote control compares the entered access code with a preset access code and transmits the control signals to the electronic alarm on the bicycle when the two access codes match. 
     The alarm  164  includes a motion detector  174  for sensing the movement of the bicycle  166 . If movement of the bicycle is detected by the motion detector  174  when the alarm has been activated, the electronic alarm  164  emits audio and/or visual warning signals to deter the potential theft. A timer  176  is included in the electronic alarm  164  to stop the warning signals after a predetermined amount of time has elapsed. 
     This bicycle alarm system which has a remote control  172  mounted in the riding helmet  162  has many advantages. Combining the remote control with the riding helmet provides significant convenience to the rider because there is no need to carry the remote control separately. Moreover, because the remote control is integrated in the helmet of the rider, the rider is less likely to lose or misplace the remote control. Furthermore, because the remote control is required to deactivate the alarm system, combining the remote control with the helmet provides an incentive for the rider to wear the helmet when riding the bicycle. In this way, the bicycle alarm system of the present invention contributes to the safety of the rider and helps the rider to obey the law requiring the bicycle rider to wear a helmet. 
     In view of the many possible embodiments to which the principles of this invention may be applied, it should be recognized that the embodiments described herein with respect to the drawing figures are meant to be illustrative only and should not be taken as limiting the scope of the invention. Therefore, the invention as described herein contemplates all such embodiments as may come within the scope of the following claims and equivalents thereof.