KEY CONTROLLED ELECTRICAL CIRCUITS

Abstract: A key operated switch for an electrical circuit, e.g. the ignition circuit of a vehicle comprises a removable key (10 - 12, 14, 17) and a socket (15, 16) arranged to receive the key. The key includes a programmable read-only memory (20) with electrical contact elements (12) which co-operate with contacts in the socket to provide an addressing circuit from the socket to the memory in the key and also to provide power supply connections to the memory from supply terminals in the socket. The addressing circuit includes a multiplexer (26) to serialise data read from the memory. In the socket or in the housing therefor or electrically connected thereto is a second read-only memory (45) with a digital comparator (49). The two memories are addressed to feed data simultaneously from corresponding addresses to the comparator in sequence and circuit means (50, 51, 54, 55) operative on completion of a cycle of data comparison to effect operation of a relay (56) only if the compared data in the two memories (20, 45) agree. Thus the relay can only be operated if a key having a correctly programmed read-only memory is inserted in the socket.

Description: "KEY CONTROLLED ELECTRICAL CIRCUITS" This invention relates to key controlled electrical circuits. It is well-known to make use of removable keys for controlling electrical circuits. Such arrangements are commonly employed for security purposes; for example the electrical ignition system for vehicles is commonly controlled by a removable key so that the vehicle cannot be operated without an appropriate key. Mechanical keys are well-known. It has been proposed in U.K.Patent Specifications Nos 1401281 and 1337233 to make use of keys containing an electrical data memory. It is one of the objects of the present invention to provide an improved form of key operated switch using an electronic data memory to enable provision to be made of a very large number of unique combinations of key and lock, that is to say combinations in which the lock and key are co-operatively arranged so that the C.l-lPI lock may be operated only by the appropriate key and in which a key can only operate the appropriate lock. More particularly it is an object of the present invention to enable such a large number of unique combinations to be provided without necessitating a large number of electrical connections being made between the key and socket. According to this invention a key operated switch for an electrical circuit comprises a removable key and a socket arranged to receive the key wherein the key includes a programmable read-only memory for a digital circuit together with electrical contact elements on the key co-operating with contacts in the socket to provide an addressing circuit from the socket to the memory in the key and also to provide power supply connections to the memory from supply terminals in the socket, the addressing circuit including a multiplexer to serialise the data read from the memory and wherein there is provided in the socket or in the housing therefor or electrically connected thereto a second read-only memory together with a digital signal comparator, means for addressing the two memories to feed data simultaneously from corresponding addresses to the comparator in sequence, and circuit means operative on completion of a cycle of data comparison arranged to effect operation of a 'relay only if all the compared data in the two memories agrees. This construction enables a programmable read-only memory to be employed in the key with the resultant large number of possible combinations of binary digital data being storable. For example, a memory containing 16 storage for 16 words each of 4 bits would give 16 possible combinations, that is about 1.8 x 10 14 It is thus readily possible with such a system to provide far more possible combinations of data than would be required to give a unique key and lock for any practical requirement. Every road vehicle could have for example its own unique key and an associated electrical circuit which might be used for controlling the ignition system or which might be an electrical locking system or other security arrangement for the vehicle or some part thereof. The programmable read-only memory may conveniently b interrogated by a counter in the key. For example using a- 16 x 4' bit memory as described ' above, this memory may b interrogated by 4 bits from a 6 bit counter. The 4 bits of data are serialised by the multiplexer which in this OMPI fay, IFO case would be a 4 bit multiplexer conveniently controlled by two further bits from the 6 bit counter, for example using a 2-4 line decoder. In one construction the multiplexer provides an output, conveniently via a line driver to provide a low impedance signal, on one of four interconnecting circuits through four contact elements on the key. A second interconnecting circuit carries, to the key, clock signals operating the counter together with a power supply whilst third and fourth contacts may be arranged, via a shorting ' link in the key, to effect a connection in the socket for the power supply source which is located in the socket or the housing therefor or associated therewith. It will be seen that such an arrangement enables a very large number of code combinations to be stored in a key yet the arrangement requires only four contacts on the key. Two of these contacts are for the shorting link which is an added safeguard to ensure that the electronic circuit in the socket or associated with the socket can only be energised when a key is inserted. As stated above, a counter may be provided in the key for interrogating the first programmable read-only memory in the key. Similarly a counter may be provided in the external circuitry in the socket or hous therefor (or associated therewith) together with a multiplexer for reading the information from the second memory in serial form. The comparator, in this case, compares one bit at a time. The output from the comparator, in the form of signals indicating coincidence of the data read from the two memories, may be fed to a further counter to check whether all the data read in a complete cycle is in agreement. In the particular example given above, 64 bits are checked in each cycle and is reset after each 64 bit byte. To synchronise the two counters, conveniently they are each reset, conveniently to zero, when the power is initially applied to the circuitry. A "missing pulse" detector may be provided which is operative to check that the number of coincidence signals in the cycle is equal to 64. The output of this detector may then be arranged to inhibit operation of the aforementioned relay. The key and socket may be made physically similar to conventional keys and lock-sockets; for example the key may be shaped so that only if the correct key is inserted, it can be turned in the socket. Such an arrangement is convenient so that the key can be inserted and rotated to a position where it is mechanically located in a correct position in the socket where co-operating electrical contacts on the key and in the socket engage one another. By using electrically coded keys as described above " , large numbers of keys, e.g. all keys for vehicles or a class of vehicles may be made visually identical in external appearance, although possibly having a registration or other identification number. The aforementioned relay is preferably located in a position such that it is not readily possible to obtain physical access to the relay. In a vehicle, such a relay might be mounted integrally in a starter motor housing and arranged so that, if the relay contacts were open, the starter motor circuit cannot be completed. A similar relay could also be physically associated with the induction coil of an ignition system to prevent the ignition system operating without closing of the relay contacts. In a vehicle having an electrical fuel pump, a further relay might be associated with the fuel pump. By such arrangements, it can readily be made almost impossible for- anyone to drive away a vehicle without the appropriate key even if deliberate attempts are made to obtain access to electrically energised components in order to short cut relay- contacts. Physically the key may be made similar to a conventional key, e.g. having a relatively large head with a shank for insertion into the lock socket. The memory in such an arrangement conveniently is embedded in the head with connections to a plurality of contacts spaced along the length of the shank. For securing the key in the socket, conveniently the key shank has a transverse projection or spigot which engages in a longitudinal slot in the socket and which, when the key is turned after insertion, holds the key in the socket. The memory units conveniently are programmable read-only memories which can be pre-set to the required unique combination for each lock and key.. Such programmable read-only memories can therefore readily be arranged so that, if required, two keys are available for a given lock or so that any one key may operate more than one lock if that is required. The following is a description of one embodiment of the invention, reference being made to the accompanying drawings in which: Figure 1 is a view in side elevation of a key; Figure 2 is a plan view of the key of Figure 1 ; Figure 3 is an end elevation of a lock showing a socket adapted to receive the key of Figures 1 and 2; Figure 4 is a block schematic diagram of the electrical components of the key,-and Figure 5 is a block schematic diagram of the electrical components of the key operated system. Referring to Figures 1 and 2, there is shown a key having a head portion 10 and a cylindrical shank 11 of electrically insulating material. The shank carries four electrical contacts 12, the function of which will be described later. Embedded in the key is a programmable read-only memory 14 which, in this particular embodiment, has a capacity of 16 words each of four bits. The key also contains further electronic components to be described later with reference to Figure 4. As shown in Figure 3, the lock has a socket 15 of generally circular section to accept the cylindrical shank of the key with the slightly protruding contact element. The socket has a guideway 16 for receiving a projection 17 on the end of the key shank so ensuring that the key has to be properly oriented about its axis for insertion into the socket. After insertion the socket and the key can be rotated so that the projection 17 enters into a co-operating recess 7 to hold the key in the socket. The socket has co-operating contacts (not shown) which engage the contact elements in the key. Referring now to Figure 4 the programmable read-onl memory in the key is shown at 20. This stores the required digital data corresponding to that in the system to be operated by the key. The four contacts of the key are indicated at 21, 22, 23 and 24. The memory is interrogated by 4 bits of a 6 bit counter 25 and the 4 bits of data from the memory are serialised by a 4 bit multiplexer 26 which is controlled by the first 2 bits of the output from the aforementioned 6 bit counter 25 via a 2-4 line decoder 27. The output signal from -the multiplexer is fed to terminal 21 via a line driver 28 which provides a low impedance output. Terminal 22 forms one of the power input terminals for energising the circuitry on the key and also constitutes the input for the clock signal. This combined signal is applied to a power and clock discriminator unit 29 which separates the clock signal, feeding this signal on a line 39 to the aforementioned 6 bit counter 25. The contacts 23 and 24 are connected within the key by a shorting link 30. These contacts provide not only the second power input connection 32 for the circuitry on the key but, by means of the shorting link, constitute a power supply connection in the socket circuitry which connection is only effective when a key is inserted in the socket. The key also includes a circuit 31 to reset the counter 25 to zero when power is switched on. As will be explained later, this is required for maintaining synchronism between the counter 25 and a corresponding counter in the external electronics associated with the socket. The external electronics has terminals 41, 42, 43 and 44 in the socket which are associated respectively with the terminals 21, 22, 23 and 24 and the key. The external circuitry includes a programmable read- only memory 45 which is similar to the memory 20 in the key and which, for the appropriate lock unit, is programmed with the same data as the corresponding key. The memory 45 is interrogated by 4 bits from a 6 bit counter 46 so that its 4 bits of data in each word are serialised by a 4 bit multiplexer 47 controlled by the first 2 bits of the counter 46 via a 2-4 line decoder 48. Thus the information in the memory is read out in serial form and is passed to a 1 bit digital comparator 49 where it is compared with the signal received from the key at terminal 41. This comparator 49 provides an output signal if the two inputs to the comparator are the same. The output signal is fed via a strobe gate 50 to a 6 bit counter 51. The strobe gate 50 is opened by output pulses from a clock 52 which also drives the aforementioned counter 46. Thus the strobe gate is only opened when the multiplexer 47 is providing one input into the comparator 49. The clock 52 drives a clock gate 53 feeding pulses to the counter 51 and this counter drives a missing pulse detector circuit 54 which gives an output if the number of pulses in a cycle from the strobe gate 50 is equal to the number of pulses from the clock gate 53. The counter 51 is reset after each 64 bit sequence by a 64th bit detector 57 so as to eliminate incorrect code detection. The missing pulse detector controls an output driver 55 operating a relay circuit 56. This circuit is arranged so that, if there is any missing pulse, in other words if the data in the key does not agree with the data in memory 45 in the external electronic equipment, no output is obtained from the driver and the relay is not operated. The external electronics also include a circuit 60 to reset the counter 46 and also the counter 51 to zero when power is initially switched on and to inhibit the clock output from the clock gate until the counters have been reset. In Figure 5 the power supply- for the external circuitry is shown at 62 with output leads 63, 64. Lead 63 includes connections via contacts 43 , 44 on the socket and 23, 24 on the key so that the output connection is only completed when the key is inserted in the socket. The electrical connections from this power circuit to the various other units shown schematically in Figure 5 have been omitted for simplicity, these being of conventional construction. The aforementioned clock gate gates power to the key. The clock pulse is impressed onto the power line so as to produce short duration negative going pulses at the clock frequency. In the key, the power and clock discriminator circuit, in this particular embodiment, includes a resistor/Zener diode combination to reduce the voltage to 5 volts and includes smoothing in the power output line for circuitry. A resistance/Zener diode combination of high impedance without smoothing in this discriminator produces negative going clock pulses C-v?ι to clock the 6 bit counter 25. The ratio of the clock pulse duration to the cycle duration corresponding to the clock pulse repetition rate is typically made between 25 to 1 and 100 to 1 so that the clock pulses can be discriminated in this way. The system response time is dependent on the pulse repetition period and, in the particular embodiment described above having 64 bits in the code, the system response time will be 64 times the pulse repetition period. The aforementioned missing pulse detector 54 conveniently comprises a pulse stretcher unit which converts the output from the 6 bit counter 51 indicating the correct number of comparison counts into a stretched pulse. Such a pulse stretcher unit may comprise a retriggerable monostable having a time constant selected so that its output pulse is slightly longer than the total time period taken to interrogate all the addresses. Thus so long as a series of comparison cycles are completed, a continuous signal will be provided from such a pulse stretcher. If there is any disagreement between the data in the memories in the key and the external circuitry, then the retri gerable monostable would not be retriggered and the output from the monostable would fall to zero. Such a monostable thus acts as a missing pulse detector. The key operated equipment described above may be used for many different purposes. A typical example is for the security of vehicles; the key socket may be on the .dashboard of the vehicle and connected by a cable to an assembly containing the electronic components, which assembly is preferably mounted integrally in an item of equipment to be controlled. The assembly might for example be in a starter motor solenoid housing with the relay contacts connected in series with the starter motor of the vehicle, thereby ensuring that the starter motor cannot be energised without the correct key having been inserted in the socket on the dashboard. Other examples of the application of the equipment are for the locking up of security areas, document storage rooms or cabinets or for the securing of households, buildings or strong rooms. C ?-

Claims: CLAIMS : 1. A key operated switch for an electrical circuit comprising a removable key and socket arranged to receive the key wherein the key includes a programmable read-only memory for a digital circuit together with electrical contact elements on the key co-operating with contacts in the socket to provide an addressing circuit from the socket to the memory in the key and also to provide power supply connections to the memory from supply terminals in the socket, the addressing circuit including a multiplexer to serialise the data read from the memory and wherein there is provided in the socket or in the housing therefor or electrically connected thereto a second read-only memory together with a digital signal comparator, means for addressing the two memories to feed data simultaneously from corresponding addresses to the comparator in sequence, and circuit means operative on completion of a cycle of data comparison arranged to effect operation of a relay only if all the compared data in the two memories agrees. 2. A key-operated switch as claimed in claim 1 wherein the key includes a counter arranged for interrogating the first programmable read-only memory. 3. A key-operated switch as claimed in either of the preceding claims wherein the key further includes a line drive for feeding serial information from.the multiplexer to an output at one of said contact elements. 4. A key-operated switch as claimed in claim 3 wherein the socket or the housing therefor or electrically connected thereto is a clock signal source providing clock signals via the socket to a second of the contact elements on the key. 5. A key-operated switch as claimed in claim 4 wherein third and fourth contact elements on the key are electrically connected, via a shorting link in the key, to effect a connection in the socket for a power supply to the electronic circuitry in the socket or the housing therefor or associated therewith. 6. A key-operated switch as claimed in any of the preceding claims wherein a counter is provided for interrogating the second programmable read-only memory together with a multiplexer for serialising the data read-out from the memory. 7. A key-operated switch as claimed in claim 6 as appendant to claim 2 wherein reset means are provided for re-setting the counters when power is applied to them. 8. A key-operated switch as claimed in any of the preceding claims wherein the key is shaped so that only if the correct key is inserted, it can be turned in the socket to a position in the socket where co-operating electrical contact elements on the key and in the socket engage one another. 9. A key-operated switch as claimed in any of the preceding claims wherein the key has a relatively large head with a shank for insertion into the lock socket. 10. A key-operated switch as claimed in ,, claim 9 wherein the memory is embedded in the head with connections to a plurality of contacts spaced along the length of the shank. 11. A key-operated switch as claimed in either claim 9 or claim 10 wherein, for securing the key in the socket, the key shank has a transverse projection or spigot which engages in a longitudinal slot in the socket and which, when the key is turned after insertion, holds the key in the socket. 12. A key-operated switch as claimed in any of the preceding claims and installed in a road vehicle wherein said electrical circuit is arranged for controlling the ignition system and/or an electrical locking system or other security arrangement for the vehicle or some part thereof. 13. A key-operated switch as claimed in any of the preceding claims and installed in a road vehicle wherein said relay is located in a position such that it is not readily possible to obtain physical access to the relay. O PI > *lϊ S 14. A key-operated switch as claimed in either claim 12 or claim 13 wherein said relay is physically associated with the induction coil of an ignition system to prevent the ignition system operating without closing of the relay contacts.

Inventors: BLOCH MAURICE, HASKELL HARRY AINSWORTH, BLOCH, MAURICE, HASKELL, HARRY, AINSWORTH
Applicants: AINSWORTH HASKELL HARRY, BLOCH MAURICE, BLOCH, MAURICE, HASKELL, HARRY, AINSWORTH
Application year: 1984
Main classification: E05B49
IPC codes: G07C9