Electronic Combination Door And Ignition Lock

Abstract

A circuit is disclosed for unlocking the door and energizing the ignition circuit of a motor vehicle in response to manual insertion of a predetermined 5-digit code selected from a choice of four digits. The circuit includes a four stage solid state register, a six stage counter and logic gates which are interconnected to energize a door unlocking solenoid in response to insertion of the code in the proper sequence from a pushbutton keyboard unit located on the door of the vehicle. A five stage counter and additional logic means is provided which responds to actuation of any of the four digits out of sequence or to actuation of any digit not forming a part of the code to reset the two counters and the register. Upon entry into the vehicle and closure of the ignition switch, the last stage in the door unlocking logic is disabled and a parallel connected logic stage is enabled. The operator must then reinsert the code from a dash mounted pushbutton keyboard in the proper sequence to arm the ignition circuit.

Description

This invention relates to motor vehicle anti-theft apparatus and more particularly to an electronic combination door and ignition lock requiring proper insertion of a predetermined code containing repeating symbols in order to obtain entry to the vehicle and reinsertion of the code subsequent to entry in order to start the vehicle.

It is an object of the present invention to provide an improved electronic combination lock circuit which is capable of producing an output signal in response to insertion of a predetermined code containing repeating symbols and which is automatically reset in response to insertion of a sequence of symbols which is not in exact correspondence with the predetermined code.

It is another object of the present invention to provide an improved electronic combination door and ignition lock circuit for a motor vehicle which requires insertion of a predetermined code containing repeating symbols from a keyboard unit mounted on the exterior of the vehicle in order to obtain entry to the vehicle and requires reinsertion of the predetermined code from a pushbutton unit mounted within the vehicle in order to energize the ignition system of the vehicle.

It is another object of the present invention to provide an improved electronic combination lock circuit including means for overcoming the adverse effects of contact bounce associated with the input units for inserting the code.

In accordance with the present invention a door unlocking solenoid is energizable from circuitry responsive to insertion of a predetermined code containing x symbols selected from a choice of y symbols where in the specific example described x = 5 and y = 4. The code thus includes a repeating symbol. Each stage of a four stage register is sequentially set under the control of the first four of a first group of five gates which in turn are controlled from a pushbutton unit mounted on the exterior of the vehicle. The five gates are enabled sequentially from a first counter which is stepped from a monostable multivibrator which in turn is triggered by actuation of one of the pushbuttons in the pushbutton unit. The monostable multivibrator insures that the counter is stepped only once for each pushbutton actuated notwithstanding repeated contact closure due to contact bounce associated with pushbutton actuation. The fifth gate is also responsive to the output of the last stage of the register and controls the energization of the unlocking solenoid. A second counter, which is stepped from the multivibrator in responsive to release of the pushbutton actuated, sequentially enables a second group of five gates which are operative to reset the first and second counters and the register if any pushbutton is actuated out of sequence or if any pushbutton not forming a part of the code is actuated. A second pushbutton unit mounted on the interior of the vehicle provides a parallel input to the circuitry. Upon closure of the ignition switch and reinsertion of the proper code, the ignition circuit is energized and the vehicle may be started.

Other objects and features of the present invention will become apparent from the following detailed description which should be read in conjunction with the drawings in which:

FIG. 1 shows a portion of a motor vehicle provided with pushbutton units mounted on the exterior and interior of the vehicle;

FIG. 1a shows the interiorly mounted unit in more detail;

FIG. 2 is a schematic diagram of the present invention with portions thereof in block form;

FIG. 3 is a detailed schematic of the block portions of the diagram shown in FIG. 1.

Referring now to the drawings and initially to FIGS. 1 and 1a, a motor vehicle 8 is shown as having a pushbutton unit 10 mounted on the left front door 12 adjacent the door handle 14. A second pushbutton unit 16 is shown as mounted on the dash 18 of the motor vehicle 8 adjacent the ignition switch (not shown). Each pushbutton unit 10 and 16 comprises two rows of five pushbuttons numbered 0- 9.

The circuitry to be described in connection with FIGS. 2 and 3 is based on the premise that the code consists of five symbols or digits selected from a choice of four symbols thus requiring that at least one of the symbols be repeated. The particular code used for illustrative purposes is 13142.

In FIG. 2 a control circuit generally designated 22 is shown as having an input terminal 24 connected with a source of DC potential 26 through a diode 28 and a voltage dropping resistor 29. The source 26 is preferably the vehicle battery and will hereinafter be referred to as such. A zener diode 30 and a parallel connected capacitor 31 regulate and filter the voltage appearing at the input terminal 24 of the control circuit 22. The pushbutton unit 10 is shown as comprising four switches 32, 34, 36 and 38 which correspond to the pushbuttons bearing the numerals 1, 2, 3 and 4 respectively. The remaining pushbuttons 0 and 5- 9 are schematically represented as a single pushbutton switch 40. The switches 32 through 40 have one side connected to a ground terminal 44 and the other side connected to terminals 46 through 54 respectively of the control circuit 22 and are connected to the input terminal 24 through the resistors 56 through 64 respectively. The dash mounted pushboard unit 16 is identical to the door mounted pushbutton unit 10 and has its individual switches designated 32'-40' connected in parallel with the switches 32-40 of the door mounted pushbutton unit 10.

Time delay networks generally designated 66 and 68 are connected between terminals 82 and 84 respectively of control circuit 22 and ground. The network 66 comprises a capacitor 70 connected in series with parallel connected resistor 74 and diode 78. The network 68 comprises a capacitor 72 connected in series with parallel connected resistor 76 and diode 80. Terminal 85 and 87 of circuit 22 are connected respectively to junctions between capacitor 70, resistor 74 and capacitor 72, resistor 76. The purpose of the time delay networks 66 and 68 will be fully described therein after in the detailed discussion of control circuit 22.

An ignition switch 20 has one side connected to the positive terminal of the battery 26 and the other side connected to ground through a voltage dividing network comprising resistors 88 and 90. The junction between the voltage dividing resistors 88 and 90 is connected to a terminal 92 of the control circuit 22.

The junction between the diode 28 and the resistor 30 designated 93 is connected through a resistor 94 to a terminal 96 of the control circuit 22 and through a resistor 98 to a terminal 100 of the control circuit 22. A drive circuit 102 comprising transistors 104, 106 and resistors 105, 107 is connected across the junctions 93 and terminal 96 for controlling energization of a door lock solenoid 108. A drive circuit 110 is connected across the junction 93 and terminal 100 and comprises transistors 112, 114 and resistors 113, 115 for controlling energization of a door unlock solenoid 116.

An ignition control circuit generally designated 118 is interposed between the ignition switch 20 and the ignition circuit of the vehicle (not shown) and includes voltage dividing resistors 120 and 122 connected between ground and an output terminal 123 of the control circuit 22. An SCR 124 has its cathode connected to ground, its gate connected to ground through a capacitor 126 and its anode connected through a diode 128 to the base electrode of a transistor 130. The emitter of transistor 130 is connected through a resistor 132 to the ignition switch 20 while its collector is connected to the gate electrode of an SCR 134. The anode electrode of the SCR 134 is connected with the ignition switch 20 while the cathode electrode of SCR 134 is connected to the ignition circuit of the vehicle. Parallel connected resistor 136 and capacitor 138 are connected between the gate and cathode of the SCR 134. A drive circuit 140 comprising transistors 142, 144 and resistors 143, 145 has an input connected through a resistor 146 to the ignition switch 20 and is adapted to connect a lamp 148 across the battery 26 in response to closure of the ignition switch 20. The lamp 148 illuminates the pushbutton unit 16 mounted on the dash 18 of the vehicle 8.

A start switch generally designated 150 is connected from the battery 26 to the start solenoid (not shown) as indicated in FIG. 2. The ignition switch 20 and the start switch 150 are shown as separate switches but it will be appreciated that these two switches may be combined in the usual fashion.

Referring now to FIG. 3, the control circuit 22 is shown in detail. The input terminals 46, 48, 50 and 52 of control circuit 22 are connected to a NAND gate 152 which triggers a monostable multivibrator generally designated 154. The multivibrator 154 comprises NOR gates 156, 158 and an inverter 160 as well as the time delay network 66 (FIG. 1). The output of the gate 152 is connected through the inverter 160 to the terminal 82 and from there through the diode 78 and capacitor 70 of network 66 to ground. The output of the gate 152 is also one input to the gate 156, the other input being from the output of the gate 158. The output of the gate 156 is one input to the gate 158 while the other input is connected to the terminal 85 and from there to the junction between the capacitor 70 and the diode 78 of network 66. All inputs to the gate 152 are normally a logic "1" and thus the output of the gate 152 is normally a logic "0." Accordingly, the capacitor 70 is normally charged from the logic "1" output of the inverter 160 through the diode 78. The gate 152 performs a logical OR function producing a logic "1" output when any of the switches 32 through 38 are closed to place a logic "0" at the input of gate 152. When any of the switches 32 through 38 are actuated the output of the gate 152 and the input to the gate 156 switches from a logic "0" to a logic "1." The output of the gate 156 and hence one input to the gate 158 switches to a logic "0." Also the output of the inverter 160 switches to a logic "0" and the capacitor 70 begins to discharge through the resistor 74 and the inverter 160. When the capacitor 70 discharges below the threshold level of the gate 158 the output of the gate 158 switches to a logic "1." Upon release of the pushbutton actuated the capacitor 72 immediately charges from the inverter 160 through the diode 78 switching the output of the gate 158 back to a logic "0." The delay provided by the multivibrator 154 between actuation of one of the switches 32-38 and a change in the state of the multivibrator 154 eliminates the possibility of contact bounce of the switches 32-38 producing several output pulses from actuation of a single pushbutton. This feature is of particular importance where, as in the present invention, a digit of the code is repeated.

The output of the multivibrator 154 is connected with the clock input of a counter 162 having respective output terminals designated 0-5. The outputs of the counter 162 are decoded and in the reset condition the output at the 0 terminal is a logic "1," while the output at the terminals 1-5 are a logic "0." Each clock pulse from the multivibrator 154 after reset of the counter 162 produces a logic "1" at the respective terminal 1-5.

First logic means generally designated 164 comprises a plurality of AND function performing gates corresponding in number to the number of symbols in the code and in the example given, comprises five NAND gates designated 166, 168, 170, 172 and 174. The gates 162 and 174 have one input connected respectively with the output terminals 1-5 of the counter 162. The switch 32 actuable by the pushbutton bearing the numeral 1 is connected with the second input of the gates 166 and 170 through an inverter 176. The switch 36 actuable by the pushbutton bearing the numeral 3 is connected as a second input to the gate 168 through an inverter 178. The switch 38 actuable by the pushbutton bearing the numeral 4 is connected as a second input to the gate 172 through an inverter 180. The switch 34 actuable by the pushbutton bearing the numeral 2 is connected as a second input to the gate 174 through an inverter 182.

The gates 166-172 control a register generally designated 184. The register 184 comprises a plurality of stages corresponding in number to one less than the number of symbols in the code; in this instance 4. Each stage is a set-reset flip-flop comprising two NAND gates 186, 188; 190, 192; 194, 196; and 198,200 respectively. The output of the gates 166-172 are connected with the set terminals S of each stage while the output of each stage is connected with the reset terminal R of the following stage.

The output of the last stage designated 202 which is normally a logic "0" is connected as a third input to gate 174. The output of the gate 200 designated 204 is normally a logic "1" and is connected through an inverter 206 to the terminal 84 which is connected to the time delay network 68 comprising resistor 76, diode 80 and capacitor 72. The output of the gate 174 is connected through an inverter 208 to the base electrode of a transistor 210 having its emitter grounded through the terminal 44 of control circuit 22 and its collector connected to the terminal 100 of control circuit 22 and thence to the drive circuit 110 for the unlocking solenoid 116.

Reset circuit means generally designated 212 comprises a counter 213 having five output terminals designated 0-4 respectively, second, third, and fourth logic means generally designated 215, 216 and 217 respectively. The counter 213 is clocked from the output of the multivibrator 154 through an inverter 214. The second logic means 215 includes a plurality of OR function performing gates corresponding in number to the number of different symbols used in the code and in the example given comprises four NAND gates 218, 220, 222 and 224. The gates 218 through 224 are respectively connected to all the pushbutton switches 32 through 40 excluding the switches actuable by the pushbuttons bearing the numerals 1, 3, 4 and 2 respectively. That is to say the gate 218 is connected to all switches except the switch 32; the gate 220 is connected to all switches except the switch 36; the gate 222 is connected to all switches except the switch 38 and the gate 224 is connected to all switches except the switch 34. The third logic means 216 comprises a plurality of AND function performing gates corresponding in number to the number of symbols in the code and in the example given comprises five NAND gates 226, 228, 230, 232 and 234. One input to the gates 226-234 is connected with the respective output terminal 0-4 of the counter 213. The other inputs to the gates 226 and 230 are from the output of the gate 218 while the other input to the gates 228, 232, and 234 are from the outputs of the gates 220, 222 and 224 respectively. Since the gates 226 through 234 are enabled sequentially by the counter 213 a logic "0" output will be obtained from one of the gates 226-234 if any of the pushbuttons other than those bearing the numerals 1, 2, 3 or 4 are actuated or if any of those four pushbuttons are actuated out of proper sequence. The fourth logic means 217 performs an OR function and comprises NAND gates 238 and 240 and an inverter 242. The inputs to the gate 238 are from the outputs of the gates 226 through 232 respectively. The output of the gate 238 is inverted by the inverter 242 and provides one input to the gate 240, the other inputs being received from the output of the gate 234 and from the capacitor 72 through the terminal 87 and an inverter 244. The output of the gate 240 is connected with the reset terminal of the counter 162 which resets the 0 terminal on the counter 162 to a logic "1" and the 1-5 terminals to a logic "0." The 0 terminal of the counter 162 is connected as one input to a NAND gate 246 which performs an AND function. The other input to the gate 246 is connected to the capacitor 70 through the terminal 85. The output of the gate 246 is connected through an inverter 248 to the reset terminal on the counter 213 which resets the output terminal 0 to a logic "1" and the output terminals 1, 2, 3 and 4 to a logic "0." The output of the gate 246 is also fed to the reset terminal R in the first stage of the register 184. Resetting the first stage of the register causes each succeeding stage to be reset producing a logic "0" at the output terminal 202.

The output of the gate 226 of the reset circuit means 212 is also fed through a NOR gate 250 to the base of a transistor 252 having its emitter grounded through terminal 44 of the control circuit 22 and its collector connected to the terminal 96 of the control circuit 22 which as shown in FIG. 1 is connected with the drive circuit 102 of the lock solenoid 108. The gate 250 has a second input connected to the ignition switch 20 through the the terminal 92 of the control circuit 22 and inverters 256 and 258 and performs a logical AND function. That is to say, the gate 250 is enabled only when a logic "0" input is obtained from gate 226 and the ignition switch 20 is open. When the ignition switch is closed a logic "1" appears at one input and disables the gate 250.

Fifth logic means including a NAND gate 254 is connected in parallel with the gate 174 having inputs connected with the output terminal 202 of the register 184; with the fifth output terminal of the counter 162; and with the switch 34 actuable by the pushbutton bearing the numeral 2 through the inverter 182. The gate 174 is connected to the ignition switch 20 from the terminal 92 of the control circuit 22 through the inverter 256 while the gate 254 is connected to the ignition switch 20 through the inverter 256 and the inverter 258. When the ignition switch 20 is opened a logic "0" appears at the gate 254 disabling this gate while a logic "1" appears at the input to the gate 174. When the ignition switch is closed the gate 174 is disabled and a logic "1" appears at the input to the gate 254. The gate 254 is connected through an inverter 260 to the terminal 123 of the control circuit 22 and from there to the ignition control circuit 118.

The operation of the circuit will now be described with reference to FIGS. 1-3. Assuming that the vehicle is locked and all circuitry in a reset state the output of the counter 162 will be 100000 at the 0-5 terminals respectively and the output of the counter 123 will be 10000 at the 0-4 terminals respectively. The unlocking sequence is as follows assuming the code of 13142. Pressing pushbutton No. 1 of the unit 10 actuates switch 32 and grounds input terminals 46 of control circuit 22 producing a logic "1" at the output of gate 152 thus triggering the multivibrator 154. After a time interval based on the discharge rate of capacitor 70 the output of the multivibrator 154 at gate 158 switches from a logic "0" to a logic "1" clocking the counter 162, placing a logic "1" on the 1 terminal and consequently at one input of the gate 166. Closure of the switch 32 also produces a logic "1" output at the inverter 176 and consequently at the other input to the gate 166. The two logic "1" inputs to the gate 166 produce a logic "0" output which is fed to the gate 186 to set the first stage of the register 184. When pushbutton No. 1 is released the capacitor 70 charges from the logic "1" output of the inverter 160 through the diode 78 and the output of the gate 158 returns to a logic "0" which clocks the counter 213 through the inverter 214 placing a logic "1" on the 1 output terminal of the counter 213. In addition, when pushbutton No. 1 is released the output of the gate 166 returns to a logic "1" and the output of the gate 186 returns to a logic "0" placing a logic "1" on the output of the gate 192 and consequently the input of the gate 190 of the second stage of the register 184. If any pushbutton other than pushbutton No. 1 is depressed a logic "0" input is applied to gate 218 producing a logic "1" input to gate 226 which combined with the logic "1" input from the 0 output terminal of the counter 213 produces a logic "0" input to the gates 238 and 250. The logic "0" input to the gate 250 combined with the logic "0" input from the open ignition switch 20 switches the output of the gate 250 to a logic "1" and renders the transistor 252 conductive to energize the door locking solenoid 108. The logic "0" input to the gate 238 resets the counter 162 through the inverter 242 and gate 240. Resetting the counter 162 produces a logic "1" input to the gate 246. Upon release of pushbutton No. 1, the logic "1" input to the gate 246 is combined with the logic "1" input from the capacitor 70 to produce a logic "0" which resets the register 184 and also resets the counter 213 through the inverter 248.

If now the operator depresses and releases pushbutton No. 3 a similar sequence of events occurs as previously mentioned in connection with depression of pushbutton No. 1 insofar as operation of the counters 162 and 213, and the register 184 is concerned. If any pushbutton other than pushbutton No. 3 is depressed the gate 228 will be enabled from the gate 220 and the 1 output terminal of the counter 213 resetting the counters 162 and 213 and the register 184. A similar sequence of events occurs upon depression and release of pushbuttons Nos. 1 and 4. Likewise if any pushbutton other than pushbuttons Nos. 1 and 4 are depressed the counters 162, 213 and the register 184 are reset.

Upon depression of pushbutton No. 4 the output of gate 200 at terminal 204 switches to a logic "0" which is inverted to a logic "1" by inverter 206 charging the capacitor 72 through the resistor 76 from the terminal 84. Also the output of register 184 at junction 202 switches to a logic "1" and thus when the operator depresses the pushbutton No. 2 the output of the gate 174 switches to a logic "0" which is inverted to a logic "1" by the inverter 208 to render the transistor 210 conductive thereby energizing the unlock solenoid 116 through the drive circuit 110 connected with the junction 100. The time constant of the timing circuit 68 comprising the resistor 76 and capacitor 72 is sufficiently long to permit the operator to press the last pushbutton unlocking the vehicle door. After a time interval determined by the value of the resistor 76 and capacitor 72 and the threshold of gate 240 the counter 162 and consequently the counter 203 and register 184 are reset.

When the operator enters the vehicle and closes the ignition switch 20 a logic "1" appears at the terminal 92 producing a logic "0" at the output of the inverter 256 disabling the gate 174. Also a logic "1" appears at the output of the inverter 258 enabling the gate 254 and disabling the gate 250. Furthermore, closure of the ignition switch 20 renders the drive circuit 140 conductive thus energizing the lamps 148 on the pushbutton unit 16. The operator now inserts the same combination 13142 and upon actuation of pushbutton numeral 2 the output of the gate 254 switches to a logic "0" which is inverted to a logic "1" by the inverter 260 thus triggering the SCR 124 rendering the transistor 130 conductive to fire the SCR 134 and connect the battery 26 to the ignition circuit. The vehicle may now be started by closing the start switch 150. In addition, when the SCR 124 conducts the drive circuit 140 is grounded deenergizing to lamp 148.

A predetermined interval of time after pushbutton numeral 4 is depressed the time delay circuit comprising resistor 76 and capacitor 72 is operative to reset the register 184 and counters 162 and 213. When the register 184 is reset a logic "0" appears at the output of the inverter 206 and the capacitor 72 discharges through the diode 80. With the counter 213 in a reset condition a logic "1" appears at one input to the gate 226 and consequently, upon opening the ignition switch 20 and leaving the vehicle the driver may lock the vehicle doors by depressing any of the pushbuttons other than pushbutton No. 1 thereby causing the output of the gate 226 to switch to a logic "0" and the output of the gate 250 to switch to a logic "1," rendering the transistor 252 to conduct and energizing the lock solenoid 108 through the drive circuit 102.

Claims

I claim:

1. A circuit for producing a control signal in response to a predetermined x symbol code selected from a choice of y symbols comprising;

y parallel connected manually actuable switch means, each switch means bearing indicia corresponding to respective ones of said y symbols;

first and second resettable electronic counter means having at least x output terminals;

triggerable switch means having an input connected with each of said y switch means and an output connected with each of said first and second counter means for clocking said first and second counter means in response respectively, to actuation and release of any of said y switch means;

first logic means including x gates performing an AND logic function, each gate having a first input connected with respective output terminals of said first counter means and a second input connected with at least one of said y switch means;

resettable electronic register means having x- 1 stages, x- 1 of the gates of said first logic means having an output connected with respective stages of said register means, the output of said register means being connected as a third input to the x.sup. th gate of said first logic means, the output of the x.sup.th gate of said first logic means producing said control signal when said switch means are actuated in a sequence corresponding to said code;

second logic means including at least y gates performing an OR logic function, each gate having inputs connected respectively with each one of different groups consisting of y- 1 of said y switch means;

third logic means including x gates performing an AND logic function, each gate having a first input connected with respective output terminals of said second counter means and a second input connected with the output of at least one of the gates of said second logic means;

fourth logic means connected with the output of each of the gates of said third logic means for resetting said first counter means when any of said y switch means are actuated in a sequence differing from said code;

and logic means responsive to reset of said first counter means and release of said y switch means for resetting said second counter means and said register.

2. In a motor vehicle provided with a source of DC potential, electrically operated door unlocking means and an ignition circuit, a circuit for controlling said door unlocking means and said ignition circuit in response to a predetermined x symbol code selected from a choice of y symbols comprising;

y parallel connected manually actuable switch means, each switch means bearing indicia corresponding to respective ones of said y symbols;

first and second resettable electronic counter means having at least x output terminals;

triggerable monostable multivibrator means having an input connected with each of said y switch means and an output connected with each of said first and second counter means for clocking said first counter means in response to actuation of any of said y switch means and for clocking said second counter means in response to release of any of said y switch means;

first logic means including x gates performing an AND logic function, each gate having a first input connected with respective output terminals of said first counter means and a second input connected with at least one of said y switch means;

resettable electronic register means having x- 1 stages, x- 1 of the gates of said first logic means having an output connected with respective stages of said register means, the output of said register means being connected as a third input to the x.sup.th gate of said first logic means, the output of the x.sup.th gate of said first logic means connected with said electrically operated door unlocking means whereby said door unlocking means are operated when said y switch means are actuated in a sequence corresponding to said code;

second logic means including at least y gates performing an OR logic function, each gate having inputs connected respectively with each one of different groups consisting of y- 1 of said y switch means;

third logic means including x gates performing an AND logic function, each gate having a first input connected with respective output terminals of said second counter means and a second input connected with the output of at least one of the gates of said second logic means;

fourth logic means having inputs connected with the outputs of respective ones of the gates of said third logic means for resetting said first counter means when any of said y switch means are actuated in a sequence different from said code;

logic means responsive to reset of said first counter means and release of said Y switch means for resetting said second counter means and said register;

time delay means responsive to one state of the last stage of said register means for resetting said first counter means a predetermined interval of time after the last stage of said register means switches to said one state;

fifth logic means comprising a gate performing an AND logic function and connected in parallel with the x.sup.th gate of said first logic means;

operator controlled switching means for disabling said x.sup.th gate of said first logic means and for enabling said fifth logic means;

said fifth logic means producing a control signal when said switch means are actuated in a sequence corresponding to said code;

normally non-conductive electronic switching means connected in said ignition circuit, said electronic switch means being rendered conductive in response to said control signal of said fifth logic means.

3. In a motor vehicle provided with a source of DC potential, electrically operated door locking and unlocking means and an ignition circuit including an ignition switch connected to said source;

a circuit for energizing said door unlocking means and for energizing said ignition circuit in response to a predetermined x symbol code selected from a choice of y symbols;

y parallel connected manually actuable switch means, each switch means bearing indicia corresponding to respective ones of said y symbols;

first resettable electronic counter means having a reset terminal, a clock terminal, a first output terminal and x additional output terminals;

monostable multivibrator means having an input connected with each of said y switch means and triggerable from a stable state to a semi-stable state a predetermined interval of time after actuation of any one of said y switch means and returning to its stable state upon deactuation of said one of said y switch means, the output of said multivibrator means being connected to the clock terminal of said first counter for clocking said first counter means, each time said multivibrator means is triggered to its semi-stable state;

second resettable electronic counter means having a clock terminal, a reset terminal, and at least x output terminals;

inverter means connecting the output of said multivibrator means to the clock terminal of said second counter means whereby said second counter means is clocked when said multivibrator means returns to its stable state;

first logic means including x gates performing an AND logic function, each gate having a first input connected with the respective x additional output terminals of said first counter means and a second input connected with at least one of said y switch means;

resettable electronic register means having x- 1 stages, x- 1 at the gates of said first logic means having an output connected with respective stages of said register means, the output of said register means being connected as a third input to the x.sup. th gate of said first logic means, the output of the x.sup.th gate of said first logic means connected with said electrically operated door unlocking means whereby said door unlocking means are operated when said switch means are actuated in a sequence corresponding to said code;

second logic means including at least y gates performing an OR logic function, each gate having inputs connected respectively with each one of different groups consisting of y- 1 of said y switch means;

third logic means including x gates performing an AND logic function, each gate having a first input connected with respective output terminals of said second counter means and a second input connected with the output of at least one of the gates of said second logic means;

fourth logic means having inputs connected with the outputs of respective ones of the gates of said third logic means for resetting said first counter means thereby producing an enabling output at said first output terminal of said first counter means;

means connected with said multivibrator means and said first output terminal for resetting said second counter and said register means when said multivibrator returns to its stable state and an enabling output appears at said first terminal of said first counter means;

time delay means responsive to one state of the last stage of said register means for resetting said first counter means a predetermined interval of time after the last stage of said register means switches to said one state;

fifth logic means comprising a gate performing an AND logic function and connected in parallel with the x.sup.th gate of said first logic means, means for disabling said x.sup.th gate of said first logic means and for enabling said fifth logic means in response to closure of said ignition switch;

electronic switching means connecting said ignition circuit in series with said ignition switch and responsive to the output of said fifth logic means for energizing said ignition circuit when said y switch means are actuated in a sequence corresponding to said code;

sixth logic means performing an AND logic function and responsive to the output of one of said gates of said third logic means and to opening of said ignition switch for energizing said door locking means.