Patent GB-1419636-A (GB)
Title: Electronic circuit for activating an electric lock
IPC: E05B49/00
Filed: 1972-11-14
Abstract: 1419636 Electric lock K J GOSS and R F PERRY 7 Nov 1973 [14 Nov 1972] 52409/72 Heading E2A An electronic circuit for operating an electric lock comprises an array of switches and logic circuitry connected to at least some of the switches, and including time delay circuitry connected between the switches, the circuit only being activated when a pre-selected combination of the switches is switched in a pre-selected sequence within a pre-selected time of switching of the preceding switch. The switches may be of the push-button or the proximity type. The first switch of the combination may be connected to the first input of a logic gate whose second input is earthed, the output of the logic gate may be connected through a monostable multivibrator to an input of a second logic gate whose other input is connected to the second switch of the combination, and so on, the pulse width of the monostable multivibrators corresponding to the pre-selected time delay so that the following gate can only be opened by switching the switch connected to its input when the monostable multivibrator connected to its other input is in its unstable state. The last but one switch may be connected to a logic gate whose output is connected through a monostable multivibrator to the input of an AND gate having another input connected to the output of a NOR gate, said NOR gate having a first input connected to earth and a second input connected to the last switch of the combination, the output of the AND gate being connected through a monostable multivibrator to a relay for activating the electric lock. The logic gates which are connected to the switches may be NOR gates. The switches of the combination may also be connected to additional logic gates and arranged such that the circuit is de-activated if selective combinations of the switches are switched simultaneously. The output of the logic circuitry for de-activating the electronic circuit in the event of certain combinations of switches being switched simultaneously is connected to a multivibrator whose QBar output is connected to the input of the AND gate preceding the monostable multivibrator activating the lock relay, said first mentioned monostable multivibrator closing said AND gate. Each of the switches forming part of the combination may be a double pole switch, the second pole of the switches being connected to the input of a counter, and the remaining switches also being connected to the input of the counter, the latter counting the switching of any one of the switches and having its output de-coded to provide a signal to activate an alarm when switches are pressed giving the wrong combinations. The counter may be arranged to be re-set by the electronic circuit being activated, the first switch being switched, or the alarm being operated. At least one of the switches of the combination may be connected through a logic gate to a counter having its output decoded and connected to the input of a following logic gate, the circuit thus providing for a combination having successive repetitions of digits. The switches may be connected to logic gates and a re-triggerable monostable multivibrator is connected between the logic gates, the pulse width of the retriggerable monostable multivibrator being chosen such that the following logic gates can only be opened if the switch connected to the first gate has been pressed a sufficient number of times, the circuit thus providing for successive repetition of digits in the preselected combinations.