Patent GB-1309593-A (GB)
Title: Electronic circuit arrangement for actuating an electrically  actuated bolt
IPC: G07C9/00
Filed: 1970-03-20
Abstract: 1309593 Releasable fastenings PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 20 March 1970 [25 March 1969] 13480/70 Heading E2A An electronic circuit arrangement for the actuation of an electrically actuated bolt (not shown) includes an electric signal generator G the output of which is connected, through a first electric circuit element I, to a first input of a comparator V, a second input of the comparator and the output of the signal generator being connected to contacts x, y and a detachable second electric circuit element II, which forms a key and which in operation, is connected between the contacts and in which the second electric circuit element determines two signal parameters of the signal applied to the second input of the comparator, and the output of the comparator is fed to a decision element B. An electronic circuit arrangement as claimed in claim 1 in which the output of the decision element is connected to a switch, in which in use the switch is closed at a time T seconds after the actuation of the unlocking sequence, to actuate the bolt, the time T seconds being determined by a monostable circuit. In the arrangement shown the signal generator produces either a sinusoidal voltage the frequency of which increases from a frequency f1 to a frequency f2 during a time T or alternatively a noise voltage; the two elements are band pass filters which are identical to each other and the comparator is a differential amplifier, the two inputs of which are connected to respective said filters. With the second filter in position identical signals are received at the two inputs of the differential amplifier and consequently the amplifier produces no output signals at its two outputs a and b. The absence of output signals from the differential amplifier causes the decision element to operate the bolt to releasing position; if the second filter is not in position or if an incorrect filter is in position the two inputs of the differential amplifier differ and thus the outputs differ and the decision element does not operate the bolt. However failure of the signal generator would also produce no output signals from the differential amplifier and to prevent the bolt being operated under such a condition a third input c of the decision element is fed directly from the signal generator and the decision element will not cause the bolt to move to releasing position unless there is input at c and no inputs at its two other inputs. The circuit of the decision element is shown in Fig. 2, the two output signals from the differential amplifier V are fed via diodes D1 and D2 to the base of a transistor T1 the base of which is also connected to earth via a resistor R1 and a capacitor C1. The collector of the transistor T1 is connected to one input of a two input AND gate P. The signal received directly from the signal generator to the input c passes to the second input of the AND gate P via a rectifying circuit. The second input of the AND gate is also connected through a diode D4 to earth, the diode D4 causing a constant potential of about 0.7 volts to be applied to the second input of the AND gate provided the signal is being received at the input c from a generator G this being interpreted by the AND gate as a logic 1 input and provided the transistor T1 is in a non-conductive state which will be the case if no inputs are being received via the diodes D1 and D2, the potential of the supply line +E volts will be applied to the other input of the AND gate which is also interpreted by the AND gate as a logic 1 input. The gate will therefore produce a logic 1 voltage at its output which causes a transistor T2 to become conductive if it is not already conductive and a transistor T3 to become non- conductive if it is not already non-conductive; the collector voltage of the transistor T3 will therefore be at E volts which is fed to a switch R which when closed applies the voltage to the electrically operated bolt to withdraw it. The transistors T2, T3 are conected to form a bistable multivibrator so that once the transistor T3 becomes non-conducting it  will remain in this condition until a further signal is received by the two transistors to change their states. The values of the resistors R5 and R6 are such that when the circuit is switched on the transistor T2 will be in the conductive state. If either of the inputs of the AND gate is at logic O, logic O will appear at the output of the AND gate so that the transistor T2 becomes non-conductive and the transistor T3 becomes conductive and this prevents the bolt being released. The switch R is closed after the time T has elapsed by means of a monostable multivibrator MV.