Patent GB-786352-A (GB)
Title: Apparatus for electrically coding information
IPC: G11C11/30
Filed: 1954-07-22
Abstract: 786,352. Electric selective signalling systems. SOC. ASSERVELEC. July 22, 1954 [July 27, 1953], No. 21393/54. Class 40 (1). An apparatus for electrically coding information in the form of intelligence symbols, each symbol having a value and a sequence order, comprises means for coding each value and its sequence order in the form of a characteristic frequency and of a characteristic duration respectively, or vice versa, the duration being the duration of the characteristic frequency. As described in Specification 783,089, operation of a keyboard causes the emission of audiofrequency signals F1, F2 ... Fn, corresponding to the keys struck, the information initially being defined by the frequencies and their order of succession in a group, and simultaneously a fixed control frequency Fa is transmitted with each element. A frequency Fi defines the end of a group. These signals are applied to a filter 20, Fig. 1, provided with as many output terminals as there are discrete frequencies, each terminal being connected to a diode V21, .V22, &c. which provides bias to open the corresponding normally blocked valve T21, T22 ... T2n, and through rectifiers Z21 all the preceding valves T, e.g. bias generated by V21 opens T21, bias generated by V22 opens T22 and T21, and so on. In this way successive voltages t1 ... tn are obtained with amplitudes which correspond with the incoming frequencies F1 &c. The control frequency Fa from the filter 20 is applied to a diode V4, Fig. 3, to provide a bias to block a normally conducting valve T41 and cause a gas-filled tube N4 to conduct and the voltage in circuit C4 to suddenly increase, the voltage returning to normal when Fa stops. These pulses are applied to a chain of n trigger circuits at 21 whose outputs C43 1 ... C43n are applied to the third grid of corresponding valves P3 1  ... P3m, Fig. 2, to render the valves successively conducting for the period of one element. The pulse in circuit C4 is also applied to the normally non-conducting valve T42 of a trigger circuit T42, T43, to allow non-conductive valve P41 of a trigger circuit P41, P42 to become conductive when a positive potential is applied to its control grid. A stabilized frequency from a source S4 is applied to the control grid of valve P42, a negative half-cycle causing P42 to cut off and P41 to conduct. The anode of P42 is connected to the second grid of normally non-conductive valve P43 of a trigger circuit P43, P44 whose control grids are controlled by the source S4 and the next position half-cycle of S4 causes P43 to conduct. In this way a positive pulse is obtained in the circuit C34 which is applied to the second grid of valves P3 1 ... P3n to determine the duration of the period in which the valves P3 may conduct. When the trigger P43, P44 reverts to normal a negative pulse over conductor C<SP>1</SP>34 returns the circuits to their initial position. Capacitors K3 1  ... K3n, Fig. 2, are identically charged at the beginning of a group elements and the voltages t1 &c. representing the information are applied to the control grids of valves P3 1  ... P3n. The resistance of each valve P3 is a function of the voltage applied to the first grid and the respective capacitors are more or less discharged in accordance with the frequencies F1 &c. contained in the group, and their order of arrival. A series of n oscillators 05, Fig. 4, each having a different frequency, are started on the arrival of a frequency Fi, indicating the end of a group, which is rectified and applied via line C7 to the third grid of the oscillators. It is stated that the duration of the oscillation of an oscillator 05 is determined by the comparison of the charge of its corresponding capacitor K3 with that of a capacitor K8 whose charge is reduced in equal steps of equal duration, and the oscillations stop when the voltage across K8 is lower than that across K3. A series of n trigger circuits P51, P52 have their corresponding capacitors K3 connected to the control grid of the normally non-conducting valve P51, the control grid of the valve P52 being controlled by the potential on the line C8. As long as the potential on C8 exceeds that on C5, valve P51 remains non-conducting and the second grid of oscillator 05 is at a sufficiently positive potential to allow oscillation. When the potential of C8 becomes less than that of C5 the reverse takes place and oscillation stops. The frequency Fi through a diode V6, Fig. 5, provides bias to control a valve T6 and cause a gas-filled tube N6 to strike and open a normally blocked pentode P6 to operate a relay R6 which is then energized through contact r66. A relay R62 whose retardation is sufficient to allow discharge of the storage device K3 1  &c. is operated over r662 and locks up over r621. R62 de-energizes R6 through r622 and closes a series of n contacts r623 to recharge the capacitors K3 1  ... K3n from a source S8. When relay R6 is energized it also operates contacts r671, r672, r681 and r682, Fig. 6, and triode T7 is blocked by the negative voltage applied to its grid, to cause a normally non-conducting valve P71 of a trigger circuit P71; P72, to become conducting when a positive half-cycle of a stabilized synchronizing frequency is applied to its control grid from a transformer TR7. The gas-filled tube N7 strikes and the voltage on C7 suddenly increases to start the oscillators 05 as previously described. The voltage on C7 is also applied to the third grid of a normally non-conducting valve P81 of a trigger P81, P82, the control grids of the valves being connected in phase opposition to the transformer TR7 so that the circuit triggers with each half-cycle from TR7. Valve P81 conducts on the positive half-cycle following that which caused a voltage to be applied to C7 and on succeeding positive halfcycles, and applies to the grid of triode T8 equally spaced pulses of equal duration. In this way the capacitor K8 is discharged in successive steps to control the oscillators 05 as previously described. The contact r682 ensures the recharging of capacitor K8 from the source S8 when relay R6 is not energized. The output consisting of discrete frequencies representing the order of succession, having a duration representing the valve of the information, . is taken from C9, Fig. 4, and may be recorded on magnetic tape or used for the direct operation of statistical machines.