GB901886A - Improvements relating to electronic counting chains - Google Patents

Abstract

901,886. Electronic counting - apparatus. WESTINGHOUSE BRAKE & SIGNAL CO. Ltd. June 12, 1959 [June 12, 1958; Nov. 13, 1958], Nos. 18769/58 and 36528/58. Class 106 (1). [Also in Group XL (c)] A multi-stable-state chain of bi-stable stages in which each stage comprises a pair of transistors cross-coupled between their bases and collectors has couplings between the stages comprising a variable impedance shunt path which is controlled by a given stage so as only to allow switching pulses to be applied to the next stage in the chain when the given stage is in a predetermined one of its stable states. Fig. 1 shows a multi-stable counting chain of which each stage is constituted by a bi-stable pair of PNP junction transistors having their bases and collectors cross-connected. The state of conductivity of each stage being controlled by negative going stepping pulses applied to leads 5, 5A under the control of which a given state of stability is progressed along the chain. If it is assumed that normally transistors TR1 A, B, C, &c. are non-conductive and transistors TR2 A, B, C, &c. are conductive, then normally the transistor TR3C will be conductive since its base is held negative by the collector of TR1B. This represents a low impedance shunt across TR2C so after a negative stepping pulse on lead 5 has changed over stage A and C at the end of the pulse stage C reverts to its normal state. When TR1A conducts it removes the negative voltage from the base of TR3B which cuts off so the next pulse which is on lead 5a triggers stage B and the next pulse reverses the state of stage C so that the sequential changing continues down the chain. In a modification, Fig. 2, the normally conducting transistor of each stable pair functions as the variable impedance for the previous stage so that the pulses are steered to trigger the next stage in the chain. In the modification shown in Fig. 5, diodes D1, D2, D3 connect the collector of the normally conducting transistor of a given stage to the corresponding transistor of the following stage in the chain. Thus since the collector of transistor TR2B is clamped at earth the stepping pulses on leads 5, 5A are ineffective on stage B until stage A has been changed over when diode D1 becomes non- conductive. Fig. 3 shows one stage of a binary counter comprising two cascaded bi-stable pairs the pulses to be counted being fed alternately to lines 6, 6A. Thus, if initially transistor TR4 is non-conductive and TR5 is conductive, a negative pulse at 6 is shunted via TR5 and thus passes via lead 7 to TR6 to reverse stage E. The next pulse at lead 6A is shunted via diode a D3 and transistor TR6 so is active only via lead 9 to reverse stage D. Thus, each one of the bi-stable stages D, E is changed to the state opposite to that prevailing in the other stage. The cycles of an A.C. waveform may be counted by inverting the positive half-cycle, Fig. 4 (not shown).