GB1426585A - Electrical impulse transmitters - Google Patents

Abstract

1426585 Impulse transmitters; powering substations R M MARCUS 15 May 1973 [22 May 1972] 23015/73 Heading H4K A push button apparatus which provides decadic impulses is powered over a telephone line and a capacitor in the apparatus is charged during interdigital pauses and "make" periods of signalling in order to supply the apparatus during break periods. The embodiment shows a push-button dialling apparatus incorporated in a subscribers subset, the integrated circuit IC including a memory for storing digits selected by depressing pushbuttons (not shown). On going off-hook switch H2 closes, and depression of a push-button opens switch S1 to supply line voltage via diode bridge DB to the positive and negative rails of the dialling apparatus, this voltage being regulated to 4À7 volts by Zener diode Z1. Transistor T2 is turned on to charge storage capacitor C1 from the rail voltage so as not to deprive the dialling apparatus of power during charging. A reset pulse is supplied to integrated circuit 1C via transistor T3, diodes D1-D2 and a pulse shaper M to cause an output O of the integrated circuit to operate a magnetically latching relay OR, thereby causing contact O1 to open and contact 02 to close, so maintaining the power supply to the apparatus on release of the push-button and shorting the transducer apparatus of the sub-set in preparation for impulsing. The relay OR may be held either by the integrated circuit output O or by timing circuit X. In known manner selected digits are stored and are read out from the circuit IC at output I to operate an impulsing relay IR to open and close contact I1, the apparatus being powered from capacitor C1 via transistor T4 and diode D4 during the break periods. On completion of impulsing the output O of circuit IC causes relay OR to release by turning on transistor T7 to discharge capacitor C5. In addition transistor T10 is biased off to turn off transistor T4 thereby ensuring no power is supplied to the rails of the dialling apparatus from either the telephone line or capacitor C1. However capacitor C1 continues to supply power to clock pulse generator G to drive circuit IC and keep relay OR released via output O while the positive rail discharges rapidly. The apparatus is protected from over-voltages on the line by Zener diode Z2 and resistor R13 and the rail voltage is limited to 5À1 volts by Zener diode Z3 should Zener diode Z1 or the emitter base junction of transistor T1 fail. Where long telephone lines are used a relay LR (not shown) may be added controlled by circuit IC to close a contact bridging contacts O1 and S1 during the first 15 ms. of each make pulse, thereby momentarily providing a low resistance signalling loop.