GB1360500A - Telephone instruments - Google Patents

Abstract

1360500 Substation circuits POST OFFICE 11 Aug 1972 [25 Aug 1971] 39912/71 Heading H4K A subscriber's sub-set is provided with an oscillator which is temporarily connected to the speech wires when the subscriber off-hooks, the oscillator providing a short tone burst on the line to indicate to a calling subscriber or operator the particular line called. Such an arrangement is preferably used in a coin operated telephone to indicate to an operator that such a telephone is being called. Exchange equipment 1 is connected to a substation in which the normal cradle switch arrangement is modified by the addition of an extra contact 15. When the hand set is on hook a capacitor 11 is connected to the wire 12 via resistor 14 and contact 15. When the hand set is lifted, the line wire 2 is connected to the wire 12 and an oscillator unit 10. Capacitor 11 then charges through the oscillator unit 10 and thereby causes a decaying tone to be transmitted to the exchange operator. The tone terminates when the capacitor 11 is fully charged. When the hand set is replaced the capacitor discharges via resistor 14 and wire 12. The oscillator is preferably a simple semi-conductor circuit, which is operable at the line voltage. Alternatively a low voltage oscillator may be used in conjunction with a Zener diode and series resistance to give a short but constant amplitude tone to the line. In addition to being provided in a coin operated telephone people such as the police and doctors may be provided with such oscillators in their telephone subsets.