Automatic exclusion circuit

• US 4,053,720 A
• Filed: 12/02/1975
• Issued: 10/11/1977
• Est. Priority Date: 12/02/1975
• Status: Expired due to Term

• Current Assignee: Alcatel SA (Nokia Corporation)
• Original Assignee: International Telephone and Telegraph Corporation
• Inventors: Wycheck, Thomas Joseph, Leibich, George Edward
• Primary Examiner(s): Claffy, Kathleen H.
• Assistant Examiner(s): Brigance, Gerald L.
• Application Number:
  US05/636,855
• Time in Patent Office: 679 Days
• Field of Search: 179/99, 179/18 DA, 179/17 B, 179/8 AD, 179/38
• US Class Current: 379/161
• CPC Class Codes: H04M 9/002 with subscriber controlled access to a line, i.e. key telephone systems

Abstract

A relay is included in a subset of a key telephone system to connect the subset to a line selected by the line button of the system when the relay is activated. A control circuit is coupled to the relay and a key system positive ground to control the operation of the relay. The "A" lead of the key telephone system is coupled to the control circuit to disable the control circuit and, hence, the relay when the positive ground is coupled into the subset on the "A" lead and to enable the operation of the control circuit and, hence, actuation of the relay when the positive ground is not coupled into the subset on the "A" lead.

Claims

1. An automatic exclusion circuit for a subset of a key telephone system comprising:

a relay to connect said subset to a selected line of said key telephone system when said relay is activated;

a first source of key system positive ground;

a control circuit coupled to said relay and said first source to control the operation of said relay; and

an "A" lead coupled to said control circuit, said "A" lead disabling said control circuit and, hence, said relay when said key system positive ground is coupled into said subset on said "A" lead and enabling the operation of said control circuit and, hence, activation of said relay when said key system positive ground is not coupled into said subset on said "A" lead;

said control circuit including

a pair of transistors each having base, emitter and collector electrodes interconnected to form a Darlington pair circuit,

a second source of operating potential,

said relay being connected between the collector electrodes of said pair of transistors and said second source,

a diode connected in shunt relation to said relay,

a first resistor having one terminal coupled to the base electrode of one of said pair of transistors,

a second resistor having one terminal connected to the emitter electrode of the other of said pair of transistors,

a capacitor having one terminal connected to the other terminal of said second resistor and the other terminal connected to the other terminal of said first resistor, and

a third resistor having one terminal connected to the other terminal of said capacitor and the other terminal connected to said second source,

said capacitor and said third resistor provide a time delay circuit for said control circuit.

2. An automatic exclusion circuit according to claim 1, wherein

each of said pair of transistors is a PNP transistor, and

said operating voltage is a negative voltage.

3. An automatic exclusion circuit according to claim 1, wherein said "A" lead is connected to the other terminal of said capacitor.

4. An automatic exclusion circuit according to claim 1, wherein

said relay includes

a first set of contacts to connect an input tip conductor to an output tip conductor when said relay is activated,

a second set of contacts to connect an input ring conductor to an output ring conductor when said relay is activated, and

a third set of contacts to connect said "A" lead to the other terminal of said capacitor when said relay is inoperative and to connect said first source to said "A" lead when said relay is activated to couple said key system positive ground out of said subset.

5. An automatic exclusion circuit according to claim 4, further including

an exclusion release switch connected between said third set of contacts and said first source.

6. An automatic exclusion circuit according to claim 5, wherein

said release switch is a momentary contact switch.

7. An automatic exclusion circuit according to claim 5, further including

a hold switch having a first armature connected to said third set of contacts, a first contact connected to said "A" lead and a second contact coupled to the one terminal of said capacitor.

8. An automatic exclusion circuit according to claim 7, further including

a hookswitch having a third contact coupled to the one terminal of said capacitor and a second armature coupled to said first source.

9. An automatic exclusion circuit according to claim 8, further including

a fourth resistor having one terminal coupled to the other terminal of said capacitor, and

a chaining bar switch having a fourth contact coupled to the other terminal of said fourth resistor, a fifth contact coupled to said first source and a third armature normally coupled between said fifth contact and said second armature.

10. An automatic exclusion circuit according to claim 1, further including

a hookswitch having a first contact coupled to the one terminal of said capacitor and a first armature coupled to said first source.

11. An automatic exclusion circuit according to claim 10, further including

a fourth resistor having one terminal coupled to the other terminal of said capacitor, and

a chaining bar switch having a second contact coupled to the other terminal of said fourth resistor, a third contact coupled to said first source and a second armature normally coupled between said third contact and said first armature.