Timing and control circuit for intercom telephone system

Claim 2

For an intercom telephone system of the type including a plurality of stations, pulsing switch means normally operated by a calling station, means for releasing said Pulsing switch means during receipt of each dial pulse from said calling station and for reoperating said pulsing switch means following each dial pulse, a source of ringing voltage, routing means having a plurality of output terminals and responsive to operation of said pulsing switch means for coupling said ringing voltage source to an output terminal corresponding to the digit dialled; a timing and control circuit comprising: a. a timing capacitance having a first terminal, b. switch means, said switch means including ringing means operative upon operation of said switch means to connect said ringing voltage source to said routing means, c. means for enabling said switch means during receipt of dial pulses, d. said first terminal of said capacitance being coupled to said switch means to operate said switch means provided that said switch means is enabled, when the potential at said first terminal reaches a first predetermined level, e. a charging circuit including a resistance, and means connecting said charging circuit to said capacitance for varying the charge on said capacitance with a first time constant, f. means responsive to receipt of each dial pulse for shifting the potential at said first terminal to a second predetermined level different from said first predetermined level and at which said ringing switch means will not operate, and then permitting the charge on said capacitance to vary through said charging circuit to vary the potential at said first terminal toward said first level following the end of such dial pulse, the difference between said first and second predetermined levels and said first time constant being such that a time greater than the time between dial pulses is required for the potential at said first terminal to reach said first predetermined level, so that said switch means and hence said ringing means will operate only after completion of receipt of a digit from said calling station, g. means responsive to operation of said ringing means to maintain said ringing means operated, h. means responsive to operation of said ringing means for increasing the resistance in said charging circuit, i. means responsive to operation of said ringing means for shifting the potential at said first terminal of said capacitance to a third predetermined level to turn off said switch means and then permitting the potential at said first terminal to vary toward said first predetermined level with a second time constant greater than said first time constant, j. and means connected to said switch means and responsive to reoperation thereof with said ringing means operated to turn off said ringing means, thereby to terminate ringing.

Claim 3

A timing and control circuit according to claim 1 wherein said switch means includes a high gain amplifier having an input and a switched output, said first terminal of said capacitance being coupled to said input of said amplifier to turn on said amplifier when the potential at said first terminal reaches said first predetermined level, said means (c) including means for biasing said amplifier off until receipt of a first dial pulse from said calling station, and means connecting said output of said amplifier to control said ringing means.

Claim 4

A timing and control circuit according to claim 2 wherein said ringing means includes a ringing relay having a plurality of contacts, and said means (h) includes a second resistance of value greater than said first mentioned resistance, and means including a contact of said ringing relay for switching said second resistance into said charging circuit in place of said first mentioned resistance.

Claim 5

For an intercom telephone system of the type including a plurality of stations, pulsing switch means normally operated by a calling station, means for releasing said pulsing switch means during receipt of each dial pulse from said calling station and for reoperating said pulsing switch means following each dial pulse, a source of ringing voLtage, routing means having a plurality of output terminals and responsive to operation of said pulsing switch means for coupling said ringing voltage source to an output terminal corresponding to the digit dialled; a timing and control circuit comprising: a. a timing capacitance having a first and second terminals, b. an amplifier, c. means coupled to said amplifer and responsive to operation of said pulsing switch means to disable said amplifier until receipt of a first dial pulse and then to enable said amplifier, d. said first terminal of said capacitance being coupled to said amplifier to turn on said amplifier provided that said amplifier is enabled, when the potential at said first terminal reaches a first predetermined level, e. a charging circuit,including a resistance having a first value,for charging said capacitance with a first time constant, f. means responsive to each release of said pulsing switch means during receipt of a dial pulse for shifting the potential at said first terminal of said capacitance to a second predetermined level different from said first predetermined level during such dial pulse and then permitting said capacitance to charge again through said charging circuit, the difference between said first and second predetermined levels and first time constant being such that said capacitance requires a time greater than the time between dial pulses to recharge to said first predetermined level, so that said amplifier will turn on only after receipt of a complete digit from said calling station, g. ringing switch means operative in response to operation of said amplifier to connect said ringing voltage source to said routing means, h. means responsive to operation of said ringing switch means to maintain said ringing switch means operated, i. means responsive to operation of said ringing switch means to shift the potential at said first terminal of said capacitance to a third predetermined level to turn off said amplifier, j. means responsive to operation of said ringing switch means for increasing the resistance in said charging circuit to a second value greater than said first value so that said capacitance will then recharge towards said first predetermined level with a second time constant longer than said first time constant, k. and means connected to said amplifier and responsive to reoperation thereof with said ringing switch means operated to terminate operation of said ringing switch means thereby to terminate said ringing after a ringing period timed by charging of said capacitance with said second time constant.

Claim 6

For an intercom telephone system of the type including a plurality of stations, pulsing switch means normally operated by a calling station, means for releasing said pulsing switch means during receipt of each dial pulse from said calling station and for reoperating said pulsing switch means following each dial pulse, a source of ringing voLtage, routing means having a plurality of output terminals and responsive to operation of said pulsing switch means for coupling said ringing voltage source to an output terminal corresponding to the digit dialled; a timing and control circuit comprising: a. a timing capacitance having a first and second terminals, b. an amplifier, c. means coupled to said amplifer and responsive to operation of said pulsing switch means to disable said amplifier until receipt of a first dial pulse and then to enable said amplifier, d. said first terminal of said capacitance being coupled to said amplifier to turn on said amplifier provided that said amplifier is enabled, when the potential at said first terminal reaches a first predetermined level, e. a charging circuit,including a resistance having a first value,for charging said capacitance with a first time constant, f. means responsive to each release of said pulsing switch means during receipt of a dial pulse for shifting the potential at said first terminal of said capacitance to a second predetermined level different from said first predetermined level during such dial pulse and then permitting said capacitance to charge again through said charging circuit, the difference between said first and second predetermined levels and first time constant being such that said capacitance requires a time greater than the time between dial pulses to recharge to said first predetermined level, so that said amplifier will turn on only after receipt of a complete digit from said calling station, g. ringing switch means operative in response to operation of said amplifier to connect said ringing voltage source to said routing means, h. means responsive to operation of said ringing switch means to maintain said ringing switch means operated, i. means responsive to operation of said ringing switch means to shift the potential at said first terminal of said capacitance to a third predetermined level to turn off said amplifier, j. means responsive to operation of said ringing switch means for increasing the resistance in said charging circuit to a second value greater than said first value so that said capacitance will then recharge towards said first predetermined level with a second time constant longer than said first time constant, k. and means connected to said amplifier and responsive to reoperation thereof with said ringing switch means operated to terminate operation of said ringing switch means thereby to terminate said ringing after a ringing period timed by charging of said capacitance with said second time constant.

Claim 7

A circuit according to claim 4 wherein said amplifier is a high gain amplifier, said first and second resistance values are high value with said first resistance being of the order of at least substantially 100,000 ohms.

Claim 8

A circuit according to claim 5 wherein said pulsing switch means is a pulsing relay having a plurality of contacts, said ringing switch means is a ringing relay having a plurality of contacts, said resistance being connected to said first terminal of said capacitance through a contact of said ringing relay, said means (f) including a contact of said pulsing relay connected to said first terminal of said capacitance and for connection to a voltage source for clamping said first terminal of said capacitance at a fixed potential during receipt of each dial pulse.

Claim 9

A circuit according to claim 6 wherein said means (f) further includes a further contact of said pulsing relay and means connecting said further contact to said second terminal of said capacitance for applying a voltage to said second terminal of said capacitance at the end of each dial pulse to shift the potential at said first terminal of said capacitance to said second level at the end of each dial pulse.

Claim 10

A circuit according to claim 4 wherein said means (i) includes a contact of said ringing relay and means responsive to operation of such contact of said ringing relay For clamping the potential at said second terminal of said capacitance at a fixed level to shift the potential at said first terminal of said capacitance to said third predetermined level.

Claim 11

A circuit according to claim 8 wherein said means responsive to operation of said contact of said ringing relay includes a slow release relay having a plurality of contacts,means for normally operating said slow release relay upon operation of said pulsing relay and during dialling, and means for releasing said slow release relay upon operation of said contact of said ringing relay, said means (g) including a normally closed contact of said slow release relay, so that after operation of said ringing relay,connection of said ringing voltage source to said routing means is delayed by the release time of said slow release relay.

Claim 12

A circuit according to claim 9 including means including contacts of said ringing and slow release relays for applying a transfer signal to said routing means after operation of said ringing relay and before release of said slow release relay, said transfer signal being adapted to operate a transfer circuit connected to a signalled output terminal of said routing means.

Claim 13

A circuit according to claim 6 wherein said means (h) and(k) together include a locking circuit, including a contact of said ringing relay, for locking said ringing relay operated upon operation of said ringing relay, said locking circuit including means responsive to operation of said amplifier subsequent to operation of said ringing relay to open said locking circuit thus to de-energize said ringing relay.

Claim 14

A circuit according to claim 1, wherein said capacitance is a foil type capacitor.