Switching circuit for telecommunications lines

Claim 2

A switching circuit for connecting and disconnecting subscriber equipment associated with a subscriber loop, in response to a voltage control signal momentarily transmitted on the subscriber loop, the switching circuit comprising: switch means including a magnetically latching relay and associated contact means, the contact means for connection in series between the subscriber loop and subscriber equipment, whereby operation of the latching relay effects a connected state or a disconnected state between the subscriber equipment and the subscriber loop via the contact means; a variable impedance means connected in series with the latching relay, the variable impedance means having high and lower impedance states and being responsive to a predetermined voltage to switch from the high to the lower impedance state and being responsive to the current flow therethrough being reduced below a predetermined level to switch to the high impedance state; switch control means connected to the switch means, the switch control means including charge storage means for connection via a predetermined impedance means to a lead in the subscriber loop, whereby the voltage control signal causes an accumulation of charge to occur in the charge storage means at a potential of up to said predetermined voltage whereafter the accumulated charge is rapidly dissipated through the variable impedance means and the latching relay causes the associated contacts to effect one of the two states.

Claim 3

A switching circuit as defined in claim 1 in which the charge storage means and the impedance comprise a resistive capacitive network including a resistive portion for connection to a lead in the subscriber loop and a capacitive portion connected to the switch means, the resistive portion being of such value that in the presence of the voltage control signal, on said lead, said charge slowly accumulates in the capacitive portion until said predetermined voltage is reached, and in the absence of the voltage control signal other signals on the subscriber loop are of insufficient voltage and duration to cause said predetermined voltage to be reached.

Claim 4

The switching circuit as defined in claim 2 in which the capacitive portion comprises a capacitor and a resistor connected in parallel, and the capacitive portion is connected across the series connection of the variable impedance means and the magnetically latching relay.

Claim 5

A switching circuit as defined in claim 2 in which first and second switch control means are connected in series for connection across the subscriber loop and in which the switch means includes first and second variable impedance means, the first variable impedance means being connected to the junction between the resistive and capacitive portions in the first switch control means, and the second variable impedance means being connected to the junction between the resistive and capacitive portion in the second switch control means whereby the magnetically latching relay is actuatable from either side of the subscriber loop.

Claim 6

A switching circuit as defined in claim 4 further comprising means for inhibiting response in one of said switch control means, in response to an inhibit signal from the associated switching facility, the inhibiting means for connection across the subscriber loop on the side of the contact means adjacent the switching facility, and including switch means connected across the capacitive portion in said one switch control circuit, whereby the state of connection of one of two subscriber equipments, each associated with the subscriber loop via contact means in first and second switching circuits respectively, is alterable without disturbing the state of connection of the other of the two subscriber equipments.

Claim 7

A switching circuit as defined in claim 2, further comprising loop terminals for connection to the subscriber loop, subscriber terminals for connection to the subscriber equipment and a reference terminal for connection to earth, and in which said contact means is connected between the loop terminals and the subscriber terminals, the capacitive portion is connected across the series connection of the variable impedance means and the magnetically latching relay, the magnetically latching relay is terminated at the reference terminal, and the resistive portion is connected to one of the loop terminals.

Claim 8

A switching circuit as defined in claim 4, further comprising loop terminals for connection to the subscriber loop, subscriber terminals for connection to the subscriber equipment and a reference terminal for connection to earth, and in which the resistive portions of the first and second switch control means are connected each to a separate one of the loop terminals, and the magnetically latching relay is terminated at the reference terminal.

Claim 9

A switching circuit for connecting and disconnecting subscriber equipment associated with a subscriber loop in response to a control signal momentarily transmitted on one of two leads of the subscriber loop, the switching circuit comprising: first and second loop terminals for connection to the leads of the subscriber loop, first and second subscriber terminals for connection to the subscriber equipment and a reference terminal for connection to earth; a magnetically latching relay having an operate coil and associated contact means, one end of the operate coil being connected to the reference terminal, the contact means being connected in series between the loop terminals and the subscriber terminals whereby the magnetically latching relay effects a state of connection or disconnection between the subscriber loop and the subscriber terminals; first and second variable impedance means each having high and lower impedance states and each being responsive to a predetermined voltage to switch from the high to the lower impedance state to conduct current therethrough; first and second charge storage means connected between the reference terminal and the first and second loop terminals respectively, the first and second charge storage means each having a discharge terminal, said first and second variable impedance means being connected in series between the other end of said operate coil and the discharge terminals of the first and second charge storage means respectively, whereby said predetermined voltage appearing at the discharge terminal of one of the charge storage means causes the associated variable impedance means to conduct and thereby discharge the one charge storage means through the operate coil to the ground terminal.

Claim 10

A switching circuit for connecting and disconnecting subscriber equipment associated with a subscriber loop in response to a control signal momentarily transmitted on one of two leads of the subscriber loop, the switching circuit comprising: first and second loop terminals for connection to the leads of the subscriber loop, first and second subscriber terminals for connection to the subscriber equipment and a reference terminal for connection to earth; a magnetically latching relay having an operate coil and associated contact means, one end of the operate coil being connected to the reference terminal, the contact means being connected in series between the loop terminals and the subscriber terminals whereby the magnetically latching relay effects a state of connection or disconnection between the subscriber loop and the subscriber terminals; first and second variable impedance means each having high and lower impedance states and each being responsive to a predetermined voltage to switch from the high to the lower impedance state to conduct current therethrough; first and second charge storage means connected between the reference terminal and the first and second loop terminals respectively, the first and second charge storage means each having a discharge terminal, said first and second variable impedance means being connected in series between the other end of said operate coil and the discharge terminals of the first and second charge storage means respectively, whereby said predetermined voltage appearing at the discharge terminal of one of the charge storage means causes the associated variable impedance means to conduct and thereby discharge the one charge storage means through the operate coil to the ground terminal.

Claim 11

A switching circuit as defined in claim 8 further comprising an inhibit relay means, and associated inhibit contact means, the inhibit relay means being connected between the loop terminals and the inhibit contact means connected in series between one of said discharge terminals and the ground terminal, the inhibit relay means being responsive to a predetermined signal appearing across the loop terminal to control operation of the inhibit contact means and thereby render said one charge storage means selectively operative or inoperative, whereby one of a plurality of the switching circuits associated with a single subscriber loop is selectably operative by the control signal.

Claim 12

A switching circuit as defined in claim 9 in which the predetermined signal is an alternating current signal of a predetermined frequency and in which the inhibit relay means includes an operate coil in a resonant circuit which is resonant at about said predetermined frequency.