| 摘要 |
Apparatus is disclosed for disconnecting and reconnecting equipment to a telephone line in response to at least one signal sent over the telephone line. The apparatus includes a voltage threshold circuit, a voltage regulator circuit, a current chargeable element such as a capacitor, a discharge circuit, a switch and a switch control. The switch is coupled to the telephone line and to the equipment and disconnects the equipment from the line in response to the signal sent over the line. The threshold circuit is coupled to the line and receives the signal. It provides an output signal to the regulator circuit only when the signal on the line exceeds a threshold voltage level. The voltage regulator circuit regulates the voltage at the output of the threshold circuit and provides a substantially constant voltage to the chargeable element. Since the voltage applied to the chargeable element is known, the time required to charge the chargeable element can be precisely determined. The chargeable element is coupled to the discharge circuit which causes the chargeable element to discharge when the signal to the threshold circuit falls below the threshold value, for example, when the signal is removed. The switch control is coupled to the discharge circuit and maintains the switch in a switched, equipment-disconnected condition while the chargeable element is discharging.
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