METHOD AND APPARATUS FOR DETECTING LONG UNTERMINATED PHONE WIRING LOOPS
A method and apparatus for detecting unterminated phone line loops. The method comprises generating a voltage differential pulse across a phone line loop, measuring a voltage differential across the phone line loop, and determining if the phone line loop is properly terminated based upon the measured differential. The apparatus comprises a voltage pulse generator, two phone wires, and a voltage pulse detector. The voltage pulse generator sends a voltage differential pulse, the two phone wires carry the voltage differential, and the voltage pulse detector measures the voltage differential across the phone wires.
1 . A method for detecting unterminated phone lines, the method comprising:
generating a voltage differential pulse across a phone line loop;
measuring a voltage differential across the phone line loop; and
determining if the phone line loop is properly terminated based upon the measured differential.
2 . The method of claim 1 , further comprising:
determining a power level and duration for the voltage differential pulse, wherein the power level and duration correspond to a particular capacitance for the phone line loop.
3 . The method of claim 2 , wherein the power level and duration are used to determine the length of the phone line loop.
4 . The method of claim 1 , controlled by a computer executing a test module for generating the voltage differential pulse and receiving the measurement of the differential.
5 . The method of claim 4 , performed as part of a Voice-over Internet Protocol (VoIP) system installation process.
6 . The method of claim 1 , further comprising identifying the phone line loop is suitable for VoIP communication if the measured voltage differential is greater than a threshold value.
7 . The method of claim 6 , wherein the threshold value is the voltage differential of the voltage differential pulse.
8 . The method of claim 6 , wherein the threshold value is determined by a controller based on a capacitance value of a particular length of wire.
9 . The method of claim 8 , wherein the particular length of wire is less than a maximum length that may be driven by a VoIP device.
10 . An apparatus for detecting unterminated phone lines comprising:
a voltage pulse generator for sending a voltage differential pulse;
two phone wires for carrying the voltage differential; and
a voltage pulse detector for measuring the voltage differential across the phone wires.
11 . The apparatus of claim 10 , further comprising a rail-to-rail output differential amplifier for applying a source single voltage pulse across the phone wires to create a voltage differential across the phone wires.
12 . The apparatus of claim 11 , further comprising a rail-to-rail input differential amplifier for converting the voltage differential across the phone wires to a single pulse.
13 . The apparatus of claim 10 , further comprising a controller for controlling the voltage differential pulse and receiving a result from the pulse detector.
14 . The apparatus of claim 13 , wherein the controller alters at least one of the duration and power of the voltage differential pulse.
15 . The apparatus of claim 10 , further comprising a switch to protect the voltage pulse generator and pulse detector from high voltages produced across the phone wires.
16 . The apparatus of claim 10 , wherein the pulse detector is at least one of an external interrupt pin or a timer input pin on a VoIP device central processor.
17 . The apparatus of claim 10 , wherein the voltage pulse generator generates a pulse with a power of 3 volts for greater than 1 microsecond and less than 3 microseconds.
18 . The apparatus of claim 10 , wherein the phone wires are a tip wire and a ring wire.