Hold detecting and control circuit for a key telephone system
First Claim
1. A hold detecting circuit for a key telephone system, for determining a telephone line state of on-hook, hold, or off-hook, comprising:
- means for periodidally detecting a line voltage to obtain a detected line voltage;
means for determining a representative stable on-hook line voltage using detected voltge obtained when the telephone line is in an on-hook state;
means for storing the value of said stable on-hook line voltage;
means for determining a representative stable off-hook line voltage using detected voltage obtained when the telephone line is in an off-hook state;
means for storing the value of said stable off-hook line voltage;
means for calculating a first transition threshold voltage separating off-hook and hold line states using the stored stable on-hook and stable off-hook voltages and known system constants;
means for calculating a second transition threshold voltage separating hold and on-hook line states using the stored stable on-hook and stable off-hook voltages and known system constants; and
means for comparing said detected line voltage with said first and second threshold voltages to determine off-hook, on-hook and hold line states.
1 Assignment
0 Petitions
Accused Products
Abstract
A key telephone system for use with at least two telephone lines that extend between a central office and two or more telephone stations. Each station is capable of responding to a manually-actuated hold select switch by establishing a hold condition on one of the lines and by connecting a line terminating impedance across the line that is to be held. Each station is further capable of monitoring the state of each line, and indicating the state of each line, without applying any indicating signals to the telephone lines. Each station furthermore determines threshold voltages for on-hook, off-hook and hold line states and determines line state by comparison of line voltage with such threshold voltages.
41 Citations
65 Claims
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1. A hold detecting circuit for a key telephone system, for determining a telephone line state of on-hook, hold, or off-hook, comprising:
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means for periodidally detecting a line voltage to obtain a detected line voltage; means for determining a representative stable on-hook line voltage using detected voltge obtained when the telephone line is in an on-hook state; means for storing the value of said stable on-hook line voltage; means for determining a representative stable off-hook line voltage using detected voltage obtained when the telephone line is in an off-hook state; means for storing the value of said stable off-hook line voltage; means for calculating a first transition threshold voltage separating off-hook and hold line states using the stored stable on-hook and stable off-hook voltages and known system constants; means for calculating a second transition threshold voltage separating hold and on-hook line states using the stored stable on-hook and stable off-hook voltages and known system constants; and means for comparing said detected line voltage with said first and second threshold voltages to determine off-hook, on-hook and hold line states. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 54)
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36. A hold detecting method for a key telephone system, for determining a telephone line state of on-hook, hold, or off-hook, comprising:
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periodically detecting a line voltage to obtain a detected line voltage; determining a representative stable on-hook line voltage using detected voltage obtained when the telephone line is in an on-hook state; storing the value of said stable on-hook line voltage; determining a representative stable off-hook line voltage using detected voltage obtained when the telephone line is in an off-hook state; storing the value of said stable off-hook line voltage; calculating a first transition threshold voltage separating off-hook and hold line states using the stored stable on-hook and stable off-hook voltages and known system constants; calculating a second transition threshold voltage separating hold and on-hook line states using the stored stable on-hook and stable off-hook voltages and known system constants; and comparing said detected line voltage with said first and second threshold voltages to determine off-hook, on-hook and hold line states. - View Dependent Claims (37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65)
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Specification