| 摘要 |
PURPOSE:To make a cable exclusively used for detection unnecessary by detecting the DC potential of a speaker line, which is pulled down by the DC resistance component of a speaker when the state of a telephone set is a connected state and pulled up at a resistor when the state of the telephone set is a separated state. CONSTITUTION:When the state of a telephone set part 2 is the one in which the part 2 is connected through a cable 3 to a body part 1, the DC potential at a (b) point is pulled down by the DC resistance component of a speaker 10 and made into L. Further, a resistance R2 and a capacitor C2 to form an LPF eliminate a voice component. Consequently, a potential at an (a) point also becomes L, a comparator 15 sends an H voltage to a control part 6, and the control part 6 controls an operation when the state of the telephone set is the connected state. When the state of the telephone set part 2 is the one in which the part 2 is separated from the body part 1, the DC potential at the (b) point is pulled up at a resistance R1 and made into H. Consequently, the potential at the (a) point also becomes H, the comparator 15 sends an L voltage to the control part 6, and the control part 6 controls another operation when the state of the telephone set is a non-connected state. Thus, the cable exclusively-used for the detection becomes unnecessary, and the number of cables can be decreased. |
