Sensor circuit for telephone line

A sensor circuit for magnetically sensing a line current in a telephone line that is connectable to a telephone and a facsimile machine, the sensor circuit comprising:

• a) line current detecting means for magnetically detecting a line current which flows in the telephone line and outputting a detection signal corresponding to the line current detected by the line current detecting means;
• b) first means for outputting a line current supervisory signal on the basis of the detection signal;
• and
• c) second means for deriving a tone signal from the detection signal, the derived tone signal indicating that the line current is to be sent to the facsimile machine and that the telephone line is to be connected to the facsimile machine, the second means including:
• 1) direct current component removing means for removing a direct current component from the detection signal output from the line current detecting means;
• and
• 2) filter means for filtering an output of the direct current removing means so as to derive a tone signal.

A sensor circuit for magnetically sensing a line current in a telephone line that is connectable to a telephone and a facsimile machine, the sensor circuit comprising:

• a) line current detecting means for magnetically detecting a line current which flows in the telephone line and outputting a detection signal corresponding to the line current detected by the line current detecting means;
• b) first means for outputting a line current supervisory signal on the basis of the detection signal, the first means including;
• 1) comparing means for comparing the detection signal output from the line current detecting means with at least one reference signal, wherein the comparing means includes first and second comparators, the first comparator compares the detection signal with a first reference signal and the second comparator compares the detection signal with a second reference signal which is different from the first reference signal;
• c) second means for deriving a tone signal from the detection signal, wherein the derived tone signal indicates that the line current in the telephone line is to be sent to the facsimile machine and that the telephone line is to be connected to the facsimile machine.