PURPOSE: To attain convenience similar to an usual subscriber's station by using a private line by providing an off-hook detecting circuit and a transmitting means for transmitting a specified frequency signal of transmission in a telephone control part of the transmission side.
CONSTITUTION: When a telephone set is off-hooked on the transmission side, a current (i) flows from a battery 28, and an off-hook detection signal is transmitted to the telephone control part MO of the transmission side telephone set. The control part MO, after receiving the signal, opens a gate 32 to transmit a signal of 400Hz into a line 1. After receiving the said signal, a control part M1 on the reception side transmits an off-hook detection signal to a private branch exchange. After receiving the said signal,the said exchange transmits a dial tone (DT) into the line. If a dialing is executed at this time, a DTMF (dialing) signal is transmitted into the line 1 through the MO, but, because a DTMF detecting circuit 33 detects this signal, the telephone set control circuit 31 closes the gate 32, and the 400Hz signal is stopped, and the MTMF signal is transmitted to the other side instead of the 400Hz signal.
UCHIDA YASUO
MATSUDA HIROSHI
ICHIRIKI HIDENAGA
