Abstract: A pulse shaping circuit, for use with two-wire telephone station sets, such as normally associated with electronic private automatic branch exchange systems. The function of the pulse circuit is to regenerate hook-switch and hold-button control signal pulses for transmission to the common switching equipment as finite loop current interruptions of predetermined pulse width. The circuit overcomes false signalling and signal recognition problems caused by loop-current transient interruptions, and by imprecise manual operation of the station hook-switch and hold-button by station users.

Abstract: An energy limiting foldback circuit for use with power supply having a power control device in its output. The energy limiting foldback circuit contains a voltage sensing device for sensing the potential drop between the input and the output of the power control device. The foldback circuit also includes a current sensing device for sensing the current through the power control device. A conduction control circuit is included which is responsive to the outputs of the voltage sensing device and the current sensing device. The conduction control circuit acts to control the operating conduction through the power control device. The energy limiting circuit can also include a pulsing circuit operative in the event of output fault to periodically pulse the power control device into a momentary conduction state.

Abstract: The lines or stations of a multi-line office telephone system are sequentially examined to detect a hold tone signal of a specified frequency or frequencies on one or more of the lines. The lines are examined for increasingly longer time periods in accordance with the type of energy sensed at each line. If the line is not active or connected in a first brief period, the scanner then proceeds to examine the next line for a hold tone signal. If wide-band energy is not detected on the line in a second, longer period, the examination of the line is terminated and the scan process is continued to the next line. If wide-band energy above a threshold is detected on the line in a third, still longer period, the detected energy is further examined to determine whether this energy includes a valid hold tone signal. If a hold tone signal is detected on a line, the line is scanned again to detect the removal of the hold tone signal therefrom, whereupon a hold status is assigned to the line.