Abstract: A music on hold system is provided for key telephone systems having key stations, central office lines, and a muting relay for load resistance termination of the central office lines when they are on hold. A music source provides a music signal which is applied to the muting relay. When the telephone system controller receives a hold command from a key station, it generates a hold signal and applies the hold signal to the muting relay. In response to the hold signal, the muting relay applies the music signal to the central office line. Before being applied to the muting relay, the music signal is conditioned by passage through a gain control, a high frequency cut off filter, an amplifier, and a DC level shifter.

Abstract: A telephone call routing and charging system using processor circuitry can automatically select the most economical route for individual telephone calls. The system includes a signal direction detector for automatically determining the time span of a call for charge purposes from the time the call is answered to the time the call is terminated.

Abstract: A speaker telephone system having hands-free telephone sets with microphones and loud-speakers and including circuitry for preventing feedback between the loud-speakers and the microphones in both the transmitting and receiving modes by automatically controlling the amplification of the signals coming from the microphones and going to the loud-speakers, as a function of the signal direction, while still maintaining the microphones and loud-speakers electrically coupled to the telephone lines.

Abstract: A solid state subscriber station network which provides transmitting, receiving and regulating functions using a single active element. The transmitted signals, the received signals and the regulatory functions can be separately varied within proscribed limits without adversely affecting the other functions.

Abstract: A two-way amplifier arrangement which automatically controls current flowing in the transmission circuits to maintain that current at a fixed level. The two-way amplifier arrangement finds utility as a conference amplifier and as a two-way trunk amplifier.

Abstract: An improved dialing system, basically powered through the line, that provides automatic dialing of stored, frequently used numbers and the last number dialed. Self-test capabilities are provided to enable and test all the stored number memory locations automatically. Outgoing call restrictions are provided with a programmable code to bypass the call restriction. The system automatically converts push button dialing to rotary outpulsing, or generates dual tone multi-frequency dialing signals.

Abstract: A push button to rotary dial converter system for converting push button telephones to provide rotary dial type pulsed outputs. The system provided is universal and can be used with almost any subscriber set that is made to provide push button signals to the telephone system and is especially useful when the telephone system involved is not equipped to receive variable frequency dialing signals. Responsive to the operation of the selected push buttons, pulses are transmitted through the line. The system is unique, among other ways, in that the connection to the network is electronically opened during out pulsing and a parallel power supply arrangement is employed; and it is applicable even when only one pair of hook switche contacts are available, and one side of the pair of hook switch contacts are tied together.