Abstract: A telephone having a hook switch is coupled to tip and ring conductors for receiving loop current from a central office responsive to an off-hook condition at the hook switch. The electronic circuity within the telephone for facilitating various functions is powered entirely from the loop current flowing from the central office during the off-hook condition.

Abstract: A telephone having a hook switch is coupled to tip and ring conductors for receiving loop current from a central office responsive to an off-hook condition at the hook switch. The electronic circuitry within the telephone for facilitating various functions is powered entirely from the loop current flowing from the central office during the off-hook condition; with loop current being maintained after termination of the off-hook condition in order to perform certain call functions.

Abstract: A toll telephone coupled to tip and ring conductors of a toll trunk and through which various toll signals flow between a central office and the telephone (such as a coin ground signal to indicate the presence of the coin) has a hook switch with an off-hook condition for instituting the flow of loop current. To allow local, coin-free calls, the telephone has electronic circuitry for applying a simulated coin ground signal to the tip conductor continuously during the off-hook condition to permit coin-free calls to be made from the toll telephone. Additionally, the telephone includes a single relay system for providing an open-loop coin check responsive to a corresponding signal from the central office. The telephone provides a notch filter for discriminating against one of the multiple frequencies of a bong tone, thus allowing the remaining frequency to be detected.

Abstract: A toll telephone connected to a coin trunk including tip and ring conductors in which loop current flows from the central office and through the telephone responsive to an off-hook condition at the telephone includes electronic circuitry for maintaining the loop current flow through the telephone for a predetermined period of time after the hook switch is opened, in order to accomplish certain telephone functions. Those functions include operation of an escrow relay, prevention of hook switch fraud, prevention of central office call termination until the call is legitimately completed and completion of certain call accounting functions.

Abstract: There is provided a telephone toll restrictor which is adapted to split the telephone line into two separate circuits for isolating the instrument from the central office during dialing. A dialing tone sensor provides signalling information to a programmed microprocessor which determines whether or not the number is permissible. A pair of filters separate the high and low frequencies of the tone and input this information to the microprocessor. If the dialing tones are permissible, then a generator regenerates the tones and passes the tones to the central office for completing the call. Furthermore, the telephone line is then recoupled and the call is permitted. If the call is not permitted, then a holding bridge, which holds the central office while the microprocessor examines the number, is opened by the microprocessor, causing the central office to time out, thus denying access to the caller.

Abstract: An improved telephone toll restrictor utilizing both current and voltage sensors having substantially infinite input impedance during the on-hook condition. A timing circuit is provided to restrict calls a predetermined time after a digit is dialed but prior to central office timeout. Furthermore, a pulse generator provides a strobe pulse to a coincidence gate which also responds to a digit pulse counter, for avoiding restriction of a digit which should not be restricted.

Abstract: There is provided a line circuit for connection to a key telephone system for indicating an incoming call, a call placed on hold, and an answered call. There is further provided a means for automatically indicating that the incoming call has been placed on hold for a predetermined time period. There is further provided a solid state device which switches telephone instrument lamp current for visual indication of the various line circuit operations.