Apparatus and method for providing a telephone user with control of the threshold volume at which the user's voice will take control of a half-duplex speakerphone conversation

A half-duplex speakerphone comprising:

• a microphone for generating a signal to be placed on a phone line;
• a speaker for generating an audio signal from an input signal, the input signal being determined by a signal received on the phone line;
• a transmit attenuator connected between the microphone and the phone line for isolating the microphone from the phone line when the transmit attenuator is on, the transmit attenuator generating an output signal that is placed on the phone line when the transmit attenuator is off;
• a receive attenuator connected between the phone line and the speaker for isolating the speaker from the phone line when the receive attenuator is on;
• attenuator controller for controlling the transmit and receiver attenuators such that one attenuator is on and one attenuator is off at any given time;
• a first variable amplifier having an input connected to the output of the microphone and an output connected to a first level detector, the first level detector comparing the output of the first variable amplifier and the signal at the input of the speaker and generating a comparison signal that is input to the attenuator controller;
• a second variable amplifier having an input connected to the input of the receive attenuator and an output connected to a second level detector, the second level detector comparing the output of the second variable amplifier and the output signal of the transmit attenuator and generating a comparison signal that is input to the attenuator controller,
• wherein the attenuation controller turns on the transmit attenuator when the second level detector indicates that the output of the second variable amplifier exceeds the signal level at the output of the transmit attenuator by a predetermined amount, wherein the attenuation controller turns on the receive attenuator when the first level detector indicates that the output of the first variable amplifier exceeds the input to the speaker by a predetermined amount, and wherein the first and second variable gain amplifiers include adjustable gain controls that are connected such that the gain of the first variable amplifier is decreased when the gain of the second variable amplifier is increased and vice versa, the adjustable gain controls being adjustable by a user of the speakerphone.