Hands-free device for use with a cellular telephone in a car to permit hands-free operation of the cellular telephone

A hands-free device adapted for use with a cellular telephone in a car to permit hands-free operation of the cellular telephone, said hands-free device comprising:

• a main terminal including:
• a first casing;
• a power supplying unit provided on said first casing and adapted to be connected electrically to a power source of the car;
• a voltage regulating circuit disposed in said first casing and connected electrically to said power supplying unit so as to generate a stable voltage signal therefrom;
• a first connector provided on said first casing and connected electrically to said voltage regulating circuit so as to receive said voltage signal therefrom;
• an audio output amplifier circuit disposed in said first casing and connected electrically to said voltage regulating circuit so as to receive said voltage signal therefrom, said audio output amplifier circuit being further connected electrically to said first connector for amplifying an audio signal received by said first connector;
• and
• a sound output unit connected electrically to said audio output amplifier circuit for reproducing said audio signal from said audio output amplifier circuit;
• a secondary terminal including:
• a second casing;
• a second connector provided on said second casing and connected removably to said first connector;
• a third connector provided on said second casing and adapted to connect removably with the cellular telephone;
• a hands-free control circuit disposed in said second casing and connected electrically to said third connector, said hands-free control circuit being adapted to control hands-free operation of the cellular telephone;
• a voltage output control circuit disposed in said second casing and connected electrically to said second and third connectors, said voltage output control circuit adjusting said voltage signal received by said first connector from said voltage regulating circuit and being adapted to provide said voltage signal to the cellular telephone via said third connector;
• and
• a gain control circuit disposed in said second casing and connected electrically to said second and third connectors, said gain control circuit being adapted to adjust level of said audio signal received from the cellular telephone via said third connector prior to supplying said audio signal to said audio output amplifier circuit via said first and second connectors;
• and
• a microphone provided on one of said main terminal and said secondary terminal for picking up voice signals to be supplied to the cellular telephone by said secondary terminal.