Interface circuit and peripheral detection method and external sensor based on interface circuit

The invention discloses an interface circuit and a peripheral detection method and an external sensor based on the interface circuit. The interface circuit comprises a control circuit, a combination switch circuit and an earphone socket. The control circuit determines the type of external equipment of the earphone socket according to the received outlet and inlet voltage values or level values of a detection pin, when it is determined that the external equipment which is connected in is an earphone, the control circuit controls the combination switch circuit to connect an earphone control line pin of the control circuit to a control line port of the earphone socket, when it is determined that the external equipment which is connected in is a sensor, the control circuit controls the combination switch circuit to connect a sensor control line pin of the control circuit to the control line port of the earphone socket, and therefore the purpose that the external sensor is connected in through an earphone output interface and is expanded is achieved.