Interface circuit, as well as external detection method and external sensor based on circuit

The invention discloses an interface circuit, as well as an external detection method and an external sensor based on the circuit. The interface circuit comprises a control circuit, a combinational circuit and an earphone socket, wherein the control circuit confirms the external equipment type of the earphone socket according to the received voltage value or level value entering and leaving detecting pins; when the access external equipment is confirmed to be the earphone, the control circuit control the combinational circuit to connect the earphone control wire pins of the control circuit with the signal wire port if the earphone socket; when the access external equipment is confirmed to be the sensor, the control circuit controls the combinational circuit to connect sensor control wire pins of the control circuit with the signal wire port of the earphone socket to achieve the purpose that the sensor is expanded by connecting the external sensor through the earphone output interface.