Patent ID: 8064613

Claim:
In a device having a USB connector, a method of detecting the coupling of an electret microphone and identifying whether there is monaural or stereo speakers coupled to the USB connector, the USB connector having VBUS, D+, D−, ID and ground terminals, comprising: coupling a current source to the ID terminal and detecting the voltage on the ID terminal; and, detecting that the voltage on the ID line is substantially below the voltage associated with any other accessory when an electret microphone is coupled between the ID terminal and the ground terminal, and coupling a microphone bias resistor to the ID line; and, on detection of an electret microphone being coupled between the ID terminal and the ground terminal, determining whether there is a monaural or stereo speakers coupled to the USB connector by detecting the impedance on the one of the D+ and D− terminals to which a monaural speaker would not be coupled.