Patent ID: 7633340

Claim:
An apparatus for determining the voltage level of a first signal from a playback device having an interface in compliance with an industrial standard, and the apparatus comprises: a signal receiving pin electrically coupled to a signal transmitting pin of the interface to receive the first signal; a first zener diode having a first breakdown voltage, where the cathode of the first zener diode is connected to the signal receiving pin; a first transistor having a first forward biased voltage, where the anode of the first zener diode is connected to the base of the first transistor and provide a first output voltage; a second zener diode having a second breakdown voltage, where the cathode of the second zener diode is connected to the signal receiving pin; a second transistor having a second forward biased voltage, where the anode of the second zener diode is connected to the base of the second transistor and provide a second output voltage; and a processor electrically coupled to the first transistor and the second transistor, where the processor can determine the voltage level of the first signal according to first output voltage and the second output voltage.