Electronic Device and Audio Accessory Having a Plurality of Passive Switches for Controlling the Audio Device

An audio accessory comprising at least one speaker adapted to provide audio output and a plurality of resistive switches, each switch having a resistive element having a resistance, the audio accessory being coupleable to an electronic device having a bias voltage source adapted to provide power to the resistive switches via an bias resistor, and a measurement module, and when the audio accessory is coupled to the electronic device, the measurement module is adapted to:

• monitor a bias point on a connection between the bias voltage source and the resistive switches to determine when at least one of the switches has been engaged;
• at least once while that switch is engaged, activate and deactivate the bias voltage source, taking a first measurement of the bias point while the bias voltage source is activated and a second measurement of the bias point while the bias voltage source is deactivated;
• determine a ground offset voltage caused by the audio output based on the second measurement;
• compensate for the ground offset voltage caused by the audio output voltage based on a voltage difference between the first and second measurements;
• and
• determine which of switches has been engaged based on the voltage difference.

An electronic device coupleable to an audio accessory having at least one speaker adapted to provide audio output and a plurality of resistive switches, each switch having a resistive element having a resistance, the electronic device comprising:

• a bias voltage source adapted to provide power to the resistive switches via a bias resistor when the electronic device is coupled to the audio accessory;
• and
• a measurement module adapted to:
• (a) monitor a bias point on a connection between the bias voltage source and the resistive switches to determine when at least one of the switches has been engaged;
• (b) at least once while that switch is engaged, activate and deactivate the bias voltage source, taking a first measurement of the bias point while the bias voltage source is activated and a second measurement of the bias point while the bias voltage source is deactivated,
• (c) determine a ground offset voltage caused by the audio output based on the second measurement,
• (d) compensate for the ground offset voltage caused by the audio output by determining a voltage difference between the first and second measurements, and
• (e) determine which of switches has been engaged based on the voltage difference.

A method for determining which of a plurality of switches in an audio accessory is engaged comprising:

• providing the audio accessory having at least one speaker adapted to provide audio output and a plurality of resistive switches, each switch having a selected resistance;
• providing an electronic device coupled to the audio accessory having a bias voltage source adapted to provide power to the resistive switches via a microphone bias resistor and a ground connection;
• monitoring a bias point on a connection between the bias voltage source and the switches to determine when at least one of the switches has been engaged;
• at least once while that switch is engaged, activating and deactivating the bias voltage source and taking a first measurement of the bias point while the microphone bias voltage source is activated and a second measurement of the bias point while the microphone bias voltage source is deactivated;
• determining a ground offset caused by the audio output;
• compensating for the ground offset caused by the audio output based on a voltage difference between the first and second measurements;
• and
• determining which of the switches has been engaged based on the voltage difference.