Apparatus and method for detecting radio accessories

A method for detecting a secondary accessory to a primary accessory, comprising:

• detecting attachment of the secondary accessory to the primary accessory;
• powering up the secondary accessory through a resistor network;
• sensing the resistance of the resistor network;
• comparing the sensed resistance to a first band of resistance values stored in a look up table of the primary accessory;
• turning on a first bias input, the first bias input being at least one of microphone bias and/or a speaker bias;
• switching in a resistor within the resistor network in response to the first bias input;
• determining a second band of operation for the resistor network;
• turning on a second bias input so that both the microphone bias and speaker bias are turned on;
• switching in another resistor within the resistor network in response to the first and second bias input;
• sensing the resistance of the resistor network with the microphone bias and speaker bias being turned on;
• and
• determining accessory type based on resistance sensed with both the first and second bias inputs turned on;
• and
• operating the secondary accessory in accordance with processing parameters associated with the determined accessory type.

A communication system, comprising:

• a radio;
• a primary accessory coupled to the radio, the primary accessory having an interface for accepting a secondary accessory, wherein the secondary accessory can be one of a plurality of different types of secondary accessories;
• the primary accessory comprising:
• a voltage reference;
• a current to voltage converter for receiving the voltage reference, the current to voltage converter generating a voltage power output for the secondary accessory;
• an analog to digital converter (ADC) for converting the voltage power output to a digital signal;
• a control circuit for sampling and averaging the digital signal into an average ADC signal and comparing the average ADC signal to values stored in a look-up table;
• a bias signal comprising a microphone bias and/or a speaker bias being generated by the primary accessory;
• the secondary accessory comprising:
• a resistor network having plurality of switchably coupled parallel resistors powered by the voltage power output of the primary accessory and controlled by the bias input of the primary accessory, wherein current sourced through the resistor network is converted to the digital signal in the primary accessory to determine accessory type within the look-up table.