receiver block 9 receives wirelessly data from the head unit 4 as will be explained herein below the base unit 2 further has u2212 5v invertor block 11 it inverts the 5v power supply from 5 u00d7 5 card to u2212 5v which is required by the signal amplification block 6 and the codec block 7 finally the base unit 2 has a connector 12 to the head unit 4 when it connects the base unit 2 to the head unit 4 it provides a power supply for the head unit operation and battery charger the head unit 4 has a connector 13 to the base unit 2 it connects the head unit 4 to the base unit 2 the head unit 4 further has a battery charger block 14 which is designed to charge two cell lithium ion battery to 8 2v a 5v regulator block 15 regulates the battery voltage to 5v required by the head unit a u2212 5v inverter block 16 inverts the 5v from 5v regulator 15 to u2212 5v which is required by signal amplification and codec blocks specified herein below the signal amplification block is identified with reference numeral 17 it amplifies the voice signal from a microphone input member 18 a codec and filtering block 19 filters and digitizes the voice analog signal from the microphone input member 18 and sends voice data to the microcontroller block 20 the microcontroller block 20 transmits the data from the codec block 19 to an infrared transmitter 21 it generates the 8 khz clock for the codec block 19 and the microprocessor series peripheral interface port spi that.