Patent ID: 7394906

Claim:
A method for operating a device for automatically controlling an audio volume based on a vehicle speed, comprising: manipulating a mode-setter provided on a car audio device to select an automatic volume control mode; calculating a vehicle speed; determining a vehicle speed level by comparing the calculated vehicle speed with a plurality of limit values of the vehicle speed level; and outputting a volume modification value related to both the vehicle speed level of the calculated vehicle speed and the selected automatic volume control mode to control the audio volume of the car audio device, wherein the outputting a volume modification value further includes generating a vehicle speed pulse based upon the calculated vehicle speed, calculating the vehicle speed based upon a voltage of the vehicle speed pulse, and determining a vehicle speed level corresponding to the calculated vehicle speed; calculating the vehicle speed further includes providing a plurality of resistors connected at a point, and receiving the vehicle speed pulse at the point, connecting at least one diode to at least one of the plurality of resistors, and connecting a plurality of switching diodes to at least a second of the plurality of resistors and to at least another resistor.