Device for entertainment during driving of a car

Device to be plugged into an electric socket in a vehicle, the socket constituting a part of an electrical system of the vehicle, the device, without any other connection, being able to detect an engine speed of the vehicle from signals unintentionally emitted from a generator, electric motor or ignition system of the vehicle and to convert the detected engine speed to sound signals, the device comprising:

• a signal processor, which assumes that the speed of an engine changes continuously and with a certain inertia, capable of identifying regular speed-generated pulses, filtering off sudden pulses other than pulses that have the engine speed as a source, the device, in cases when the signal processor cannot calculate a given speed from the incoming pulses, takes the lowest pulse frequency that is unchanged over a certain time, and use it as a benchmark for normal idling speed.