Indicator of the air pressure in the pneumatic tires of a vehicle based on a capacitive coupling

A device for monitoring tire air pressure in each one of the wheels of a vehicle at any time, and providing the driver of the vehicle with a warning signal in case the pressure in any one of the vehicle's tires deviates from a normal predetermined value. The device includes a tire pressure gauge mounted onto the rotating tire, connected to a pair of air capacitors formed by four metallic annular strips, these capacitors being used as a timing capacitor in an oscillator producing two discrete frequencies depending on the ON-OFF position of the tire pressure gauge. Eventually a voltage comparator produces a square train pulse whenever its input falls below a certain level determined by a trimmer and the amplitude of the square train pulse is increased by a monostable multivibrator, the output of which drives an indicating LED to warn the vehicle's driver of the faulty air pressure in one of his tires.