Alarm device for continually indicating the state of air pressure in a plurality of tires

An alarm device for informing reduction of pneumatic pressure of tires comprising a transmitter means including a group of transmitters provided at wheels having tires and each consisting of an oscillator circuit, an electric power supply source for said oscillator, a switch for closing an electric power supply circuit to supply the voltage to the oscillator when the internal pressure of the tire is lowered to less than a prescribed value and a radiation antenna for electromagnetic waves;

• a receiver means including at least one receiver antenna for reception of electromagnetic waves from the transmitters, and a receiver turning circuit capable of continuously tuning over a range of a predetermined tuning frequency covering a plurality of frequency sections;
• a sweep generator for sweeping said tuning circuit;
• a signal processing means including a comparison circuit for comparing the sweeping output of the sweep generator with reference voltages to generate gate control outputs of the multiple channels corresponding to the number of the sweep frequency sections, gate circuits for sequentially gating the output of the receiver means by said gate control signals, monostable circuits operated by the outputs of the gate circuits, pulse noise elimination circuits consisting of smoothing filters and for smoothing the outputs of the monostable circuits and comparators for comparing the smoothed DC outputs of the pulse noise elimination circuits with reference signals for discrimination of the operated transmitter;
• and alarm display means operated by the outputs of the signal processing means for generating and displaying alarm information.