Abstract: A vehicle horn with an electronic solid state energizing circuit is described. The horn has an electromagnet for driving a diaphragm assembly which has a resonant frequency of mechanical vibration. The energizing circuit generates a DC pulse train for energizing the coil of the electromagnet to drive the diaphragm. The circuit has an adjustment for setting the pulse repetition rate of the pulse train substantially equal to the resonant frequency. It also has an adjustment for independently setting the duty cycle of the pulse train. The circuit further includes a compensator for varying the duty cycle inversely with changes in the supply voltage. An electronic power switch is connected in series with the vehicle battery and the horn coil through an unswitched power circuit. A horn switch is connected in an on/off circuit which connects the battery to a control circuit for generating the pulse train and applies it to the electronic power switch.

Abstract: Adjustment of the pulse energizing frequency and duty cycle of a vehicle horn is described. The horn is blown by a test energizing circuit with a varying pulse frequency and the and the frequency at which the horn produces the maximum sound pressure level is taken as the predetermined resonant frequency. Then the horn is blown by the test energizing circuit at the resonant frequency with a varying duty cycle value of duty cycle which produces a predetermined striking force of the plunger against the pole piece is taken as the predetermined impact-producing duty cycle which is used for setting the operating duty cycle of the horn in a manner depending upon the type of the horn. The horn is then blown by its own electronic energizing circuit and the actual pulse frequency thereof is adjusted, preferably by laser trimming of a resistor, to match the resonant frequency.

Abstract: A liquid level indicator uses a conductive probe and when the circuit is energized a logic signal indicates whether the liquid is above or below a certain level. The signal is processed by a logic circuit and the output of the logic circuit controls an indicator circuit. An inhibit circuit provides an input to the logic circuit and prevents the indicator circuit from indicating low liquid within a start time delay period after energization of the sensing circuit. The logic circuit includes a time constant circuit which interposes time delays in the logic signal output of the logic circuit to prevent false indications from momentary changes in liquid level.

Abstract: An electric horn has a diaphragm driven by a plunger which is vibrated by a coil having a pole piece. A small air gap between the plunger and the pole piece is required to assure that they will not touch during vibration. The gap is adjusted by assembling the horn with the gap small enough to permit the plunger to be pulled into contact with the pole piece by magnetic force when a preset direct current is applied to the coil. After assembly a calibration procedure is to apply the preset current to the coil, mechanically pull the pole piece away from the plunger until the diaphragm force overcomes the magnetic force causing the plunger and pole piece to separate, electrically detect the time of separation, and then stop or optionally pull the pole piece an additional fixed amount to set the required gap. Apparatus automatically performs the calibration procedure.