Importance

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Abstract

The invention provides an electronic horn for an alarm circuits of the type in which the d.c. power supply for the horn will be of a particular polarity to indicate an alarm condition. The circuit provides a piezo sounder connected across the terminals of the power supply, an inductor connected in parallel with the piezo sounder to form a tank circuit therewith and current modifying means connected in series with the tank circuit to modify the current through the tank circuit in response to the output of an R/S flip-flop which is periodically set by a clock signal at a frequency corresponding to the frequency desired for the fundamental audible tones of the sounder. The duration of the clock output pulse which makes the modifying means conductive must be such that the capacitance of the sounder is charged by the supply before the output of the clock permits a change of state in the flip-flop to make the modifying means nonconductive. A source of reset signals is connected to detect the current in the series circuit and is operable to produce a reset signal which will cause the change of state to thereby cut off the current through the tank circuit when the current detected exceeds a predetermined value after changing the sounder capacitance, at which time the tank circuit will go into a decaying oscillation to provide overtones in the sound output. Current through the tank circuit is limited during the charging of the sounder and current through a capacitor used for smoothing the supply is also limited by another current modifying means in circuit with the smoothing capacitor and the supply.

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First Claim