Electronic siren
AssigneeWhelen Engineering Company, Inc.
InventorDavid P. Dornfeld
Life of this patent
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Abstract
An electronic siren emulates the sound of a mechanical siren using a dynamic algorithm and look up tables to generate a series of wave sets, each wave set including one fixed frequency wave and one variable frequency wave. A micro controller stores the algorithm and look up tables and executes the algorithm on command to produce a digital output emulating the mechanical siren. The digital output is converted to an analog signal that is applied to a class D amplifier. A switching power supply provides 70 VDC to the output stage of the amplifier. This arrangement produces 126 dB of sound pressure at a distance of 10 feet from the reverse folded horn speaker. The electronic siren generates little heat and requires only 10 amps of current from the vehicle electrical system.
Claims20
An electronic siren comprising:
- a command unit for selectively generating at least one command signal;
- a microprocessor programmed with at least one algorithm;
- a memory accessible by said microprocessor, said memory containing look up tables defining values used by said algorithm to emulate the frequency range, the rate of frequency change Δf and amplitudes as a function of frequency for at least a sweep up-down siren sound;
- a class D amplifier which receives and amplifies a signal generated by said microprocessor;
- and
- a speaker operatively connected to said amplifier,
- wherein said microprocessor executes said algorithm in response to a said command signal and said algorithm utilizes said data to produce a series of digital outputs emulating said siren sound and said digital pattern is converted to an audio signal which is applied to said amplifier.
A method for emulating a mechanical siren comprising the steps of:
- storing at least one algorithm for emulating the sound pattern of a mechanical siren in memory accessible by a microprocessor, said algorithm comprising a plurality of look up tables defining values used by the algorithm to emulate:
- the frequency range of the siren,
- the harmonic characteristics of the siren sound over said frequency range, and
- the relationship of frequency change with respect to time Δf for the siren sound over said frequency range,
- executing said algorithm to combine values from said look up tables to produce a train of digital outputs corresponding to the sound of the mechanical siren;
- converting said digital output to an analog signal;
- applying said analog signal to a class D amplifier to produce an amplified signal;
- and
- communicating said amplified signal to a speaker.
Dependencies are inferred from the claim text.