Communications: electrical – Selective – Having indication or alarm
Patent
1977-11-04
1979-06-12
Caldwell, Sr., John W.
Communications: electrical
Selective
Having indication or alarm
340 32, 340171R, G08G 100
Patent
active
041581903
ABSTRACT:
The detecting circuit is used on cars to indicate the presence of emergency vehicles utilizing wailing sirens the instant invention residing in the unique circuitry itself to result in an extremely inexpensive electronics package for carrying out the desired function. Essentially, the circuit utilizes a band pass filter having a voltage tunable center frequency. Dominant frequencies in a sound spectrum received through the band pass filter are converted to voltages by means of a frequency to voltage converter and fed back to the band pass filter to shift the center frequency of the filter thereby tracking the dominant frequency signal. When the dominant frequency results from a wailing siren, the fed back voltage from the frequency to voltage converter constitutes a slowly continuously varying AC signal corresponding to the pitch variation of the siren. This signal is detected by a low pass filter and differentiating circuit to operate a flasher to indicate the presence of the siren. When the dominant frequency results from noise or steady state sounds or the like resulting in a random shifting of the center frequency of the band pass filter, further filter and integrating means responsive to such random signals generate an inhibiting signal preventing spurious operation of the flasher.
REFERENCES:
patent: 2355607 (1944-08-01), Shepherd
patent: 3399378 (1968-08-01), Carter et al.
patent: 3568144 (1971-03-01), Streb
patent: 3626365 (1971-12-01), Press et al.
patent: 3735342 (1973-05-01), Helliker et al.
patent: 3859623 (1975-01-01), Koehler
Caldwell Sr. John W.
Groody James J.
Pastoriza Ralph B.
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