Wailing siren detecting circuit
US4158190A · kind A · utility
Inventor
Key dates
| Filing date | Nov 4, 1977 |
| Grant date | Jun 12, 1979 |
| Priority date | — |
| Expiry date | Nov 4, 1997 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG08G1/0965
- WIPO fieldControl
- WIPO sectorInstruments
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 re…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.