Communications – electrical: acoustic wave systems and devices – Echo systems – Presence or movement only detection
Patent
1981-10-30
1985-09-10
Swann, III, Glen R.
Communications, electrical: acoustic wave systems and devices
Echo systems
Presence or movement only detection
340554, 343 5PD, G08B 1316
Patent
active
045410801
ABSTRACT:
An ultrasonic alarm device has a detector for detecting a reflected ultrasonic wave in a watching area to obtain a Doppler signal due to motion of a person, a Schmitt circuit for converting the detection output into a pulse output and a waveform shaping circuit for shaping the pulse output into a pulse train having a certain pulse width. The output of the waveform shaping circuit is fed in parallel to two band-pass digital filters, one for the Doppler signal and the other for noise signals. Each of the filters comprises two monostable multivibrators connected in parallel and an AND gate having three inputs of which one is connected through an inverter to the output of one monostable multivibrator, a second is connected to the output of the second monostable multivibrator and the third to the input of the monostable multivibrators. The output of the Doppler signal filter is fed through a first integrator to a level decision circuit while the output of the noise signal circuit is fed through a second integrator to the first integrator. The level decision circuit is connected through a third integrator to an output circuit which produces an alarm signal when the signal level is above a predetermined value. Through this circuitry, the Doppler signal due to motion of a person is distinguished from external disturbances such as those due to wind, a telephone bell, an electric click or movement of a small animal, bird or insect.
REFERENCES:
patent: 3465336 (1969-09-01), Fishbein et al.
patent: 3681745 (1972-08-01), Perlman et al.
Adams Bruce L.
Burns Robert E.
Lobato Emmanuel J.
Swann III Glen R.
Uro Denshi Kogyo Kabushiki Kaisha
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