US 4,541,080 A · Ultrasonic alarm device

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.

Claims9

Dependent claims

An ultrasonic alarm device in which an ultrasonic wave is transmitted to a watching area, and the ultrasonic wave reflected is detected by a detector to obtain a Doppler signal in a predetermined frequency band due to motion of a person, thereby to form an alarm output;

which comprises:
(a) a Schmitt circuit which receives a detection output of said detector and which provides an output at a logic level "1" when said detection output exceeds a predetermined Schmitt level, and provides an output at a logic level "0" when said detection output does not exceed said predetermined Schmitt level, thus converting said detection output into pulses;
(b) a waveform shaping circuit responsive to leading edges of the pulses output by said Schmitt circuit for shaping a pulse output of said Schmitt circuit into a pulse train having pulses of constant narrow pulse width, whereby frequency discrimination of the Schmitt circuit outputs is possible, and
(c) a digital band pass filter for transmitting, of a pulse output of said waveform shaping circuit, a pulse train having a frequency included in the frequency band of said Doppler signal,
(d) means for integrating the output of said digital filter, and
(e) means for producing an alarm output when the output of said integrating means is above a predetermined level for a predetermined time.

3 more elements

An ultrasonic alarm device in which an ultrasonic wave is transmitted to a watching area, and the ultrasonic wave reflect is detected by a detector to obtain a Doppler signal in a predetermined frequency band due to motion of a person, thereby to form an alarm output;

which comprises:
(a) a Schmitt circuit which receives a detection output of said detector and which provides an output at a logic level "1" when said detection output exceeds a predetermined Schmitt level, and provides an output at a logic level "0" when said detection output does not exceed said predetermined Schmitt level, thus converting said detection output into pulses;
(b) a waveform shaping circuit for shaping a pulse output of said Schmitt circuit into a pulse train having a predetermined pulse width;
(c) a first digital band pass filter for transmitting, of a pulse output of said waveform shaping circuit, a pulse having a frequency included in the frequency band of said Doppler signal;
(d) a first quick discharge type integration circuit for integrating an output of said first digital filter;
(e) a second digital filter for transmitting, of said pulse output of said waveform shaping circuit, a pulse having a frequency included in a frequency band other than the frequency band of said Doppler signal;
(f) a second quick discharge integration circuit for integrating an output of said second digital filter, to clear said first integration circuit when the integration result of said second integration circuit reaches a predetermined level;
and
(g) a level decision circuit for providing an alarm output when an output of said first integration circuit reaches a predetermined level.

6 more elements

An ultrasonic alarm device in which anultrasonic wave is transmitted to a watching area and the ultrasonic wave reflected is detected by a detector to obtain a Doppler signal in a predetermined frequency band due to motion of a person in said area and to form an alarm signal, which comprises:

a Schmitt circuit which receives a detection output of said detector and which provides an output at a logic level "1" when said detection output exceeds a predetermined Schmitt level and provides an output at a logic level "0" when said detection output does not exceed said predetermined Schmitt level, thereby converting said detection output into pulses,
waveform shaping means receiving the output of said Schmitt circuit and shaping said output into a pulse train having pulses of a constant pulse width,
a first digital band pass filter receiving the output of said waveform shaping means and passing pulses having a frequency included in the frequency band of said Doppler signal,
first integrating means for integrating the output of said first digital band pass filter, a second digital band pass filter receiving the output of said waveform shaping means in parallel with said first digital band pass filter and passing pulses in a frequency band higher than the frequency band of said Doppler signal,
second integrating means for integrating the output of said second digital band pass filter and having an output connected with said first integrating means, to reset said first integrating means,
level decision circuit means for evaluating the output of said first integrating means and providing an output signal when the level of said output is above a predetermined value for a predetermined time and
output circuit means receiving said output signal of said level decision means and providing an alarm signal.

4 more elements

Dependencies are inferred from the claim text.

Ultrasonic alarm device

Life of this patent

Ultrasonic alarm device

Life of this patent

Abstract

Claims9