Occupancy sensor

• US 4,661,720 A
• Filed: 06/09/1986
• Issued: 04/28/1987
• Est. Priority Date: 06/09/1986
• Status: Expired due to Fees

• Current Assignee: The Watt Stopper Incorporated (Legrand SA)
• Original Assignee: WATT Watchers Incorporated
• Inventors: Mix, Jerome M., Hu, Charles C., Cameron, Maclyn C. Jr.
• Primary Examiner(s): Shoop, Jr., William M.
• Assistant Examiner(s): Ip, Shik Luen Paul
• Application Number:
  US06/872,308
• Time in Patent Office: 323 Days
• Field of Search: 307/116, 307/117, 340/551, 340/552, 340/553, 340/554, 340/550, 340/506, 340/514, 340/562, 340/578, 340/627, 340/507, 340/546, 340/529, 340/572, 367/93, 367/94, 367/96, 367/92, 367/95, 367/197, 367/198, 200/61.62, 200/61.64, 200/61.68, 310/317, 310/319, 310/324, 343/5 PD
• US Class Current: 307/117
• CPC Class Codes: G01S 15/523 for presence detection burglar, theft or intruder alarms G08B13/00, e.g. G08B13/16
• CPC Class Codes: H03K 17/94 characterised by the way in which the control signals are generated

Abstract

An improved apparatus for switching off power to an electric load in the absence of the detection of movement from the doppler shift of a transmission signal. An oscillator generates an ultrasonic transmission frequency which is transmitted via a transmission plate coupled to the oscillator. A plurality of receivers detect reflections of the ultrasonic sound signal and supply the detected signal to a bandpass filter which passes the transmission frequency. A low-pass demodulator will detect any doppler signal which modulates the transmission signal and will supply it to an amplifier for amplification. The amplified signal is then provided to a narrow band filter which will pass only a narrow band of doppler-shift signals which correspond to the frequencies of human movement. The signal is then supplied to a switching means which, when activated, will discharge a first node. The first node is charged via a resistor and a capacitor coupled to a voltage source. A comparator is coupled to the first node and is also coupled to a voltage reference. The comparator will produce an output signal when the first node has a higher voltage than the voltage reference, thereby enabling a control means which will supply current to the electric load. The detected doppler signal discharges the capacitor voltage thus insuring that an output signal is supplied while movement is detected in the room to keep the electric load supplied with current.

Claims

1. An apparatus for switching off power to an electric load in the absence of the detection of movement from the doppler shift of a transmission frequency, comprising:

oscillator means for generating an ultrasonic transmission frequency;

a transmission plate, coupled to said oscillator means, for emitting ultrasonic sound at said transmission frequency;

a plurality of receivers for detecting reflections of said ultrasonic sound;

a bandpass filter coupled to said receivers for passing said transmission frequency;

a lowpass demodulator coupled to said bandpass filter for passing a doppler-shift signal;

amplifier means, coupled to said lowpass demodulator, for amplifying said doppler-shift signal;

narrow band filter means, coupled to said amplifier means, for passing a band of said doppler-shift signal corresponding to human movement;

switching means, coupled to said narrow band filter means, for discharging a first node;

a resistor and capacitor coupled to said first node and to a voltage source for charging said first node to above a first voltage level in a first, predetermined time;

comparator means, having a first input coupled to said first node and a second input coupled to a voltage reference, for producing an output signal when said first input has a lower voltage than said second input; and

control means, coupled to said comparator means, for supplying current to said electric load in response to said output signal.

2. The apparatus of claim 1 wherein four of said receivers are used, each of said receivers being equally spaced around said transmission plate.

3. The apparatus of claim 1 wherein said transmission plate is circular and has a diameter greater than 75 mm.

4. The apparatus of claim 1 further comprising a test switch for coupling a second resistor to said first node and said voltage source to change the time constant of said resistor and capacitor.

5. The apparatus of claim 1 further comprising a potentiometer coupled in series with said resistor to enable a user to adjust the time constant of said resistor and capacitor.

6. The apparatus of claim 1 wherein said amplifier means includes a potentiometer which is user adjustable to vary the gain of said amplifier means.

7. The apparatus of claim 1 further comprising a power supply for supplying power to said apparatus.

8. An apparatus for switching off power to an electric load in the absence of the detection of movement from the doppler shift of a transmission frequency, comprising:

oscillator means for generating an ultrasonic transmission frequency;

a circular transmission plate, greater than 75 mm in diameter, coupled to said oscillator means, for emitting ultrasonic sound at said transmission frequency;

four receivers equally spaced around said transmission plate for detecting reflections of said ultrasonic sound;

a bandpass filter coupled to said receivers for passing said transmission frequency;

a lowpass demodulator coupled to said bandpass filter for passing a doppler-shift signal;

amplifier means, coupled to said lowpass demodulator, for amplifying said doppler-shift signal, said amplifier means including a user adjustable potentiometer for varying a gain of said amplifier means;

narrow band filter means, coupled to said amplifier means, for passing a band of said doppler-shift signal corresponding to human movement;

switching means, coupled to said narrow band filter means, for discharging a first node;

a potentiometer and a capacitor coupled in parallel to said first node and to a voltage source, for charging said first node to above a first voltage level in a first, predetermined time, said time being variable by user adjustment of said potentiometer;

a test switch for coupling a second resistor in parallel with said potentiometer and capacitor, said second resistance having a smaller value than said potentiometer;

comparator means, having a first input coupled to said first node and a second input coupled to a voltage reference, for producing an output signal when said first input has a lower voltage than said second input; and

control means, coupled to said comparator means, for supplying current to said electric load in response to said output signal.