MXPA98002794A - Infrared rays motion detection signal sampler - Google Patents

Abstract

The present invention relates to a digital sample circuit possessing an output signal of a high gain analog amplifier having as input an output signal of the infrared detector and a filtered feedback signal of negative low pass. The output signal of the amplifier is a substantially square pulse signal having an irregular frequency and duty cycle and having an average duty cycle indicative of a DC level and a slow change in the DC level of the output signal of the amplifier. detector. The sample circuit includes a detector circuit for detecting the amplifier output signal and discriminating a high / low state of the output signal at regular intervals, and generating a detected output signal. The high / low state of the output signal is analyzed on a predetermined number of intervals to obtain a ratio value to produce a digital signal sample value. The digital sample value is a measure of the DC level and the change in the DC level of the detector output signal. The digital sample is accurate and requires a single comparator and relatively simple circuit

Description

INFRARED RAY MOTION DETECTION SIGNAL SAMPLER FIELD OF THE INVENTION The present invention relates to a digital signal sampling circuit for detecting movement by infrared rays. More specifically, the invention relates to a sampling circuit integrated in the feedback loop of a high gain analog amplifier for processing an output signal of the amplifier. The amplifier has as input an output signal from the infrared motion detector and a negative feedback signal. The output signal of the amplifier is a substantially square, substantially saturated pulse signal having an irregular frequency and duty cycle, and an average duty cycle of the output signal of the amplifier is indicative of a DC (direct current) level and a change in the DC level of the motion detector output signal.

BACKGROUND OF THE INVENTION Passive infrared motion detectors are well known in the art. Such detectors typically include a small housing, a lens for directing infrared light from a small housing, a lens for directing infrared light from a zone to be controlled to an infrared sensor element. The most common type of sensor element is a pyroelectric sensor that generates a small electrical voltage but can be detected in response to changes in infrared radiation that affect it. Due to the lenses of the known detectors, the movement of a person in or from the controlled area changes the intensity of infrared light that hits the sensor and produces a voltage variation. A discriminating circuit controls the output signal of the sensor and generates an alarm signal with the condition that certain characteristics are present in the sensor output signal. These characteristics can be energy, amplitude peaks, number of oscillations, etc. An example of prior art detectors is found in the U.S. Patent. 5,077, 549, co-invented by the inventor of the present invention. It is known from this reference to provide an infrared ray motion detector circuit that uses a detector logic circuit to discriminate the sensor output signal. The signal amplitude of the sensor is converted by a controlled voltage oscillator (OVC) to a pulse frequency, and a counter-circuit counts the pulses to detect the energy of the sensor signal and to generate the alarm signal. In the past, the use of a microprocessor having an analog to digital converter (CAD) has been prohibitively expensive to use in a commercially competent motion detector discriminator circuit. In the current market, several commercially available microcontrollers or microprocessors are inexpensive to compete with the normal "hard connection" integrated circuit technology. Although the use of a microprocessor improves the flexibility and possible quality of signal analysis and discrimination, it still requires a circuit to generate a digital signal from the analog output of the sensor, such as a high-gain bandpass amplifier and a CAD , which represents a significant part of the current cost of the detector circuit.

BRIEF DESCRIPTION OF THE INVENTION An object of the present invention is to provide a digital sampling circuit for infrared ray motion detection to process an infrared sensor output signal to generate digital displays without requiring an analog to digital converter.

Another object of the invention is to provide said digital sampling circuit, integrated in the feedback loop of the bandpass amplifier, which may depend on the capabilities of the microprocessor to obtain the desired digital displays when reading the output signal of an analog amplifier. high gain that has as input the output signal of the infrared motion detector and a negative feedback signal filtered from low pass and provide a negative feedback signal control to the input of the amplifier. Another object of the invention is to provide a digital signal processor for an infrared ray motion detector using a microprocessor and a single operating amplifier. In accordance with the invention, a digital infrared ray motion detection sampling circuit is provided to process an output signal from a high gain analog amplifier having as input an output signal from the infrared motion detector and a filtered feedback signal from low negative step, the output signal of the amplifier being a substantially square pulse signal, substantially saturated having an irregular frequency and duty cycle, an average duty cycle of which is indicative of a DC level and a slow change in the DC level of the detector output signal. The detection circuit comprises means for detecting the output signal and discriminating at a substantially regular intervals a high / low state of the output signal; means for generating a high / low feedback signal corresponding to the high / low state of the detected output signal over a number of the regular intervals to obtain a high / low ratio value and to send this ratio value as a value of sample of digital signal. In this way, the digital signal sample value is a measure of the DC level and the slow change in the DC level of the detector output signal on the desired frequency scale of the detector, approximately 0.1 Hz to 10 Hz.

Preferably, the means for analyzing comprises a digital counter. Alternatively, the output signal can be integrated to obtain an analogous value representing the signal sampling. The invention further provides a signal processor circuit of the infrared motion detector comprising a high gain analog amplifier having as input an infrared ray motion detector signal and a negative low pass filtered feedback signal, and it produces an output signal which is a substantially square, substantially saturated pulse signal having an irregular frequency and a duty cycle. The average duty cycle of the square pulse signal is indicative of a DC level and a slow change in the DC level of the motion detector signal. The motion detection circuit further comprises means for detecting the output signal and discriminating at substantially regular intervals a high / low state of the output signal, means for generating a high / low feedback signal corresponding to the high / low state of the output signal. the output signal over a number of the intervals to obtain a high / low ratio value and to send the ratio value as a digital signal sample value. In this way, the digital signal sample value is a measure of the DC level and the slow change in the DC level of the detector output signal on the desired frequency scale of the detector, approximately 0.1 Hz to 10 Hz.

BRIEF DESCRIPTION OF THE DRAWING The invention will be better understood by means of the following detailed description of a preferred embodiment of the invention with reference to the accompanying drawing wherein: Figure 1 is a schematic block diagram of the infrared ray motion detection sampling circuit in accordance with the preferred modality.

DETAILED DESCRIPTION OF THE PREFERRED MODALITY As shown in Figure 1, the infrared motion detector 10 in accordance with the preferred embodiment comprises a pyroelectric sensor 12 connected to the positive input of a high gain amplifier 14. The sensor is a pyroelectric Heimann LHI958 sensor. The sensor output signal is filtered by a high pass filter 21 and then a low pass filter 22 and a DC bypass reference level 23 is added to the filtered output signal before being connected to the amplifier 14. The filter high pass 21 has a threshold of 0.2 Hz, and low pass filter 22 has a threshold of 7.0 Hz. The high-pass filter is a first-order filter, and the low-pass filter is a second-order filter to eliminate aliases. The level of DC derivation generated by circuit 23 is 1 .0V. The gain of the amplifier 14 is typically higher than 100000. The feedback circuit comprises a pulse detector 24 which detects the output of the analog amplifier 14 and discriminates the voltage in a low or high signal. The high / low digital signal is repeated by a feedback pulse generator 27 and fed back to the amplifier 14 by means of a temperature compensator 28 and an integrator 18. The integrator 18 in the preferred embodiment has a resistance of 1 MO and a capacitance 100μF The integrator 18 may also comprise a low pass filter which filters the high frequency of the amplifier output and passes through the low frequency voltage level present at the output of the amplifier. The digital signal level is thus reduced below the minimum input signal that can be detected, that is, below 1 mV. The temperature compensation circuit 28 includes a thermistor in a voltage divider arrangement for adjusting the feedback and gain voltage in accordance with the temperature in order to increase the sensitivity as the ambient temperature increases. Increased sensitivity is required at higher temperatures, since the difference between levels of infrared radiation emitted by the environment and a person moving through a detection zone decreases with higher ambient temperatures. As a result of temperature compensation, the duty cycle at the output of the pulse train of the amplifier 14 increases with temperature. The DC level of the feedback voltage fed to the amplifier 14 thus changes with the temperature as a result of the circuit 28. Changes in temperature thus cause a change in the basic duty cycle at the output of the amplifier. By controlling this basic duty cycle, the temperature compensation circuit 28 can also be used to obtain a temperature reading that can be used to change the way in which the digital signal samples are interpreted to generate an alarm signal. The amplifier 14 is arranged as a non-inverted differential amplifier having an output which is a substantially square pulse signal, substantially saturated. Due to the high gain of the amplifier 14, a small difference between the filtered sensor signal and the integrated feedback signal produces a saturated maximum output voltage from the amplifier 14, or a saturated output voltage of zero depending on the polarity of the amplifier. the difference . The maximum voltage of amplifier 14 is adjusted to 5V. The output of the amplifier 14 has an average duty cycle proportional to the sum of a change in the DC level at the positive input and the DC level itself. The feedback loop is designed to provide a reliable measure of millivolt changes at the sensor output. The square pulse signal output of the amplifier 14 has an irregular frequency and pulse amplitude. The frequency of the square pulse output of the amplifier 14 depends on the response of the loop loop and also the feedback pulse period, but the frequency is not important to obtain samples. The maximum high speed at low to high can be very high and depends on the loop speed of the components of the circuit, as well as the speed at which the output of the amplifier is detected and fed back by the generator 27. The amplifier 14 in accordance with the preferred embodiment is a differential amplifier that operates in a non-inverted mode, however, a differential amplifier can also be used in an inverted mode. In the case of an inverted mode amplifier, the sensor signal is connected to the negative input together with the feedback with a suitable resistance connected between the integrator and the negative input, and a DC reference voltage is connected to the positive input of the amplifier. The pulse detector 16 samples at a substantially regular frequency of about 16Hz. The detector 16 decides whether the analog output of the amplifier 14 is high (i.e. 5V) or low (i.e. OV) and sends a single pulse signal. In the preferred embodiment, the pulse detector is part of a microprocessor and detection of the output of the amplifier 14 is made by reading a digital input signal connector on a regular basis controlled by the interruption of the microprocessor. Due to the finite gain of amplifier 14, an unsaturated output will occur (ie, not 5V or OV) when the feedback voltage is very close to the positive input voltage. Said intermediate voltage levels will be interpreted randomly by the discriminator in the pulse detector 24, and said random or erroneous interpretation will lead to variations in the feedback and will contribute to the output of the pulse train of the amplifier 14 having a random, irregular character. Counter 25 counts the number of high pulses ('1' bits) in 255 cycles. The result of the counter gives a single sample that can be stored in a data bit. The counting and storage of data is done in a computer program by the microprocessor in the preferred mode. This produces approximately 62 samples per second, which is more than adequate to analyze the motion sensor output signal of less than 15Hz. The digital signal analysis is done in a digital signal processor 26, which in the preferred embodiment is provided by a computer program in the microprocessor. Since the feedback speed is controlled by digital sampling and feedback signal generation speed, the output signal of the amplifier will have a maximum interruption frequency lower than the feedback signal generation speed, and thus the analysis of the high / low state of the amplifier output to obtain the digital signal sample value can be done efficiently at the speed of the feedback signal generation. The digital displays obtained by using the present invention represent a sum of the DC signal and a change in the DC signal input to the amplifier 14. This represents the ratio of the high to low state of the amplifier input. As an example, a constant duty cycle of 25% may be present when the amplifier input is constant, that is, the sensor output is stable to OV and the DC derivation is at its predetermined level. The only byte sample value can be around 64 for a 25% duty cycle. A small change in the sensor voltage, namely + 2mV, would only result in a small change in the constant duty cycle, namely it may rise to 25.05%. In this way, the digital sample value that has a magnitude of 255 can only change by one digit. However, during the change in input voltage, the duty cycle represents the base DC level plus the rate of change (tilt) of the sensor output. A change of 2mV over 0.2s is a speed of 10mV / s of change that can cause the work cycle to increase by 5 percentiles to 30% over the period of 0.2s. Likewise, a drop in the sensor output by 2mV in 0.2s would cause the duty cycle to fall by 5 percentiles to 20% during the voltage decline. This results in transition work cycles that produce changes that can be easily detected in the digital sampling values, for example, approximately 15 units. It will be appreciated that each digital sample results from a simple count or the sum of the voltage level of the detected amplifier output over a sufficiently long period to compensate for random variations in the pulse train and obtain an accurate measure of the change in signal of the sensor output 12. The analog amplifier can be a differential amplifier, a comparator or an input amplifier. The analog amplifier may be an external component or an internal integral part of a microcontroller. Although the invention has been described with reference to the preferred embodiment, it is to be understood that the foregoing description is intended merely to illustrate the invention and not to limit the scope of the invention as defined in the appended claims.

Claims (18)

1 .- A digital sampling circuit of infrared motion detection to process an output signal of a high gain analog amplifier that has as input an output signal from the infrared motion detector and a filtered feedback signal from low pass, negative, said output signal being a substantially saturated and substantially square pulse signal having an irregular frequency and a duty cycle, an average duty cycle that is indicative of a DC level and a slow change at that level of DC and said output signal of the detector on a desired frequency scale of said output signal of the motion detector, said detection circuit comprising: means for detecting said output signal and discriminating at substantially regular intervals a high / low state of said output signal; means for generating a high / low feedback signal corresponding to said high / low state of said detected output signal; means for analyzing said high / low state of said output signal over a number of said intervals to obtain a high / low ratio value and for sending said ratio value as a signal sample value, whereby the sample value of signal is a measure of said DC level and said change in said DC level of said detector output signal.

2. The circuit according to claim 1, wherein said means for analyzing comprise a counter circuit that samples said high / low state at said regular intervals, said ratio value being a digital counter value.

3 - The circuit according to claim 1, wherein said detector output signal is connected to a second order low pass filter, whereby substantially aliases are eliminated.

4 - The circuit according to claim 1, wherein said feedback signal is connected to a temperature compensation circuit.

5. The circuit according to claim 2, wherein said detector means comprises a microprocessor, said intervals being determined by interruptions, said analyzer means being provided by said microprocessor.

6. The circuit according to claim 5, wherein said predetermined number of intervals is 256 and said signal sample value is stored as a byte.

7. The circuit according to claim 6, wherein an output frequency of said signal sample value is greater than 30 Hz.

8 - The circuit according to claim 1, further comprising filter means for filtering said output signal from the motion detector, said filter means comprising a high pass filter, a low pass filter and a DC bypass.

9. The circuit according to claim 1, wherein said negative feedback signal passes through an integrator to provide flat frequency response on said desired frequency scale of said output signal of the motion detector.

10. A signal processor circuit of the infrared motion detector comprising: a high gain analog amplifier having as input an infrared ray motion detector signal and a negative low pass filtered feedback signal, and produces an output signal, said output signal being a substantially square pulse signal, substantially saturated having an irregular frequency and a duty cycle, an average duty cycle which is indicative of a DC level and a slow change in said DC level of said motion detector signal on a desired frequency scale of said motion detector signal; means for detecting said output signal and discriminating a high / low state of said output signal at substantially regular intervals;

m ItiIds to generate a high / low feedback signal corresponding to said high / low state of said detected output signal; means for analyzing said high / low state of said output signal over a number of said intervals to obtain a high / low ratio value and for sending said ratio value as a signal sample value, whereby the sample value signal is a measure of said level of DC and said change in said DC level of said detector output signal, 1 - The circuit according to claim 10, wherein said analyzer means comprises a counter circuit that samples said high / low state at said regular intervals, said relationship value being a digital counter value.

12 - The circuit according to claim 10, wherein said detector output signal is connected to a second order low pass filter, whereby substantially aliases are eliminated.

13. The circuit according to claim 10, wherein said feedback signal is connected to a temperature compensation circuit.

14. The circuit according to claim 1, wherein said detector means comprises a microprocessor, said intervals being determined by interruptions, said analyzer means being provided by said microprocessor.

15. - The circuit according to claim 14, wherein said predetermined number of intervals is 256 and said signal sample value is stored as a byte.

16 - The circuit according to claim 15, wherein an output frequency of said signal sample value is greater than 30Hz.

17. The circuit according to claim 10, further comprising filter means for filtering said output signal from the motion detector, said filter means comprising a high pass filter, a low pass filter and a DC bypass. .

18. The circuit according to claim 10, wherein said negative feedback signal passes through an integrator to provide flat frequency response on said desired frequency scale of said output signal from the motion detector.