Motion Sensors for Classroom

8/3/2019 Motion Sensors for Classroom

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Motion sensors controlled light & fan for classroom

The present invention utilizes a latching relay having on and off inputs for

controlling power to a load. The on and off inputs of the relay are controlled bypulse generators which are in turn controlled by an occupancy sensor circuit.These pulse generators provide pulses when movement is initially detected in aroom and when no movement has been detected for a predetermined time,respectively. The outputs of the pulse generators are coupled to an isolationcircuit which isolates the power supply for the occupancy sensor from the pulsesduring each pulse to prevent damage to the power supply.

Motion sensors control lights and other electric loads by detecting body motion ina wide area. An sensor would typically out signal which then reflect off of objectsin the room and are detected by one or more receivers. A doppler shift of the

reflected signals indicates the presence of movement within the room, and canbe detected by body heat changes. In the absence of a detected doppler shift, anelectric load can be switched off via microcontroller .

passive infra-red (PIR) motion detector circuitry with circuit improvements thatgreatly reduce incidents of false activation. The motion detector includes one ormore infra-red sensors and circuitry for amplifying and filtering the signal from thesensors. The amplification and filtering circuitry has a pass band for signals fromthe one or more sensors corresponding to a range of speeds of motion of aperson moving in the field of view of the motion detector. The ability of the motiondetector circuitry to filter out certain environmental sources of false activations is

enhanced by providing the pass band with a very steep rolloff at the lower cutoff.In one embodiment the amplification and filtering circuitry is provided with threeop amp stages, each stage being configured to contribute a nominal 6 db peroctave rolloff to the lower cutoff. The amplification and filtering circuitry is alsoconfigured to provide the lower cutoff of the pass band with a fourth-order rolloff,which provides greatly enhanced protection against false activations from signalsbelow the cutoff.


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Block diagram


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Circuit diagram


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PCB LAYOUT


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How PIR Motion Sensors Work

There are many different ways to create a motion sensor. Motion is detectedwhen an infrared emitting source with one temperature, such as a human body,passes in front of a source with another temperature, such as a wall. It is

common for stores to have a beam of light crossing the room near the door, anda photosensor on the other side of the room. When a customer breaks the beam,the photosensor detects the change in the amount of light and rings a bell. Manygrocery stores have automatic door openers that use a very simple form of radarto detect when someone passes near the door. The box above the door sendsout a burst of microwave radio energy and waits for the reflected energy tobounce back. When a person moves into the field of microwave energy, itchanges the amount of reflected energy or the time it takes for the reflection toarrive, and the box opens the door. Since these devices use radar, they often setoff radar detectors. The same thing can be done with ultrasonic sound waves,bouncing them off a target and waiting for the echo.

All of these are active sensors. They inject energy (light, microwaves or sound)into the environment in order to detect a change of some sort.

The "motion sensing" feature on most lights (and security systems) is a passivesystem that detects infrared energy. These sensors are therefore known as PIR(passive infrared) detectors or pyroelectric sensors. Often, PIR technology will bepaired with another model to maximise accuracy and reduce energy usage. Inorder to make a sensor that can detect a human being, you need to make thesensor sensitive to the temperature of a human body. Humans, having a skintemperature of about 93 degrees F, radiate infrared energy with a wavelength

between 9 and 10 micrometers. Therefore, the sensors are typically sensitive inthe range of 8 to 12 micrometers.

The devices themselves are simple electronic components not unlike aphotosensor. The infrared light bumps electrons off a substrate, and theseelectrons can be detected and amplified into a signal.

You have probably noticed that your light is sensitive to motion, but not to aperson who is standing still. That's because the electronics package attached tothe sensor is looking for a fairly rapid change in the amount of infrared energy itis seeing. When a person walks by, the amount of infrared energy in the field of

view changes rapidly and is easily detected. You do not want the sensordetecting slower changes, like the sidewalk cooling off at night.

Your motion sensing light has a wide field of view because of the lens coveringthe sensor. Infrared energy is a form of light, so you can focus and bend it withplastic lenses. But it's not like there is a 2-D array of sensors in there. There is asingle (or sometimes two) sensors inside looking for changes in infrared energy.


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If you have a burglar alarm with motion sensors, you may have noticed that themotion sensors cannot "see" you when you are outside looking through awindow. That is because glass is not very transparent to infrared energy. This, bythe way, is the basis of a greenhouse. Light passes through the glass into thegreenhouse and heats things up inside the greenhouse. The glass is then

opaque to the infrared energy these heated things are emitting, so the heat istrapped inside the greenhouse. It makes sense that a motion detector sensitiveto infrared energy cannot see through glass windows.


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Infrared motion detector components work

Infrared Radiation_____________

Infrared radiation exists in the electromagnetic spectrum at a wavelength that islonger than visible light. It cannot be seen but it can be detected. Objects thatgenerate heat also generate infrared radiation and those objects include animalsand the human body whose radiation is strongest at a wavelength of 9.4um.Infrared in this range will not pass through many types of material that passvisible light such as ordinary window glass and plastic. However it will passthrough, with some attenuation, material that is opaque to visible light such asgermanium and silicon. An unprocessed silicon wafer makes a good IR windowin a weatherproof enclosure for outdoor use. It also provides additional filteringfor light in the visible range.

Pyroelectric Sensors_____________

The pyroelectric sensor is made of a crystalline material that generates a surfaceelectric charge when exposed to heat in the form of infrared radiation. When theamount of radiation striking the crystal changes, the amount of charge alsochanges and can then be measured with a sensitive FET device built into thesensor. The sensor elements are sensitive to radiation over a wide range so afilter window is added to the TO5 package to limit detectable radiation to the 8 to14mm range which is most sensitive to human body radiation.

Typically, the FET source terminal pin 2 connects through a pulldown resistor ofabout 100 K to ground and feeds into a two stage amplifier having signalconditioning circuits. The amplifier is typically bandwidth limited to below 10Hz toreject high frequency noise and is followed by a window comparator thatresponds to both the positive and negative transitions of the sensor output signal.A well filtered power source of from 3 to 15 volts should be connected to the FETdrain terminal pin 1.


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The PIR325 sensor has two sensing elements connected in a voltage buckingconfiguration. This arrangement cancels signals caused by vibration,temperature changes and sunlight. A body passing in front of the sensor will

activate first one and then the other element whereas other sources will affectboth elements simultaneously and be cancelled. The radiation source must passacross the sensor in a horizontal direction when sensor pins 1 and 2 are on ahorizontal plane so that the elements are sequentially exposed to the IR source.A focusing device is usually used in front of the sensor

The figure below shows the PIR325 electrical specifications and layout in its TO5package. Note the wide viewing angle without an external lens.
http://www.glolab.com/focusdevices/focus.htmlhttp://www.glolab.com/focusdevices/focus.html


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This is a typical application circuit that drives a relay. R10 and C6 adjust theamount of time that RY1 remains energized after motion is detected.

Fresnel Lens_____________

A Fresnel lens (pronounced Frennel) is a Plano Convex lens that has beencollapsed on itself to form a flat lens that retains its optical characteristics but ismuch smaller in thickness and therefore has less absorption losses.

Our FL65 Fresnel lens is made of an infrared transmitting material that has an IRtransmission range of 8 to 14um which is most sensitive to human bodyradiation. It is designed to have its grooves facing the IR sensing element so thata smooth surface is presented to the subject side of the lens which is usually theoutside of an enclosure that houses the sensor.


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The lens element is round with a diameter of 1 inch and has a flange that is 1.5inches square. This flange is used for mounting the lens in a suitable frame orenclosure. Mounting can best and most easily be done with strips of Scotch tape.Silicone rubber can also be used if it overlaps the edges to form a captive mount.There is no known adhesive that will bond to the lens material.

The FL65 has a focal length of 0.65 inches from the lens to the sensing element.It has been determined by experiment to have a field of view of approximately 10degrees when used with a PIR325 Pyroelectric sensor.

This relatively inexpensive and easy to use Pyroelectric Sensor and Fresnel Lenscan be used in a variety of science projects, robots and other useful devices.


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Component used

AT 89S51/52/PIC MICROCONTROLLER----1LM 7805 VOLTAGE REGULATOR-------------112 VOLT SPST RELAY----------------------------5HEAT SENSOR--------------------------------------1PIR MOTION SENSOR----------------------------4220AC TO 12VOLT STEP DOWN --------------1BC 548 NPN TRANSISTER-----------------------511 MHz CRYSTEL OSCILATOR-----------------1OTHERSCAPACITORRESISTANCE

SWITCHLEDWIRESOLDER

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Motion Sensors for Classroom