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Infrared Movement Detector By BRANCO JUSTIC ley E·lectronics In this article, we show you how to build a passive infrared movement detector (PIR) with performance equivalent to that of expensive commercial units. The unit is very easy to build and can be used to monitor large areas such as rooms and entrances. Alternatively, when fitted with the optional narrow angle lens, it can be used for property perimeter protection or as a shop entry detector. Until fairly recently, passive infrared (PIR) movement detectors have been fairly expensive devices, due mainly to the cost of the pyroelectric sensors. That situation no longer prevails. With the development of low cost sensors and plastic lenses, the price of PIR detectors has dropped in recent years so that they are now an attractive and economical proposition for use in domestic alarm systems. In fact, a PIR detector is now virtually a must for any home burglar alarm system. This type of detector has excellent sensitivity and has a lower incidence of false alarms than ultrasonic detectors. In addition, they are easy to install and adjust. You can build this high-performance passive infrared movement detector for just $60. The PIR detector described here features a high-quality dualelement fresnel lens and filter combination that offers superior performance to single element types. The unit can either be used to trigger a central alarm system or, by increasing the triggered on time, as a self-contained alarm system. The useful range of the unit varies according to the lens fitted. The prototype wide angle unit produced a useful range of more than 10 metres, while fitting the narrow angle lens resulted in a useful range of more than 25 metres. The pyroelectric sensor At the heart of our PIR is a pyroelectric sensor which is sensitive to body heat in the range 8-10µ,m (micrometres). A pyroelectric sensor generally combines a filter, a heat-sensitive crystal, and a FET buffer stage in one package. An external filter is also often used Here is a view of the assembled printed circuit board. The wide-angle lens assembly is installed over the pyroelectric sensor at mid-left. DECEMBER 1987 33 D 2 (a) NARROW ANGLE LENS - SAME PLAN ANO SIDE VIEW ~00"•~ ~ • Wm SIDE VIEW (b) WIDE ANGLE LENS - ASSUMES 2 METRE HEIGHT ANO APPROXIMATELY 15• TILT Fig. 2 Fig.2: these diagrams show the behaviour of the narrow angle lens at (a) and the wide-angle lens at (b). With the wide angle lens, a range of up to 20-metres can be expected. to help filter out wavelengths outside the range of interest. This external filter generally consists of a white-coloured plastic sheet. Although this is almost opaque to visible light, it is transparent to wavelengths associated with BAND-PASS FILTER {WINDOW) ~ "CRYSTALS"(LiTa0 3) Fig. 1 THE INTERNALS OF A PYROELECTRIC DETECTOR 34 SILICON CHIP unit insensitive to the presence and movement of human beings in a room, which is why a lens system is needed to make the unit work. If we focus the output of a multiple lens system on the pyroelectric unit; a signal is produced when more heat falls on one of the elements than the other. A person walking across the area scanned by a multiple lens system will thus produce a voltage across one of the elements and a voltage of opposite polarity across the other. The differential voltage produced by a dual element sensor is therefore twice that produced by a single element sensor. In summary, a dual element sensor rejects heat which is common to both sensors (the common-mode signal) and produces a differential output when a person enters the capture area, due to the fresnel lens system. Fig.2 shows the behaviour of the two alternative lenses available with this project. body heat. The external filter used in our unit is actually combined with the fresnel lens. Fig.1 illustrates the internal circuitry of the pyroelectric sensor used in this project. Note that two heat sensitive lithium titanate elements (LiTaO 3) are used and these are wired so that their outputs oppose each other. This means that light which is common to both elements produces very little output (theoretically zero), a feature that makes the unit insensitive to normal heat which is distributed across large areas, such as in a room. It also makes the How it works Fig.3 shows the complete circuit diagram for the PIR Detector. Here's how it works. The infrared energy is focussed on the pyroelectric sensor (ICl) by the fresnel lens. The FET inside ICl is connected as a source follower with its output coupled via C2 to the input of non-inverting amplifier stage IC2. This stage has a voltage gain of 471 and a bandwidth of approximately 7Hz. R7 and C5 set the high frequency response while R6 and C4 roll off the response below about 0.75Hz. R3, R4 and R5 bias the pin 3 input to about 1.7V. The output of IC2 is coupled via C6 and RB to pin 2 of IC3. This is an inverting amplifier stage with a voltage gain of 100 (40dB) and a bandwidth of approximately 16Hz. From there, the signal is fed via R12 to a detector circuit consisting of Dl, R13 and Cl0. This produces a DC voltage which is directly proportional to the AC voltage produced by the pyroelectric sensor. This DC voltage is then applied to the noninverting (pin 3) input of comparator stage IC4. Trimpot VRl R1 1k r-----'tWr-------+------+------+-------+-------+-----+----A CB .01 FRESNEL ( },. LENS + 1.4V VR1 4.7k R2 47k R5 4.7M C10 R13 1M 0.1 R21 4.7k +5V C14 + 7BL05 100+ 1NOour GND R16 1M B EOc VIEWED FROM BELOW R15 220k _ __ R17 1M _ _____,..__ _ _....__ _ _ _ _ _ _ _ _ _ _ _ _____,..__ _ _ _--<1GND .,. PASSIVE INFRARED MOVEMENT DETECTOR 31-1287 Fig.3: the output from the pyroelectric sensor (IC1) is amplified by IC2 and IC3, detected by D1 and applied to comparator IC4. IC4 drives comparator IC5 which turns on Qt and the relay. (sensitivity) sets the comparator threshold voltage on IC4's inverfing input. When the detector output exceeds the comparator threshold, the output of IC4 switches high and quickly charges Cl 2 via DZ and R14. When this happens, pin 6 of comparator stage IC5 also switches high and turns on transistor Ql. Ql in turn drives the relay and a LED indicator circuit (R18 and LED 1). Diode D3 protects Ql against the back-EMF generated by the relay coil when the relay turns off. R15 and C12 sets the time constant on pin 3 of IC5 to one second. This makes the unit continually retrigger while ever there is movement within the area scanned by the sensor. If required, the time constant can be increased (by increasing the value of R15) , to make the unit function as a free-standing alarm. The relay output can either be used to trigger the central alarm console or, when the long time constant is employed, to switch on an external siren circuit. Construction A complete kit of parts for this project is available from Oatley Electronics [see parts list). All the parts, except for the LED, are mounted on a small printed circuit board measuring 61 x 114mm. The wide-angle lens assembly is made from blank PCB material and tin plate and is soldered to four large PC stakes at one end of the board. Install the parts on the PCB as shown in Fig.4, with particular attention paid to the orientation of the transistors, diodes, electrolytic capacitors and ICs . IC sockets were fitted to the prototype, but these are optional. The relay, trimpot and the pyroelectric sensor are best left till last. Mount the sensor flush against the PCB with its metal tab oriented as shown in the wiring diagram (Fig.4). Now the wide-angle lens as sembly can be made. Fig.5 shows the dimensions of the top and side pieces (note: the drawings are not DECEMBER1987 35 Altronics Will Deliver Any Of These Quality Products To Your Door Faster Than An Other Australian Su lier (Within 24 Hours To Every Capital City and Suburbs - Allow Addltonal 24 - 48 Hours For Country Areas) 1111111111 IIIIIHIIIII IIIIII IIIU 111111111 llllll lllllllllllllllllllllllllllll 11111111111111111111111111 IIU Ill II111111111111111 II IIIIIIIIIIIIII IIIIIIIIIIIIIIIIII IIIIIIIIIII111111111111111 es Operate■ From 12V Car Battery Massive 600 Watt Inverter Operatea from 12 or 24 Volt IyItemI via Internal wiring connection ■ Thermal Over Load. Current Regulated. Current Overload Big brother to our 300W Model this brilliant design can be internally connected for either 12 or 24Voperation . Full SOO watt output - and that will power a fantastic array of appliances e.g . Lighting , Electric Motors , Electric drills, Hi Fi , TV Sets, Computer. 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Horizontal hold, horizontal position. 75 Ohm/ 10K switch selectable 18MHz 900 lines at centre screen RCA Composite Video 1V P-P This Month $199 -. , This view shows the lens supporting assembly, prior to installation of the fresnel lens. Be sure to install the lens the right way up (see Fig.2). '~if ' . --" ~ .=.__.....;__ _ 1!j + - "- Fig.4: parts layout for the PCB. The pyroelectric sensor (ICl} is mounted flush against the board. The wide-angle lens assembly covers the pyroelectric sensor and is soldered to four PC stakes. PARTS LIST 1 1 1 1 1 1 printed circuit board SPST 1 2V relay fresnel lens (see text) 4-way terminal block 4 7kQ horizontal trimpot aluminium case (70 x 40 x 130mm) 1 sheet of tin plate (1 00 x 30mm) 1 sheet of single-sided PCB (50 x 100mm) 6 PC stakes (4 large , 2 small) Resistors 5%, 0.25W) 4 x 4.7MQ, 6 x 1 MQ , 1 x 220kQ, 1 . x 47kQ, 2 x 10kQ, 1 X 4 . 7kQ, 1 x 2.2k0, 5 x 1 kQ Semiconductors Miscellaneous 1 RPY97 dual element pyroelectric detector 1 78L05 5V regulator IC 4 TL071 op amps 1 BC337 NPN transistor 2 1 N41 48 silicon diodes 1 1 N4004 silicori diode 1 5mm red LED Hookup wire , machine screws and nuts , mounting brackets Capacitors 2 1 00µF 16VW PC electrolytic 4 22µF 16VW low-leakage PC electrolytics 38 1 4. 7 µF 16VW low-leakage PC electrolytic 3 0 .1 µF monolythics 2 0.01 µF metallised polyester 1 0.0047µF metallised polyester SILICON CHIP Where to buy the parts: a complete kit of parts for this project is available from Oatley Electronics, 5 Lansdowne Pde (PO Box 89), Oatley, NSW 2223. Telephone (02) 579 4985. Prices are $57.95 for the wide-angle version, and $53.95 for the narrowangle version. Add $2.00 for pack and post. actual size). These can be cut to shape using a pair of tin snips and finished with a file. The lens unit can now be assembled by first tack-soldering the various pieces together. Make any adjustments that may be necessary, then run a fillet of solder along each of the internal corners. Finally, the plastic lens can be installed through the rear of the unit and glued in position. This is not a difficult procedure, as the lens is simply a flat sheet of plastic and will automatically assume the correct shape when correctly positioned. Note that the smooth side of the lens faces outwards. Push the lens in so that it is 1-2mm from the front of the assembly and secure it by applying super-glue along the joints. Avoid spreading the glue across the lens face, as this will alter its characteristics. The completed lens assembly can now be soldered to the PC stakes. matching cutout in the lid. Note that both the wide and narrow angle lenses have a focal length of 30mm. You don't have to worry about this if you are using the wide angle lens, since the correct focal length is automatically set by the lens assembly. If the narrow angle lens is used, you will have to carefully adjust the height of the PCB in the case so that the lens is 30mm above the surface of the sensor (ie, the board should be stood of the base by about 5mm). 30mm R 7 2 OFF SINGLE SIDED PCB ...__---+--~7T i------50mm------i l Testing This is the long-range version, fitted with the narrow-angle lens. Check that the lens is the right way up (see Fig.2) and that there is sufficient clearance around the corner mounting holes. The narrow angle lens doesn't require a supporting assembly. Instead, the lens is simply glued to a circular cutout in the lid of the case, directly over the pyroelectric sensor. A simple folded aluminium case measuring 70 x 40 x 130mm is used to house the circuit board. For the wide-angle version, the PCB should be mounted about 12mm above the base, so that the entire surface of the fresnel lens protrudes through a Nova-15 loudspeakers the impedance drop below 7 ohms and at its maximum the value was just above 17 ohms at two points in the frequency range, around 80Hz and 2kHz. This impedance characteristic means that the Nova 15s are very tractable speakers, able to be driven without problems by virtually any amplifier. Listening tests with a sine wave generator indicated that the Nova 15s were quite smooth across the whole frequency range. We noticed some prominence in the region of 4kHz and l0kHz and a slight colouration in the region of 2 to 3kHz. In the bass region, the response · is well maintained down to lO0Hz Double check the locations of all the components, then apply power to the unit. Note that several minutes of settling time are required after applying power due to some of the long time constants used in the circuit. This does not cause any real problems since, in an actual alarm installation, the unit will have power applied to it continuously. To test the unit, set trimpot VRl to about two-thirds travel (starting from the maximum anticlockwise position) and mount the unit about two metres above ground level (see Fig.2). Assumimg that the unit has an approximate 15° tilt, a range of about 10 metres should be possible. Note, however, that passive infrared detectors are much more sensitive to movements across their beams than along their beams. The voltages shown on the circuit ctd from page 17 or so, with useable output available down to about 70Hz. Below that, if the speaker is driven hard, there is a tendency to "frequency double". The latter effect means that there is more apparent bass than there really should be. On music, the Nova 15s could be described as "forward sounding" and giving some prominence to brass instruments. Overall they have a bright sound quality with good bass and clean treble. For listening on classical music though, we preferred to use a judicious amount of treble cut, so that the high end was toned down just a little. !-----2-0-FF-TI-NP-LA_TE_ _ _.J ,-~---45mm----...J~ Fig.5: the wide-angle lens assembly is made from tinplate and blank PCB material. diagram were measured in a still large room, with the sensitivity control at the two-thirds setting. The quiescent current ·was BmA from a 12V DC supply. Finally, the two-thirds sensitivity setting was found to produce reliable operation in a fairly large room. As a general rule, advance the sensitivity control only as high as it needs to be for reliable triggering. And remember, it is whole body movement we are trying to detect, not just hand movement. ~ Where the Nova 15s really score is with their efficiency which is well above the average. They can be driven to good sound levels with quite modest amplifiers which may be rated as low as 10 watts per channel. This means that they are a good match for modestly powered amplifiers and stereo receivers although Tandy state that they are suitable for amplifiers with output powers of up to 60 watts per channel. Tandy's current price on the Nova 15s is $169 each which makes them very keenly priced as they are. However, we understand that for the month of December they will be two for the price of one. At that price, they are a real bargain. ~ DECEMBER1987 39