2.1 Proximity Sensor
These are sensor that can on there own detect objects or obstructions on their path or way without physical contact, they often emit electron beam and detects or notice changes in the field or environment, proximity sensor targets or demand different sensors, a capacitive or a photoelectric sensor or an inductive proximity sensor can also be used which might require a metal target ,looking at capacitive proximity sensor the object in question changes the dielectric constant between the two plates within a range in some cases which is relatively close to water, because sudden changes in capacitance of objects sometimes takes relatively long time to switch range within the 50Hertz,a normal capacitive proximity sensor do have about 10-12mm sensing range and about 30 mm in diameter, in most cases setting the output of a proximity sensor is quite difficult, hence proximity sensor designers always add hysteresis, excitation voltage etc.most capacitance proximity sensor can make measurements in 100u sec with resolution of 10⁶,probes put into use in capacitive proximity sensor have either flat disc or rectangular sensing element, the main advantage of capacitive proximity sensor is that they are mostly unaffected by containers, allowing them to be replaced by optical devices.
2.2 Passive infrared sensor (PIR).
In most security systems ,motion is required to be detected in a monitored environment, in most cases the passive infrared motion sensor is preferred to detect changes and upon detection motion sensors generally transmit a notification or indication to the systems host then an intrusion or activation of an alarm system to perform various operations ,in order to monitor a large space with only one or two detector ,most PIR sensor is designed with numerous optical components (mirror or lenses) then each component of such compound optics focuses the infrared radiation from objects within a respective sub-volume of the monitored space into an image appearing over the detector then monitored sub-volume can be interleaved with non-monitored sub-volumes and then radiation producing target (human) passing from the sub-volume to sub-volume causes a target radiation or background radiation /target radiation pattern in detector for humans the pattern leads to a change in the IR radiation in detector .
For PIR sensor there is the need to reduce false alarms and then minimizing processing requirement ,the PIR sensor using a minimal number of detector could generate false alarm from time to time ,definitely a radiation of wavelength outside the required micron band as a result false alarm would triggered in order to reduce false alarms from triggering ,optical filters could be added as detector windows to screen out white light and IR light then coating for mirrors and additives for lenses would be added to prevent focusing of white and near infrared light on detectors hence reducing the chances of motion ,PIR sensor producing false alarms when detectors include pairs of equally sized elements of opposing polarities, Non focused out of band radiation is equally incident on both elements ,then causing signals from equal and opposite elements to roughly cancel one another ,equal elements of opposite polarity reduce false alarms from shock and temperature change, there are chances that PIR sensors can be improved upon to reject interferences and determination of motion direction and detecting a moving object in a monitored space from a non-moving object characterized by non-constant radiation includes receiving a first frequency from the first passive PIR detector then receiving the second frequency from a second passive IR detector, hence the first and second frequencies not being equal ,this method involves outputting a signal are received simultaneously then signal indicate the presence of object is not output.
The PIR (passive infrared Red) is a low cost PIR detector used for motion or human detection which can be a simple pyroelectric detector because the detector can be a significant part of the cost (5-10%) of a typical PIR motion sensor, most PIR motion sensor would only employ just one or two of such detectors ,normally the human body radiates infrared waves ranging between 8 to 12 micrometers, as a result should anyone move in any direction ,there will be a change in the quantity of infrared energy providing a low frequency and small amplitude signal, there are possibilities that the same signal can be amplified and decoded using microcontroller, ideally PIR sensor can detect changes in the quantity of infrared energy in small ranges of distance approximately 10-13 inches, in order to detect motions at larger distance, infrared radiation will have to be focused, the focusing is done with the use of a Fresnel lens in most cases usually divide the whole area into different zones hence any movement within the zones already divided into will certainly lead to a change in the infrared energy received by the sensor, Fresnel lenses depends on the range (distance) and basically coverage angle looking at volumetric lenses and certain then the PIR sensor unit will then decide whether the infrared light is from a warm moving body or not ,it is always a lot better when PIR sensor could have one or more inner sensing elements so that with relevant electronics and Fresnel lens, it could sense direction from up to down and right to left and show required output signal.
2.2.1 Uses of PIR Sensor
They are basically used for automatic security lightning say when human moves across its path or view or sensor for instance a floodlight is switched on automatically and left on for a fixed period of time say 90 seconds and can provide light when you arrive at home.
2.2.2 Advantages of PIR
PIR sensor does not require any form of maintenance, however should in case of any form of fault, it can be easily replaced so for optimum performance, it is advisable to remove any accumulated dust with low power cleaners.
2.2.3 Weakness of PIR sensor.
PIR sensor do have its own limitation and these limitations in a way does let it work properly.PIR sensor would not detect stationery or slowly moving body or object in most cases the environment change in terms of cooling off of a nearby wall could actually activate the sensitivity of a sensor and when someone walk straight pass or towards a PIR it would not detect them until close by, they are actually temperature sensitive and work optimally at ambient air temperature of around 16-21 degrees celcius,in most cases when the temperature raises is about 32 degrees ,the field of view narrows and the sensor becomes less sensitive and vice-versa should the temperature drop below 12 degrees, the field view widens up and smaller or more at a distance object might activate the sensor .
2.3 MULTIPLE PIR SENSOR CIRCUIT
Situations or scenarios will arise that you would require to use one or more PIR sensor within a system, where one could be at the front and the other at the end or the rear, it is virtually not possible to join them together the output from more than one PIR sensor, in a case like this an AND gate logic is deployed, in logic high voltage is shown by 1 and low voltage by 0 hence the output from a PIR sensor upon detecting motion shows 0 and is 1,the rest of the time, we want an output of 0 when either of the PIR sensor is output is 0,that can be shown in the truth table below .
|PIR # 1||PIR # 2||PIR # 1 & PIR # 2|
These truth table is exactly the same as that for an AND gate, basically a logic device that gives an output of 1 only when its two output are both 1, the basic symbol for an AND gate is below.
In order to make use of the output signal from a PIR sensor we would need to invert it turn a 12v output to 0 v and a 0 v output into 12v,when motion is detected by a PIR sensor, the 0 v sensor signal is inverted to 12v signal .
2.3.1 NAND GATE
Looking at putting two or more PIR sensor together in a circuit, it is not required to put PIR sensor signals through an AND gate ,then through a NOT gate rather i would use a NAND gate, the truth table for it could be seen below .
|PIR # 1||PIR # 2||PIR # 1 & PIR # 2|
Setting the signal of the sensor from two or more PIR sensor through a NAND gate will result to a 12v output unless both PIR sensor signal is 12v in a case where neither is detected in terms of motion then the output is 0v that is what we need.
The basic diagram of an NAND gate can be seen below
How NAND gate is physically connected to a PIR sensor in a circuit, AND gates could be gotten from integrated circuits with the 4000 series applicable to the 12 volt DC system as shown below, the schematic diagram of a Quad 2 input NAND gate with chip 4 NAND gates, each collecting two inputs, that can be seen in the diagram below.
The maximum output current from the 4000 series is about 4 to 10 mA, slightly enough to light an LED, hence we might require it to amplified through a transistor so that it can power light couple of hundred mA or perhaps energise a coil of a relay, below a schematic diagram showing how the PIR sensor output could be put through a NAND gate and the result amplified through a transistor (NPN).
In conclusion as regards to motion detection,PIR sensor is the most sensitive and advanced option that i am aware of and their light options makes it ideal for security systems .
The arduino platform is based on making things work using simple electronics, it is all about tinkering and creating something with the board with its functions defined below.
Just above is the diagram of the arduino board and what each element of the board does will be defined below as well.
14 Digital IO (pins 0-13,) can be inputs or outputs as set in software
6 Analogue out (pins 0-5) are dedicated analogue input pins, these take analogue values (voltage readings) and convert it to numbers between 0 and 1023.
3 Analogue out (pins 9, 10, 11) this is just 3 of the digital pins and can be reassigned to do analogue output.
The board could be powered through the USB port or from any power socket around, this arrangement could be changed with a jumper marked SV1 in the diagram, if the jumper is closest to the USB plug then the board is powered from there but if the jumper is on 2 pins closest to the DC connector then it is powered from there.
2.5 Interaction Design
The essence of interactive design is all about creativity, being able to express your own design in a form of experience to create something between humans and artifacts, making designs through an interactive process based on prototypes of ever increasing fidelity, there are chances that design in future could be extended to include phototypes in technology with reference to electronics, basically interacting with each other as long as humans have been a species, so having interactive design has been applied to development of different solutions, creating or exploring ideals between human and technology, it involves creating products and systems which users can interact with individually, in order to achieve the ideals that you would like to realize within complex technology, systems making use of basic or simple electronics components like software packages and mobile devices, which can be applicable to several other devices and services, since interactive design defines behaviour though some principles of cognitive psychology shows how prepared the ground is for interactive design in terms of mental models and mapping etc and there are chances of creating human computer interaction (HCI),which is the methods of describing and testing the usability of communicating with interfaces, in most cases design are emphasized in users goals and experience, one of the essence of interactive design is to improve usability then the experience of the end product by understanding what is required to implement the design in question, after a system on has been designed by getting users involved on frequent basics, only then will designers be able to optimize and properly tailor the usability, it is quite an essence that the users that the designer is designing for is fully aware of the system capabilities from the onset in order to contain expectations from users, interactive design makes use of various photo type techniques to check variety of areas of design, ideas could be grouped into three, testing the role of the artifact itself ,test of its implementation ,prototype could be physical or digital ,high or low fidelity .
2.6 Physical Computing
In previous years making use of basic electronics makes dealing with engineers always kept systems designers from playing directly or indirectly with the medium, almost all tools require good understanding and was meant for engineers, physical computing involves putting together interactive physical components making use of software and hardware components and then having to get a respond the analog settings, could be reffered to as a framework to understand human relationship with the digital world, system using sensor and microcontroller to actualize analog input to a software system and to control several mechanical devices such as motors etc and variety of hardware applications, physical computing is used in various areas and applications making interesting link between the physical world and computer world, understanding the way or pattern in which humans communicate putting their expressions within their design, mini computers like the microcontroller have become cheap and easier allowing the making of better tools and the arduino making use of the physical computing and system designer getting to know the elementary of electronics and get to know that you can construct phototypes with little investment .
2.7 SERIAL COMMUNICATION.
Looking at the arduino diagram below, the USB connection that is used by the IDE to pass across codes into the processor and exciting news is that the connection will be used by programmer to communicate with the arduino to send data back to the computer and receive commands from it.
2.8 Bread board
From the diagram below what a bread board looks like can be seen, it is just a plastic board filled up with holes and each contains spring loaded contact and component required leg could be put into the holes, each hole is about 2.53 mm distance from each other and then all components have their own legs, though not all contact on the board are equally created, the top and bottom row are connected horizontally and are used to carry power across the board so when power is required, there is always a hole or gap in the middle as wide as a chip, showing the vertical line of holes so pin will not be short circuited ,the essence of the breadboard is to allow you to alter connections between components in the fastest and most practical and non destructive way possible.
The micro controller are constantly used in automatically controlled products and devices, they fit into design well because of one of its advantages which is low power consumption, they consume relatively low power in mill watts and do have the ability to sleep when waiting for an input like pressing a button before it carrys out the operation so while sleeping it might be using just nanowatts,the micro controller allows you to integrate additional elements like read-write memory for data storage ,peripheral devices and input/output interfaces ,they also operate at very low speed compared to today’s microprocessors.
2.10 Driving Bigger Loads
The pins of an arduino board will only power devices that use up to 20 milliamps, though that is quite small which barely light an LED, trying to drive some else with far much more power will definitely stop the systems from working and definitely burn out the processor, in order to drive larger loads like coils etc, an external component that can switch such things ON and OFF by an arduino pin, a mosfet transistor will be required, which is an electronic switch that can be seen that the motor takes its power system having different power supply from the one used by arduino which is purely an advantage and the mosfet connected to pin 9 .
2.11 Analogue Input
circuit could be reffered to as quantized electrical signal with a certain range and can generated by a sensor and received by a controller it changes constantly a definite manner in relation to a property, analogue signals produced by some sensors could be conditioned by converting higher-level standard signal which would be transmitted over wires to the receiving controller. Analogue inputs are converted to digital signals by the analogue to digital converter, in most cases located at the controller, in most cases limited to a small range of DC voltage. The three type of analogue input signals are current, resistance, voltages used in controls are within 1-5 volts and direct convert (VDC), 2-10 VDC as regards to current the 4-20 MA signal has become the industry standard convert signal for use with analogue and digital controllers, resistance are mostly associated with direct inputs from temperature sensing devices. A basic circuit diagram below is a typical example of analogue inputs configurations.
The arduino can sense voltage out across to one or any of its pins and shows it through digital real functions, this is used by the arduino in lots of applications, in most cases we need to know exactly what the amount of voltage we are putting across, hence in order to determine the exact voltage across and we would need a different type of pin. The lower right part of the arduino board has 6 sets of pins marked analogue in. These set of pins would not only tell u the voltage applied to them or not but also its value making use of the analogue read function. Voltage applied to one of the set of pins can be read using the scale, the function returns a number between 0 and 1023 representing voltages between 0 and 5 volts, hence if a voltage of 2.5 volts is applied to pin 0. The analogue read (0) will return 512 etc, hence constructing a circuit using 10k or 4.7k resistor and putting the codes through. You find the lead blinking at the rate that depends on the amount of light that hits it.
2.12 Pulse Width Modulation
Pulse width modulation of the power source or signal involves the modulation of its duty cycle to carry messages over a communication link or rather control the amount of power sent to a load,PWM makes use of square wave, whose pulse width is constantly modulated resulting in variation of average value of the waveform, the best method to generate PWM signal is intersective method which requires a saw tooth or a triangle waveform which can be generated PWM signals e.g. micro controller, making use of a counter that increments periodically connected directly or indirectly to the clock of the circuit and sets back after the end of every period of PWM, there are three types of PWM signals
-(leading edge modulation) the pulse lead edge can be held at the lead edge of the window and tail edge
– (trailing edge modulation) the pulse center may be fixed in the center of time window and both edges of the pulse moved to compress or expand the width.
-the tail edge can be fixed and lead edge modulated.
PWM could be used to reduce the total amount of power delivered to a load without losses due to the fact that the average power delivered is proportional to modulation duty cycle, PWM are used in controlling electrical power supply to other system like speed control in electric motors, PWM is used in efficient voltage regulators by switching voltage to the load with required duty cycle
In conclusion the PWM is a way of digitally encoding analog signal level the diagram below shows the three possible PWM signals, the first figure showing the PWM outputs at 10% duty cycle and the other figures showing the PWM outputs at 50% and 90% duty cycle respectively, hence the three PWM outputs encode three different analog signal values at 10%, 50% and 90% of the full strength, the supply is 7v and the duty cycle is 10%, a 0.7 v analog signal result.
Below a simple Pulse Width Modulation circuit can be shown.
11. Arduino booklet (2002), Massimo banzi, Erica calogero, David Guartielles, Jeff Gray, Tom Igoe, David Mellis
12. Barr .Michael, embedded systems Programming, September 2001, pp. 103-104
13. Making things talk: Practical Methods for Connecting Physical Objects by Tom Igoe (Paperback -September 28, 2007)
14. Physical Computing: sensing and controlling the physical world with computers by Tom Igoe, Dan O’ Sullivan. Thomson Course Technology, Boston, Massachusetts, May 2004
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