COMPUTER SCIENCE PROJECT

Group Number 2

SensorsGroup Members:

Muhammad IrtizaTaimoor Ahmed

Fahad DayalaAyaz Ahmed

Light Sensor

What is a Light sensor?A Light Sensor is something that a robot can use to detect the current ambient light level - how bright or dark it is. There are a range of different types of light sensors, including 1. Photoresistors (LDR)2. Photodiodes3. Phototransistors.

What is it?A photo resistor is a light-dependent resistor which slowly loses its resistance when exposed to high levels of ultraviolet light. As a result, photo resistors convert light energy into electrical energy.

How it works?Photo resistors are made of highly resistant semiconductors that are sensitive to high photonic frequencies. As photons (light particles) come in contact with the semiconductor, they cause electrons that were bound to the metal to jump to another piece of the semiconductor. As more photons hit the semiconductor, more electrons are knocked loose. This creates a very effective conductive flow of electricity that only travels through the semiconductor when in the presence of light.

Photo resistor Light Sensor

What are it’s Applications?Photo resistors are used for a wide variety of purposes, all of which require light to determine whether a device should be on, off, or set to a particular position. Photo resistors are responsible for turning street lights on/off and measuring the amount of light that a camera picks up. They are also used in some types of alarms and clocks. Photo resistors are used in dynamic compressors to control gain reduction and can be calibrated to respond to infrared light.

How it Looks like?Take a look for yourself:

Photodiode Light SensorWhat is it?The Photodiode sensor is a system accessory for lighting control systems. It allows control of lighting levels based on how much natural light is present.

How it works?When a photon(light particle) of sufficient energy strikes the diode, it creates an inner photoelectric effect. If the absorption occurs in the junction's depletion region, or one diffusion length away from it, these carriers are swept from the junction by the built-in electric field of the depletion region. Thus holes move toward the anode, and electrons toward the cathode, and a photocurrent is produced. The total current through the photodiode is the sum of the dark current (current that is generated in the absence of light) and the photocurrent, so the dark current must be minimized to maximize the sensitivity of the device.

What are it’s applications?Photo sensors may be used to respond to incident light, or to a source of light which is part of the same circuit or system. A photodiode is often combined into a single component with an emitter of light, usually a light-emitting diode (LED).However, it is being used at a major scale in homes for automatic lighting and in vehicles for the same purpose.

How does it look like?:Take a look below!

Phototransister Light Sensor

What is it?A phototransistor uses the level of light it detects to determine how much current can pass through the circuit. So, if the sensor is in a dark room, it only lets a small amount of current through. If it detects a bright light, it lets a larger amount of current through.

How it works?A Phototransistor is an electronic switching and current amplification component which relies on exposure to light to operate. When light falls on the junction, reverse current flows which is proportional to the luminance. Phototransistors are used extensively to detect light pulses and convert them into digital electrical signals. These are operated by light rather than electric current. It is capable of converting light energy into electric energy. Phototransistors work in a similar way to photo resistors commonly known as LDR (light dependant resistor) but are able to produce both current and voltage while photo resistors are only capable of producing current due to change in resistance. Phototransistors are transistors with the base terminal exposed. Instead of sending current into the base, the photons from striking light activate the transistor.

What are it’s applications? Punch-card readers. Security systems Encoders – measure speed and direction IR detectors photo electric controls Computer logic circuitry. Relays Lighting control (highways etc) Level indication Counting systems

How it looks like?Well, take a look below!

Type of Light Sensor Advantages Disadvantages

Photoresistor Moderate response time Low cost Bi-directional

Rugged in nature Resistance varies

continually(analog)

Photodiode Quicker response time Low cost Digital in nature

Temperature sensitive Uni-directional

Phototransistor Phototransistors produce a higher current than photo diodes.

Phototransistors are relatively inexpensive, simple, and small enough to fit several of them onto a single integrated computer chip.

Phototransistors are very fast and are capable of providing nearly instantaneous output.

Phototransistors produce a voltage, that photo-resistors cannot do so.

Phototransistors that are made of silicon are not capable of handling voltages over 1,000 Volts.

Phototransistors are also more vulnerable to surges and spikes of electricity as well as electromagnetic energy.

Phototransistors also do not allow electrons to move as freely as other devices do, such as electron tubes.

Sound Sensor

What is it?Sound sensors (microphones) are dynamic and use induction coil positioned in the magnetic field of a permanent magnet attached to the diaphragm. When you make a sound, the diaphragm vibrates and thus the attached coil moves in the magnetic field, producing current. There are several types of sound sensors (microphones) like:

dynamic microphone condenser microphone ribbon microphone carbon microphone

How does it work?Most microphones today use electromagnetic induction (dynamic microphones), capacitance change (condenser microphones) or piezoelectricity (piezoelectric microphones) to produce an electrical signal from air pressure variations. Microphones typically need to be connected to a preamplifier before the signal can be amplified with an audio power amplifier or recorded.

What are it’s applications?Everywhere, from offices to homes, from outdoor to indoor.

How does it look like?Take a look below:

Temperature Sensor

What is a temperature sensor?Temperature sensors are devices used to measure the temperature of a medium. It is difficult, however, to directly measure the energy of molecular movement, so temperature sensors are generally designed to measure a property which changes in response to temperature. The types of temperature sensors are:

Electrical Temperature Sensors Mechanical Temperature Sensors

Thermistor Thermometer

Thermocouple Bi-metallic Strip

Resistance

Silicon Bandgap

ThermometerWhat is a thermometer?A thermometer is a device that measures temperature or a temperature gradient using a variety of different principles.

Mechanical Temperature Sensors:

How does the thermometer work?Operating principles of thermometers include the thermal expansion of solids or liquids with temperature, or the change in pressure of a gas on heating or cooling. Radiation-type thermometers measure the infrared energy emitted by an object, allowing measurement of temperature with out contact.Liquid in glass thermometers specifically use a liquid (mostly mercury or alcohol) to measure the change in temperature, by application of thermal expansion, as particles gain heat on higher temperature and their volume rises, enabling us to read the increase on the scale.

What are the applications of thermometer?Thermometers are widely used in industry to control and regulate processes, in the study of weather, in medicine, and scientific research.

But How does it look like?Take a look at the image below please.

Bi-Metallic StripWhat is ‘Bi-Metallic Strip’?A bimetallic strip consists of two different metals welded together which are used to convert a temperature change into mechanical displacement. Take a look at this picture for an idea of this simple mechanism.

How does it work?The strip consists of two strips of different metals which expand at different rates as they are heated, usually steel and copper, or in some cases steel and brass. The strips are joined together throughout their length by brazing or welding. The different expansions force the flat strip to bend one way if heated, and in the opposite direction if cooled below its initial temperature. The metal with the higher coefficient of thermal expansion is on the outer side of the curve when the strip is heated and on the inner side when cooled.

It looks like this

What are the applications of Bi-Metallic Strips?1. Clocks:These are used in clocks to measure temperature change as it can lead to errors in time keeping.

2. Electrical Devices:Bimetal strips are used in miniature circuit breakers to protect circuits from excess current. A coil of wire is used to heat a bimetal strip, which bends and operates a linkage that unlatches a spring-operated contact. This interrupts the circuit and can be reset when the bimetal strip has cooled down.

3. Thermostats & Fire alarms:Some thermostats operate on High temperatures, so when an optimum temperature has been obtained, the Bi-Metallic strip expands and switches off the Thermostat valve. Similarly, in some fire alarms, it expands to complete curcuit and start. off the fire alarm.

Other than this, Bimetal strips are also used in time-delay relays, lamp flashers, and fluorescent lamp starters. In some devices the current running directly through the bimetal strip is sufficient to heat it and operate contacts directly.

Electrical Temperature Sensors:Thermistor

What is a Thermistor?What is a thermistor? A thermistor is a temperature-sensing element composed of semiconductor material which exhibits a large change in resistance proportional to a small change in temperature. Thermistors usually have negative temperature coefficients which means the resistance of the thermistor decreases as the temperature increases.

How does a Thermistor work?The thermistor acts as the temperature sensor and it is placed on the body whose temperature is to be measured. It is also connected in the electric circuit. When the temperature of the body changes, the resistance of the thermistor also changes, which is indicated by the circuit directly as the temperature since resistance is calibrated against the temperature. The thermistor can also be used for some control which is dependent on the temperature. Main calculations of thermistors are done using a sophisticated formulae.

Applications of Thermistor:There are many applications for a thermistor. Three of the most popular are listed below: Temperature sensing:The most obvious application for a thermistor is to measure temperature. They are used to do this in a wide range of products such as thermostats. In rush current limiting:In this application the thermistor is used to initially oppose the flow of current (by having a high resistance) into a circuit. Then as the thermistor warms up (due to the flow of electricity through the device) it resistance drops letting current flow more easily. Circuit protection:In this application the thermistor is used to protect a circuit by limiting the amount of current that can flow into it. I’ve too much current starts to flow into a circuit through the thermistor this causes the thermistor to warm up. This in turn increases the resistance of the thermistor reducing the current that can flow into the circuit.

How a thermistor looks like?See the image below to understand.

Thermocouple

What is a thermocouple?A thermocouple is a temperature-measuring device consisting of two different, metallic conductors that contact each other at one or more spots. It produces a voltage when the temperature of one of the spots differs from the reference temperature at other parts of the circuit.

What are the working principals of Thermocouple?In 1821, the German–Estonian physicist Thomas Johann Seebeck discovered that when any conductor is subjected to a thermal gradient, it will generate a voltage. This is now known as the thermoelectric effect or Seebeck effect. Basically, when we connect two non-identical conductors which have different temperatures, an Electro-Motive Force (EMF) is produced and it consequently produces a minimal amount of voltage, depending on the difference in temperatures. The thermocouple can then be attached to a multimeter to measure the temperature. thermocouples are self powered and require no external form of energy to operate. The main limitation with thermocouples is accuracy, as system errors of less than one degree Celsius (°C) can be difficult to achieve.

What are the applications of thermocouple?Applications of thermocouple are limited to temperature measurement only.

What does it look like?Take a look below.

Resistance Temperature Detector

What is an RTD?Quite similar to a thermocouple, an RTD is a temperature sensor which measures temperature using the principle that the resistance of a metal changes with temperature. In practice, an electrical current is transmitted through a piece of metal located in proximity to the area where temperature is to be measured. They are slowly replacing the use of thermocouples in many industrial applications, due to higher accuracy and repeatability.

How do they work?RTDs work on a basic correlation between metals and temperature. As the temperature of a metal increases, the metal's resistance to the flow of electricity increases. Similarly, as the temperature of the RTD resistance element increases, the electrical resistance, measured in ohms (Ω), increases. RTD elements are commonly specified according to their resistance in ohms at zero degrees Celsius (0° C). The most common RTD specification is 100 Ω, which means that at 0° C the RTD element should demonstrate 100 Ω of resistance.Platinum is the most commonly used metal for RTD elements.

What are the applications of RTD?Similarly, RTD use is limited to temperature measurement, but it is replacing thermocouple.

How it looks like?Look down.

Silicon Bandgap Temperature Sensor

What is Silicon Bandgap?The silicon bandgap temperature sensor is an extremely common form of temperature sensor (thermometer) used in electronic equipment. Its main advantage is that it can be included in a silicon integrated circuit at very low cost.

How it Works?The principle of the sensor is that the forward voltage of a silicon diode, which may be the base-emitter junction of a bipolar junction transistor (BJT), is temperature-dependent, An electronic circuit can therefore be used to calculate the temperature of the diode. The result remains valid up to about 200 °C to 250 °C, when leakage currents become large enough to corrupt the measurement. Above these temperatures, materials such as silicon carbide can be used instead of silicon.The voltage difference between two p-n junctions (e.g. diodes), operated at different current densities, is proportional toabsolute temperature (PTAT).

Applications of Silicon Bandgap Sensor:None other than measuring temperature.

What it Looks like?Scroll your eyes below.

Pressure Sensor

What is a pressure sensor?

A pressure sensor usually acts as a transducer; it generates a signal as a function of the pressure imposed. For the purposes of this article, such a signal is electrical. Pressure sensors are used for control and monitoring in thousands of everyday applications. Pressure sensors can also be used to indirectly measure other variables such as fluid/gas flow, speed, water level, and altitude.

Pressure sensors are used for a range of diverse applications in industries such as

medical, aerospace, transportation, and general industry and for test and measurement.

Types of pressure sensors• Absolute pressure sensor: measures the pressure relative to perfect vacuum.• Gauge pressure sensor: measures the pressure relative to atmospheric pressure.• Vacuum pressure sensor: Vacuum pressure sensors measure pressure that is less

than 0 PSI.(per square inch)• Differential pressure sensor: measures the difference between two pressures

points.• Sealed pressure sensor: Measures the pressure relative to some fixed pressure.

Where they are used?• The computer devices and smart phones that have touch screen displays come

with pressure sensors. Whenever slight pressure is applied on the touch screen through a finger or the stylus the sensor determines where it has been applied and accordingly generates an electric signal that informs the processor.

• In automotive industry pressure sensors form an integral part of the engine and its safety. In the engine these sensors monitor the oil and coolant pressure and regulate the power that the engine should deliver to achieve suitable speeds.

• In instruments like digital blood pressure monitors and ventilators, pressure sensors are needed to optimize them according to patient’s health and his requirements

• Pressure sensors are used to monitor gases and their partial pressures in industrial units so that the large chemical reactions take place in precisely controlled environmental conditions.

• In the airplanes these sensors are needed to maintain a balance between the atmospheric pressure and the control systems of the airplanes

Pressure sensor technologies

Piezoelectric Uses the piezoelectric effect(it is the electric charge that accumulates in

certain solid materials in response to applied mechanical stress) in certain materials such as quartz to measure the strain due to pressure. Used to measure high dynamic pressures.

Advantages:-They generate a voltage proportional to the velocity the crystal is

deformed so require no local power source

Disadvantages:-They are high impedance and can pick up stray voltages in the

connecting wires. The crystal is also prone to cracking if overstressed

Strain gage Strain gages are an example of passive transducer that converts a

mechanical displacement into a change of resistance. Types1. Mechanical 2. Electrical3. Semi conductor4. Photo electric

Advantages:-1. There is no moving part2. It is small and inexpensive

Disadvantages:-3. It is non-linear4. It needs to be calibrated

Applications:-5. Residual stress6. Vibration Measurement7. Torque Measurement8. Strain Measurement9. Compression and tension Measurement

Capacitive Uses a diaphragm and pressure cavity to create a variable

capacitor to detect strain due to applied pressure.

Advantages:-It reduces interference in the signal to our

amplifiers therefore making our system cleaner. SQ cars use these typically. They can help with dimming lights.

Disadvantages:-It reduces voltage slightly and interfere with direct

current flow. As fast as they discharge they are almost useless in providing anything for long drawn out bass notes

Electromagnetic Measures the displacement of a diaphragm by means of

changes in inductance, LVDT, Hall Effect, or eddy current principle.

Advantages:-1. Very highly sensitive to atmospheric quantity2. Very good operating speed- fast3. Very low power requirement for operation4. They are portable and used any where5. Wide temperature sensors

Disadvantages:-6. Designing is complicated rather than mechanical system7. Costly than mechanical system

Moisture Sensor

What is moisture sensor?Moisture sensors measure the water content in soil. A soil moisture probe is made up of multiple soil moisture sensors. Measuring soil moisture is important in agriculture to help farmers manage their irrigation systems more efficiently. Not only are farmers able to generally use less water to grow a crop, they are able to increase yields and the quality of the crop by better management of soil moisture during critical plant growth stages.

How it works?The moisture sensor works when the series of discs in the sensor expands they get wet, and to a certain size, they flip a micro switch, this interrupts the current going from the controller to the valves, whereby the controller will tell the valves to start watering in the middle of a rainstorm, if the valves do not get the memo then they don't turn on. When the discs dries out in the sun and the wind, then the switch flips back, and the valves will water when the controller tells them to start watering.

TypesTensiometers

Tensiometer probes are water-filled tubes that you insert into the soil to the depth of plant roots. At the bottom of the probe is a porous ceramic tip, and at the top of the probe is an above-ground gauge. Water from the tube leaves the porous cap and enters the soil around it. As the moisture inside the tube reaches equilibrium with the soil moisture outside the tube, the moisture tension registers on the gauge. When soil is dry, a plant must use greater suction to extract the available water from the soil. The tensiometer gauge reflects this soil water suction -- the higher the reading, the drier the soil.

Gypsum BlocksAnother type of sensor that measures soil water tension is a gypsum block, also called an electrical resistance block. A porous block, typically made of gypsum, is placed on top of the soil and must maintain firm contact with it. The block contains two embedded electrodes into which wires are inserted. The other ends of the wires penetrate the soil surface. As water moves through the block to maintain equilibrium with the soil moisture, the electrodes measure the electrical resistance that the water generates. A portable meter converts the resistance readings to water tension values.

Applications of moisture sensors• Agriculture

Irrigation of crops represents 90% of the water used worldwide. Monitoring soil moisture in the root zone of crops will optimize irrigation. The benefits of optimizing irrigation scheduling with soil moisture sensors includes increasing crop yields, saving water, protecting local water resources from runoff, saving on energy costs, saving on fertilizer costs and increasing the farm's profitability.

• Dust ControlPoor air quality from particulates in air can have negative consequences

to not only human health but regional ecosystems. Vehicular traffic on unpaved roads can lead to major dust problems. In areas of the Southwestern US, the soil is naturally abundant in several types of asbestos. Local officials close unpaved roads based on soil moisture conditions to prevent dangerous dust situations.

• Phytoremediation

Phytoremediation is the method by which plants are used to remove pollution from soil. After the pollution is taken up by the plant, the pollutant accumulates in the plant tissue and the plant can be disposed of, or the pollutant is transpired into the air where the sun will chemically break it down into harmless daughter components. Soil moisture sensors insure that the toxins are not leached downward from over irrigation and ensure that the plants get enough water to effectively remove the pollutant from the soil.

• Landslide StudiesChanges in land use may increase the likelihood of landslides dangers.

Each year, millions of dollars in damage to property and lives are lost due to land slides. Predicting and preventing landslide hazards is becoming very important in some urban areas. The inputs to landslide prediction models are; slope, vegetation, toe slope, soil cohesiveness, and soil moisture. In some areas that experience perched water tables, the soil in the perched water table becomes very heavy as the soil becomes saturated thus becoming more influenced by gravity. Monitoring soil moisture is an important indicator for landslide hazards.

pH sensors

What is a pH sensor?A pH meter is an electronic device used for measuring the pH of a

liquid (though special probes are sometimes used to measure the pH of semi-solid substances). A typical pH meter consists of a special measuring probe (a glass electrode) connected to an electronic meter that measures and displays the pH reading. The probe is a key part of a pH meter; it is a rod like structure usually made up of glass. At the bottom of the probe there is a bulb, the bulb is a sensitive part of a probe that contains the sensor.

pH meters range from simple and inexpensive pen-like devices to complex and expensive laboratory instruments with computer interfaces and several inputs for indicator and temperature measurements to be entered to adjust for the slight variation in pH caused by temperature. Specialty meters and probes are available for use in special applications, harsh environments, etc. There are also holographic pH sensors, which allow the measurement pH calorimetrically.

Examples of pH sensors• Litmus paper• Phenolphthalein• Methyl orange

Applications of pH sensors• Cheese making

All cheeses must fall within a fairly narrow pH range in order to ripen normally and develop flavor and texture

• Pool MaintenanceThe pH level is an essential part of your pool care as it affects how comfortable the water is to swim in as well as chlorine’s ability to sanitize your water.

• Measure soil pH for happier, healthier plants.When the soil pH is too acid (low pH) or alkaline (high pH), nutrients present in the soil become locked-up or unavailable. Correcting the pH has the same effect as applying fertilizer since it unlocks plant nutrients already present.

• Stain Removal and pH levelsKnowing the pH level of a stain is a key step in identifying the best method to remove it. A flat surface pH meter lets you read pH levels of fabric and carpet easily.

Advantages: 1. They give you a numerical value of the pH 2. pH meters can give you the exact pH 3. They give you an idea as to how acidic and basic the substance is

Disadvantages: 1. They are too expensive 2. pH papers only give you a rough estimate 3. pH meters need to be calibrated

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