Light sensors seminar

light sensors complete lecture in engineering physics by S.MALAIAPPAN SRIKANTH B.E CSE (MADURAI)

1. LIGHT SENSORS S.MALAIAPPAN SRIKANTH ( CSE-B ) 20UCS0 79

2. CONTENTS INTRODUCTION A LIGHT SENSOR IS TYPES OF LIGHT SENSOR Components Applications CONCLUSION (WITH A PRACTICAL ACTIVITY)

3. Introduction Light sensor is a simple powerful concept. It automatically switches ON lights when the sunlight goes below the visible region of our eyes and automatically switches OFF lights when Sunlight fall on it (in morning), by using a sensor called LDR (Light Dependent Resistor) which senses the light just like our eyes.

4. Light Sensors (or) Dark Sensors? Light sensors measure the amount of light impacting a photocell , ( Photocell is basically a resistive sensor: the light effects the amount of resistance . ) The resistance of a photocell is low when it is brightly illuminated, ( i.e ., when it is very light); it is high when it is dark. In that sense, a light sensor is really a "dark" sensor . In setting up a photocell sensor, you will end up using the equations we learned above you will need to deal with the relationship of the photocell resistance Rphoto , and the resistance and voltage in your electronics sensor circuit.

5. A LIGHT SENSOR IS The light sensor is a passive device that converts the light energy into an electrical signal output, which is used to detect light. Light sensors are more commonly known as Photoelectric Devices or Photo Sensors because they convert light energy (photons) into electronic signal (electrons ). Phototransistors, photoresistors , and photodiodes are some of the more common type of light intensity sensors.

6. Light sensors are used to detect the presence and Intensity of light . These can be used to make a light seeking robot and are often used to simulate insect intelligence in robots. Light Sensors

7. Light Sensors Analog sensor -- Change resistance in response to light stimuli CdS photocell (or other resistive sensor)

8. What can be measured by Light Sensors? Just like switches, light sensors can be used in many different ways: Light sensors can measure: light intensity (how light/dark it is) differential intensity (difference between photocells) break-beam (change/drop in intensity) Light sensors can be shielded and focused in different ways Their position and directionality on a robot can make a great deal of difference and impact

9. TYPES OF LIGHT SENSORS

10. Basic types of light sensors Light sensors indicate light intensity by measuring radiant energy of photons in a range of frequencies . There are 2 main categories of light sensors, each with its own operating principle(s) Generates electricity when illuminated Photo-emissive Photo-voltaic Changes electrical properties when illuminated Photo-conductive Figure 1: Summary of light sensor operating principles

11. Photo-emissive sensors Operation : Photons hit a light-sensitive material, releasing free electrons Electrons are collected in anode, forming a current The current is measured, and is dependent on photon intensity and frequency Photo-emissive (phototube) operation

12. Photo-voltaic sensors Operation: Photons hit a light-sensitive semiconductor, producing electron-hole pairs Electrons move across the semiconductor’s p-n junction, producing a voltage across it The current produced by this voltage is measured Photo-voltaic cell operation

13. Photo-conductive sensors Operation: Photons hit a light-sensitive semiconductor, producing electron-hole pairs Instead of accumulating a voltage (as in the photo-voltaic process), this semiconductor reduces its resistance This increases the amount of current flowing through the semiconductor, which is ten measured Photo-conductive operation

14. Light sensor characteristics : responses to light Photo-voltaic cell (G = solar irradiance) Photo-emissive (vacuum) phototube Photo-conductive photoresistor

15. Interface electronic circuits OBSERVATIONS: Needs usually an amplifier The output depends on the load resistor Change in wavelength changes the sensitivity response Input voltage is needed so the sensor is not passive Low pass filter is required parallel with the load resistor to decrease the noise Typically white light is used Sample electronic configuration for an ambient light photo sensor

16. Components L i ght Dependen t Res i s t or (LDR) I nte g rated C i rcu i t ( I C) Var i abl e Res i s t or Resistance Transistor Diode Relay

17. Circuit Diagram

18. Light Dependent Resistor (LDR) A photoresistor or light-dependent resistor (LDR) or photocell is a light-controlled variable resistor. The resistance of a photoresistor decreases with increasing incident light intensity. In other words, it exhibits photoconductivity. A photoresistor can be applied in light-sensitive detector circuits, and light- and dark- act i v a t ed sw i tch i ng circuits.

19. Integrated Circuit (IC) An i n tegr a ted c i r c u i t o r mono l i t h i c i nt e grated c i rc u i t (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small plate ("chip") of semiconductor material, normally silicon. Extremely small size, small weight, reduce cost, extremely reliable, low power consumption, easy replacement. I C T erm i nolog i es: Bond i n g , Ch i p , D i f f us i on m a sk, En c apsula t i on, Et c h i ng

20. Variable Resistor The resistor whose electrical resistance value can be adjusted as per requirement by adjustable component attached to it is called variable resistor. Also kno w n as por t an d potent i omet e r . A variable resistor is a strip of a material such as graphite which resists the flow of electricity. There is a fixed terminal attached to one end of the resistor. There is also a moving device touching the graphite called a wiper.

21. Resistance Resistance is the opposition that a substance offers to the flow of electr i c current. T he s t and a rd un i t of res i s t anc e i s the ohm. I t i s def i ned a s the rat i o of the v olta g e appl i ed to the ele c tr i c cur r ent wh i ch flows through i t:

22. Diode A d i ode i s a spec i a l i zed electron i c com pone n t w i th two electrod e s calle d the anode an d the cathode. Mo s t d i ode s a re m a de with semiconductor materials such as silicon, germanium. I t a ls o wor k a s sw i tch. D i odes can b e used a s re c t i f iers, s i gnal l i m iters, v oltage reg u l a tor s , sw i tches, s i gnal modu la t ors, signal mixers, signal demodulators, and oscillators .

23. Relay A relay i s an ele c tr i cal l y o p erated sw i tch . T he ad v antag e of us i ng a relay is that a s m a l l current can b e u s ed to sw i tch on a nd off a c i rcu i t w i th a larg e current . The output from IC is send to relays which results in i ts exc i tation an d ge t s a ct i v a te d .

24. W hen the sw i tch i s c l osed , cu r re n t flows an d the i r on ro c ker ar m at t ra c ted to the electromagnet that rotate a n d pus h es t h e co n tacts together. I t may ha v e a la r ge cu r re n t fl o w i ng thr o ugh it , t o ope r ate a powerfu l m otor o r v ery br i ght l i ghts. U se d to con trol m otors, heater s , la mps or A C c i r cu i ts wh i c h themselves can dra w a l o t more e le c tri c a l po w er. Rel a y Relay

25. Common Applications S t reet lamps A lar m clo c ks Ho m e law n an d Parks B ur g la r al a rms C a mera l i g h t met ers L i ght i nten s i ty meters

26. Specific Applications Burglar alarm where the light is send from one to another sensor, if the light is interrupted, the alarm will go on Barcode scanner where the scanner illuminates the barcode and collects information Remote control with infrared light sensor Telecommunication use light emitting diode to send information with the optical fiber Mobile phones have many different light sensors Barcode scanner and typical photoelectric sensor components

27. Let us just Summarise through a video

28. Thank You I HOPE YOU ALL HAVE A CLEAR IDEA AND UNDERSTANDING about LIGHT SENSOR !