SENSORS

INTRODUCTION A device which detects or measures a physical property and records, indicates, or otherwise responds to it. Examples of physical properties: Light, motion, temperature, magnetic fields, gravity, humidity, moisture , vibration, pressure, electric fields , sound, and other physical aspects of the external environment

BASICS Transducer: A transducer is a device that converts one form of energy to another form of energy. Energy types include(but are not limited to) electrical, mechanical, electromagnetic(including light), chemical, acoustic, and thermal energy. Ex: a loud speaker converts an electric signal to sound.

BASICS Thermocouple: A thermoelectric device for measuring temperature, consisting of two wires of different metals connected at two points, a voltage being developed between the two junctions in proportion to the temperature difference.

LM35(temperature sensor)

The LM35 series are precision integrated-circuit temperature devices with an output voltage linearly proportional to centigrade scale. FEATURES: Calibrated Directly in Celsius (Centigrade). Linear + 10-mV/°C Scale Factor. Rated for Full −55°C to 150°C Range. Operates from 4 V to 30 V. Less than 60-μA Current Drain. Low Self-Heating, 0.08°C in Still Air.

APPLICATIONS: Fire alarm systems Fire extinguisher robots Battery management

IR sensor Range:700 nm – 1 mm Frequency:430 THz – 300 GHz This sensor consists of an IR transmitter and an IR receiver.

WORKING On giving proper power supply, the IR transmitter emits IR radiation which is received by the IR receiver on being reflected by an obstacle.

PRINCIPLE OF OPERATION When photons incident on reverse biased junction of Rx, electron-hole pairs are generated, resulting in reverse leakage current. 􀁺Amount of electron-hole pairs generated is proportional to intensity of incident IR radiation

CIRCUIT

PHOTO TRANSISTOR:

ULTRASONIC SENSOR

WORKING

Ultrasonic transducers are transducers that convert ultrasound waves to electrical signals or vice versa. Those that both transmit and receive may also be called ultrasound transceivers; many ultrasound sensors besides being sensors are indeed transceivers because they can both sense and transmit. These devices work on a principle similar to that of transducers used in radar and sonar systems, which evaluate attributes of a target by interpreting the echoes from radio or sound waves, respectively. Active ultrasonic sensors generate high frequency sound waves and evaluate the echo which is received back by the sensor, measuring the time interval between sending the signal and receiving the echo to determine the distance to an object.

INTERNAL MECHANISM Capacitive micro machined ultrasonic transducers (CMUT) is a relatively new concept in the field of ultrasonic transducers. Most of the commercial ultrasonic transducers today are based on piezoelectricity. CMUTs are the transducers where the energy transduction is due to change in capacitance. CMUTs are constructed on silicon using micromachining technique. A cavity is formed in a silicon substrate, and a thin layer suspended on the top of the cavity serves as a membrane on which a metalized layer acts an electrode, together with the silicon substrate which serves as a bottom electrode.

INTERNAL MECHANISM If signal is applied across the biased electrodes, the vibrating membrane will produce ultrasonic waves in the medium of interest. In this way it works as a transmitter. On the other hand, if ultrasonic waves are applied on the membrane of biased CMUT, it will generate alternating signal as the capacitance of the CMUT is varied. In this way, it works as a receiver of ultrasonic waves REFERENCE: http://en.wikipedia.org/wiki/Capacitive_micromachined_ultrasonic_transducers

APPLICATIONS: to measure the distance to targets in many automated factories and process plants.  liquid level measurement. assisting in autonomous UAV(unmanned aerial vehicle..i.e., drones) navigation. DEMERITS: 1)It fails in case of sound absorbers. 2)If obstacle is too far. 3)0bjects bouncing sound away from it.

ACCELEROMETER(ADXL335)

INTRODUCTION The ADXL335 is a small, thin, low power, complete 3-axis accelerometer with signal conditioned voltage outputs. The product measures acceleration with a minimum full-scale range of ±3 g. It can measure the static acceleration of gravity in tilt-sensing applications, as well as dynamic acceleration resulting from motion, shock, or vibration.

FEATURES: *3-axis sensing *Small, low profile package *Low power : 350 μA (typical) *operation: 1.8 V to 5 V *shock survival *Excellent temperature stability

INTERNAL MECHANISM Capacitive plates - when distance between fingers changes we get change in capacitance… this change in capacitance is later converted into voltage.

APPLICATIONS: Cost sensitive, low power. motion- and tilt-sensing applications Mobile devices Gaming systems .

LDR(Light dependent resistor) A photo resistor or light-dependent resistor (LDR) or photocell is a light-controlled variable resistor. The resistance of a photo resistor decreases with increasing incident light intensity; in other words, it exhibits photoconductivity.

PRINCIPLE OF OPERATION A photo resistor is made of a high resistance semiconductor. In the dark, a photo resistor can have a resistance as high as a few mega ohms (MΩ), while in the light, a photo resistor can have a resistance as low as a few hundred ohms. If incident light on a photo resistor exceeds a certain frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electrons (and their hole partners) conduct electricity, thereby lowering resistance.

CIRCUIT

PIR(Passive infrared sensor)

PIR(Passive infrared sensor) Active and Passive? A passive infrared sensor (PIR sensor) is an electronic sensor that measures infrared(IR) light radiating from objects in its field of view. Difference between IR sensor and PIR sensor? What is absolute zero temperature?

PRINCIPLE OF OPERATION: All objects with a temperature above absolute zero emit heat energy in the form of radiation. Usually this radiation is invisible to the human eye because it radiates at infrared wavelengths, but it can be detected by electronic devices designed for such a purpose. ****The term passive in this instance refers to the fact that PIR devices do not generate or radiate any energy for detection purposes. They work entirely by detecting the energy given off by other objects.PIR sensors don't detect or measure "heat"; instead they detect the infrared radiation emitted or reflected from an object****

INTERNAL MECHANISM The change in temperature modifies position of atoms slightly within crystal structure…polarization of material changes… this gives rise to voltage across the crystal..

APPLICATIONS: Alarm applications Motion detection systems Automatically-activated lighting systems REFERENCE: http://en.wikipedia.org/wiki/Passive_infrared_sensor

MICROPHONE

INTERNAL MECHANISM capacitors were historically called condensers. Here, the diaphragm(in acoustics)i.e., transducer acts as one plate of a capacitor, and the vibrations produce changes in the distance between the plates. With a DC-biased microphone, the plates are biased with a fixed charge (Q). The voltage maintained across the capacitor plates changes with the vibrations in the air, according to the capacitance equation (C = Q⁄V), where Q = charge in coulombs, C = capacitance in farads and V = potential difference in volts. The capacitance of the plates is inversely proportional to the distance between them for a parallel-plate capacitor.

APPLICATIONS: Sound system applications Clap switch(project) Sound detection robots

TACTILE sensors: senses the touch and temperature. Ex: mobile phone touch. Reason: piezoelectric capacitive sensors. Other sensors: Flex sensors Gyroscope Proximity sensor Humidity sensor

HOW TO INTERFACE WITH MICROCONTROLLER USING ADC PROGRAMMING??

HOW TO INTERFACE WITH MICROCONTROLLER WITHOUT ADC PROGRAMMING??

HOW TO INTERFACE WITH ARDUINO??

THANK YOU G . Chanakya The Robotics Club SNIST