Sensors

What Are Sensors?•Devices that change resistance due to –Light–Pressure–Position (angle)–etc…Haptic Perception -involves sensors in the skin as well as the hand and arm. These different receptors contribute to a neural synthesis that interprets position, movement, and mechanical skin inputs.

• Thermal• temperature sensors: thermometers, thermocouples, temperature

sensitive resistors (thermistors and resistance temperature detectors), bi-metal thermometers and thermostats

• heat sensors: bolometer, calorimeter • Electromagnetic• electrical resistance sensors: ohmmeter, multimeter • electrical current sensors: galvanometer, ammeter • electrical voltage sensors: leaf electroscope, voltmeter • electrical power sensors: watt-hour meters • magnetism sensors: magnetic compass, fluxgate compass,

magnetometer, Hall effect device, • metal detectors • Mechanical• pressure sensors: altimeter, barometer, barograph, pressure gauge, air

speed indicator, rate of climb indicator• gas and liquid flow sensors: flow sensor, anemometer, flow meter, gas

meter, water meter, mass flow sensor • mechanical sensors: acceleration sensor, position sensor, inclinometer,

switch, strain gauge

• Chemical• Chemical sensors detect the presence of specific chemicals or classes of

chemicals. Examples include oxygen sensors, also known as lambda sensors, ion-selective electrodes, pH glass electrodes, and redox electrodes.

• Optical and radiation• electromagnetic time-of-flight. Generate an electromagnetic impulse,

broadcast it, then measure the time a reflected pulse takes to return. Commonly known as - RADAR (Radio Detection And Ranging) are now accompanied by the analogous LIDAR (Light Detection And Ranging. See following line), all being electromagnetic waves. Acoustic sensors are a special case in that a pressure transducer is used to generate a compression wave in a fluid medium (air or water)

• light time-of-flight. Used in modern surveying equipment, a short pulse of light is emitted and returned by a retroreflector. The return time of the pulse is proportional to the distance and is related to atmospheric density in a predictable way.

• Ionising radiation• radiation sensors: Geiger counter, dosimeter, Scintillation counter, Neutron

detection • subatomic particle sensors: Particle detector. Wire chamber, cloud

chamber, bubble chamber. See Category:Particle_detectors

Non-ionising radiationlight sensors, or photodetectors, including semiconductor devices such as photocells, photodiodes, phototransistors, CCDs, and Image sensors; vacuum tube devices like photo-electric tubes, photomultiplier tubes; and mechanical instruments such as the Nichols radiometer. infra-red sensor, especially used as occupancy sensor for lighting and environmental controls. proximity sensor- A type of distance sensor but less sophisticated. Only detects a specific proximity. May be optical - combination of a photocell and LED or laser. Applications in cell phones, paper detector in photocopiers, auto power standby/shutdown mode in notebooks and other devices. May employ a magnet and a Hall effect device. scanning laser- A narrow beam of laser light is scanned over the scene by a mirror. A photocell sensor located at an offset responds when the beam is reflected from an object to the sensor, whence the distance is calculated by triangulation focus - SICK. A large aperture lens may be focused by a servo system. The distance to an in-focus scene element may be determined by the lens setting. Ex. binoculars. Two images gathered on a known baseline are brought into coincidence by a system of mirrors and prisms. The adjustment is used to determine distance. Used in some cameras (called range-finder cameras) and on a larger scale in early battleship range-finder interferometer. Interference fringes between transmitted and reflected lightwaves produced by a coherent source such as a laser are counted and the distance is calculated. Capable of extremely high precision. Scintillometers measure atmospheric optical disturbances.

• Acoustic• sound sensors: microphones, hydrophones, seismometers. • acoustic: uses ultrasound time-of-flight echo return. Used in mid 20th century polaroid

cameras and applied also to robotics. Even older systems like Fathometers (and fish finders) and other 'Tactical Active' Sonar (Sound Navigation And Ranging) systems in naval applications which mostly use audible sound frequencies.

• Other types• motion sensors: radar gun, speedometer, tachometer, odometer, occupancy sensor,

turn coordinator • orientation sensors: gyroscope, artificial horizon, ring laser gyroscope

• Non Initialized systems• Gray code strip or wheel- a number of photodetectors can sense a pattern, creating a

binary number. The gray code is a mutated pattern that ensures that only one bit of information changes with each measured step, thus avoiding ambiguities.

• Initialized systems• These require starting from a known distance and accumulate incremental changes in

measurements.

• Quadrature wheel- An disk-shaped optical mask is driven by a gear train. Two photocells detecting light passing through the mask can determine a partial revolution of the mask and the direction of that rotation.

• whisker sensor-whisker sensor- A type of touch sensor and proximity sensor.

Sharp Infrared Sensors• Analog and Digital with varying distance

measurements

• The photo sensors are built with a daylight filter that prevents most visible light in the environment from reaching the detector chip

Triangulation• In trigonometry and elementary geometry,

triangulation is the process of finding coordinates and distance to a point by calculating the length of one side of a triangle, given measurements of angles and sides of the triangle formed by that point and two other known reference points, using the law of sines.

' -----[ General Description ]---------------------------------------------'' The Sharp GP2D02 distance measuring sensor measures distance using' optical triangulation.'' This software is for using the sensor with a Basic Stamp 2 computer.' -----[ Detailed Description ]--------------------------------------------'' The distance is reported as a number in the range 225 to 70, which' corresponds to distances from 4 inches to 3 feet. Distances greater' than 3 feet are reported as three feet.' -----[ BS2-IC Wiring Connections ]----------------------------------------'' pin 23 Ground | pin 1' pin 21 +5VDC out | pin 3' pin 20 IO15/Clock Out | pin 2 Distance sensor' pin 19 IO14/Data In | pin 4 type gp2d02'' Note: The sensor performs best if two 10K resistors are used. Connect one' 10K resistor from pin 20 to pin 2. The other 10K resistor goes from' pin 2 to ground.' -----[ Constants ]-------------------------------------------------------'PinClock CON 15PinData CON 14' -----[ Variables ]-------------------------------------------------------'alpha VAR word ' Sensor reading, approx 75 for 31 inches,' 135 for 8 inches.' -----[ Main Code ]-------------------------------------------------------INPUT PinData ' Initialize the electronics.HIGH PinClockPAUSE 500MainLoop:GOSUB ReadTheSensorpause 1000 ' Display sensor information for onesecond.GOTO MainLoop ' Then read the sensor again.ReadTheSensor:LOW PinClock ' Start process by driving the clock low for 70 mS.PAUSE 70SHIFTIN PinData,PinClock,msbpost,[alpha] ' Then shift in the data,HIGH PinClock ' and set theclock high.PAUSE 2debug dec ? alpha ' Display sensor reading on a pc.RETURN' -----[ End of Software ]-------------------------------------------------------

Sometimes you can substitute sensors to measure other values

• Voltage Regulator acting as a temperature sensor (Models LM234, LM 235)– Manufactured by ST (www.st.com)

• Photo transistor acting as a light sensor (Model LM135)– Manufactured by Fairchild Semiconductors

(www.fairchildsemi.com)

Laser Range Finder

• The Nikon LaserCaddy is a highly compact laser rangefinder that will accurately measure distance from 11 yards to over 500 yards with unparalleled precision

• Nikon’s advanced digital processor and high grade optics.

• Laser Range Finder SICK 200 is a very precise laser that produce high quality map. The drawback of this sensor is the weight (10 pounds !!!) and the power consumption (12V

at 1.6A).

Laser range finders are sensors that measure the distance to objects in the closer surrounding by evaluating the time of flight of an emitted laser pulse. The Sick LMS 200 is very common in the robotics community. Its horizontal field of view is 180°, and it can sense objects in distances of up to 40 to 60 meters, depending on the object's reflectivity. There is a rotating mirror inside. Although the horizontal resolution of 1° or .5° is quite large, Sick laser range finders have one important drawback: They can only scan in horizontal dimension, in a plain. A real 3D scanner would be worthwhile, especially in outdoor terrain where the robot moves in 3D. Addition of laser arrays.

Gyroscope

• A rotating wheel whose axis is free to turn but maintains a fixed direction unless perturbed, esp. Used for stabilization or with the compass in an aircraft, ship, etc. Concise Oxford Dictionary Oxford University Press - Precession

• A gyroscope in operation with freedom in all three axes. The rotor will maintain its spin axis direction regardless of the orientation of the outer frame.

• Two sensors in one – gyroscope and accelerometer in one board.

Due to the low zero rate output drift, high resolution (better than

0.1 degrees/sec) and high dynamic range, accurate

positioning can be guaranteed even when satellite reception is

lost over long distances.

A gyroscope is used to maintain the accuracy of GPS instruments in situations where satellite reception is lost, for example in tunnels, between tall buildings and mountainous terrain.

• What is an accelerometer?An accelerometer measures acceleration (change in speed) of anything that it's mounted on. How does it work? Inside an accelerator MEMS (Micro Electro-Mechanical System) device are tiny micro-structures that bend due to momentum and gravity. When it experiences any form of acceleration, these tiny structures bend by an equivalent amount which can be electrically detected.

Typical Specs for Accelerometers• Product Description• The DE-ACCM3D is the most advanced analog accelerometer

solution to date, featuring a triple axis ±3g accelerometer chip. It also has integrated op amp buffers for direct connection to a microcontroller's analog inputs, or for driving heavier loads.

• The ACCM3D has an onboard 3.3V LDO regulator, allowing you to power the board with 3.5V to 15V sources. You can also use this regulator to power an external microcontroller with up to 50mA. For operation as low as 2.0V, you can bypass the voltage regulator and choose your own operating voltage.

• It is designed to fit in the DIP-16 form factor, making the DE-ACCM3D suitable for breadboarding, perfboarding, and insertion into standard chip sockets. To keep things as simple as possible, there are only 5 pins - two for power, and three for the X, Y and Z analog outputs.

Additional circuitry ensures that the product won't be damaged by reversed power connections.

• Possible uses for accelerometers in robotics:

• Self balancing robots • Tilt-mode game controllers • Model airplane auto pilot • Alarm systems • Collision detection • Human motion monitoring • Leveling sensor, inclinometer • Vibration Detectors for Vibration Isolators • G-Force Detectors

Nintendo WII

These controllers use different accelerometers