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Sensors you should know about Thomas Edwards http://www.t11s.com Passive Infrared (PIR) Sensor • Detects motion of warm moving objects • If nothing is moving, there is no detection • Commonly used in security systems • Very Long range (50 feet) • Binary or relay opening output • ~$10 http://www.mpja.com/directview.asp?product=15840+SC http://www.parallax.com/detail.asp?product_id=555-28027 Microwave Motion Detector • Uses microwave doppler shift to detect motion • Range 10 feet • May have fewer “false positives” than PIR detectors • ~$35 kit http://www.ramseyelectronics.com/cgibin/commerce.exe?preadd=action&key=MD3C Active IR Sensors • • • • Bounces invisible IR beam off of target Uses triangulation to determine distance Range up to 5 feet Analog distance output or binary fixed range detection output • ~$10-$20 http://www.acroname.com/robotics/parts/c_Sensors.html Ultrasonic Sensors • Uses travel time of sound echos to detect distance • Range up to 15 feet • Outputs can be analog, serial, or PWM • Old, expensive Polaroid sensor • New, cheaper ones today ~$25 http://www.maxbotix.com/ Accelerometers • New ones based on Micro-ElectroMechanical Systems (MEMS) devices very small • Can measure acceleration in up to three axes • Even can sense gravitational pull of earth • ~$25 and up http://www.sparkfun.com/commerce/product_info.php?products_id=692 Magnetic Reed Switches • Magnet in one part causes reed switch to open/close on second part • Commonly used in security systems • Range very short (~1 inch) • Good for limit switch • ~$5 or under Force Sensing Resistors • Pressure reduces resistance • Analog voltage measured across resistor divider circuit • Can measure a few ounces to 100 lbs depending on model • ~$10-$25 http://www.parallax.com/detail.asp?product_id=30056 http://www.phidgetsusa.com/cat/viewsubcategory.asp?category=5000&sub category=5210 Touch Sensors • Measure changes in capacitance • Can sense touch through 4 inches of dielectric objects (glass, plastic) • ~$10-$20 http://www.phidgetsusa.com/cat/viewproduct.asp?category=50 00&subcategory=5100&SKU=1110 CMU Cam • • • • • • • Microcontroller and camera combo Track user defined color blobs Track motion using frame differencing Controls up to 5 servos Other video processing capabilities Serial I/O $169 http://www.cs.cmu.edu/~cmucam2/ Laser Range Finder • Very accurate distance measurement • Time-of-flight determines distance • Range 4m • 270 degrees of measurement • 0.36 degrees angular resolution • RS-232/USB output • $2695 http://www.acroname.com/robotics/parts/R283-HOKUYOLASER1.html Sensors you should know about Thomas Edwards http://www.t11s.com
