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Distance Sensors

Distance Sensors. Kyle Zhang Jeff Peil Kristian Kalaj. Agenda. How Ultrasonics Work. Uses a transducer to convert electrical energy into higher frequency sound waves (ultrasonic) When the echo of the emitted waves returns, it converts the sound back into electrical energy and evaluates.

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Distance Sensors

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  1. Distance Sensors Kyle Zhang Jeff Peil Kristian Kalaj

  2. Agenda

  3. How Ultrasonics Work • Uses a transducer to convert electrical energy into higher frequency sound waves (ultrasonic) • When the echo of the emitted waves returns, it converts the sound back into electrical energy and evaluates http://www.education.rec.ri.cmu.edu/products/nxt_video_trainer2/resources/helpers/nxt_sensors/ultrasonic.html

  4. How Ultrasonics Work (cont..)

  5. How We Used Ultrasonics In Lab • A signal is raised high when the sound is sent • The same signal is lowered when the sensor receives the echo of that sound • Counted the # of clock cycles the signal was high to calculate distance

  6. Another Way to Interface with Ultrasonics • An ultrasonic sensor uses the IN/OUT port of an FPGA • Requirements of a typical sensor • 5 volt power supply and ground • One pin from the FPGA that has the ability to work as input and output (example: GPIO)

  7. Things to Be Careful About • Limited Range • ex: 28015-ND sensor is 20mm-3m • Mechanical Echo • Must be filtered out for data to be accurate

  8. Things to Be Careful About (cont.) • Since we are reflecting a sound wave, certain materials may not reflect as well • Density • Sound absorption • Shape of a surface may affect reflection/detection • Sphere • Angles http://www.societyofrobots.com/member_tutorials/node/71

  9. Examples of Ultrasonic Sensors • RB-Dfr-11 • Price: $14.50 • Range: 4 cm to 5m http://www.robotshop.com/media/files/pdf/datasheet-sen0001.pdf • 28015-ND • Price: $29.99 • Range: 20 mm to 3 m http://www.digikey.com/product-detail/en/28015/28015-ND/1774419 • US-T50/R25 • Price: $300 • Range: 0 - 50 cm http://www.wolfautomation.com/assets/15/US-T50R25.pdf

  10. Ultrasonic Shortcomings

  11. How IR Sensors Work • Emits beam of infrared light, detects reflection • Susceptible to quantity of light in environment • Measures angle of reflection, not time • Outputs an appropriate voltage to represent the distance, but not always http://www.societyofrobots.com/member_tutorials/node/71

  12. IR Behavior Problems • Bad behavior for very close objects • After ‘initial spike,’ non-linear behavior then linear behavior • https://engineering.purdue.edu/ece477/Webs/S11-Grp03/nb/myersar.html

  13. How to Deal with Bad Behavior • Make it stand in the corner! • But seriously…… • Reposition sensor to compensate

  14. Types of IR Sensors • Different Types • Binary/Proximity • Outputs either high or low • Cheap • Good at detecting proximity/threshold • Multiple Bit/Ranging • Output actual distance from sensor • Analog or digital format • More expensive but still relatively cheap

  15. Sharp IR Sensor Graph

  16. Examples of IR Sensors • TSOP38238 • Price: $1.95 • Range: N/A http://www.adafruit.com/products/157#Description • SHARP GP2Y0A21YK0F • Price: $11.75 • Range: 10cm - 80cm http://www.robotshop.com/en/sharp-gp2y0a21yk0f-ir-range-sensor.html • SHARP GP2Y0A02YK • Price: $15.95 • Range: 20 cm-150 cm http://www.adafruit.com/products/1031?gclid=CKemybT7t7oCFeYWMgod1XgAHQ

  17. IR Pros and Cons • Pros • Cheap • Outputs voltage based on distance • Precise detection of objects • Cons • Outputs voltage based on distance • Non-linear behavior • Susceptible to light influences

  18. Conclusion Ultrasonic vs. IR • Use Ultrasonics when: • You care about distance accuracy • There will be light influences • You have money to spend • Use IRs when: • You want to detect movement or thresholds • You are on a budget • You need precision in what you are detecting

  19. Further Reading • Infrared vs. Ultrasonic • http://www.societyofrobots.com/member_tutorials/node/71 • Parallax Sensor and General Ultrasonic Usage Tips • http://dc254.4shared.com/doc/fiS_Vzyu/preview.htm • IR Tutorials • http://www.intorobotics.com/use-infraredir-sensors-tutorials/

  20. Questions?

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