1. Distance Sensors Kyle Zhang Jeff Peil Kristian Kalaj

2. Agenda Ultrasonic Sensors How They Work Interfacing Things to Be Careful About Examples IR Sensors How They Work Behavioral Problems Examples Ultrasonic vs. IR Sensors

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_trainer 2/resources/helpers/nxt_sensors/ultrasonic.html

4. How Ultrasonics Work (cont..) Calculates the time interval between the sound wave being transmitted to when it is received and outputs a matching pwm signal to an FPGA Distance = (T * speed of sound) / 2 Speed of sound varies depending on environment

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 o 5 volt power supply and ground o 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 o ex: 28015-ND sensor is 20mm-3m Mechanical Echo o 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 o Density o Sound absorption Shape of a surface may affect reflection/detection o Sphere o Angles http://www.societyofrobots.com/member_tutorials/node/71

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

10. Ultrasonic Shortcomings Deficiencies Can be quite expensive (~$25) Must be careful of what you are trying to detect Reflection, echoes, materials Absorbent materials (ex: sponges) don’t work well with Ultrasonic sensors Wave propagation property

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! o But seriously…… o Reposition sensor to compensate

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

15. Sharp IR Sensor Graph

16. Examples of IR Sensors TSOP38238 o Price: $1.95 o Range: N/A http://www.adafruit.com/products/157#Description SHARP GP2Y0A21YK0F o Price: $11.75 o Range: 10cm - 80cm http://www.robotshop.com/en/sharp-gp2y0a21yk0f-ir-range-sensor.html SHARP GP2Y0A02YK o Price: $15.95 o 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: o You care about distance accuracy o There will be light influences o You have money to spend Use IRs when: o You want to detect movement or thresholds o You are on a budget o You need precision in what you are detecting

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

20. Questions?