1. E NGINEERING D ESIGN L AB II ENGR-102 W EEK 2 L ECTURE - R OBOTICS Pramod Abichandani, Ph.D. Richard Primerano, Ph.D. 1 T OUCH, D ISTANCE, AND L IGHT S ENSORS L AB W EEK 2 O VERVIEW

2. L AST W EEK Basics of Robot Motion Basics of the NXT Kit 2

3. T ODAY Sensors Touch Distance Light 3

4. S ENSORS 4

5. Devices to sense the environment Provide capabilities for situational awareness When connected to electronic components, Convert a physical signal to an electrical signal Called transducers Different types of sensors for the NXT system Touch (Week 2) Distance (Week 2) Light (Week 3) Sound 5

6. T OUCH S ENSOR Using Switches 6

7. T OUCH S ENSING AND C OLLISION D ETECTION 7

8. D IFFERENT T OUCH A CTIONS 8

9. D ISTANCE S ENSING Ultrasound Sensor 9

10. U LTRASONIC D ISTANCE S ENSOR The ultrasonic sensor transmits an ultrasonic pulse (40kHz) and measures the amount of time taken for the signal to bounce off a distant object and reflect back. Sound travels approximately 1,126 ft/sec in air (13.5 in/ms). Note that the ultrasonic sensor measures the round trip time of the sound wave. 6.76 inches per millisecond of delay 10

11. U LTRASONIC D ISTANCE S ENSOR The NXT handles all of the pulse timing and reports a distance in inches or centimeters directly. Use centimeter mode. This gives higher resolution. The sensor’s performance varies depending on the size, shape, location, and absorption of the target. 11

12. I NSIDE THE U LTRASONIC S ENSOR 12 RX transducer TX transducer TX driver RX amplifier Microcontroller 4-bit, 3.58 MHz Some ultrasonic modules use a single transducer.

13. T HE E FFECT OF T ARGET G EOMETRY ON R ETURNED E CHO 13 The largest signal reflection will be achieved when the target’s surface is normal to the incident acoustic pulse.

14. T HE E FFECT OF T ARGET G EOMETRY ON R ETURNED E CHO 14 How large should the target be to get a good return? How much misalignment can be tolerated?

15. W HICH WILL HAVE A LARGER RETURN ECHO ? 15 A B

16. T HE E FFECT OF T ARGET G EOMETRY ON R ETURNED E CHO 16 If multiple targets are present, errors or erratic behavior can be observed. Some ultrasonic sensors are able to resolve multiple reflections (from multiple targets). Bonus simulation!

17. C HARACTERIZING YOUR ULTRASONIC SENSOR Populate the following table Use Excel’s trend-line fitting to find the line Estimated Distance = (slope)(Average Measurement) + (intercept) Demonstration provided in lecture 17

18. U LTRASONIC S ENSOR AND C OLLISION A VOIDANCE Use the line to perform collision avoidance 18

19. T HANK YOU ! 19