ECE 437 LABORATORY #6 Fall 2007 ULTRASONIC AND INFRARED

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					ECE 437                               LABORATORY #6                                     Fall 2007

                         ULTRASONIC AND INFRARED SENSORS


Goals: The goals of this laboratory are to investigate the limitations and behaviors of ultrasonic
and infrared sensors with different target materials and cross sections.

Learning Objectives: After completing this laboratory, you should be able to:
1. Explain the operating principles, advantages, and disadvantages of ultrasonic sensors.
2. Explain the operating principles, advantages, and disadvantages of infrared sensors.
2. Determine the critical issues for sensor choice and circuit implementation for a range of
   application scenarios.



Laboratory Preparation: In preparation for this laboratory, you should:
1. Attend the lecture session on ultrasonic sensors, read over this laboratory activity, and
   examine the data sheets provided (Appendix A & B) for the ultrasonic and infrared sensors
   used in this laboratory.

       PQ1: Design a voltage divider circuit that can be used to scale data from the ultrasonic
       sensor such that the output voltage from the divider is suitable for input into the ADC.
       Keep the output voltage in the 0-5V range assuming the sensor is powered by a single-
       pole output, +20V power supply. Show the sensor wire ports on your diagram.

2. List two kinds of applications that would call for ultrasonic sensing. For each application,
   answer the following questions (PQ2-PQ4):
       PQ2: What kind of accuracy is necessary?
       PQ3: How repeatable do the measurements have to be?
       PQ4: What is the result of an incorrect or inaccurate sensor reading?

       PQ5: List one sensing environment in which you would not want to use an infrared
       sensor


Laboratory Tasks and Questions: During the laboratory, you will configure and explore a
sensing system using ultrasonic and infrared sensors.

Ultrasonic Digital Sensor:

1. Using the provided data sheets, proto-board, and resistors, construct the voltage divider
   circuit designed in the prelab activities. Verify your connections with the TA before applying
   power to the circuits. Connect the ultrasonic sensor and use the oscilloscope to examine the
   output. Based upon what you see on the oscilloscope, create a VI that implements a trigger
   to tell you when the sensor is “ON” and “OFF”.

   Q1: What is the output of the sensor when it is “ON” or “OFF”? Sketch (or screen capture) a
   waveform showing both states and label the axes.
ECE 437                               LABORATORY #6                                     Fall 2007

                         ULTRASONIC AND INFRARED SENSORS


MINI-EXPERIMENT 1: Examine the effects of material type and orientation on the
performance of the sensor. Using the cardboard, metal-covered cardboard, and your hand,
examine the effect, if any, material type has on the sensor performance. Rotate each material to
present a different cross-section to the sensor and document if and at what angle the sensor turns
off. Make sure that your sensor’s range is at its maximum setting before examining rotation
angles. You may want to use one of the vice-grips to hold the sensor stable.

Record the results of your experiment for at least 3 different distances. Include 3 separate tables
of material versus rotation angle, one table per distance.

   Mini-Experiment Purpose
   Mini-Experiment Equipment and Setup
   Mini-Experiment Hypotheses
   Mini-Experiment Results
   Mini-Experiment Conclusions

   To help lead your Mini-Experiment write-up, consider the following questions…

       •   Can the ultrasonic sensor reliably discriminate between different materials?
       •   Can the sensor sense each object regardless of orientation? If not, why not?
       •   Is there a single cut-off for detection as the amount of area presented to the sensor is
           reduced?
       •   How does the distance of the object from the sensor change your results?



       Q2: Explain why the orientation and cross-section size seen by the sensor determines
       whether or not the object is detected.


MINI-EXPERIMENT 2: For the three objects provided in the lab, determine the range of
lateral angles over which the objects can be sensed at different ranges.

   Mini-Experiment Purpose
   Mini-Experiment Equipment and Setup
   Mini-Experiment Hypotheses
   Mini-Experiment Results
   Mini-Experiment Conclusions

   To help lead your Mini-Experiment write-up, consider the following questions…
      • What is the maximum lateral distance (from the center of the sensor) where each
          object can be detected? List results for at least 3 distances.
      • Make a drawing of the beam transmitted by the sensor based upon your results.
ECE 437                               LABORATORY #6                                     Fall 2007

                         ULTRASONIC AND INFRARED SENSORS


MINI-EXPERIMENT 3: Examine the effects of the potentiometers on the ultrasonic sensor
performance. Using information from the data sheet, find and adjust the turn-on and turn-off
points for the sensor’s hysteresis control.

   ***Change your sensor’s range to its minimum setting before examining hysteresis!***

   Mini-Experiment Purpose
   Mini-Experiment Equipment and Setup
   Mini-Experiment Hypotheses
   Mini-Experiment Results
   Mini-Experiment Conclusions

   To help lead your Mini-Experiment write-up, consider the following questions…
      • What is the minimum distance from the sensor where a simple object (e.g., a metal
          block, your hand) can trigger initial detection?
      • What is the maximum distance from the sensor where the object stays within the
          hysteresis range??


Infrared Analog Sensor:

3. Before connecting the IR sensor, switch your voltage input leads to the +/- 6V terminals on
   your bench’s power supply. This will ensure that the sensor does not exceed its maximum
   allowed supply voltage.

4. Using the provided data sheets and protoboard, construct a circuit to interface with the
   infrared sensor. Construct a VI that displays the sensor output in both graphical and
   numerical form.

5. Test your circuit by placing an object in front of the sensor and varying its distance from the
   sensor.

       Q3: How does the voltage change as you vary the distance? Is this how the ultrasonic
           sensor operated?
       Q4: At a constant distance, how stable is the voltage? How could you improve stability
           of the output voltage?
       Q5: Construct a graph showing distance vs. sensor output voltage for the infrared
           sensor. Investigate values within the range of 0 – 100cm using 5cm increments.
           Find the maximum voltage to within 2 cm by using finer increments near the
           suspected maximum value.

6. Test the infrared sensor’s sensitivity to materials by using the materials from Mini-
   Experiment 1, above.
ECE 437                               LABORATORY #6                                       Fall 2007

                         ULTRASONIC AND INFRARED SENSORS

       Q6: Does the infrared sensor sense one material better than others? If so, which does it
           sense best?

7. Return all materials and sensors to their storage positions and clean up your bench.



Student Post-Lab Questions and Conclusions
Ultrasonic Digital:
1. Explain the operation of the ultrasonic sensor.
2. What are two advantages and two disadvantages of using the ultrasonic sensor to indicate the
   presence of an object?
3. Explain why an application would require that the sensor exhibit hysteresis in detection.

Infrared Analog:
4. Explain the operation of the infrared sensor.
5. What are two advantages and two disadvantages of using the infrared sensor to indicate the
    presence of an object?

6. Briefly describe one sensing scenario where a digital proximity sensor (ON/OFF like the
   ultrasonic sensor) would be a better choice than an analog proximity sensor (like the infrared
   sensor). Primarily discuss the digital versus analog aspect for the given application.

7. Briefly describe one sensing scenario where a sensor with an analog output is a better choice
   than one with a digital output. Primarily discuss the digital versus analog aspect for the given
   application.

8. What are two important lessons that you learned from this lab that deal with the
   implementation of ultrasonic and infrared proximity sensors?

Plots, Figures, and Tables:
    • Ultrasonic Digital Sensor – Voltage Divider Circuit (Prelab)
    • Trigger VI Front Panel
    • Trigger VI Block Diagram
    • “ON” and “OFF” Sensor State Sketch / Screen Capture

   •   Material Type / Cross-Section Testing System Diagram (Mini-Experiment 1)
   •   Material Type and Cross-Section Test Results Spreadsheet (Mini-Experiment 1)

   •   Lateral Range Sensor System Diagram (Mini-Experiment 2)
   •   Lateral Range Results Spreadsheet (Mini-Experiment 2)

   •   Hysteresis Testing Sensor System Diagram (Mini-Experiment 3)
   •   Distance versus Voltage plot for Infrared Sensor (Q5)