The George Washington University Electrical

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The George Washington University Electrical
Computer Engineering Department ECE 002

• Dr. S. Ahmadi
• Lab 1

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Class Agenda

• Digital Sensors
• Analog Sensors
• Light Sensors.
• Optical Rangefinder Sensors.
• Ultrasonic Sensors (Sonar).
• Analog Sensor Characterization

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(No Transcript)
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Two Distinct Categories of Sensors

• Digital and Analog
• Digital sensors have two states 0 or 1
• Analog sensors have a range of states depending
  on their input
• Example
• A door can be open or closed
• What type of representation of the condition of
  the door is this?
• How far the door is open (0 to 180 degrees!)
• What type of representation of the condition of
  the door is this?

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Hooking up Sensors to the Handyboard
Hook up additional Analog sensors To these ports
(20-23)
Hook up DIGITAL Sensors To these ports 7-15
Hook up ANALOG sensors To these ports (2-6)
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Digital Sensor The Bumper Sensor

• Digital sensor
• Returns either a 0 or 1.
• Connect to DIGITAL ports 7-15
• Access with function digital(port)
• 0 indicates switch is open (nothing has
  happened). Normally, switch will be 0.
• 1 indicates switch is closed (Switch has been
  hit).

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• For more information on different digital sensors
  available to you, refer to the Botball Kit
  Documentation, slides 42, 43, 51.

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Bumper Sensor Procedure and Test Code

• / Program to beep if a bumper on port 13 has
  been hit. /
• void main()
• while(start_button()0) // Waits for user
  to press start button.
• while(stop_button()0) // Keep program
  running until press stop button
• printf(Switch on port 13 is open!\n)
• // Bumper connected to port
• // 13. If it is hit, sends
• if (digital(13) 1) // 1 to handyboard.
• printf(Switch on port 13 has been
  closed!\n)
• beep()

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Analog Sensors

• Output a range of values, depending on the input
  read.
• The main analog ports are ports 2 6, and ports
  20 23.
• Actual ports that should be used will depend on
  the sensor being used.
• The three main analog sensors that we will be
  using are the Light Sensor, the Optical
  Rangefinder Sensor and the Ultrasonic Sensor,
  also known as the Sonar.

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Light Sensors

• Access with function analog(port)
• Connected to ports 2-6 or 20-23
• Analog values range from 0 - 255.
• A low value indicates bright light, and vice
  versa.

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Optical Rangefinder Sensors

• Access with function analog(port)
• Connected to ports 16-19
• Analog values range from 0 - 255.
• Low values indicate far distance from an obstacle
  
• High values indicate close proximity to an
  obstacle 4 inches

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Ultrasonic Sensors (Sonar)

• Connect red to upper deck board - port 0
• Connect gray to Digital 7
• Access with function sonar()
• Returned value is distance in mm to closest
  object in field of view
• Range is approximately 30-2000 mm
• When objects are too close or too far, gives
  value of 32767

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Sonar Sample Code

• / Program that measures the sonar reading at
  different input values.
• /
• void main()
• int range0
• printf(\n Sensor Sample Program")
• while(!start_button()) // Press Start Button
• while(1) // Continue infinitely
• sleep(0.5)
• range sonar()
• printf(\nOutput is d, range)

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Analog Sensor Characterization

• The purpose of this exercise is to tabulate the
  readings from the three different analog sensors
  mentioned, when different inputs are sensed
• Light Sensor Using the attached color scale,
  move the light sensor along the sheet, and record
  the values read at different intervals.
• Optical Rangefinder Using the provided boards,
  at different distances record the outputs read
  from the sensor.
• Ultrasonic Sensor Similar to the Optical
  Rangefinder, record the output from the sensor at
  different input distances.

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Light Sensor Color Scale
½
0
100
50
16
½
½
½
½
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Lab Requirements

• Collect Data for at least one sensor. (Data to
  be handed in at end of lab, and youll need it
  for your HW.)
• FOR LIGHT SENSOR Take 10 equally spaced
  readings.
• FOR SONAR SENSOR Take enough readings to
  characterize sensor (more when measurements are
  non-linear, less when data is predictable)
• Insert the data into an Excel spreadsheet
• Plot the data (X-axis for distance, Y-axis for
  sensor readings).
• Email the spreadsheet to all group members to
  complete HW

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Sensor Range

• Sensors have an established operating range.
  Determine what this is for your sensor.
• Choose your ten points so that they span the
  complete operating range of the sensor.

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Example Plot of Sensor Characterization RANGE
FINDER SENSOR
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Due in Lab Today

• After tabulating the results, plot the graph for
  each sensor type, to see if the relationship
  turns out linear or not. Draw the curve to fit
  the graph.
• Note To simplify your work, write a short
  program that can continually print out the
  reading of the sensor on the Handyboards display.
• Take a look at HW1(Comprehensive Report on the
  Characterization of Robots Sensors), save your
  data/graphs for HW1.