Lecture Notes: Teaching Your Raspberry Pi About Echolocation

Introduction

• Presenter: Paul McCarter from talktechboy.com
• Episode: #20 in the Raspberry Pi Tutorial Series
• Sponsor: Sun Founder with their Raphael Kit

Topic Overview

• Primary Focus: Echolocation
• Definition: Using sound to detect objects and measure distances.

Examples of Echolocation in Nature and Technology

• Animals:
  • Bats: Use echolocation to navigate in dark caves.
  • Whales: Employ echolocation for long-distance communication underwater.
• Technology:
  • Radar: Uses radio waves to detect objects and measure their distances.
  • Sonar: Employs sound waves to detect objects underwater, commonly used in submarines.

Practical Application with Raspberry Pi

• Device: HC-SR04 Ultrasonic Sensor for echolocation.
• Setup Instructions:
  • Connect Trigger Pin to GPIO pin 23.
  • Connect Echo Pin to GPIO pin 24.
  • Leftmost pin: Positive Voltage (3.3V)
  • Rightmost pin: Ground
  • Power and Ground rail configuration

Coding the Echolocation Functionality

Libraries and Setup

• Libraries: RPi.GPIO, time
• GPIO Mode: BCM numbering system
• Pin Setup:
  • trig_pin = 23
  • echo_pin = 24
  • GPIO.setup(trig_pin, GPIO.OUT)
  • GPIO.setup(echo_pin, GPIO.IN)

Main Program Loop

• Use a try-except for clean exit on keyboard interrupt:

  try:
      while True:
          # Ping Send: Set trigger pin to low, wait, set high, wait, set low
          GPIO.output(trig_pin, 0)
          time.sleep(2e-6)
          GPIO.output(trig_pin, 1)
          time.sleep(10e-6)
          GPIO.output(trig_pin, 0)
  
          # Echo Wait: Wait for echo pin to go high, then start timer
          while GPIO.input(echo_pin) == 0:
              pass
          start_time = time.time()
  
          # Timer Stop: Wait for echo pin to go low, then stop timer
          while GPIO.input(echo_pin) == 1:
              pass
          stop_time = time.time()
  
          # Calculate Ping Travel Time
          ping_travel_time = stop_time - start_time
          ping_travel_time_microseconds = int(ping_travel_time * 1e6)
  
          # Print Result
          print(ping_travel_time_microseconds)
  
          # Sleep to avoid ping overlap
          time.sleep(0.2)
  except KeyboardInterrupt:
      GPIO.cleanup()
      print("GPIO Good to Go")
  

Testing and Validation

• Initial Measurements: Use a ruler to measure and validate ping travel times:
  • E.g., At 3 inches, expect ~385 microseconds; at 1.5 inches, ~159 microseconds.

Homework Assignment

• Task: Calculate and print the distance to a target based on ping travel time.
• Hint: Use the speed of sound and convert it to inches per microsecond.
  • Distance = Speed * Time / 2 (divided by 2 since it's a round trip).
• Submission: Post your solution on YouTube, link it to the lecture video.

Engineering Best Practices

• Lay Out Plans on Paper: Sketch designs and problem-solving steps before coding.
• Understand the Concepts: Know the underlying principles to facilitate troubleshooting.

Additional Tips

• Ensure target is perpendicular to the sensor for accurate measurements.
• Avoid extraneous objects in the sensor's path.
• Check the useful range of your sensor through experimentation.

Conclusion

• Engagement: Encourage feedback and interaction to promote engineering learning.
• Final Thoughts: Engineering problem-solving over passive consumption.