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Seeing Hands for the Blind

Seeing Hands for the Blind. Ethan Stubblefield Paul Jones. The Big Idea. Increase ease of mobility for visually impaired persons by providing information about object locations within their immediate environment The device should be useable in conjunction with a cane or other mobility aid.

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Seeing Hands for the Blind

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  1. Seeing Hands for the Blind Ethan Stubblefield Paul Jones

  2. The Big Idea • Increase ease of mobility for visually impaired persons by providing information about object locations within their immediate environment • The device should be useable in conjunction with a cane or other mobility aid

  3. Design Requirements • Range of approximately 20 feet • Portable, as compact as possible • Doesn’t interfere with other senses • Continuous feedback • The device should not be annoying or harmful to others.

  4. Original Design

  5. Block Diagram

  6. Implementing Design Blocks • Emitters: IR Light Emitting Diodes • Low power • Not visible to human eye • Sensors: IR Phototransistor • Visible light cutoff • Amplifier Stage • One amplifier for each sensor

  7. Implementing Design Blocks • DSP • Integrate the 5 separate signals into 1 set of information • Distribute feedback to user based on differences in signals • Pressure Switches • Provide tactile feedback to the user • Continuous range of values

  8. Design Changes • Multiple sensors not needed • Consequently, DSP stage not needed • Amplifier stage must now provide very high gain. • Pressure pads replaced with variable-speed, unbalanced motor.

  9. Initial Calculations • Light source • How much power are we putting out? • Sensor • How much power are we receiving? • Motor I/V characteristic • What range of power do we need to provide? • Amplifier Gain

  10. Light Source Light source should illuminate a 2’ in diameter circular area on a wall at 20’. This means lambda = atan(1/20). Consequently, the focal length of the lens must be the radius of the LED over tan(lambda), or, the radius of the LED times 20.

  11. Radiant Intensity • Ratings for LED’s given in mW/steradian • At 80 mA, we get 10 mW/steradian • Area of sphere subtended by solid angle/radius of sphere ^ 2 = angle in steradians • Radiant Intensity = 10 / distance to the illuminated wall ^ 2

  12. Sensor • Assume light is reflected in all directions (2*pi steradians) • We collect the light in (area of phototransistor)/(distance to wall)^2 • Since light reflects in all directions, we collect light from the entire illuminated area on the wall

  13. Sensor • Total power to wall = (Radiant Intensity) * (area of wall illuminated) • Total collected power = (total power to wall) * ( (area of phototransistor)/(distance to wall)^2)/ 2*PI • Therefore, signal strength will drop off as 1/(distance to wall)^2

  14. Motor’s I/V Characteristic

  15. Infrared LED I/V Characteristic

  16. Amplifier Gain • Testing of phototransistor yeilds an emitter current of .4 mA at maximum illumination (wall 1 foot away) • The maximum current we will run the motor at is 400 mA • This gives a current gain of 1000 A/A

  17. Amplifier Configuration • Common Collector Amplifier • High current gain • Voltage gain less than unity • Cascading 2 together gives the gain we needed.

  18. Transmitter Circuit Diagram

  19. Receiver Circuit Diagram

  20. Testing

  21. Difficulties • Phototransistor did not cut out visible light. • Sunlight caused DC current value in emitter • Florescent lights caused large 60Hz signal • Florescent lights also emit infrared light • No focusing lens for the light source • Larger area illuminated on wall • Less power collected by phototransistor

  22. Overcoming Difficulties • Turn off lights • Can’t block out all ambient light • Add large DC block capacitor to amplifier and oscillate the light source • Capacitor decreases our gain in strong light • Signal becomes negative at output – need to rectify it to power our DC motor

  23. Some Success…. • Current through the load did decrease in magnitude according to distance to the object • Measured range of ~5 feet • Recognizable signal under strong ambient light conditions.

  24. Making the Design Viable • Filter out ambient light • Use a phototransistor that is not affected by visible light • Use an infrared-pass filter on the existing circuit • Problem: there may be other sources of infrared light

  25. Making the Design Viable • Isolate our signal more effectively in the amplifier • Filter the signal with a high-pass filter that cuts off just below the operating frequency • Raise operating frequency for better isolation • Use an amplifier configuration that is not affected by a DC level in the signal

  26. Summary • The design is feasible if difficulties with ambient light are addressed • The design will still be useful to the visually impaired • Can trade range for smaller size • Can get more range with more powerful LED’s

  27. Any Questions?

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