Laser Range Finder

1
Laser Range Finder

• Group 3
• Dhruv Aggarwal and Saad Raja
• ECE 445 Senior Design
• July 31, 2007

2
Introduction

• A device which uses a laser beam to determine the
  distance to an object
• Common methods of range finding include
  triangulation, multiple frequency phase shifting,
  and time of flight.

3
Features

• USB wireless interface
• Modular design for extension options
• Generates a unique ID for each measurement which
  can be labeled at the base station.
• Quick and accurate measurements can be taken off
  nearly all surfaces.

4
Laser Rangefinder Overview

• User can work Independently
• All the data is saved on computer which can be
  reviewed later

5
Output Source

• Initial Plan was to use a VCSEL but due to very
  low output power the idea was dropped
• Two Semiconductor Laser diodes were used
• Steady output power 0.003 microW
• Pulsed output power 3.002 microW
• Wavelength Chosen 850nm

6
Detecting the Input

• IR Photosensor was used to detect the reflected
  beam
• Max sensitivity at 850nm
• Output signal was amplified
• using non-inverting amplifier
• with a gain of 10

7
The Mechanics of Reflection.

• Photosensor was placed right on top of the laser
  diode so it could detect the maximum reflected
  beam
• Output from the sensor was amplified using a
  differential amplifier with a gain of 10
• Output voltage from sensor was seen on the
  oscilloscope when laser beam was reflected by
  different materials

8
Oscilloscope Plots

• Reflection off White paper
• 10 cm 100cm

9

• Reflection off Cardboard
• 10cm 100cm

10
Voltage due to Reflection Vs Target distance
11
The Need for Speed

• Time Distance/Speed? Sounds simple
• Speed of light is 2.99792108 m/s
• In only one microsecond the passes 300 meters.
• A high resolution in place therefore demands
  highest resolution in time.

12
Time to Distance Conversion

• TDC-GP2
• If the resolution has to be 1cm we already need a
  time resolution of 67ps
• 50ps resolution

13
Overcoming the timing limits

• Triggersignal from laser is connected to the
  stop1 input
• Detector signal connected to the stop2 input
• Any further loss in signal is compensated by
  sampling

14
Wireless Data Transmission

• Xbee radios received the UART commands from
  the PIC successfully
• Enabled A/D conversion on one of the pins to
  do distance measurement using the voltage method

15
User Interface
16
User Interface

• Coded using the Processing 1.0 programming
  language.
• Reads the data from the specified USB port and
  extracts useful information from the data.
• Gives a realtime distance output.

17
Ethical Considerations

• The IEEE code of ethics includes the phrase to
  avoid injuring others, their property,
  reputation, or employment by false or malicious
  action , and we abide that
• Need to be careful while working with the laser,
  it shouldnt be pointed directly into the eyes
• Our laser is a class 3B laser which will not
  cause permanent eye damage unless there is direct
  exposure for a long duration

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Future Hardware Development

• Addition of a beamsplitter for more exact time
  measurements
• Use of the TDC-GPX for a resolution of 10ps
• Obtaining a good quality pulsed VCSEL for longer
  distance measurements.

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Future Software Development

• Obtaining a 2-D scan of the image by just
  sweeping the laser over the object.
• Uploading all data to a central server for
  automated distance measurements.

20
Credits

• Professor Gary Swenson
• Professor Kent Choquette
• Tony Mangognia
• Dwayne Hagerman
• The folks at the part shop

21
Thank You