Electronic Instrumentation

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Electronic Instrumentation

• Project 2
• 1. Optical Communications
• 2. Transmitter Circuit
• 3. Receiver Circuit
• 4. Signal Reconstruction
• 5. Project Report
• 6. Practical Questions

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Optical Communications
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Transmitting an audio signal using light
Transmitter Circuit
audio signal
Receiver Circuit
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Modulation

• Modulation is a way to encode an electromagnetic
  signal so that it can be transmitted and
  received.
• A carrier signal (constant) is changed by the
  transmitter in some way based on the information
  to be sent.
• The receiver then recreates the signal by looking
  at how the carrier was changed.

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Amplitude Modulation
http//cnyack.homestead.com/files/modulation/modam
.htm
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Frequency Modulation
http//cnyack.homestead.com/files/modulation/modfm
.htm
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Pulse Width Modulation
http//cnyack.homestead.com/files/modulation/modpw
m.htm
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Pulse Position Modulation
http//cnyack.homestead.com/files/modulation/modpp
m.htm
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Optoisolators

• Optoisolators use light to transfer a signal
  between two devices rather than a direct
  electrical connection.
• You can buy computer cards with optoisolating
  connectors that protect the computer from devices
  connected to it. Good for industrial
  applications.

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Servo-motor control

• The servo-motors are controlled by the computer
  through an optoisolating card.
• The low voltage DC computer is protected
  (isolated) from the high voltage AC power needed
  to turn the motors.

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Transmitter Circuit
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555-Timer in Astable Mode
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Input and Modulated Output
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Special Capacitors
DC Blocking Capacitor (High Pass Filter)
Bypass Capacitor (Low Pass Filter)
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Sample Input and Output

• As input rises, pulses are longer
• As input falls, pulses are shorter

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Your signal is what?

• Called pulse position modulation in .pdf file
• Also looks like pulse frequency and pulse width
  modulation

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Sampling Frequency

• The pot (used as a variable resistor) controls
  your sampling frequency
• Input frequency in audible range (0-4K Hz)
• Sampling frequency should be between 8KHz and 48K
  Hz to reconstruct sound
• Input amplitude should not exceed 1V

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Receiver Circuit
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Receive Light Signal
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Inverting Amplifier (Pre-Amp)
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Audio Amplifier
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Audio Amplifier Details
increases gain 10X (optional)
386 audio amplifier
high pass filter
volume
low pass filter
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Special Capacitors
DC Blocking Capacitor
Bypass Capacitor
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Signal Reconstruction

• The signal is reconstructed well enough by this
  design that it will be audible.
• In order to improve the quality of the signal,
  you will add an integrator, which will more
  exactly reconstruct it.
• Types of integrators
• passive integrator (low pass filter)
• active integrator (op amp integrator circuit)

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Passive Integration
Integration works only at high frequencies w gtgt
wc. Unfortunately, your amplitude will
also decrease.
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Active Integration
Integration does not work at frequencies below
wc. Your gain goes from -Rf/Ri to -1/RiC
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Signal Reconstruction

• integration
• pulse on slope
• pulse off -- slope
• ratio determines rise and fall
• design parameters
• sampling frequency
• type of integrator
• integrator components

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Comparing Output of Blocks

• location of points A-H are indicated in the
  project write-up
• function of each block you should be able to
  determine from these notes and the experiments
• take two measurements at a time
• A on channel 1 and B on channel 2
• B on channel 1 and C on channel 2
• take all measurements relative to ground

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Project Report

• Introduction
• Application Goals
• Educational Goals
• Basic Design
• Identify function of each block
• Identify input frequency and amplitude
• Circuit diagram
• Circuit built and witnessed
• Take data at specified points

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Final Design

• What type of integrator?
• What components?
• Calculations
• Circuit Diagram
• Testing Plan
• Design Changes
• Problems Encountered
• Take data at specified points
• Have changes improved audio quality?

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Analysis and Comparison

• Analyze each block
• PSpice or hand analysis
• Show calculations or explain plot output
• Compare experimental with theoretical results
• How are they different?... the same?
• Why are they different?
• Compare basic and final design
• signal reconstruction
• sound quality

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Personal Responsibilities

• Make a list of all tasks to be completed as part
  of this project
• Testing plan
• Keep everyone on task
• Assign responsibility for each task to one person
  (tasks cannot be shared)
• Have task assignment list checked out

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Appendices

• Useful data or results from experiments
• Information resources
• From the web
• From the library or other sources
• Only attach useful information
• Useless information will result is a loss of
  points
• Explain the purpose of each piece of info

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Practical Questions

• The participation points for this project will be
  determined based on practical skills. To test
  practical skills, students will be asked to
  perform simple practical tasks related to this
  project in a timely fashion. The instructor or
  the TA will assign the points.
• Please notice that the practical questions are
  meant to be answered individually.

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Sample Practical Questions

• set up scope to compare the output of two blocks
  
• set function generator to get a signal comparable
  to an audio signal
• capture the scope signal both as a picture and
  data, using Agilent Intuilink
• adjust sampling frequency
• choose integrator component values

• describe the goal and the methodology
• identify components and parts of each circuit
• debug the circuit
• connect the circuits to the power supply and to
  the scope
• use PSpice traces and cursors.
• draw Capture circuit