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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. Optical Communications. Transmitting an audio signal using light. Transmitter Circuit. audio signal.

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electronic instrumentation

Electronic Instrumentation

Project 2

1. Optical Communications

2. Transmitter Circuit

3. Receiver Circuit

4. Signal Reconstruction

5. Project Report

6. Practical Questions

optical communications
Optical Communications

ENGR-4300 Electronic Instrumentation

transmitting an audio signal using light
Transmitting an audio signal using light

Transmitter Circuit

audio signal

Receiver Circuit

ENGR-4300 Electronic Instrumentation

  • 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.

ENGR-4300 Electronic Instrumentation

amplitude modulation
Amplitude Modulation


ENGR-4300 Electronic Instrumentation

frequency modulation
Frequency Modulation


ENGR-4300 Electronic Instrumentation

pulse width modulation
Pulse Width Modulation


ENGR-4300 Electronic Instrumentation

pulse position modulation
Pulse Position Modulation


ENGR-4300 Electronic Instrumentation

  • 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.

ENGR-4300 Electronic Instrumentation

servo motor control
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.

ENGR-4300 Electronic Instrumentation

transmitter circuit
Transmitter Circuit

ENGR-4300 Electronic Instrumentation

555 timer in astable mode
555-Timer in Astable Mode

ENGR-4300 Electronic Instrumentation

input and modulated output
Input and Modulated Output

ENGR-4300 Electronic Instrumentation

special capacitors
Special Capacitors

DC Blocking


(High Pass Filter)

Bypass Capacitor

(Low Pass Filter)

ENGR-4300 Electronic Instrumentation

sample input and output
Sample Input and Output
  • As input rises, pulses are longer
  • As input falls, pulses are shorter

ENGR-4300 Electronic Instrumentation

your signal is what
Your signal is what?
  • Called pulse position modulation in .pdf file
  • Also looks like pulse frequency and pulse width modulation

ENGR-4300 Electronic Instrumentation

sampling frequency
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

ENGR-4300 Electronic Instrumentation

receiver circuit
Receiver Circuit

ENGR-4300 Electronic Instrumentation

receive light signal
Receive Light Signal

ENGR-4300 Electronic Instrumentation

inverting amplifier pre amp
Inverting Amplifier (Pre-Amp)

ENGR-4300 Electronic Instrumentation

audio amplifier
Audio Amplifier

ENGR-4300 Electronic Instrumentation

audio amplifier details
Audio Amplifier Details


gain 10X


386 audio


high pass



low pass filter

ENGR-4300 Electronic Instrumentation

special capacitors23
Special Capacitors

DC Blocking




ENGR-4300 Electronic Instrumentation

signal reconstruction
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)

ENGR-4300 Electronic Instrumentation

passive integration
Passive Integration

Integration works only

at high frequencies

w >> wc. Unfortunately,

your amplitude will also


ENGR-4300 Electronic Instrumentation

active integration
Active Integration

Integration does not work at frequencies below wc.

Your gain goes from -Rf/Ri to -1/RiC

ENGR-4300 Electronic Instrumentation

signal reconstruction27
Signal Reconstruction
  • integration
    • pulse on = + slope
    • pulse off = -- slope
    • ratio determines rise and fall
  • design parameters
    • sampling frequency
    • type of integrator
    • integrator components

ENGR-4300 Electronic Instrumentation

comparing output of blocks
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

ENGR-4300 Electronic Instrumentation

project report
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

ENGR-4300 Electronic Instrumentation

final design
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?

ENGR-4300 Electronic Instrumentation

analysis and comparison
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

ENGR-4300 Electronic Instrumentation

personal responsibilities
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

ENGR-4300 Electronic Instrumentation

  • 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

ENGR-4300 Electronic Instrumentation

practical questions
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.

ENGR-4300 Electronic Instrumentation

sample practical questions
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

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

Sample Practical Questions

ENGR-4300 Electronic Instrumentation