Electronic Instrumentation

Transcription

1 Electronic Instrumentation Project 4: Optical Communication Link 1. Optical Communications 2. Initial Design 3. PSpice Model 4. Final Design 5. Project Report

2 Why use optics? Advantages of optical communication (over Radio Frequency) Wider bandwidth Larger capacity Lower power consumption More compact equipment Greater security against eavesdropping Immunity from interference ion/introduction%20(light)/intlight%201%20sm all.jpg

3 1. Optical Communications

4 Lighting the way to a revolution The exponential increase of sharing information is largely due to optical communication technology A few revolutionary technologies based on or effected by optical communication Internet (ex. Ethernet LAN based on Infrared Technology) Cell phones Satellite communication Others? 1966 Dr. Kao and George Hockham: fiber optics to carry information with light

5 Transmitting an audio signal using light In free space (air) Transmitter Circuit Receiver Circuit

6 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.

7 Modulation 8.0V 7.0V 6.0V 5.0V 4.0V 3.0V Modulating Input signal 2.0V 1.0V 0V -1.0V -2.0V -3.0V Carrier signal -4.0V 0s V(R2:1) V(R1:1) Time 4.0ms Output (modulated carrier) depends on the type of modulation used

8 Modulation Types General Frequency Modulation Amplitude Modulation Pulse Pulse Width Modulation Pulse Position Modulation Pulse Frequency Modulation

9 Amplitude Modulation Frequency of carrier remains constant. Input signal alters amplitude of carrier. Higher input voltage means higher carrier amplitude.

10 Frequency Modulation Amplitude of carrier remains constant. Input signal alters frequency of carrier. Higher input voltage means higher carrier frequency.

11 Pulse Modulation Remember duty cycle definition and equation T on T off Duty _ Cycle Ton T T Ton Toff Duty _ Cycle Pulse_ width Period Carrier has a constant variable Pulse Width Modulation - Period is constant Pulse Position Modulation - Pulse width is constant Pulse Frequency Modulation - Duty cycle is constant Input modulates carrier and effects other two variables

12 Pulse Width Modulation Period of carrier remains constant. Input signal alters duty cycle and pulse width of carrier. Higher input voltage means pulses with longer pulse widths and higher duty cycles.

13 Pulse Position Modulation Pulse width of carrier remains constant. Input signal alters period and duty cycle of carrier. Higher input voltage means pulses with longer periods and lower duty cycles.

14 Pulse Frequency Modulation Duty cycle of carrier remains constant. Input signal alters pulse width and period of carrier. Higher input voltage means pulses with longer pulse widths and longer periods.

15 2. Initial Design transmitter receiver The initial design for this project is a circuit consisting of a transmitter and a receiver. The circuit is divided into functional blocks. Transmitter: Block A-B and Block B-C Transmission: Block C-D Receiver: Block D-E, Block E-F, Block F-G, and Block G-H You will need to examine each block of the circuit.

16 RRC with variable resistor: Changes sampling frequency (of carrier signal) Transmitter Circuit 5V V1 Rpot 100k C8 330u R3 1k.001uF C2 R2 0 27k 4.7uF C3 Function_Gen_ VCC 8 GND 1 X1 TRIGGER RESET OUTPUT CONTROL THRESHOLD DISCHARGE 555D R19 100ohms LED 3 D1 555 Timer Similar to astable multivibrator configuration: Pin five input alters frequency of pulses

17 Transmitter Circuit: Input and Modulated Output Rpot 100k 5V V1 C8 330u R3 1k.001uF C2 R2 27k 4.7uF C3 Function_Gen_ VCC 8 GND 1 X1 TRIGGER RESET OUTPUT CONTROL THRESHOLD DISCHARGE 3 555D R19 100ohms LED D1 Input signal: function generator or audio 0 Output signal: Light modulation from LED

18 Special Capacitors 5V V1 Rpot 100k C8 330u R3 1k.001uF C2 R2 27k 4.7uF C3 Function_Gen_ VCC 8 GND 1 X1 TRIGGER RESET OUTPUT CONTROL THRESHOLD DISCHARGE 3 555D R19 100ohms LED DC Blocking Capacitor (High Pass Filter) Keeps DC offset from 555 Timer from interfering with input D1 Bypass Capacitor (Low Pass Filter) 0

19 Sample Input and Output When input is higher, pulses are longer When input is lower, pulses are shorter

20 Your signal is what? The type of modulation this circuit creates is most closely categorized as pulse frequency modulation. But the pulse width is also modulated and we will use that feature.

21 Sampling Frequency The pot (used as a variable resistor) controls your sampling frequency Input frequency in audible range max range (20-20kHz) representative range (500-4kHz) Sampling frequency should be between 8kHz and 48kHz to reconstruct sound Input amplitude should not exceed 2Vp-p Function generator can provide 1.2Vp-p

22 Receiver Circuit 56k Add a 100 Ohm resistor in series with the speaker to avoid failures.

23 Receive Light Signal 56k Add a 100 Ohm resistor in series with the speaker to avoid failures.

24 Inverting Amplifier (Pre-Amp) 56k Add a 100 Ohm resistor in series with the speaker to avoid failures.

25 Audio Amplifier 56k Add a 100 Ohm resistor in series with the speaker to avoid failures.

26 Audio Amplifier Details increases gain 10X (not needed) 386 audio amplifier high pass filter volume Add a 100 Ohm resistor in series with the speaker to avoid failures. low pass filter

27 Special Capacitors 56k Not needed Bypass Capacitor DC Blocking Capacitor Add a 100 Ohm resistor in series with the speaker to avoid failures.

28 3. PSpice Model You will compare the performance of your circuit to a PSpice model. The PSpice for the initial design will be given to you. You will use the PSpice to help you make decisions about how to create your final design.

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30 Comparing Output of Blocks Take pictures of the signal on each side of the circuit block. A on channel 1 and B on channel 2 B on channel 1 and C on channel 2 Take all measurements relative to ground Does the block behave as expected? How does it compare to the PSpice output?

31 10V 5V 0V Comparing Output of Blocks wide-angle view Shows overall shape and size of input and output -5V 8.0ms 8.4ms 8.8ms 9.2ms 9.6ms 10.0ms V(R1:1) V(L1:2) Time 1.0V 0V -1.0V 8.301ms V(R1:1) 8.400ms 8.500ms 8.600ms 8.700ms V(L1:2)/10 Time 8.799ms close-up view Output divided by 10 Shows sampling frequency Shows shape of samples

32 4. Final Design The signal is reconstructed well enough by the initial 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) You will then improve the signal further with a smoothing capacitor.

33 Vin Passive Integration E R1 C1 Vout 500mV 250mV V f out C 0 1 V RC 1 2 RC in dt 0V 1.0Hz 10KHz 100MHz V(R1:2) Frequency Integration works only at high frequencies f >>fc. Unfortunately, your amplitude will also decrease.

34 Active Integration E F 500mV 250mV 0V 1.0Hz 10KHz 100MHz V(R1:2) Frequency V out f 1 R C C i V in 1 2 R dt f C Integration works at f >>fc Your gain goes from -R f /R i to -1/R i C The amplitude of your signal will decrease or increase depending on components

35 Input at A vs. Output at H 10V 5V 0V -5V 8.0ms 8.4ms 8.8ms 9.2ms 9.6ms 10.0ms V(R1:1) V(L1:2) Before addition Time of integrator 4.0V 2.0V 0V -2.0V 8.0ms 8.4ms 8.8ms 9.2ms 9.6ms 10.0ms V(V4:+) V(L1:2) Time After addition of integrator

36 Effect of Smoothing Capacitor D1 V D1N4148 V VOFF = 0 VAMPL = 5v FREQ = 1k V1 R1 1k C1 5u 0 Recall what the smoothing capacitor did to the output of the half wave rectifier.

37 Input at A vs. Output at H 4.0V 2.0V 0V -2.0V 8.0ms 8.4ms 8.8ms 9.2ms 9.6ms 10.0ms V(V4:+) V(L1:2) Before smoothing Time capacitor 2.0V 0V -2.0V 8.0ms 8.4ms 8.8ms 9.2ms 9.6ms 10.0ms V(V4:+) V(L1:2) -v(l1:2) After smoothing Time capacitor

38 Project Packet Initial Data with Function Generator PSpice Mobile Studio plots from circuit Brief Comparison Block Description For Blocks: A-B, A-C, A-D, A-E, A-F, A-G Overall System: A-H Initial Data with Audio Mobile Studio plots from circuit For E-F and A-H

39 Project Packet Final Data (integrator only) with Function Generator PSpice Mobile Studio plots from circuit Brief Comparison For E-F and A-H Final Data (integrator and smoothing) PSpice only PSpice Compare to without smoothing For E-F and A-H

40 Project Packet Final Data with Integrator (and possibly Smoothing) with Audio Mobile Studio plots from circuit For E-F and A-H Extra Credit Mobile Studio picture of A-H with input from function generator and integrated, smoothed output. Indicate values of components and where used.

41 Work in teams Put the transmitter on one protoboard and the receiver on a second. One pair do the transmitter circuit This is the easier circuit, so maybe also start the PSpice simulation. The other pair build the receiver circuit One report for the entire team Report is closer to an experiment report than a project report See details in handout.