Transcript Project 4 - Rensselaer Polytechnic Institute

Electronic Instrumentation
Project 4
•1. Optical Communications
•2. Initial Design
•3. PSpice Model
•4. Final Design
•5. Project Report
1. Optical Communications
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Transmitting an audio signal using light
Transmitter Circuit
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
Frequency of carrier
remains constant.
Input signal alters
amplitude of carrier.
Higher input voltage
means higher carrier
amplitude.
http://cnyack.homestead.com/files/modulation/modam.htm
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Frequency Modulation
Amplitude of carrier
remains constant.
Input signal alters
frequency of carrier.
Higher input voltage
means higher carrier
frequency.
http://cnyack.homestead.com/files/modulation/modfm.htm
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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.
http://cnyack.homestead.com/files/modulation/modpwm.htm
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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.
http://cnyack.homestead.com/files/modulation/modppm.htm
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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.
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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.
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Transmitter Circuit
Rpot
V1
2
4
5
6
7
27k
1k
5V
C8
4.7uF
C3
X1
TRIGGER
RESET OUTPUT
CONTROL
THRESHOLD
DISCHARGE
3
GND
R2
1
R3
VCC
8
100 k
555 D
330 u
R19
.001u F
100 ohms
C2
Fun ctio n_Gen _1
LED
D1
0
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Input and Modulated Output
Rpot
V1
2
4
5
6
7
27k
1k
5V
C8
4.7uF
C3
X1
TRIGGER
RESET OUTPUT
CONTROL
THRESHOLD
DISCHARGE
3
GND
R2
1
R3
VCC
8
100 k
555 D
330 u
R19
.001u F
100 ohms
C2
Fun ctio n_Gen _1
LED
D1
0
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Special Capacitors
Rpot
V1
2
4
5
6
7
27k
1k
5V
C8
4.7uF
C3
X1
TRIGGER
RESET OUTPUT
CONTROL
THRESHOLD
DISCHARGE
3
GND
R2
1
R3
VCC
8
100 k
555 D
330 u
R19
.001u F
100 ohms
C2
Fun ctio n_Gen _1
LED
D1
Bypass Capacitor
(Low Pass Filter)
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DC Blocking
Capacitor
(High Pass Filter)
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Sample Input and Output
• When input is higher, pulses are longer
• When input is lower, pulses are shorter
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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.
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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
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Receiver Circuit
56k
Add a 100 Ohm resistor in series with the
speaker to avoid failures.
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Receive Light Signal
56k
Add a 100 Ohm resistor in series with the
speaker to avoid failures.
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Inverting Amplifier (Pre-Amp)
56k
Add a 100 Ohm resistor in series with the
speaker to avoid failures.
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Audio Amplifier
56k
Add a 100 Ohm resistor in series with the
speaker to avoid failures.
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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.
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low pass filter
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Special Capacitors
56k
Not needed
DC Blocking
Bypass
Capacitor Capacitor
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Add a 100 Ohm resistor in series with the
speaker to avoid failures.
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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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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?
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Comparing Output of Blocks
10V
“wide-angle” view
• Shows overall
shape and size
of input and
output
5V
0V
-5V
8.0ms
V(R1:1)
8.4ms
V(L1:2)
8.8ms
9.2ms
9.6ms
10.0ms
Time
1.0V
0V
-1.0V
8.301ms
V(R1:1)
8.400ms
V(L1:2)/10
8.500ms
8.600ms
8.700ms
8.799ms
“close-up” view
• Output divided
by 10
• Shows
sampling
frequency
• Shows shape
of samples
Time
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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.
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Passive Integration
Vin
Vout
R1
500mV
E
C1
0
1
Vout 
Vin dt

RC
1
fC 
2RC
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250mV
0V
1.0Hz
V(R1:2)
10KHz
100MHz
Frequency
Integration works only
at high frequencies f >>fc.
Unfortunately,
your amplitude will also
decrease.
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Active Integration
F
500mV
E
250mV
0V
1.0Hz
V(R1:2)
10KHz
100MHz
Frequency
Vout
1

Vin dt

Ri C
1
fC 
2R f C
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• Integration works at f >>fc
• Your gain goes from -Rf/Ri to
-1/RiC
• The amplitude of your signal
will decrease or increase
depending on components
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Input at A vs. Output at H
10V
5V
0V
-5V
8.0ms
V(R1:1)
8.4ms
V(L1:2)
8.8ms
9.2ms
Before addition of integrator
9.6ms
10.0ms
Time
4.0V
2.0V
0V
-2.0V
8.0ms
V(V4:+)
8.4ms
V(L1:2)
8.8ms
9.2ms
After addition of integrator
9.6ms
10.0ms
Time
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Effect of Smoothing Capacitor
D1
D1N4148
V
V
V1
VOFF = 0
VAMPL = 5v
FREQ = 1k
R1
1k
C1
5u
0
Recall what the smoothing capacitor did to the output of
the half wave rectifier.
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Input at A vs. Output at H
4.0V
2.0V
0V
-2.0V
8.0ms
V(V4:+)
8.4ms
V(L1:2)
8.8ms
9.2ms
Before smoothing capacitor
9.6ms
10.0ms
9.6ms
10.0ms
Time
2.0V
0V
-2.0V
8.0ms
V(V4:+)
8.4ms
V(L1:2)
-v(L1:2)
8.8ms
9.2ms
After smoothing capacitor
Time
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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
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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
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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.
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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.
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