EXPERIMENT 7C:
MICROPHONES, FILTERS, OSCILLOSCOPES, AND AMPLIFIERS
Objectives
Build a generator/microphone/filter/speaker
system
Analyze the frequency
response of a system
Match input and output
requirements of a system
Equipment and
Supplies
BK Precision 1651 A Triple
5-Pin Connector
Protoboard
Resistors (1 kW,10 kW, and 100 kW)
Capacitors (0.01mF and 0.1mF)
Operational Amplifier
Microphone
Global Specialties 2001A
Function Generator
Tektronix TDS210
Oscilloscope
Additional
Reference Material
A traditional introductory
electrical engineering principles and applications text like: Hambley, A.R., Electrical
Engineering Principles and Applications, 1997, Prentice Hill, Chapter 6
“Frequency Response, Bode Plots, and Resonance” and Chapter 8 “Amplifiers:
Specifications and External Characteristics”.
Or, Rizzoni, G., Principles and Applications of Electrical
Engineering, 3rd Ed., McGraw Hill, Chapter 6 “Frequency Response
and System Concepts,” and Chapter 9, “Transistor Fundamentals.”
Function Generator
Description and Specifications at: http://www.globalspecialties.com/2001a.html
Hint:
go to the MEL Web Site and click on these links
Microphone and
Amplifier System
A circuit diagram is shown
in Figure 7-5 for a microphone/signal conditioning product discussed in
Experiments 7a and 7b. Wire the circuit keeping the wire lengths short in order
to avoid unwanted noise/capacitance effects.
Start with the feedback portion of the circuit.
What is the gain for the
circuit? Use the oscilloscope to verify your prediction (use clip leads to
measure signals at strategic places in the circuit).
Add a speaker/amplifier
combination with the signal generator (2 kHz) to provide a signal to the
microphone. See Table 7-1 for speaker
wiring.
Why is 5 V applied to the
microphone? Why is a capacitor in the circuit?
What type of circuit does this resemble from the early portion of the
lab and what would a critical frequency for this circuit be? Again, use the oscilloscope and verify your
answers.
Make a Bode Plot of the
signal generator/microphone/amplifier system to determine frequency response.
Identify the 3dB roll off point as well as the characteristic roll off rate.
Which component causes which roll off characteristic?
Figure 7-5. Microphone
Amplifier
Table 7-1. Speaker Wiring
Red (or Purple) -------12 V
White
-------------------Signal Input (+)
Green
-------------------Signal Input (-)
Black
(or Gray) -------Ground
The other two connections of
brown (or orange) and blue wires should be connected to each other, but NOT to ground.
Note that a experiment 7c
uses a non-inverting amplifier (as compared to the inverting amplifier in
experiment 7b) since the microphone output signal contains a DC bias voltage.
Experiment 7C Preparation Results
DATE___________ NAME___________________________________
GROUP
MEMBER NAMES__________________________________________________________
LABORATORY
BENCH NUMBER_____________
1. Predict
the gain for the 7-5 circuit. Show your calculations clearly and
completely. Define any variables
used. (5 pts)
2. Attach
copies of the procedures that you plan to use in Experiment 7c. (20 pts)
3. Attach
copies of the circuit and wiring diagrams that you plan to use in Experiment
7c. (20 pts)
Experiment 7C Report
DATE___________ NAME___________________________________
GROUP
MEMBER NAMES__________________________________________________________
LABORATORY
BENCH NUMBER_____________
*identifies
questions that require the same answer for the entire group. All other questions require individual
answers.
1. For the
evaluation of the proposed product, measure the frequency response of the
microphone system. Measure the relative
response of the following frequencies making certain to maintain the relative
position of the microphone and speaker.
Frequencies that should be used are 100, 200, 400, 800, 1000, 1500,
2000, 3000, 5000, 10,000, 12,000 Hz.
Present the data in a Bode Plot format that is attached to this
report. Correctly format the plot. (8 pts.)
2. Comment
on the structure of the curve and explain the behavior. (5 pts)
3. What is
the gain for the Figure 7-5 microphone amplifier circuit? (2 pts)
4. Why is 5
V applied to the microphone in the microphone amplifier circuit? (2 pts)
5. Why is a
capacitor included in the Figure 7-5 microphone amplifier circuit? (2 pts)
6. What type
of circuit does this resemble from the early portion of the lab? (2 pts)
7. What
would a critical frequency be for this circuit (Properly name the frequency and
give its value.)? (2 pts)
8. Draw a
simple block diagram of the main components of the test/experiment system and
the microphone system and attach it to this report. (Do not draw
a VI block diagram). (5 pts)
9. Give
specifics, item and value of the outputs and inputs from each of the components
in the block diagram. The value should
include units and range of values for that unit. (5 pts)