DESIGN PROJECT – AUDIO AMPLIFIER CIRCUIT

DESIGN PROJECT – AUDIO AMPLIFIER CIRCUIT
ENGR 100A – INTRODUCTION TO ENGINEERING
Project completion & testing (week 10)
1 PROJECT BASICS
I. Summary - the final project will consist of the following tasks:
A. Plan, layout, & construct a simple audio amplifier circuit
B. Purchase the kit from the SAC bookstore.
C. IMPORTANT – do not GET HURT!
II. Summary
The audio amplifier circuit is an important part of many electronic devices with an audio interface.
In this project, we will use an LM386 IC chip. IC stands for “integrated circuit”. The circuit below
shows the LM386 in a high-gain configuration (A = 50). The 10k potentiometer will give the amplifier a
variable gain from zero up to the maximum (i.e., it will allow you to adjust the volume).
III. Grading
A. Grading – starts with performance score & deductions are made for items below.
B. Performance & neatness/simplicity
1. 95 = (it worked fine, circuit is neat)
2. 85 = (it worked fine, circuit kinda neat)
3. 75 = (it did not work correctly, or NOT neat)
4. lower scores – partial or no work done
C. Deductions – actual values will be judged by instructor on individual basis based on following:
1. Effort/teamwork – effort, contribution to project, presence on testing day
a. Based on instructor observation or teammate input
b. Let me know if a teammate is not participating.
2. Conduct – adherence to safety (self & others), care for room, tools, etc.
a. Graded “as a class” so look out for fellow students in violation.
b. Additional deductions for individual students if I notice them.
+9 V
(+ side of
battery)
VS
DC blocking
6
2
Vin
(audio in)
1
8

5
LM 386
10k
pot
3
+
7
4
also connect to (-)
side of audio input
(as well as to battery gnd)
"snubber"
circuit
(hi freq
stabilization)
ground (GND)
(or (-) side of battery)
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C2
250 F
+
R2
10 
+ C
3
0.05 F
speaker
2 DESIGN & MATERIALS
I. Design REQUIREMENTS (you MUST comply with these)
A. There is little design freedom in this particular project. Mainly, you must correctly wire up the
circuit and get it working.
B. Wire up your circuit NEATLY. A sloppy circuit is hard to “debug” (finding errors). A picture of a
neat circuit is shown below.
C. Do NOT run wires over the top of the chip. If the chip must be replaced, you cannot do it
without removing wires.
D. Keep wires “flush” to the breadboard whenever possible. Do NOT trim the wire “leads” of
resistors (having the color bands) and capacitors (cylindrical black & white components).
These components will NOT be flush to the breadboard.
+9 V
(+ side of
battery)
VS
DC blocking
6
1
2
Vin
(audio in)
8

5
LM 386
3
10k
pot
+
+
speaker
+C
3
7
4
also connect to
(-) side of audio input
(& also to battery gnd)
C2
250 F
0.05 F
"snubber"
circuit
(hi freq
stabilization)
R2
10
ground (GND)
(or (-) side of battery)
100 F
use two 100F capacitors
in parallel (total 200 F)
since we don't have 250F caps
after DC
blocking
direct output
of chip
100 F
+9V
use THIS wire
to disconnect
battery from circuit
9V
BATTERY
8
6
5
2
3
.047 F
4
220 
1
7
LM 386
MP3 PLAYER
(ANY AUDIO
SOURCE/)
speaker
0 v (GND)
POT
use a .047 F
cap (instead of .05)
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use 220  resistor
if 10  resistors aren't available
3 CONSTRUCTION
I will provide the components for constructing your project. Some tools must be shared with other
students. Again, BE CAREFUL and take your time when building. It is critical that you not get hurt
while doing this project. There is plenty of time for construction and there is no prize for finishing first.
Also be careful because the IC chip can get HOT enough to burn you if you touch it.
I. Construction requirements
A.
B.
C.
D.
E.
F.
NEATNESS!
Construct the circuit with power (battery) NOT attached.
When the circuit is complete, ask the instructor to check out your set up. Get okay.
THEN connect power.
After connecting power, confirm the circuit works (sound comes from speaker).
Try changing the volume by turning the potentiometer
A MESSY CIRCUIT
A NEAT CIRCUIT
II. Important Information
A. The IC chip has its legs numbered based on the U-notch on the chip. Number the chips as in
the same direction as you draw the letter “U”.
U-notch
(use as reference)
LM 324 pinout
Gain
1
 input
2
+ input
3
Gnd
4

+
8
Gain
7
Bypass
6
VS
5
Vout
number
the pins
as if you
are drawing
a "U"
B. The circuit is powered by a common 9V battery.
C. A potentiometer (a kind of adjustable resistor) is used to adjust the volume.
D. The barrel-shaped capacitors are “electrolytic”, and should be positioned with the correct
“polarity”.
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Potentiometer
Capacitor Polarity
C
A
2.5
10
B
2.5
10
B
A

C
+
Resistor 4-color-band code
- the first 3 bands specify the R value, the 4th band specifies tolerance
- (silver = 10%, gold = 5%)
EXAMPLE:
No.
0
1
2
3
4
Color
Black
Brown
Red
Orange
Yellow
No.
5
6
7
8
9
Color
Green
Blue
Violet
Gray
White
1st Color Band (e.g., brown = 1)
2nd Color Band (e.g., black = 0)
Multiplier Color Band (e.g., red = 2)
Tolerance Color Band
1 0
2 5%
10 x 102  5%
Resistor leads
1000  5%
1k  5%
4 TESTING & EVALUATION
After constructing the circuit, you should test it. Apply an audio input signal (a cell phone is a
good example). Adjust the potentiometer to verify that the volume goes up and down. Note that
electric circuits are unforgiving. ANY mistake will likely cause the circuit not to work AT ALL (or cause
something to burn up).
I. Performance testing
A. You will plug your audio input device to the circuit and demonstrate that it works.
B. The volume must go up and down with the turning of the potentiometer.
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