University of Portland
School of Engineering
5000 N. Willamette Blvd.
Portland, OR 97203-5798
Phone 503 943 7314
Fax 503 943 7316
Final Report
Frequency Response Audio Visualizer
Team Members:
Jake Nylund (Fall Team Lead)
Kevin Ratuiste (Spring Team Lead)
Alex Arlint (Treasurer)
Robert Rodriguez (Secretary)
Industry Representatives:
John Turner – Impinj, Inc.
Faculty Advisors:
Dr. Joseph Hoffbeck
Clients:
Will Taylor – Student
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REVISION HISTORY
Rev.
Date
Author
Reason For Changes
0.9
21 Mar 2014
Team
First draft submitted to advisor
0.95
28 Mar 2014
Team
Second draft submitted to advisor
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Table of Contents
REVISION HISTORY ...................................................................................................................................................... 2
INTRODUCTION ............................................................................................................................................................. 4
HIGH LEVEL ARCHITECTURE............................................................................................................................. 5
HARDWARE AND SOFTWARE DESIGN ......................................................................................................... 6
User Interface ............................................................................................................................................................. 7
Arduino Due Microcontroller .............................................................................................................................. 7
Software ........................................................................................................................................................................ 9
Electromagnet .......................................................................................................................................................... 10
Mechanical Components ...................................................................................................................................... 12
Assumptions ............................................................................................................................................................. 12
Changes ....................................................................................................................................................................... 13
Risks ............................................................................................................................................................................. 13
MILESTONES ............................................................................................................................................................ 14
CONCLUSION .............................................................................................................................................................. 15
GLOSSARY.................................................................................................................................................................... 15
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INTRODUCTION
Frequency Beats, the name given to this project, is a frequency response audio
visualizer. The overall goal of the device was to visualize the spectrum of an audio signal.
The input is an analog line level audio signal connected via a standard 3.5mm headphone
jack. This signal enters the microcontroller where it is processed and filtered to separate the
various frequencies in the audio signal. Implementing the filters digitally allowed more
flexibility in how the microprocessor processed the signal as well as the resulting action or
response. Once the frequencies of the audio signal were separated, they were output to the
electromagnets, which, in turn, manipulated the ferromagnetic fluid creating a visual
representation of the audio signal.
A front view of the final product is shown below in Figure 1, illustrating the front of
the apparatus, consisting of three glass chambers partially filled with ferrofluid. Each glass
chamber has a handmade electromagnet fixed to the top of it.
<< figure deleted >>
Some highlights of the implementation phase were building electromagnets, building
electromagnets that worked, constructing circuitry that accurately and reliably limits and
amplifies the amount of current and voltage going into the arduino’s input pins and coming
out of the PWM output pins, implementing a working program for the microcontroller that
does the processing required and seeing that the project works in parts. The team has been
unable to get the project working as a whole up to this point.
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The biggest challenge the team faced was getting the Fast Fourier Transform (FFT)
algorithm to work on the Arduino Due. This led to many hours of frustration and debugging
that ultimately ended in a major change to the project. Another challenge was trying to
produce three, mostly identical electromagnets that would generate a strong enough
electromagnetic field to actuate the ferrofluid. The first attempts produced depressingly subpar results and extra assistance was requested for the next trial.
Throughout this design and construction process, the team faced several challenges
related to the software implementation and display construction. Each of these challenges
was addressed according to the team’s list of anticipated challenges in the design document
and was ultimately overcome. The team noticed early in the Spring Semester that their
milestones were, perhaps, overly ambitious and were not necessarily in the ideal order for
completion.
Overall, the team did well sticking to their original design, communicating with each
other to anticipate, and plan for, any potential future challenges, and solving problems
quickly as they arose in order to stay on schedule. The team could have done better in
regards to testing individual components on a smaller scale as they were assembled, rather
than testing larger sets of components towards the end and final assembly.
The following sections of this document will detail the technical and process
outcomes including the differences between the team’s original designs and the final
product, how the implementation was different than intended, and a discussion of
assumptions, changes, milestones, and risks the team faced. Additionally, there is a glossary
at the end of this document.
HIGH LEVEL ARCHITECTURE
The figure below shows the high level architecture of Frequency Beats. The key
component of this project is the MSGEQ7 (not pictured), which is an IC that takes the audio
signal as its input, analyzes seven frequency bands of the signal, and then outputs a DC
representation of each frequency band. The seven frequencies are then passed into the
Arduino Due where they are consolidated into three frequency bands, low, mid, and high,
scaled for interaction with the electromagnets, then sent out as three DC frequency
representations of the audio signal. The outputs of the Arduino are smoothed out by a low
pass filter and then used to control the electromagnets by a Darlington Pair. Frequency
Beats utilizes a 12V power supply for the electromagnets and Arduino. As you can see,
there are only a couple differences between the schematic below and the team’s original
plan. This includes the addition of a 2N3904 transistor to help the Arduino drive the TIP102
power transistor, elimination of the biasing circuit, and the addition of a flyback diode to
protect the circuitry from voltage spikes.
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12V Power
Supply
Electromagnet
(Low-Range)
LPF
Electromagnet
(Low-Range)
Electromagnet
(Low-Range)
TIP102
Darlington Pair
2N3904
Transistor
Low-Range Out
Audio Inpu t
Arduino
MSGEQ7
Mid-Range Out
TIP102
Darlington Pair
2N3904
Transistor
LPF
High-Range Out
TIP102
Darlington Pair
2N3904
Transistor
LPF
Powered
Speaker
Figure 2. High Level Architecture
HARDWARE AND SOFTWARE DESIGN
This section will go into the multiple components that make up the project. Both
hardware and software designs will be discussed. Figure 3 below shows the overall final
schematic of Frequency Beats.
BAT42
12V
Electromagnet
(Low-Range)
BAT42
Electromagnet
(Mid-Range)
BAT42
Electromagnet
(High-Range)
GPB554B05BB
100
O.1uF
TIP102
3
LPF
2
2
2N3904
1
1
100
SUBJECT TO CHANGE
5K
GPB554B05BB
150
5V
O.1uF
MSGEQ7
O.1uF
Audio Input
33pF
11 Low-Range Out
Mid-Range Out
Arduino5112 High-Range Out
13
3
2 53 51
LPF
100
0.1uF
3
2
2
TIP102
2N3904
1
1
100
O.1uF
5K
100
GPB554B05BB
150
Powered Speaker
SUBJECT TO CHANGE
LPF
100
0.1uF
3
3
2
TIP102
2
2N3904
1
100
1
5K
150
3
Figure 3. Circuit Schematic
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User Interface
The user can plug in their audio signal via a 3.5mm standard line level audio cable
on the back side of the project device. Once connected, the user presses play on the audio
device (Ipod, Iphone, etc.) and watches the audio visualization of his or her music choice on
the front side of the device. Additionally, the user will be able to hear the music, via external
powered speakers, while viewing the ferrofluid displays with the aid of a 3.5mm headphone
splitter; the user will not have to interact with this component as it is a passive piece on the
back side of the device. Originally, the team had planned on using buttons on the face of the
apparatus to manipulate the ferrofluid without music, but toggle switches were easier to
incorporate.
Additionally, the user is able to hear the music, via external powered speakers. The
following figure shows the three switches and audio cable that the user will be able to
interact with.
[need a picture of finished displays and the toggle switches]
Figure 4. Toggle Switches
Arduino Due Microcontroller
The first primary digital component utilized in the project is the MSGEQ7 integrated
circuit. This little IC can accept a single audio source, analyze seven frequency bands of the
audio, and output a DC representation to represent the average amplitude of each frequency
band. This isn’t super accurate or calibrated in any way, but it works. The second primary
digital component is the Arduino Due, which is a microcontroller board based on the Atmel
SAM3X8E ARM Cortex-M3 CPU. It is the first Arduino board based on a 32-bit ARM core
microcontroller. It has 54 digital input/output pins, 12 analog inputs with 12 bits of
resolution each, and 12 PWM output pins.
The audio signal enters the MSGEQ7 where the signal is broken into seven
frequency bands (as seen in Figure 5) to be further processed by the Arduino Due. When the
signal reaches the Due, the Due combines bands 0-2, 2-4, and 4-6, separating the signal into
low-range (630 - 400 Hz), mid-range (400 - 2.5 kHz), and high-range (2.5 - 16 kHz)
groupings, averages the DC representation to produce three frequency bands, then scales the
amplitudes to correctly reflect the presence of each frequency range, and finally outputs
those three signals to individual power transistor current amplifiers.
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Figure 5. Frequency Response of MSGEQ7
Originally, the team had hoped to utilize Fast Fourier Transform (FFT) on the
Arduino Due to separate the frequency bands, but problems within the Arduino integrated
development environment (IDE) caused so many setbacks that a work-around IC was used
instead.
<< figure deleted>>
<< figure deleted >>
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Software
The key software utilized in the design will be the Arduino integrated
development environment (IDE), which is a cross-platform application written in java. The
team will use this software to write the code necessary for filtering the input audio signal.
An overview of the process to be implemented via code is shown below.
Figure 8. Software Flowchart
Figure 8 shows the general process that the signal will undergo as it is sampled by
the Arduino. Simply stated the Arduino will continually sample the input of the MSGEQ7.
The following is a list of the functions the Arduino will be performing.
Init
Initialize I/O pins and variables for the sampling and output process
sampleLoop
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Samples input from MSGEQ7 in the form of a seven element long array. The
Arduino then combines elements 0, 1, and 2, for low frequencies, 2, 3, and 4, for mid
frequencies, and 4, 5, 6, for high frequencies. Each of the 3 bands is added together and
divided by 3 to get an average value for the low frequencies. That number is then scaled to a
value between 0 and 255 for the PWM analogWrite function on the Arduino. As of now to
get a better LED visual we are subtracting 200 from the value of each of the seven
frequencies. This is purely aesthetic and will be changed in its final form; there may be a
refining of that method. The output is on pins 13, 12, and 11 for high, middle and low
respectively.
//Final with FFT (SUBJECT TO CHANGE)
This loop will continually sample the audio input in Analog format. Using FFT it
will split the signal and output onto three separate pins for high, low, and band pass
frequencies. Sample code for the FFT algorithm can be found here:
http://www.drdobbs.com/cpp/a-simple-and-efficient-fft-implementatio/199500857
FFT will output several complex numbers, or rather a real and complex part of each
number in the form of doubles. Each of the outputs will be sent to each of their
corresponding output pins as a combine value, putting the real and complex portions into
one value. The values will be continually recalculated in the loop to continually send to their
respective pins, for example pins 22, 23, and 24 on the Arduino. The signal will then pass
throw a low pass filter in order to create the proper DC current output for the circuit.
Electromagnet
Power Supply
The signal from the Arduino was not strong enough to drive the electromagnet.
Thus, the electromagnets were powered by a 6.5A, 12V power supply.
Control
The signal from the Arduino’s PWM output pins was passed through a LPF ,which
acts as a simple DAC, allowing the electromagnets to be powered to any level within a
certain range. TIP102 Darlington Pair, which acts as the “on/off” switch for the
electromagnet, is controlled by the signal from the Arduino that is boosted by a 2N3904
NPN transistor. The team had to diverge slightly from the original plan since the maximum
current from the Arduino is approximately 8mA, less than the originally anticipated 40mA.
As a result, a 2N3904 NPN transistor had to be used in order to boost the current high
enough to trigger the TIP102. In other words, a 2N3904 was needed provided the additional
current needed to turn on the TIP102. When there is current seen at the base of the TIP102,
current from the 12V power supply is able to flow through the electromagnet, thus turning
the electromagnet on.
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A small change that was also made was the addition of a flyback diode. This
protected the circuitry from the voltage spikes that occur when the electromagnet is
suddenly turned
off.
12V
BAT42
From Arduino
3
2
TIP102
2N3904
1
Electromagnet
2
1
100
5K
150
3
Figure 9. Electromagnet Control Circuit
Build
Each electromagnet was made with of approximately 500 feet of 26 gauge magnet
wire and wrapped around a 1/4” diameter iron core that is 5 inches in length. The internal
resistance of the wire was approximately 13Ω (greater than the originally anticipated 5.7 Ω).
The electromagnets were mounted above the ferrofluid display. After many unsuccessful
attempts at hand wrapping electromagnets, the team finally found success using a lathe to
slowly wrap each individual electromagnet. Each magnet took approximately 3 hours to
manufacture. Figure 10 below illustrates a hand wrapped electromagnet (on the right) and
one wrapped carefully using a lathe (on the left)
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<< figure deleted >>
Mechanical Components
The team’s project incorporates several simple mechanical devices. One of which
was the casing that houses the Ferro fluid. For this, the team originally planned to use
plexiglass cylinders, each with a diameter of approximately 2 inches and height of 5 inches.
However, the plexiglass allowed the ferrofluid to stick to the sides thus blacking the display
out and making it unusable. To correct this, the team decided to use glass cylinders instead,
since glass didn’t allow the ferrofluid to stick to the sides. The electromagnets were
mounted above the cylinder. Additionally, we constructed a wood base to mount the three
Ferro-fluid displays as well as the Arduino and support circuitry.
Assumptions
The team originally made several assumptions (listed below) that all proved to be
true throughout the construction, testing, and assembly process. No issues arose in regards
to these assumptions, which are listed below.
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Alan Hansen will be available to help with the construction of the base and
container for the ferrofluid
All hardware will be available and function properly
Some hardware components, such as resistors and capacitors, will be
available from the University and are not necessary to purchase.
There was, however, an assumption that was not listed in the team’s functional
specifications that should have been, which was the assumption that the Arduino would
output a sufficient current to switch the TIP102. This was not the case, and as a result, the
team needed to debug, and then correct the issue by adding a 2N3904 to add enough current
to switch the TIP102.
Changes
There were several changes that the team made during the implementation
phase of the project:
 An MSGEQ7 IC was used to analyze seven frequency bands outside of the Arduino
Due, rather than inside as originally planned.
 This change was necessary because problems in the Arduino IDE prevented
proper operation and even compilation when trying to implement the FFT on
the Arduino Due.
 This happened as a direct result of the fourth assumption in the previous
section. The team had researched if it was possible to, and how to implement,
an FFT algorithm on an Arduino, but the overlooked fact was that each
implementation was done on an Arduino Uno.
 The Arduino Due’s IDE is in beta and has very little support to help debug
such implementation problems. Additionally, the team could not revert to the
Arduino Uno because that board lacks the processing speed to analyze audio
signals in real time.
 The addition of the MSGEQ7 IC drastically changes the difficulty of the
project because the FFT implementation was the core EE concept of the
project; with a chip doing that part on auto-pilot, the project is complete, but
far easier.
 This oversight could have been prevented if the team had understood that
there was virtually no support for the Arduino Due IDE and that it was still in
beta before the projected was started.
Risks
The risks for the project have been stated previously in the Functional Specifications
Document and the Design Document. Please refer to that as there have been no changes in
the risks. Documentation can be found at:
http://wordpress.up.edu/egr13couchstreet/visualizer-status/.
The only risk that became a reality was the potential for issues with the plexiglass
containers, as discussed previously. The team’s contingency proved helpful. The team was
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able to effectively utilize their resources to find an alternative material (glass) to house the
ferrofluid. There were not any risks that were not identified in the Functional Specifications.
MILESTONES
Task
Order all parts
Build base and get audio input
Finish building one display
Finish digital signal processing
Test signal with one display
Testing and debugging of first display
Build other displays and add processing
Final assembly and testing
Final report
Founder’s Day presentation
Date Due
12/1/13
1/17/14
1/24/14
1/31/14
2/3/14
2/7/14
2/28/14
3/14/14
4/4/14
4/8/14
Date Complete
12/1/13
3/17/14
3/13/14
3/12/14
3/17/14
3/20/14
3/13/14
-
Several milestones were achieved late for two primary reasons. First, the milestone
due dates were set back during the Fall Semester and ended up not being in the most
efficient order. For example, the milestones called for the base to be built first and early in
the semester. However, the base ended up being one of the last parts to be constructed
because it made a lot more sense to build the displays first to ensure the base is built
appropriately. Second reason was due to the team’s overly ambitious goal setting at the
beginning of the year coupled with the fact that despite a team’s best attempts to anticipate
any and all potential problems, no team can foresee all issues that will occur. This was
precisely the case with team Couch Street. The team encountered problems with
manufacturing the ferrofluid displays that put them behind schedule. These problems
included difficulty developing a method of accurately manufacturing the electromagnets, the
unexpected problem of the ferrofluid sticking to the plexiglass, and the team trying to create
their own ferrofluid from the start rather than purchasing it. These issues were all ultimately
corrected, but resulted in the team falling behind schedule.
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CONCLUSION
The ferromagnetic fluid audio visualizer is a different way of seeing different
frequencies used in different types of music. It visually represents the low, middle and high
frequency ranges by processing the sound from a standard 3.5mm headphone jack, and
using the processed signal to drive electromagnets, which will manipulate ferrofluid.
Overall, the team’s final prototype was almost identical to their original design as
outlined in the Design Document. The only significant changes were that of adding a
2N3904 NPN transistor before the TIP102, eliminating the biasing circuit, eliminating the
FFT, and adding a flyback diode to eliminate any potential voltage spikes.
The team did a great job of communicating with each other, planning and adapting
as issues arose, and keeping focused on the end goal. The team’s primary mistake was not
anticipating more potential problems throughout the assembly and testing phases.
GLOSSARY
IC: (Integrated Circuit) is a microelectronic circuit manufactured on a thin substrate of a
semiconductor material such as silicon.
Microcontroller: is a small computer on a single integrated circuit containing a processor
core, memory, and programmable input/output peripherals.
Arduino: is a single-board microcontroller to make using electronics in multidisciplinary
projects more accessible.
Electromagnet: is a type of magnet in which the magnetic field is produced by electric
current.
Ferrofluid: is a liquid which becomes strongly magnetized in the presence of a magnetic
field.
LED: (Light Emitting Diode) A semiconductor diode that emits light when a voltage is
applied to it and that is used especially in electronic devices (as for an indicator light).