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
FINAL REPORT
TEAM COUCH STREET
REV. 1.1
PAGE 2
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
1.0
3 Apr 2014
Team
Final draft submitted to advisor
1.1
7 April 2014
Kevin Ratuiste Updated Schematics (Figures 3 and 6)
FINAL REPORT
TEAM COUCH STREET
REV. 1.1
PAGE 3
TABLE OF CONTENTS
REVISION HISTORY .................................................................................................................................................. 2
INTRODUCTION........................................................................................................................................................... 4
HIGH LEVEL ARCHITECTURE............................................................................................................................. 5
HARDWARE AND SOFTWARE DESIGN ......................................................................................................... 6
User Interface ............................................................................................................................................................. 7
Arduino Due Microcontroller .............................................................................................................................. 8
Software ........................................................................................................................................................................ 8
Electromagnet ............................................................................................................................................................ 9
Mechanical Components ...................................................................................................................................... 12
Miscellaneous Changes ......................................................................................................................................... 12
ASSUMPTIONS............................................................................................................................................................ 12
RISKS ............................................................................................................................................................................... 13
MILESTONES ............................................................................................................................................................... 13
CONCLUSION .............................................................................................................................................................. 14
GLOSSARY.................................................................................................................................................................... 15
FINAL REPORT
TEAM COUCH STREET
REV. 1.1
PAGE 4
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 1. Front of Apparatus
Some highlights of the implementation phase were building electromagnets,
designing and building a circuit that takes the Arduino’s PWM outputs and controls the
electromagnets, and implementing a working program for the microcontroller that does the
processing required and seeing that the project works in parts.
FINAL REPORT
TEAM COUCH STREET
REV. 1.1
PAGE 5
The two biggest challenges the team faced was implementing the Fast Fourier
Transform (FFT) algorithm on the Arduino Due and to design a circuit that can be
controlled by the Arduino’s PWM outputs. Another minor 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 sub-par results and
extra assistance was needed to produce electromagnets of proper quality. Each of these
challenges were addressed according to the team’s list of anticipated challenges in the
design document and was ultimately overcome.
While the team noticed early in the Spring Semester that their milestones were
overly ambitious and not in the ideal order for completion, the team did well at sticking to
their basic 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 and utilizing circuit simulation software, rather than
testing larger sets of components towards the end and final assembly.
The following sections of this document will address how the team handled the
challenges mentioned above, as well as, 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 three
components to note are the Arduino, Low-Pass Filter (LPF), and the control circuit. First,
the audio signal is processed by the Arduino and broken up into its low, mid and high
frequencies. This is output as a PWM signal, which is then smoothed out to a DC signal by
the LPF. This DC signal is then sent to the control circuitry, which turns the electromagnet
on or off.
FINAL REPORT
TEAM COUCH STREET
REV. 1.1
PAGE 6
12V Power
Supply
Electromagnet
(Low-Range)
LPF
Electromagnet
(Low-Range)
Electromagnet
(Low-Range)
Control Circuitry
Low-Range Out
Audio Inpu t
Biasing
Circuit
Mid-Range Out
Arduino
LPF
Control
ControlCircuitry
Circuit
High-Range Out
LPF
Powered
Speaker
Control Circuitry
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.
Electromagnet
(Low-Range)
BAT42
Electromagnet
(Mid-Range)
BAT42
BAT42
Electromagnet
(High-Range)
3.3k
12V
3.3V
2.7k
2
LPF
100
33uF
1
2
10k
3
2N3904
4.7k
1
10k
NC
IRF3205
3
NC
Audio
Source
Audio Input
100uF
1k
Vcc
3.3V
Arduino
11 Low-Range Out
Mid-Range Out
12
13 High-Range Out
2
LPF
100
33uF
1k
1
3
2N3904
4.7k
2
10k
10k
IRF3205
1
3
NC
Powered Speaker
2
LPF
100
33uF
Figure 3. Circuit Schematic
1
4.7k
2
10k
3
2N3904
10k
IRF3205
1
3
FINAL REPORT
TEAM COUCH STREET
REV. 1.1
PAGE 7
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. When looking at the front of the apparatus, having the switch to the left, forces
the electromagnet on, to the right, the electromagnet is controlled by the audio input, and in
the middle, the electromagnet is always off.
Figure 4. Toggle Switches
FINAL REPORT
TEAM COUCH STREET
REV. 1.1
PAGE 8
Arduino Due Microcontroller
The primary digital component that will be utilized in the design 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.
This component will be used to digitally filter the input audio signal using a Fast
Fourier Transform (FFT) algorithm, separating it into low-range, mid-range, and high-range
frequency bands, averages the amplitudes to produce a single DC voltage representation of
each band, and outputs those three signals to the electromagnets.
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 5. Software Flowchart
Figure 5 shows the general process that the signal will undergo as it is sampled by
the Arduino. Simply stated the Arduino will continuously sample the input on one of the
analog input pins using a loop. From there, using FFT, the signal will be separated as low
FINAL REPORT
TEAM COUCH STREET
REV. 1.1
PAGE 9
pass, band pass, and high pass filters. These frequencies will range from 20Hz - 160Hz for
the low frequencies, 160Hz – 7.5kHz for mid-range frequencies, and 7.5kHz - 15kHz for the
high frequencies. Each signal will be output to three different digital output pins. The
Arduino will process the audio input with a buffer size of 1024 and a sample rate of
44100Hz. The Arduino output is a Pulse Width Modulation (PWM) signal between 1 and
3.3 volts. These outputs will be combined by taking the magnitude of each output, and then
summed. This value will then be scaled to a number between – 85 and 255 (the PWM output
which comes out around 500Hz). 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
This loop will continuously 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.
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
through 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
As seen in the figure below, the signal from the Arduino’s PWM output pins is
passed through a LPF, which acts as a simple DAC, allowing the electromagnets to be
powered to any level within a certain range. A 2N3904 BJT is controlled by the low-passed
PWM signal from the Arduino, which in turn controls an IRF3205 MOSFET. Together they
act as the “on/off” switch for the electromagnet. At 3.3V the IRF3205 begins to saturate and
the electromagnet begins to turn on. At 5V or higher, the MOSFET is completely saturated
and the electromagnet is fully on. However, since the maximum voltage of the PWM signal
after the LPF is only approximately 2V and thus never high enough to saturate the
MOSFET, the signal could not be input directly into the IRF3205.
In order to provide enough voltage so that the MOSFET turns on, 6V is connected to
its base and the 2N3904 controls when the IRF3205 base voltage is pulled high or low. This
control was done by setting the base of the 2N3904 to 1.5V, so that when 2V or higher is
seen at the emitter, in other words Ve is greater than Vb, the BJT turns off. With the 2N3904
FINAL REPORT
TEAM COUCH STREET
REV. 1.1
PAGE 10
off, the IRF3205 is pulled high, thus turning the electromagnet on. As for when less than
1.5V is at the emitter, the 2N3904 is on, which pulls the base of the IRF3205 to below 3.3v,
turning the electromagnet off.
The team had to diverge from the original plan since the maximum current from the
Arduino was less than the originally anticipated 40mA and could not trigger the TIP102.
The team tried multiple fixes, including cascading another BJT in front of the TIP102, but
none worked. In addition, it was difficult to observe the current coming out of the Arduino’s
PWM outputs hindering debugging. Subsequently, the circuit was completely reworked to
what it is now so that it was dependent on voltage level as opposed to current.
Another small change that was 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
3.3V
(From Arduino)
3.3k
BAT42
Electromagnet
2.7k
NC
From Arduino
2
LPF
100
1
33uF
3
2N3904
4.7k
2
10k
IRF3205
1
10k
Figure 6. Electromagnet Control Circuit
3
FINAL REPORT
TEAM COUCH STREET
REV. 1.1
PAGE 11
Build
Each electromagnet was made with of approximately 270 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.
Figure 7. Lathe vs Hand-Coiled Electromagnets
FINAL REPORT
TEAM COUCH STREET
REV. 1.1
PAGE 12
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 ferrofluid stuck to the sides of the plexiglass, completely blacking out the
display, and making it impossible to see inside the display. To address this, the team decided
to use glass cylinders instead, since the ferrofluid did not stick to glass. The electromagnets
were mounted above the cylinder. Additionally, a wood base was constructed to mount the
three Ferro-fluid displays, control circuit, and Arduino.
Miscellaneous Changes
Most changes that occurred were explained in the above sections, but there were
some other minor changes that the team also had to make during the semester.
LEDs
As of now, the team unfortunately was not able to incorporate LEDs to pulse with
the music as stated in the Functional Specification Document. The setbacks caused by
trouble with the FFT code, unexpected behavior of the ferrofluid display material, and the
redesigning of the circuit ultimately resulted in final testing of the displays and Arduino not
happening until 2 April. In addition to the need to complete the Final Report and
presentation by 4 April, the team had to prioritize and abandon the implementation of the
LEDs.
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.



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
entire control circuit had to be redesigned.
FINAL REPORT
TEAM COUCH STREET
REV. 1.1
PAGE 13
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
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
3/28/14
3/29/14
3/13/14
4/2/14
4/3/14
-
Table 1. Milestones Due Date and Completion Dates
As it can be seen in Table 1 above, many milestones were achieved late. This was
due to three 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 it after
the displays to ensure that it is built appropriately. Second reason was due to the team’s
overly ambitious goal setting at the beginning of the year. 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, which leads to the third reason. The team
encountered several problems over the semester causing multiple setbacks and delays. 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. Another
delay causing problem the team ran into was getting the Arduino to control transistors,
which ultimately lead to a whole redesign of the control circuit. The FFT also took longer to
implement than anticipated. These issues were all ultimately corrected, but resulted in the
FINAL REPORT
TEAM COUCH STREET
REV. 1.1
PAGE 14
team falling behind schedule. However in the end, most importantly, everything was
completed on time for Founders Day.
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 digitally processing the sound from a standard 3.5mm headphone jack,
and then uses the processed signal to control the electromagnets on and off, which
manipulates ferrofluid.
From the client’s perspective, the team’s final project was visually identical to the
original design as outlined in the Design Document. However, there were a few schematic
changes that were made, which are not noticeable to the end user, as outlined in this
document.
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.
FINAL REPORT
TEAM COUCH STREET
REV. 1.1
PAGE 15
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).