Transcript Frequency Dependent Audio Visualizer

By: Devon Schmidt & Kyle Da Rif
Instructor: Stanislaw Legowski
Senior Design 2012/2013
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An electronic device which analyzes an input
stereo audio signal and turns LED arrays on
and off based upon the frequency
information of the input signal in real time.
Generally used in professional lighting and
music applications
◦ Concerts
◦ Parties
◦ Sporting or other major events

Receives an input in the form of a stereo
signal from source
◦ MP3 Player, iPod, Smart-Phone, etc.
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Filters frequency information of signal into
set number of bands
◦ Information is separated by active analog filters
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Filtered information is output to LED arrays
associated with each band.
LEDs will now illuminate when input
frequency information falls within the band
connected to those LEDs.
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Master / Slave chip configuration with integrated
speakers.
◦ Master filters information to Slaves which drive the LEDs
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Input stereo signal is sent to the Master chip and
an amplifier for each speaker
Master is programmed to filter signal into 8
frequency bands per channel
Two bands are then assigned to each Slave chip.
16 LEDs assigned to each band
256 Total LEDs
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Couldn’t find a way to have the Master and
Slaves communicate
SPI bus (Serial Peripheral Interface)
◦ As the name states the information is output in a
serial fashion
◦ Required a Parallel output to update the Slaves at
once
 Otherwise LEDs would lag behind the audio signal
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Had to restructure project to an analog
format
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Replaced Master chip and individual speaker
amplifiers with a single amplifier and a filter
bank using HPFs, LPFs, and BPFs
Replaced Slaves with RMS to DC Converters,
PWMs, and LED Drivers
Reduced the number of LEDs per band to 4
LED Total: 64
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The amplifier receives the input stereo signal
and outputs an amplified signal to both
speakers and the filter bank.
Filter bank separates frequency information
of the input into 8 bands per channel
In each band, a RMS to DC converter modifies
the AC waveform into a true RMS signal
PWM uses RMS signal to control duty cycle of
output waveform
LED Driver utilizes duty cycle signal to
illuminate LEDs associated with specific band
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1 Texas Instruments TPA3100D2 Class-D Amplifier Evaluation
Board
2 Polk Audio 4Ω-Load Speakers
Filter bank
◦ 28 Analog Devices OP177 Operational Amplifiers
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16 Analog Devices AD736 True RMS-to-DC Converters
16 Linear Technology LTC6992-1 Voltage-Controlled Pulse
Width Modulators
16 Diodes Inc. AL5802 Adjustable Current Sink LED Drivers
16 Texas Instruments LM741 Operational Amplifiers
16 Vishay Siliconix IRF530PBF-ND N-Channel MOSFETs
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16 Texas Instruments LM7805CT 5 Volt Voltage Regulators
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◦ Required for Dimming Effect in LED Drivers
◦ Required for RMS to DC Converter and PWMs
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15W/channel given a
4Ω-Load and 12V
supply
Highly efficient
Class-D structure
Left and Right
channel outputs
Utilizes stereo RCA
input
◦ Converted to 3.5mm
“headphone jack” to
allow a wider range of
source devices
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Polk Audio DB461
◦
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◦
◦
◦
4” x 6” Speaker
4Ω-Load Impeadence
120 Watt Peak Power
40 Watt RMS Power
75Hz – 22kHz
Frequency Response
Polk Audio DB461 4” x 6” Speaker, Photo, n.d.,
http://www.productwiki.com/upload/images/polk_audio_db461.jpg, Web, April
.
25, 2013
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Wanted to keep as much frequency
information as possible
Final Bank Structure (1 Channel)
◦ LPF at lowest frequency (31.25 Hz)
◦ 6 BPFs at intermediate frequencies
◦ HPF at highest frequency (≥4k Hz)
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Total number of filters for both channels: 16
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Filter center and
limit frequencies
found using table
Three Considered
Filter
Configurations
◦ Second order HPF
◦ Second order LPF
◦ Fourth order BPF
Octave Bands
Band #
f_low (Hz)
f_ctr(Hz)
f_hi (Hz)
%BW
1
22.097
31.25
44.194
70.711
2
44.194
62.5
88.388
70.711
3
88.388
125
176.777
70.711
4
176.777
250
353.553
70.711
5
353.553
500
707.107
70.711
6
707.107
1000
1414.214
70.711
7
1414.214
2000
2828.427
70.711
8
2828.427
4000
5656.854
70.711
"Center Frequencies and High/Low Frequency Limits for Octave Bands, 1/2and 1/3-Octave Bands." N.p., n.d. Web. 25 Apr. 2013.
<http://courses.physics.illinois.edu/phys406/Lab_Handouts/Octave_Bands.p
df>.
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2nd Order Active-HPF
All capacitors assumed
C = 0.1µF
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2nd Order Active-LPF
All resistor assumed
R = 10kΩ
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Capacitor Calculations for LPFs
Given:
𝑓𝑐 = center frequency of LPF
Q = 0.707; R = 10kΩ
𝜔0 = 2𝜋𝑓𝑐 =
1
3
1
𝑅 𝐶1 𝐶2
𝐶1
𝐶2

𝑄=
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Rearranging To solve for capacitor values
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𝐶1 =

𝐶2 =
1
𝐶2 𝜔02 𝑅2
𝐶1
9𝑄 2
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Resistor calculations for HPFs
Given:
𝑓𝑐 = center frequency of HPF
Q = 0.707; C = 0.1µF
1
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𝜔0 = 2𝜋𝑓𝑐 =

𝑄=
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Rearranging to solve for resistor values
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𝑅1 =
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𝑅2 =
1
3
𝐶 𝑅1 𝑅2
𝑅1
𝑅2
1
𝑅2 𝜔02 𝐶 2
𝑅1
9𝑄 2
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4th Order BPF
◦
2nd Order HPF in series with 2nd order LPF
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High pass center frequency set to the f_low value of the selected
band
Low Pass center frequency set to the f_hi value of the selected band
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Center frequency given by the equation 𝑓𝑐 =

𝑓ℎ𝑖 −𝑓𝑙𝑜
70.7%
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General purpose
operation amplifier
12V operating
voltage
Used for simple
amplification and
inverting
LM741 Operational Amplifier, Photo, n.d., http://1.bp.blogspot.com/-
PG_LIg86xQ/UHBAryRVeSI/AAAAAAAAAbY/apbM8MjOwws/s1600/lm741.jpg,
Web, April 25, 2013.
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Uses 12V input to
provide 5V output
Utilized as simple
solution to provide
5V to circuit
Well-Protected
◦ Internal currentlimiting
◦ Thermal Shutdown
7805CT 5V Regulator, Photo, n.d.,
http://shop.rabtron.co.za/catalog/images/7805CT.jpg, Web, April 25,
2013.
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Wide voltage range
◦ +2.8V, -3.2V ± 16.5V
 Uses ±5V source to
match PWM
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High Accuracy
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Standard DIP 8
Package
◦ Total Error: ±0.3mV ±
0.3% of signal
◦ Easy for breadboard
testing
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Low Supply Current
◦ 200µA
AD736 RMS-to-DC Converter, Photo, n.d.,
http://sigma.octopart.com/14099183/image/Analog-DevicesAD736AQ.jpg, April 26, 2013.
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Highly Flexible
◦ Programmable
Oscillator frequency
and frequency divider
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Low Operating
Voltage
◦ 2.25V – 5.5V
 Required Voltage
Regulator
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Small Size
◦ Required Break-Out
Board for testing
LTC6992-1 PWM Generator, Photo, n.d.,
http://elcodis.com/photos/28/17/281718/6-tsot_mdp.jpg, April 26, 2013.
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N-channel
enhancement
MOSFET
Fast switching
◦ Allows LED driver to
utilize PMW signal
IRF530 N-EMOSFET, jpeg, n.d.,
http://sigma.octopart.com/14176178/image/Vishay-IRF520PBF.jpg, Web,
April 25, 2013.
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Utilizes N-Channel
MOSFET for LED
Dimming
◦ PWM Signal applied to
MOSFET
 MOSFET output signal
received at the Enable Pin (Pin
3)
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Simple Construction
◦ 2 NPN Transistors
 Q1 measures current using an
external resistor
 Q2 regulates current
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0.8V to 30V operating
voltage
Driving current 20mA to
100mA
AL5802 LED Driver, Photo, n.d., http://pinoutcircuits-images.dz863.com/114/AL5802.jpg, April
26, 2013