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Touchpad-Controlled Parametric Equalizer

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Touchpad-Controlled Parametric Equalizer ECE 445 Group #24 Anthony Mangognia Alexander Spektor Farsheed Hamidi-Toosi TA: Chad Carlson Introduction Goal: To create a ... – PowerPoint PPT presentation

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Title: Touchpad-Controlled Parametric Equalizer


1
Touchpad-ControlledParametric Equalizer
  • ECE 445
  • Group 24
  • Anthony Mangognia
  • Alexander Spektor
  • Farsheed Hamidi-Toosi
  • TA Chad Carlson

2
Introduction
  • Goal To create a real-time audio filtering
    solution for musicians and sound engineers
  • Goal To provide independent control over filter
    parameters center frequency, bandwidth, and gain
  • Goal To create a geometrically-intuitive input
    device for the filter

3
Existing Alternatives
  • X-Band Equalizers
  • Sliders or knobs
  • Limited control
  • Takes time to adjust
  • Discrete frequency bands
  • Digital Parametric Equalizers
  • Pseudo-continuous frequency sweep
  • Cumbersome software-based control

4
Design Overview
  • Input Device Pressure-sensitive touchpad.
  • Horizontal position center frequency
  • Vertical position gain
  • Overall Pressure bandwidth
  • Input-Filter Interface RS-232 serial connection
  • Filter DSP-implemented algorithm
  • Second-order IIR filter (based on Mitra-Regalia
    topology)
  • Filter coefficients update in real-time

5
Design Block Diagram
Audio In
DSP Parametric Equalizer Filter
Microcontroller Positioning Algorithm Touchpad
?DSP interface
Audio Out
Touchpad
6
1. Touchpad Process
Pressure Sensor Voltage Differential
Bias cancellation/Tuning Circuit
830x Amplifier
PIC A/D
7
Touchpad
  • Four corner-mounted pressure sensors on
    height-adjustable shelves
  • Pressure sensor output voltage varies with finger
    position
  • Positioning algorithm
  • Surface much larger than typical
    commercially-available touchpads

8
Touchpad Design
Touchpad Surface
Sensor Mount
Pressure Sensors
Slide-in touchpad
Birds Eye View
Height-adjustable sensor mount
Sensor Mount
9
Pressure Sensors
  • Honeywell 125PC30G1
  • Pressure range 0-30 psi
  • Sensitivity 8.33mV/psi

V-
GND
V
10
Amplifier
10
Touchpad Signal Amplification
  • Instrumentation Amplifier AD622AN
  • Low-cost 4.90
  • Gain 2-1000x, external resistor control
  • 56O ? 830x gain
  • Easy integration wide power supply voltage gain
    (2.6V-15V)
  • Large gain ? Large bias voltage
  • Solved with 1MO pull-down resistors at inputs and
    100k potentiometer (calibration)

11
2. Microcontroller-EnabledTouchpad ? DSP
Interface
Four sensor A/D
Positioning Algorithm
Serial Transmission
12
Analog to Digital Conversion
  • 8-bit A/D conversion for quicker calculations
  • 10-bit possible for PIC16F877A, but doubles
    number of bytes for mathematical operations
  • Decreases resolution to 256 points maximum
  • More than enough to simulate continuous operation
  • Read 8 values for each sensor and average
  • Functions as a digital LPF

13
Positioning Algorithm
Sensor 1 V1 (0, Ymax)
X2 V2 Xmax / (V2 V1)
Sensor 2 V2 (Xmax, Ymax)
Touchpad Surface
Y1 V1 Ymax / (V1 V0)
Y2 V2 Ymax / (V2 V3)
(X,Y) Finger Position
Sensor 3 V3 (Xmax, 0)
Sensor 0 V0 (0, 0)
X1 V3 Xmax / (V3 V0)
14
Positioning Algorithm
Sensor 1 V1 (0, Ymax)
X2
Sensor 2 V2 (Xmax, Ymax)
Touchpad Surface
Y1
(Xavg,Yavg) Average
Y2
Sensor 3 V3 (Xmax, 0)
Sensor 0 V0 (0, 0)
X1
15
Positioning Algorithm
Sensor 1 V1 (0, Ymax)
Sensor 2 V2 (Xmax, Ymax)
X X1 (Ymax-Yavg) X2 (Yavg)
Touchpad Surface
(X,Y) Weighted Average
Y Y1 (Xmax-Xavg) Y2 (Xavg)
Sensor 3 V3 (Xmax, 0)
Sensor 0 V0 (0, 0)
16
Data Sent to DSP
  • Three-byte start sequence 230 x3
  • Four sensor readings S0, S1, S2, S3
  • Two one-byte positioning words (x3)
  • One three-byte stop sequence 232 x3

230
S0
230
230
S1
S2
S3
X
X
X
Y
Y
Y
232
232
232
17
Serial Data Transmission
  • Data transmitted at 38400kbps
  • Default rate for DSP
  • Data Format
  • Sent over standard serial cable
  • DB-9 connector

1 START BIT
8 BIT WORD
1 STOP BIT
18
RS-232 Voltage Level Conversion
  • PIC output at TTL levels
  • 0 - 5V
  • DSP input at RS-232 levels
  • 12V swing
  • Conversion with MAX232 line driver

38400kbps serial data at TTL from PIC
MAX232 Line Driver
38400kpbs serial data at RS-232 to DSP
19
3. DSP Audio Filtering
Receive/Decode Data from Touchpad
Update Filter Coefficients
Apply Filter to Audio Input and Send to Speakers
20
Filter Design
  • Based on Mitra-Regalia second-order IIR
  • Design Equations
  • ß cos(?c)
  • k 10(GAIN/20 dB)
  • a (1 tan (BW/2)
  • (1 tan (BW/2)
  • Programmed in C for TI-54x fixed-point DSP

A(z) All-Pass Lattice
Mitra-Regalia Topology
21
Src Montana University Web site.
http//www.coe.montana.edu/ee/rmaher/ECEN4002/lab4
_020226.pdf
22
Design Challenges Touchpad
  • Pressure sensor noise
  • Problem 30mV peak-to-peak noise level
  • Solution 8-point averaging filter after PIC A/D
  • PIC A/D crosstalk
  • Problem Changes in one pressure sensor affected
    values read for other
  • Solution Pull-down 0.1µF capacitors at A/D input
    pins
  • Serial communication pins
  • Problem PIC?PC communication and PIC?DSP
    communication use different DB-9 transmit pins
  • Solution Internal rewiring to accommodate both

23
Design Challenges Filter
  • Filter type change
  • Problem Original algorithm (Chamberlin) produced
    undesirable resonance frequencies
  • Solution Switched to Mitra-Regalia topology
  • IIR Instability
  • Problem Direct form two implementation caused
    overflow
  • Solution Implemented lattice structure to reduce
    overflow
  • Quantization
  • Problem Fixed-point quantization of coefficients
  • Solution Lattice structure ensures pole-zero
    cancellation

24
Internal Component Test
  • Pressure Sensor Amplifier
  • Unwanted signal oscillation 60mV peak to peak
  • Due to conflicting RC networks
  • Too high for 1V sampling range
  • Solution Removed analog smoothing filter

25
Bandwidth Test
26
Center Frequency Test
27
Gain Test
28
GWN Input Boost Tests
29
GWN Input Cut Tests
30
Finished Product Test
  • Amplitude test performed with oscilloscope
  • Input 11 kHz Sine Wave, 200 mV peak-to-peak
  • Tests gain 2 and gain .5 at 11kHz by
    measuring peak-to-peak voltage of output using
    the scope
  • Amplitude resolution is .24 dB from -6dB to 6dB
  • Exceeded design requirement which stated 2-3 dB
    amplitude resolution

Gain Output P-P
1 200mV
2 400mV
0.5 100mV
31
Finished Product Test
  • Frequency tests performed with scope
  • Fix bandwidth, set gain 2
  • Inputs Sine at set frequencies, Gaussian White
    Noise
  • Using FFT on scope, can see if frequencies
    boosted by 2x at desired center frequency
  • Proposed frequency resolution 1 Hz (not
    necessary)
  • Total of 200 center frequencies possible,
    distributed them logarithmically since hearing is
    logarithmic
  • High resolution for low frequencies, less
    resolution for higher frequencies
  • Results Filter works for all frequencies within
    hearing range (20Hz-20kHz)

32
Finished Product Test
  • Bandwidth Tests
  • As total pressure increases, increase bandwidth
  • Tested using FFT on scope
  • Input signals Gaussian white noise, music
  • Test to see if bandwidth varies from 50Hz to
    22050Hz as pressure increases
  • Passed tests, including aural tests

33
Finished Product Test
  • Latency Tests
  • The target of less than 100ms system latency was
    achieved
  • Delay due to pressure sensors negligible
  • Delay due to PIC negligible (assembly code
    minimized cycles)
  • DSP initially had some latency, but code was
    optimized by eliminating FOR loops (less than
    30000 cycles at MHz)
  • Usability tests confirm that system latency is
    not an issue when using this system, negligible

34
Finished Product Test
  • Usability Tests and Conclusions
  • Tested on music signals and white noise signals
  • Qualitative analysis
  • Was the filtering audible?
  • Did the touchpad respond as desired?
  • How intuitive was it to find a desired
    frequency?
  • Is this design marketable? If so, why?
  • How much would this cost to manufacture?

35
Final Thoughts
  • Improvement Better pressure sensors
  • Higher output voltage ? Less amplification
  • Improvement Cascade feature
  • A button to keep current settings and use new
    settings in cascade
  • Other applications Large touchpad has many
    applications
  • Computer input device for the disabled and kids

36
Acknowledgements
  • Chad Carlson
  • Marty other ECE 445 TAs
  • Profs. Haken Beauchamp
  • Machine Shop Scott McDonald
  • Parts Shop

37
Questions?
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