Project

1
Project 9Guitar Effect Pedal

• Project Advisor Dr. Nutter
• Group Members
• Jonathan Fong
• Bryan Hill

2
Project Objective

• Build a digital effect pedal for a guitar which
  will change the original sound of the guitar and
  create a reverb output.

3
Presentation Outline

• Block Diagram
• External Memory
• Input Signal
• ADC and DAC Chip
• Capture Schematic
• DC Offset
• Low Pass Filter
• Simulink Diagrams
• User Interface
• Connection between MSP and DSP
• Gantt Chart
• Budget

4
Block Diagram
JF
ADC
XTAL Oscillator 11.2896 MHz
LPF/ Level Shift
Guitar Input
Serial 2 RX 16 bit
Serial 2 Clock
Serial 1 Clock
Serial 2 Clock
MSP (Master)
DAC
DSP Eval board (Slave)
Amp
Serial 1 TX 8 bit
Serial 2 TX 16 bit
GPIO
GPIO
Footboard Switch
LCD Display
5
Memory For DSP
JF

• The DSP has 512 kbits (64kbytes) of on-chip RAM
• There is no EPROM
• There are interfaces for additional RAM and EPROM
• Supports 32 bit memory

6
Memory Interface
JF
http//focus.ti.com/docs/apps/catalog/resources/ap
pnoteabstract.jhtml?abstractNamespra639a
7
Analog Devices AD74111
JF

• 2 in 1 ADC and DAC
• Supply Voltage
• 2.5 V
• Sampling
• 16/20/24 bit
• 8 kHz 48 kHz
• Performance
• 20 Hz 20 kHz range
• 85 dB ADC
• 93 dB DAC
• Serial Output
• Applications
• Voice/Audio Processing
• Price - 3

http//www.digikey.com/scripts/DkSearch/dksus.dll?
Detail?Ref335527Row194786SiteUS
8
Input Signal
JF
9
DC Offset and LPF
JF

• Input Signal is sinusoidal
• 300 mV Peak to Peak
• Max 3 V Peak to Peak
• ADC voltages
• Minimum 0 V
• Maximum 4.5 V (absolute)
• Negative Voltage needs to be offset
• A LPF will be used to eliminate high frequencies
  not wanted

10
Pre-ADC Circuit
JF
11
Simulation Results
JF
12
Low-Pass Cutoff
JF
13
Buttons Layout
JF
14
Milled Board with Components
15
Physical Connection
JF

• DB 9 Connector
• TX / RX (3,2)
• Frame Sync
• Clock
• Ground (5)
• Only need 4 pins

Male Connection
Female Connection
http//www.arcelect.com/rs232.htm
16
SPI Registers

• Controls
• General SPI Mode, Master Mode, 8-bit Data word
• Transmit Frame Sync enable, UCLK
• Receive Not Used
• Modulation Not Used
• Baud Rate Clock / 2
• Buffers
• Receive Not Used
• Transmit
• Enable
• Module Not Used
• Interrupt Not Used

17
SPI Serial Code
18
Buttons Flow Chart
JF
No
Arrow Button? Cancel Button Save Button? (Poling)
Save Buttons
Yes
Arrow Button
Control Temp
Cancel Button
Show Main Screen
U/D
L/R
Sent Control -gt Buffer
Change Temp Control Word
Scroll Screens
Temp Control
19
Effects Definitions
BH

• Reverberation
• Reverb is used to simulate the acoustical effect
  of rooms and enclosed buildings. In a room, for
  instance, sound is reflected off the walls, the
  ceiling and the floor. The sound heard at any
  given time is the sum of the sound from the
  source, as well as the reflected sound. An
  impulse (such a hand clap) will decay
  exponentially. The reverberation time is defined
  as the time taken for an impulse to decrease by
  60dB of it's original magnitude.

20
Effects Definitions
BH

• Chorus
• The chorus effect is so named because it makes
  the recording of a vocal, or instrument, track
  sound like it was sung by two or more people
  singing in chorus. This is achieved by adding a
  single delayed signal (echo) to the original
  input. However, the delay of this echo is varied
  continously between a minimum delay and maximum
  delay at a certain rate. Typically, the delay is
  varied between 40ms and 60ms at a rate of about
  0.25Hz.

21
Effects Definitions
BH

• Distortion
• Distortion is usually achieved using one of the
  clipping functions mentioned below. However, more
  musically useful distortion can be achieved by
  digitally simulating the analog circuits that
  create the distortion effects. Different circuits
  produce different sounds, and the characteristics
  of these circuits can be digitally simulated to
  reproduce the effects.
• Symmetrical/Asymmetrical clipping - signal
  multiplied with the hard-limit transfer function
  (distortion).
• Half wave/full wave rectification - clipping of
  one half of the waveform/absolute value of input
  samples.
• Arbitrary waveform shaping - input signal
  multiplied by arbitrary transfer function. Used
  to perform digital valve/tube distortion
  emulation, etc.

22
DSP Coding
BH

• DSP was originally coded with Simulink, but due
  to complications in defining controllable
  variables C is now being used

23
Reverb
BH
Circular buffer Declare an array that is sized
according to the amount of delay desired and add
the newest sample to the oldest sample
24
Reverb Distortion
BH
Multiply the signal by the desired gain and then
limit it at the desired boundaries
25
Chorus
BH
Same circular buffer used in reverb effect except
the newest sample in the array is added to a
sample that is located at a varied position
within the array.
26
Complete
BH
27
DSP User Control
BH
28
Complete - Distortion
BH
Multiply the signal by the desired gain and then
limit it at the desired boundaries
29
Complete Reverb
BH
Circular buffer Declare an array that is sized
according to the amount of delay desired and add
the newest sample to the oldest sample
30
Complete Chorus
BH
Same circular buffer used in reverb effect except
the newest sample in the array is added to a
sample that is located at a varied position
within the array.
31
Control Flow Chart
BH
Distortion
Chorus
MSP Input
Word Sorting
Reverberation
Switches
Enable Effects
32
Functional Capture Schematic
33
New Board Layout
BH
34
Top Layer
BH
35
Bottom Layer
BH
36
Whats Finished?

• Pre-ADC Circuit
• Level Shifter
• Low Pass Filter
• DSP Digital Effects in Simulink and C
• Reverb
• Distortion
• Chorus
• MSP Coding
• Serial Connection to DSP
• Buttons Interface
• Board Layout
• Main Component Board
• Button Interface - Milled
• Acquired All Necessary Parts

37
Whats Not?

• Main Board
• Board could not be milled
• Parts couldnt be soldered on milled board
• Coding
• LCD screens
• Parameter Changes
• Saving User Settings

38
Try and finish

• Still going to try and get the main board milled
  again
• Solder on all the parts
• Test the board

39
Gantt Chart
40
Budget
41
References

• 1.http//www.geocities.com/gitaarwerk/fxexp/reverb
  /Reverb.htm
• 2.http//www.digit-life.com/articles2/theoryofreve
  rb/
• 3.http//www.ti.com
• 4.http//users.chariot.net.au/gmarts/fx-desc.htm
  Cho
• 5.http//users.iafrica.com/k/ku/kurient/dsp/effect
  s.htmltimedelay
• 6. DAFX-Digital Audio Effects,
• Dr. Brian Nutter