Effects Pedal Management and Routing System

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Dec 10, 2013 (3 years and 8 months ago)

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Western Washington University

Electronics Engineering Technology

May 9, 2013



Effects Pedal Management
and Routing System

Hardware

Description

Trevor Owen


Effects Pedal Management and Routing System



Page
1


I.

INTRODUCTION

The guitar pedal router management system is
a device that will allow the user to have
complete control over their effects pedals. It will be a portable system will consist of the
main unit that the pedals plug into and the foot switch module that will connect to the main
unit by a cat5 cable. The
cat5 will also supply the foot switch module with power. The
power for the whole system will be provided by a wall

wa
rt power supply that will

connect

by a 5 pin din connector to the main unit.

II.

POWER SUPPLY

The power requirements for the system will be +/
-
12V and

5V. This will be provided by
w
all

wa
rt power supply that t
akes in a voltage of 120V at 60Hz
. The supply will provide the
voltages needed for the whole project. The amperage levels of the supply are

+12V at 1A,
the

-
12V at .5A
,

and the 5V at 3A.

There will also be a LE33CZ
-
TR

voltage regulator to take
the 5V and regulate it down to 3.3V for the RN
-
41 Bluetooth module.


III.

AD8113

The AD8113 is a 16x16 switch matrix for audio and video signals. To differentiate
between

the two
types of signals the
chip is either supplied with +/
-
12V for audio or +/
-
5V
for video. Since audio is the signal type that this project deals with +/
-
12V will be used. The
chip will have decoupling capacitors of the value .01uF on all the input +/
-
12V pins. The
way the AD81
13 is programmed is by SPI interface coming from the micro controller. There
will be a header for the signals to be sent from the microcontroller to the AD8113. There
will be resistors on these data lines to clean up the signals. During testing it was d
iscovered
that there were some spikes on the clock signal and several of the enable signals. To take
these down 220 ohm resisto
r
s are placed in series to cut down on the reflections that are
caused by the signa
ls hitting high impedance pins

on the AD8113.


There are a total of 16 inputs and 16 outputs on the device, but only 6 of each will be
needed for the system.
To prevent any noise from being introduced by unused input and
output pins they will be tied to ground through 75 ohm resistors
. This is sho
wn in the
datasheet for the device and was also confirmed through conversation with the Analog
Devices technical support team.

Effects Pedal Management and Routing System



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For the
used inputs the only one that is not going to be directly connected to an input is
the guitar input. This pin will be co
nnected to the output of the filter and amplifier that will
be discussed later.

For the outputs of the device they will have to go through a voltage divider that simply
cuts the gain in half. The device contains amplifiers on all of the channels and whe
n a signal
is sent through the chip it will come out on the output with a gain of 2. By using a simple
voltage divider using two 1K ohm resistors the gain is then negated. The output that goes to
the amplifier has a voltage divider, but it is different i
n that it negates the +2 gain from the
device, but it also negates the gain from the amplifier when the signal is input into the
device. Since the gain from the amplifier is +25 the voltage divider on the amplifier output
will be made up of a 1K ohm resis
tor and a 27k ohm resistor.


IV.

AMPLIFIER

I will be connecting directly to the guitar through a ¼” mono jack and this will be sent to
the AD8113 to be routed to the effects pedals and then sent out to the amplifier. The signal
that will be coming in will be
a very small signal around the magnitude of 60mV
-
200mv.
This signal needs to be amplified to be able to be sent through the AD8113 successfully. A
non
-
inverting amplifier will be used using the LM833 audio op
-
amp chip. This op
-
amp was
chosen because it
has a wide dynamic range (> 140dB), low input noise voltage, high slew
rate, high gain bandwidth product, and low distortion.

The gain I chose to use was a + 25 to get the voltage up around 5V which will be more
than enough to be accepted by the AD8113.

V.

FILTER

A low pass filter will be implemented using the LM833 audio operational amplifier chip.
This package comes in a DIP package and will be used for the low pass filter and the
amplifier which will be discussed next. The LM833 is beneficial for

this a
s one chip can be
used since two operational amplifiers exist on one chip.

The filter will be implemented as a Sallen
-
Key low pass filter with a cutoff of around 1.7
KHz.
The value for the cutoff was chosen based on removing noise that the guitar pickup
s
will introduce, but trying to preserve as much of the original guitar signal as possible. I did
not want to alter the guitar signal in anyway other than clean it up so that no noise would
be amplified in the AD8113 or in the non
-
inverting amplifier.




Effects Pedal Management and Routing System



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VI.

FOOT CONTROL MODULE

The foot control module will contain all the foot switches for the user to interact with
the pedals that are connected in the system. This will be connected to the main module by
a cat5 cable. The cat5 cable will carry the supply
voltage and ground to th
e foot module.
The cat5 cable will also carry all the signals needed by the shift registers that handle
capturing the foot switch presses and set the LEDs on the foot module. This works by daisy
chaining two 74HC595 serial in para
llel out shift registers with two 74hc165 parallel in serial
out shift registers.

The microcontroller will communicate with the foot module using SPI communication.
Three of the lines on the cat5 cable

will be the MOSI, MISO and CLK signals for the SPI
co
mmunication. To perform the communication the microcontroller will shift in two bytes
of data for the 74HC595 shift registers telling them the state of the LEDs. As this is being
shifted in the 74HC165 shift registers will be shifting out the status of t
heir switches. It is
designed to be a wrap around system where one bit is being shifted out and one is being
shifted into the microcontroller.


The LEDs for the foot module will be bi
-
color to let the user know when a switch has
been selected. To accompl
ish this two 74HC04 inverters must be used. The signal coming
from the 74HC595 shift registers will be sent out and go through a current limiting resistor
before it reaches the inverters. The signal will then go into the invert which is fed to the red
LE
D anode. The signal before the inverter is also fed to the
green LED anode. Depending
what is sent out by the 74HC595 will determine what color is used. A one will turn the
green LED on and a 0 will turn the red LED on.

The 74HC165 shift registers will
be connected to the momentary SPST switches that
when pressed will connect the pins to 5V and set the shift register pin high. When it is not
being pressed there will be a 1K pull down resistor to make sure the pin is low and not
floating whe
n the shift r
egister is queried by the microprocessor.


VII.

MICRO CONTROLLER


The microcontroller I chose f
or this project was the CY85368AXI
-
106

P
soC
5 with a ARM
Cortex M3 from Cypress Semiconductor. This microcontroller was chosen for familiarity
and because it prov
ides

all the SPI and UART
communication necessary with built in
features
. The PsoC5 is a 32
-
bit bus system that has a maximum operating frequency of
67MHz. It has 256Kb of Flash memory, 64Kb of SRAM, and 2Kb of EEPROM.
The memory of
Effects Pedal Management and Routing System



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4


the device was a large r
eason for selecting it. Since there will be presets for the user to
choose from these will have to be stored in memory for fast recall.
The microcontroller will
be power by 5V for simplicity of the system even though it could be power on 3.3V or 1.8V
as
well.

The PsoC
5 will provide 6
0

GPIO pins that can be configured for the project. Only 13 of
these pins will be needed, but with the amount of pins available it will be
convenient

to
have so many selections when setting up the board. Besides the power
connections the
device only requires several decoupling capacitors on the power inputs. The device will
come in a TQFP 100 pin surface mount package.

The PsoC5 has digital and analog blocks present. I will be using several of the digital
blocks to imple
ment two SPI modules for communicating
with the foot switch module and
the AD8113. The other digital block that will be used is for the UART for communication
with the Bluetooth module that is linking the microcontroller to the android user interface.




VIII.

USER INTERFACE

The user interface will be done completely in Android for mobile devices. This will interact
with the system using the Roving networks RN
-
41
Bluetooth module. This will
communicate

with
the

microcontroller using UART and based on the state

determined by
the interface the microcontroller will know what state to put itself into and what part of the
hardware to interact with.