Download Circuit Description of Effects Box

Circuit Description of Effects Box/Tuner
Lon Johannes
Etec 474
Spring 2002
Circuit Description – Effects Box
Table Of Contents
General Description……………………….
Circuit Description………………………...
Power……………………………...
Ground…………………………….
Microcontroller……………………
Crystal……………………………..
Reset……………………………….
BDM……………………………….
Input……………………………….
Guitar Tuner……………………….
Sound Effects……………………...
Distortion………………….
Reverberation……………...
Auto-Wah………………….
User Interface……………………...
PDA………………………..
Volume…………………….
Sound Effects Enabling……
Output……………………………...
Memory Map………………………………
Parts List…..………………………………
Schematic………………………………….
Pg. 2
Pg. 2
Pg. 2
Pg. 2
Pg. 2
Pg. 2
Pg. 2
Pg. 2
Pg. 2
Pg. 3
Pg. 3
Pg. 3
Pg. 3
Pg. 3
Pg. 4
Pg. 4
Pg. 4
Pg. 4
Pg. 4
Pg. 5
Pg. 6
Pg. 7
1
Circuit Description – Effects Box
2
GENERAL DESCRIPTION
This project is a tool used by amateur musicians. It performs two main functions. The
box adds sound effects to an electrical guitar signal and can be used to tune a guitar. The
effects box consists of three different sound effects: distortion, reverberation, and autowah. The effects are controlled with an optional expression pedal and foot switch. The
Effects Box/Tuner interfaces with a personal digital assistant (PDA).
CIRCUIT DESCRIPTION
Power
The Effects Box/Tuner is powered through a wall transformer that supplies 9Vdc and 1A.
SW1 connects and disconnects the circuit from the power source. A 7805 voltage
regulator supplies 5V while 9V is taken from the wall transformer. To reduce noise from
the wall transformer the supply has two capacitors (C20, C21) shunted to ground.
Ground
The Effect Box/Tuner consists of analog and digital components. To reduce noise there
are two ground plains that are separated at the power supply. All the analog components
are connected to the analog ground while the digital components are connected to the
digital ground.
Microcontroller
The microcontroller is the MC68HC912B32. It is a 16-bit microcontroller unit (MCU)
composed of standard on-chip peripherals. MC68HC912B32 has 32-Kbyes of FLASH
electrically erasable; programmable read only memory (EEPROM), 32Kbyte ROM, 768byte and 1K-byte RAM. The peripherals used for the Effects Box/Tuner consist of the
A/D converter, SCI, SPI and Pulse Accumulator. Four general purpose I/O ports are used,
PP0-PP3, for the control of the analog switches (MAX4533).
Crystal
The crystal used to generate the system clock is 16MHz. It is connected in parallel to the
EXTAL and XTAL pins with a 10Mohm resistor (R50). It also has two 24pF capacitors
(C27, C28) in series to ground from each pin.
Reset Circuitry
Low-voltage detection is performed by the MC34064 (U7). It detects if the power supply
falls below +4.5V and pulls the /RESET pin low.
BDM
To interface with the 68HC12 a 2x6 header (J5) is connected to power and the BKGD
pin. It allows the programming of the flash memory and debugging.
Input
A guitar is connected to the box through a ¼ in. jack socket (J1).
Circuit Description – Effects Box
3
Guitar Tuner
The hardware for the guitar tuner consists of an op-amp (LM324, U5A), a voltage
comparator (LM311, U6) and a pulse accumulator. The signal from the guitar has an
amplitude range from 0 to 30mV so the LM324 conditions the signal for a range of 0 –5V
to match the input level need for the LM311. The output of the op-amp is fed into the
negative input of the voltage comparator. A voltage of 1.5 volts is put on the positive
input of the voltage comparator with a voltage divider. The output from the voltage
comparator goes low whenever the guitar input exceeds 1.5V, creating a pulse train at the
fundament frequency. This frequency is fed into the pulse accumulator on the HC12.
Sound Effects
Distortion
The distortion sound effect is a diode clipping circuit. The guitar signal is fed through a
high gain transistor (Q1) and two diodes (D1, D2) that clip the signal on the positive and
negative peaks.
Reverberation
The reverberation circuit is an echo-reverb kit by Cana-Kits. It is based off the NTE1641
(U3), which is a 1024 stage bucket brigade delay chip. Bucket brigade chip adds delay to
a signal by passing the input signal through a number of circuit cells that introduce a
small delay. The total delay is dependent on the total number of cells and the clock
frequency. The NTE1639 (U4) is used to drive the bucket brigade chip giving a delay of
51ms. The whole circuit works by passing the input signal through two multiple feedback
low-pass filters (U1A, U1B) that condition the signal for the NTE1624. The NTE1624
then outputs two signals, the original from pin 7 and the delayed from pin 8. The two
signals are passed through a resistor-summing network (R15-18) and filtered through two
more multiple feedback low-pass filters (U2A, U2B). The feedback that is sent to the
input and the time that it takes for the echoes to die out is adjusted through a 20Kohm
potentiometer (R27).
Auto-Wah
A Danelectro auto-wah foot switch produces the auto-wah sound effect. Auto-Wah sound
effects also commonly called envelope-controlled filters. The effect shapes the tone of
the signal in response to the amplitude. The signal is passed through a envelope detector
that produces A DC voltage that corresponds to the overall amplitude of the input signal.
The voltage is used to control the cutoff frequency of a bandpass filter. As the signal
varies in amplitude or the guitarist strums harder or softer, the pass band of the filter
varies up and down creating the desired wah effect.
Circuit Description – Effects Box
4
User Interface
PDA
All of the visual aspects of the user interface are done through a PDA. The SCI is used to
interface the HC12 and the PDA. The SCI is configured at a baud rate of 9600bps. The
HC12 and PDA are connected with a 9PIN male (P3) and female (J6) serial connectors.
Volume Control
The volume of each sound effect can be adjusted independently. To adjust the volume the
signals are sent through a 100Kohm potentiometer and the output is taken from the wiper
to analog ground. A DS1806 (U8) is used so the adjustments can be done through the
HC12. The DS1806 is controlled by the SPI and pins SS, SCK, MOSI. The user either
adjusts the volume through the PDA or uses an expression pedal. The expression pedal is
connected to the A/D converter through a ¼ in. jack and socket (J3, P2). The high voltage
reference for the A/D converter is set through a voltage divider (R39, R40) that feeds the
maximum voltage that can be dropped over the expression pedal or 4.5V.
Sound Effects Enabling
To turn on and off the sound effects a digital switch is used (MAX4533, U10). The
MAX4533 is a quad SPDT switch that is control through ports PP0-PP3 on the HC12.
The user can either toggle the sound effects through The PDA or a foot switch. A foot
switch is connected with a ¼ in. jack and socket (J2, P1) to port PS2 on the HC12.
Output
When more then one effect is enabled the signals have to be mixed. This is done with an
op-amp (LM324, U5B) in a unity gain, summing configuration. A 3.3V reference voltage
is fed to the positive input with resistors R47 and R48, so the full analog signal can be
passed. The output of the op-amp is connected to a ¼ in jack (J4).
Circuit Description – Effects Box
5
Memory Map
The HC12 is configured in the normal single-chip mode. The bus system is not available
externally and PORTA and PORTB can be used as general inputs or outputs. The
interrupt and reset vectors must be loaded into the Flash EEPROM since they are located
from $FF00 to $FFFF.
$0000
Internal Registers
$01FF
$0200
Unused
$07FF
$0800
On-Chip RAM
$0BFF
$0C00
Unused
$0CFF
$0D00
$0FFF
0
$1000
Byte-Erasable
EEPROM
Unused
$7FFF
$8000
Flash EEPROM
(Enabled)
$FFFF
Memory Map for Normal Single–Chip Mode
Circuit Description – Effects Box
Parts List
Item
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
Quantity
1
1
1
5
2
2
2
2
4
2
2
2
1
2
1
3
1
1
1
1
2
1
1
4
1
2
3
1
3
3
1
1
1
3
1
1
Part Description
Resistor - 2.4Kohm 1%
Resistor - 6.8Kohm 1%
Resistor - 10Kohm 1%
Resistor - 120Kohm 1%
Resistor - 33Kohm 1%
Resistor - 220Kohm 1%
Resistor - 43Kohm 1%
Resistor - 39Kohm 1%
Resistor - 100Kohm 1%
Resistor - 5.6Kohm 1%
Resistor - 56Kohm 1%
Resistor - 47Kohm 1%
Resistor - 15Kohm 1%
Resistor - 500ohm 1%
Resistor - 2.8Kohm 1%
Resistor - 1Kohm 1%
Resistor - 1Mohm 1%
Resistor - 2.2Mohm 1%
Resistor - 680ohm 1%
Resistor - 10Mohm 1%
Resistor - 5.49Kohm 1%
Resistor - 50Kohm 1%
Resistor - 2Kohm
1%
Resistor - mixer in
Resistor - mixer feed
Potentiometer - 20Kohm, Linear
Electrolytic capacitor - 4.7uF/25V, Radial
Electrolytic capacitor - 47uF/25V, Radial
Ceramic disc capacitor - 220pF
Tantalum capacitor - 4.7uF/25V
Polystyrene capacitor - 0.0018uF
Polystyrene capacitor - 0.0022uF
Polystyrene capacitor - 0.0027uF
Polystyrene capacitor - 0.0033uF
Electrolytic capacitor - 2.2uF/25V, Radial
Polystyrene capacitor - 0.001uF
9
Electrolytic capacitor - 0.1uF/25V, Radial
38
39
2
Ceramic disc capacitor - 24pF
5
Electrolytic capacitor - 0.33uF/25V, Radial
40
41
42
43
44
1
1
1
1
1
Crystal - 16MHz
Wall Transformer - 120VAC/9VDC
IC - LM324 Quad Op-Amp, 14DIP
IC - NTE1641 1024 Stage BBD, 8DIP
IC - NTE1639 CMOS Clock Generator, 8DIP
Designators
R26
R25
R24
R23,R14,R5,R28,R6
R22,R13
R29,R10
R7,R19
R20,R21
R8,R9,R15,R18
R16,R17
R11,R12
R31,R2
R30
R36,R51
R37
R38,R41,R47
R35
R1
R3
R50
R39,R42
R40
R48
R43,R44,R45,R46
R49
R4,R27
C3,C6,C17
C11
C7,C10,C15
C5,C16,C19
C12
C13
C14
C4,C8,C9
C6
C18
C1,C2,C20,C35,C23,
C24,C25,C26,C34
C27,C28
C29,C30,C31,C32,
C33
X1
T1
U5
U3
U4
6
Circuit Description – Effects Box
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
1
1
1
2
1
1
1
1
1
1
1
2
4
1
1
1
2
1
1
1
1
IC - DS1806 Digital Sextet Potentiometer, 20DIP
IC - LM311 Voltage Comparator, 8DIP
IC - MC68HC912B32 MCU 80-PIN QFP
IC - NTE1529 Dual Op-Amp, 9SIP
IC - LM7805 Series Voltage Regulator, TO-220
IC - MAX562 Series Interface, 28-PIN SO
IC - MC3406P5 Low Voltage Detector
IC - MAX4533 SPDT Analog Switch, 20SSOP
Transistor - 2N3904
Diode - 1N34A, 100V, 100mA REC
Diode - 1N4001, 50V, 1A REC
Diode - 1SS119
1/4 inch Jack Socket
BDM 6PIN Connector
9PIN Serial Connector, Female
9PIN Serial Connector, Male
1/4 inch Jack
Switch - Push-to-Make
Expression Pedal
Foot Switch
PDA
U8
U6
U11
U1,U2
U12
U9
U7
U10
Q1
D1
D2
D3,D4
J1, J2, J3, J4
J5
J6
P3
P1,P2
SW1
7