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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