Angad Bector Joel Spadin Ruichen Zhao MIDI CONTROLLED SLIDE GUITAR Group 4 ECE 445 Senior Design April 29, 2013

 Single-stringed, robotic slide guitar  Control via MIDI data for real-time performance or playback of prerecorded performance  Digital audio effects  Simple, modular design:  MIDI input  Motor control and mechanical systems  Audio processor INTRODUCTION

 Entertainment  Education  MIDI allows musicians to play guitar using an instrument they already know MOTIVATION

 Safety  Moving parts  High voltages  Credit contributions ETHICAL ISSUES

SYSTEM OVERVIEW

 sbRIO 9632  400 MHz processor  FPGA with 40 MHz clock  3.3V digital IO (110 channels)  16-bit analog input (16 differential channels)  Requires 19-30V power supply  Supplies 5V power to digital circuits NATIONAL INSTRUMENTS SBRIO

 120V 60Hz AC input  24V DC output  8A fuse  Originally planned to use two smaller supplies and isolate sbRIO from motors  This supply powerful enough to drive both  Simplifies design POWER SUPPLY

 Receives 5V serial communication  Electrically isolates MIDI source from microcontroller  Passes serial communication to microcontroller  Uses standardized MIDI input circuit MIDI INPUT

MIDI INPUT CIRCUIT

 MIDI messages  Status byte  0 or more data bytes  Running status  Listen for Note On, Note Off, Pitch Bend, and Controller Change messages  Provides note and controller data to motor control and audio processing software MIDI INPUT SOFTWARE

 5V ±10% power supply  Data is reliably transferred  MIDI data is read properly  Note starts, pitches, and velocities  Note ends  Pitch bends  Continuous controllers MIDI INPUT REQUIREMENTS

MECHANICAL SYSTEM

 Pitch slide holds down string to change frequency of string vibration  Driven by motorized belt  Two guitar picks on motorized wheel  Rotate 180° to pick once  Picks must be flexible to avoid shattering MECHANICAL SYSTEM

 Control pitch slide and guitar pick  Minertia Motors F-Series with encoder  5-30V, 1.2A peak current  2000 count optical encoder  Cytron MD10C motor controllers  Bidirectional DC motor driver  14-25V input, 10A max current  Speed control with 10KHz PWM (3.3V or 5V) MOTORS

 Motor speed control with PWM outputs  Motor position feedback with encoders  Used PID controllers  Picking control  Increase setpoint by 180° every pick  Offset from string by 15°  Remove offset to dampen string  Pick on note start  Pick on high velocity notes during legato phrases MOTOR CONTROL

 Pitch control  Calculated conversion from motor rotation to slide position (44.8° per cm)  Calculated conversion from note number (pitch) to slide position for each fret  Linear interpolation for fractional note numbers  Portamento switch for controlled speed of pitch changes  Separate PID gains for smooth movement MOTOR CONTROL

 24V ±5% power supply to motor controllers  Motor controllers function  Can drive motors in both directions  PWM signal varies motor speed  Voltage under load does not drop > 5%  Motor current does not exceed 1A  5V ±10% power to encoders  Encoders report motor positions accurately MOTOR REQUIREMENTS

 Controls guitar picks properly  Rotates once per pick  Does not overshoot and strike string twice  String damping stops string vibration  Controls pitch slide properly  Pitch slide moves quickly and accurately  Pitch slide moves smoothly with small changes and portamento slides  Pitch slide and picking are coordinated MOTOR CONTROL REQUIREMENTS

PICKUP

 Originally planned to build humbucking pickup  Two coils cancel external noise  Preamp to boost signal  Impractical to fabricate  Used commercial guitar pickup with high output impedance (8KΩ)  sbRIO analog input sensitive enough that we did not use preamp PICKUP

 Output signal is large enough to be detected  Output signal does not saturate analog input  Saturation level configurable  Used 200mV level PICKUP REQUIREMENTS

AUDIO SOFTWARE

 Implemented completely inside FPGA  Sampled at 44.1KHz  FPGA has 40MHz clock: 906 cycles per sample  LPF rejects environmental noise  Simple distortion effect  Envelope follower matches signal amplitude to volume from MIDI instrument  Output in Left-Justified format for DAC  Effects controlled by MIDI controllers AUDIO SOFTWARE

AUDIO EFFECTS

LEFT JUSTIFIED FORMAT

 Outputs Left-Justified audio data with proper timing  44.1KHz ±5%  Applies audio effects to input signal  Audio effects respond to MIDI data AUDIO SOFTWARE REQUIREMENTS

 Uses Texas Instruments PCM5100 DAC  Accepts I 2 S or Left-Justified audio data  Supports wide range of sampling frequencies including 44.1KHz  Outputs 2.2V analog signal  5V from sbRIO stepped down to 3.3V for DAC DIGITAL TO ANALOG CONVERTER

DAC CIRCUIT

 3.3V ±10% power supply to DAC  4.4V or greater to voltage regulator  DAC reproduces audio from Left-Justified signal  Sine wave test DAC REQUIREMENTS

 Build array of instruments for polyphony  Soundproofing to reduce mechanical noise  Enclose circuits for safety and aesthetics  Preamp on pickup for better input resolution  Power amplifier for output volume  Humbucking pickup to reduce environmental noise  Dedicated DSP or more powerful processor for audio effects FUTURE WORK

 Responds quickly to real-time input  Picking and small pitch changes work reliably up to 16 th notes at 120bpm (0.125Hz)  Can pick 2,147,483 times before encoder position overflows (3 days of continuous picking)  Could increase to 9.22×10 15 picks by using 64-bit integers (36 million years) SYSTEM PERFORMANCE

 David Switzer and Scott McDonald (ECE Machine Shop)  Mark Smart, Wally Smith, Skot Wiedmann, and Dan Mast (ECE Electronics Service Shop)  Kevin Colravy  Prof. Scott Carney and Mustafa Mukadam  National Instruments  Texas Instruments CREDITS

 Software Credits  National Instruments  Christian Loew: FPGA FIR filter  Navarun Jagatpal, Fred Rassam, Young Jin Yoon, Elton Chung: FPGA distortion effect  Bram (musicdsp.org user): envelope follower algorithm CREDITS

THANK YOU