EGAFT Electronic Guitar Audio Frequency Tuner Eric Nelson & Peter Sulcs September 23, 2003.

EGAFTElectronic Guitar Audio

Frequency Tuner

Eric Nelson & Peter SulcsSeptember 23, 2003

Project ObjectivesProject Objectives

Design and build a device that will automatically tune a guitar

Once setup, it operates hands-free

SpecificationsSpecifications

ResolutionThe tuner will know the strings’

frequencies to +/- 2 cents or +/- 0.12%Accuracy

A tuned guitar’s strings will tested for accuracyagainst a store-bought tuner.

RangeRange

70Hz – 500Hz Covers just below low E (82.41Hz)

and just above high E (329.63Hz)

How does it work?How does it work?

Four subsystemsStrummerPeg TunerFrequency AnalyzerController

StrummerStrummerEasily attaches to

guitar with suction cups

Stepper motor belt drive

Plucks one stringMutes all other

strings

Strummer – Pick ShuttleStrummer – Pick Shuttle

Reliable feedback through micro switches

StableHigh precision: .022”

per Step

Strummer - Back RailStrummer - Back Rail

Stabilizes pick shuttleSupports the damper wireLocation of shuttle travel end stops

Peg Tuner DetailPeg Tuner Detail

Rubber coated binder clipTwo interlocking pins

Peg Tuner ConfigurationPeg Tuner Configuration

Servos are positioned to fit guitarRubberized Aluminum plates bolt togetherStraps attach over guitar headstock

Peg TunerPeg Tuner

Controlled by modified servo motorsUses special MUX (dubbed SpMUX)

EN S2 S1 S0 Y7 Y6 Y5 Y4 Y3 Y2 Y1 Y00 0 0 0 W W W W W W W X0 0 0 1 W W W W W W X W0 0 1 0 W W W W W X W W0 0 1 1 W W W W X W W W0 1 0 0 W W W X W W W W0 1 0 1 W W X W W W W W0 1 1 0 W X W W W W W W0 1 1 1 X W W W W W W W1 d d d W W W W W W W W

Frequency AnalyzerFrequency Analyzer

Electric guitars have an output jackA sound wave of a given frequency

is a nice sine wave


A nice sine wave can be convertedto a nicer square wave with a TTL-compatible comparator


The HCS12 can calculate the timebetween edges using it’s timer

This is the string’s periodBut is the HCS12’s timer fast enough

to give adequate precision?


The reading is skewed when the inputand timer are not synchronized


CLK

2string

measuredstring, f

fΔf

fCLK = 250 kHz

fstring Error (Hz) Error (Cents)

500 1 3.46

200 0.16 1.38100 0.04 0.69


This problem is fixed by counting timeover multiple periods.


TCLK = 100kHz

Periods fstring Error (Hz) Cents Periods fstring Error (Hz) Cents

1 2000 40 34.28 11 2000 3.64 3.142 2000 20 17.23 12 2000 3.33 2.883 2000 13.33 11.50 13 2000 3.08 2.664 2000 10.00 8.63 14 2000 2.86 2.475 2000 8.00 6.91 15 2000 2.67 2.316 2000 6.67 5.76 16 2000 2.50 2.167 2000 5.71 4.94 17 2000 2.35 2.048 2000 5.00 4.32 18 2000 2.22 1.929 2000 4.44 3.84 19 2000 2.11 1.8210 2000 4.00 3.46 20 2000 2.00 1.73

CLK

2string

measuredstring, f * Periods

fΔf


Easy! Now, just

hook up the output to the guitar jackAdmire the perfect sine wavesit backrelax


Frequency Analyzer - FilterFrequency Analyzer - Filter

Frequency Analyzer - FilterFrequency Analyzer - Filter

Frequency Analyzer - Amplifier

Frequency Analyzer - Amplifier

System Block DiagramSystem Block Diagram

Division of WorkDivision of Work

Electrical system – EricMechanical system – Peter

Electrical PlanElectrical Plan

Completed workResearched ideas for Frequency AnalyzerMade 5 Servos ConsistentBuilt 1 Circuit for Frequency AnalyzerBought all partsWrote PAL SpMUX code

Electrical PlanElectrical Plan

Work to do:Program SpMUXBuild rest of Frequency Analyzer circuitsWrite code for each subsystemInterface everythingTest everything

Mechanical PlanMechanical Plan

Completed workDevelop firm design planCAD drawingsBought all parts

Mechanical PlanMechanical Plan

Work to do:Build StrummerBuild Peg TunerInterface everythingTest everything

Test PlanTest Plan

Unit testing is most important!Integration testing will happen between

First between Peg Tuner and Frequency AnalyzerThen Peg Tuner/Frequency Analyzer combo. With

StrummerThe last two weeks before project is due

are reserved for verification testing.

Power ConsumptionPower Consumption

All Electrical Components Rated at 5VExcept Op-Amps at +/- 5V


Device Max Current Typical Current

Servo Motors (6) 200mA (Full Load) 80mA (Slow Speed)10mA (off)

Stepper Motor 1.2A 0.55A (Moving)0A (Off)

Stepper Driver ON – 84mAOFF – 24mA

ON – 32mAOFF – 18mA


Device Max Current Typical Current

HCS12 100mA 100mA

Op-amps (19) 2.8mA 1.4mA

Comparators (8) 4mA 2.5mA

PAL 155mA 50mA


Steady State Current – <500mAServos 60mA Stepper 0AStepper Driver 24mAHC12 & PAL 255mASignal Conditioning 112mA


Peg Tuner In-Action Current – <700mAServos 250mA Stepper 0mAStepper Driver 24mAHC12 & PAL 255mASignal Conditioning 112mA


Strummer In-Action Current – <1100mAServos 60mA Stepper 550mAStepper Driver 84mAHC12 & PAL 255mASignal Conditioning 102mA


‘D’ Battery lasts 18,900 mA-Hours Source: Energizer.com

Maximum Life – 36 hoursMinimum Life – 17 hours

System Cost - ElecticalSystem Cost - ElecticalPart Quantity Retail Price

(ea.)

HCS12 1 $150

LM393 Comparators 4 $1

L293D Stepper Driver 1 $2

MAX4239 Op-amps 19 $0.60

Micro Switches 4 $0.26

System Cost - MechanicalSystem Cost - MechanicalPart Quantity Retail Price

(ea.)

Servos 6 $10

Stepper Motor 1 $3

Belts/Pulleys/Suctions cups - $24.68

Raw Material (Rubber sheeting, Aluminum)

- $20

Hardware (Bolts, Screws) - $30

Safety PrecautionsSafety Precautions

No danger of excessive heat or voltageLargest risk is a string breaking

Kill switch built-in to avoid “runaway servo”in event of software crash

EGAFT Electronic Guitar Audio Frequency Tuner Eric Nelson & Peter Sulcs September 23, 2003.

Documents

frequency analyzer slide

strings slide

hz slide

spmux slide

parts slide

handsfree slide

synchronized slide

step slide