Arduino based electric guitar tuner

 / *
 * Arduino Guitar Tuner
 * by Nicole Grimwood
 *
 *
 * Based upon:
 * Arduino Frequency Detection
 * created October 7, 2012
 * by Amanda Ghassaei
 *
 * This code is in the public domain.
* /


// data storage variables
byte newData = 0;
byte prevData = 0;
unsigned int time = 0; // keeps time and sends vales to store in timer [] occasionally
int timer [10]; // storage for timing of events
int slope [10]; // storage for slope of events
unsigned int totalTimer; // used to calculate period
unsigned int period; // storage for period of wave
byte index = 0; // current storage index
float frequency; // storage for frequency calculations
int maxSlope = 0; // used to calculate max slope as trigger point
int newSlope; // storage for incoming slope data

// variables for deciding whether you have a match
byte noMatch = 0; // counts how many non-matches you've received to reset variables if it's been too long
byte slopeTol = 3; // slope tolerance- adjust this if you need
int timerTol = 10; // timer tolerance- adjust this if you need

// variables for amp detection
unsigned int ampTimer = 0;
byte maxAmp = 0;
byte checkMaxAmp;
byte ampThreshold = 30; // raise if you have a very noisy signal

// variables for tuning
int correctFrequency; // the correct frequency for the string being played

void setup () {
  
  Serial.begin (9600);
  
  // LED pins
  pinMode (7, OUTPUT);
  pinMode (6, OUTPUT);
  pinMode (5, OUTPUT);
  pinMode (4, OUTPUT);
  pinMode (3, OUTPUT);
  pinMode (2, OUTPUT);
  pinMode (A3, OUTPUT);
  pinMode (A4, OUTPUT);
  pinMode (A5, OUTPUT);
  pinMode (A1, OUTPUT);
  pinMode (A2, OUTPUT);
  pinMode (8, OUTPUT);
  pinMode (9, OUTPUT);
  
  
  // Beginning LED sequence
  digitalWrite (7.1);
  digitalWrite (6.1);
  digitalWrite (5.1);
  digitalWrite (4.1);
  digitalWrite (3.1);
  digitalWrite (2.1);
  digitalWrite (8.1);
  analogWrite (A1,255);
  delay (500);
  digitalWrite (9.1);
  analogWrite (A2,255);
  delay (500);
  digitalWrite (A5,255);
  analogWrite (A3,255);
  delay (500);
  analogWrite (A4,255);
  delay (500);
  
  
  
  cli (); // disable interrupts
  
  // set up continuous sampling of analog pin 0 at 38.5kHz
 
  // clear ADCSRA and ADCSRB registers
  ADCSRA = 0;
  ADCSRB = 0;
  
  ADMUX | = (1 << REFS0); // set reference voltage
  ADMUX | = (1 << ADLAR); // left align the ADC value- so we can read highest 8 bits from ADCH register only
  
  ADCSRA | = (1 << ADPS2) | (1 << ADPS0); // set ADC clock with 32 prescaler- 16mHz / 32 = 500kHz
  ADCSRA | = (1 << ADATE); // enabble auto trigger
  ADCSRA | = (1 << ADIE); // enable interrupts when measurement complete
  ADCSRA | = (1 << ADEN); // enable ADC
  ADCSRA | = (1 << ADSC); // start ADC measurements
  
  sei (); // enable interrupts
}

ISR (ADC_vect) {// when new ADC value ready
  
  PORTB & = B11101111; // set pin 12 low
  prevData = newData; // store previous value
  newData = ADCH; // get value from A0
  if (prevData <127 && newData> = 127) {// if increasing and crossing midpoint
    newSlope = newData - prevData; // calculate slope
    if (abs (newSlope-maxSlope)  9) {
          reset ();
        }
      }
    }
    else if (newSlope> maxSlope) {// if new slope is much larger than max slope
      maxSlope = newSlope;
      time = 0; // reset clock
      noMatch = 0;
      index = 0; // reset index
    }
    else {// slope not steep enough
      noMatch ++; // increment no match counter
      if (noMatch> 9) {
        reset ();
      }
    }
  }
  
  time ++; // increment timer at rate of 38.5kHz
  
  ampTimer ++; // increment amplitude timer
  if (abs (127-ADCH)> maxAmp) {
    maxAmp = abs (127-ADCH);
  }
  if (ampTimer == 1000) {
    ampTimer = 0;
    checkMaxAmp = maxAmp;
    maxAmp = 0;
  }
  
}

void reset () {// clean out some variables
  index = 0; // reset index
  noMatch = 0; // reset match couner
  maxSlope = 0; // reset slope
}

// Turn off 5 out the 6 LEDs for the guitar strings
void otherLEDsOff (int LED1, int LED2, int LED3, int LED4, int LED5) {
  digitalWrite (LED1,0);
  digitalWrite (LED2,0);
  digitalWrite (LED3,0);
  digitalWrite (LED4,0);
  digitalWrite (LED5.0);
}

// Determine the correct frequency and light up
// the appropriate LED for the string being played
void stringCheck () {
  if (frequency> 70 & frequency <90) {
    otherLEDsOff (2,3,5,6,7);
    digitalWrite (2.1);
    correctFrequency = 82.4;
  }
  if (frequency> 100 & frequency <120) {
    otherLEDsOff (2,3,4,5,6);
    digitalWrite (3.1);
    correctFrequency = 110;
  }
  if (frequency> 135 & frequency <155) {
    otherLEDsOff (2,3,4,6,7);
    digitalWrite (4.1);
    correctFrequency = 146.8;
  }
  if (frequency> 186 & frequency <205) {
    otherLEDsOff (2,3,5,6,7);
    digitalWrite (5.1);
    correctFrequency = 196;
  }
  if (frequency> 235 & frequency <255) {
    otherLEDsOff (2,4,5,6,7);
    digitalWrite (6.1);
    correctFrequency = 246.9;
  }
  if (frequency> 320 & frequency <340) {
    otherLEDsOff (3,4,5,6,7);
    digitalWrite (7.1);
    correctFrequency = 329.6;
  }
}

// Compare the frequency input to the correct
// frequency and light up the appropriate LEDS
void frequencyCheck () {
  if (frequency> correctFrequency + 1) {
    analogWrite (A3,255);
  }
  if (frequency> correctFrequency + 4) {
    analogWrite (A2,255);
  }
  if (frequency> correctFrequency + 6) {
    analogWrite (A1,255);
  }
  if (frequency  correctFrequency-1 & frequency  ampThreshold) {
    frequency = 38462 / float (period); // calculate frequency timer rate / period
  }
  
  stringCheck ();
  frequencyCheck ();
  
  delay (100);
 
}