Guitar Tuner by using Arduino Uno. How to Diy?

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dondon pramis
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Guitar Tuner by using Arduino Uno. How to Diy?

Mon Sep 17, 2018 11:19 pm

Arduino-Guitar-Tuner-Circuit.jpg
Arduino-Guitar-Tuner-Circuit.jpg (95.19 KiB) Viewed 836 times
Before we move to the electronics, its important to understand the principle behind the build. There are 7 major musical notes denoted by the alphabets; A, B, C, D, E, F, G and usually end with another A which is always at an octave higher than the first A. In music several versions of these notes exists like the first A and the last A. These notes are distinguished each one from their variation and from one another by one of the characteristics of sound known as pitch. Pitch is defined as the loudness or lowness of sound and its indicated by the frequency of that sound. Since the frequency of these notes are known, for us to determine if the guitar is tuned or not, we only need to compare the frequency of the note of particular string to the actual frequency of the note that the string represents.

The frequencies of the 7 musical notes are:

A = 27.50Hz

B = 30.87Hz

C = 16.35Hz

D = 18.35Hz

E = 20.60Hz

F = 21.83Hz

G = 24.50 Hz

Each variation of these notes is always at a pitch equal to FxM where F is the frequency and M is a non-zero integer. Thus for the last A which as described earlier, is at an octave higher than the first A, the frequency is;

27.50 x 2 = 55Hz.

The guitar (Lead/box guitar) usually has 6 strings denoted by the notes E, A, D, G, B, E on open string. As usual, last E will be at an octave higher than the first E. We will be designing our guitar tuner to help tune the guitar using the frequencies of these notes.

According to the standard guitar tuning, the note and corresponding frequency of each string is shown in the table below.
Strings Frequency Notation
1 (E) 329.63 Hz E4
2 (B) 246.94 Hz B3
3 (G) 196.00 Hz G3
4 (D) 146.83 Hz D3
5 (A) 110.00 Hz A2
6 (E) 82.41 Hz E2
The project flow is quite simple; we convert the sound signal generated by the guitar to a frequency then compare with the exact frequency value of the string being tuned. The guitarist is notified using an LED when the value correlates.

The frequency detection/conversion involves 3 main stages;
1. Amplifying
2. Offsetting
3. Analog to Digital conversion(sampling)

The sound signal being produced will be too weak for the Arduino’s ADC to recognize so we need to amplify the signal. After amplification, to keep the signal within the range recognizable by the Arduino’s ADC to prevent clipping of the signal, we offset the voltage of the signal. After offsetting, the signal is then passed to the Arduino ADC where it is sampled and the frequency of that sound is obtained.

The following components are required to build this project:
Arduino Uno x1
LM386 x1
Condenser Mic x1
Microphone / Audio jack x1
10k potentiometer x1
O.1uf capacitor x2
100 ohms resistor x4
10 ohms resistor x1
10uf capacitor x3
5mm yellow LED x2
5mm green LED x1
Normally Open Push Buttons x6
Jumper wires
Breadboard

Here is the complete CODE:

Code: Select all

int buttonarray[] = {13, 12, 11, 10, 9, 8}; // [E2, A2, D3, G3, B3, E4]
// each pin represents a guitar string
// next we create and array with frequencies matching each of the strings above
// such that when 13 is selected the freq matching the note e is selected).
float freqarray[] = {82.41, 110.00, 146.83, 196.00, 246.94, 329.63};//sll in Hz

int lowerLed = 7;
int higherLed = 6;
int justRight = 5;

#define LENGTH 512

byte rawData[LENGTH];
int count = 0;

// Sample Frequency in kHz
const float sample_freq = 8919;
int len = sizeof(rawData);
int i,k;
long sum, sum_old;
int thresh = 0;
float freq_per = 0;
byte pd_state = 0;

void setup(){
  for (int i=0; i<=5; i++)
  {
    pinMode(buttonarray[i], INPUT_PULLUP);
  }
  pinMode(lowerLed, OUTPUT);
  pinMode(higherLed, OUTPUT);
  pinMode(justRight, OUTPUT);
  Serial.begin(115200);
}
void loop(){
  
  if (count < LENGTH) 
  {
    count++;
    rawData[count] = analogRead(A0)>>2;
  }
  else {
    sum = 0;
    pd_state = 0;
    int period = 0;
    for(i=0; i < len; i++)
    {
      // Autocorrelation
      sum_old = sum;
      sum = 0;
      for(k=0; k < len-i; k++) sum += (rawData[k]-128)*(rawData[k+i]-128)/256;
      // Serial.println(sum);
      
      // Peak Detect State Machine
      if (pd_state == 2 && (sum-sum_old) <=0) 
      {
        period = i;
        pd_state = 3;
      }
      if (pd_state == 1 && (sum > thresh) && (sum-sum_old) > 0) pd_state = 2;
      if (!i) {
        thresh = sum * 0.5;
        pd_state = 1;
      }
    }
    // Frequency identified in Hz
    if (thresh >100) {
      freq_per = sample_freq/period;
      Serial.println(freq_per);
      for (int s=0; s<=5; s++)
      {
        if (digitalRead(buttonarray[i])== HIGH)
        {
          if (freq_per - freqarray[i] < 0)
          {
            digitalWrite(lowerLed, HIGH);
          }
          else if(freq_per - freqarray[i] > 10)
          {
            digitalWrite(higherLed, HIGH);
          }
          else
          {
            digitalWrite(justRight, HIGH);
          }
         
        }
      }
    }
    count = 0;
  }
}
Our Circuit Diagram
Arduino-Guitar-Tuner-Circuit-Diagram.png
Arduino-Guitar-Tuner-Circuit-Diagram.png (64.14 KiB) Viewed 836 times
Note:
To tune a particular string, the guitarist selects the string by pressing the corresponding pushbutton and strums the plays an open string. The sound is collected by the amplification stage and passed on to the Arduino ADC. The frequency is decoded and compared. When the input frequency from the string is less than the specified frequency, for that string one of the yellow LEDs come on indicating that the string should be tightened. When the measured frequency is greater than the stipulated frequency for that string, another LED comes on. When the frequency is within the stipulated range for that string the green LED comes on to guide the guitarist.


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