Introduction: Arduino Guitar Tuner

About: Hey! I am an Electrical Engineer and I love making fun and useful electronics projects. I am also interested in crafts of all sorts. In particular, I enjoy baking and sewing. Check out what I've made!

Build your own electric guitar tuner using the Arduino! I decided to make this because I wanted to experiment with audio input and frequency detection. I used Amanda Ghassaei's method for Arduino Frequency Detection in order to get frequency readings using the Arduino. I used LEDs that light up according to the frequency of the audio input, indicating whether the string being played is sharp, flat, or in tune. This works like any other guitar tuner, but you can make it yourself!

Step 1: What You Need

(x1) Arduino Uno (RadioShack #276-128)
(x1) TL082 Dual JFET Input Op Amp (RadioShack #276-1715)
(x1) 6x4x2" project enclosure (RadioShack #270-1806)
(x6) 5mm Yellow LED (RadioShack #276-021)
(x6) 5mm Red LED (RadioShack #276-041)
(x1) 5mm Green LED (RadioShack #276-022)
(x13) 150 Ohm Resistor (RadioShack #271-1109)
(x2) 9V Battery (RadioShack #23-1134)
(x2) 9V Snap Connector (RadioShack #270-324)
(x1) M-type power plug (RadioShack #274-1569)
(x1) SPST Rocker Switch (RadioShack #275-693)
(x1) 1/4" Mono Audio Jack (RadioShack #274-255)
(x1) Matching Printed Circuit Board (RadioShack #276-170)
(x1) Grid-Style Printed Circuit Board (RadioShack #276-149)
(x3) 100kOhm Resistor (RadioShack #271-1347)
(x1) 22kOhm Resistor (RadioShack #271-1339)
(x1) 10uF Capacitor (RadioShack #272-1025)
(x1) 100nF Capacitor
(x1) 6x4x.125" Acrylic Sheet

Step 2: Drill

Drill a starter hole on the side of your enclosure using a 1/8" drill bit. Drill into the starter hole using a 13/16" spade bit to create a larger hole for the SPST rocker switch. The rocker switch will serve as an on/off switch for the tuner.

Drill a hole beneath the on/off switch hole using a 23/64" bit. This hole is for your audio jack.

Step 3: On/Off Switch

Solder the red end of one of your battery snaps to one of the lugs on the switch and solder a red wire to the other lug of the switch.

Feed the snap and wire through the 13/16" hole in your enclosure and fasten it in place with its mounting nut.

Step 4: Audio Jack

Solder a green wire to the output terminal and a black wire to the ground terminal on the audio jack.

Insert the audio jack in the 23/64" hole you drilled and fasten it in place with its mounting nut and washer. 

Step 5: Power Plug

Take apart the M-type power plug. 

Solder a red wire to the plug's tip terminal, and a black wire to the plug's barrel terminal.

Thread both wires through the black casing and screw the casing back onto the plug.

Step 6: Amplify and Offset

The audio signal coming from the electric guitar needs to be amplified to be about 5V peak to peak and and offset to be centered around 2.5V as opposed to 0V. The signal needs to be between 0 and 5V in order for it to be read by the Arduino's analog pin. It should also have the greatest amplitude possible without clipping in order to get more accurate frequency calculations.

Above is a schematic of the circuit you will need to do this.

I recommend building this circuit on a breadboard and testing it out using an oscilloscope before soldering it together. Your audio input should be the green wire of the audio jack. Connect the black wire of the jack to ground.  Attach your scope probe to the output of the DC offset (where the circuit is attached to A0 on the Arduino). Turn the volume on your guitar all the way up and plug your guitar into the audio jack. Play every string and check on the oscilloscope to make sure your signal is centered around 2.5V and that the signal is close to but does not exceed 5V peak to peak. 

Try running this modified version of Amanda's code for Arduino Frequency Detection to test out the Arduino's frequency calculation. The only thing I have changed from her code is I removed the clipping indicator LED and instead printed "clipping" in the serial monitor whenever the signal clips.  

The serial monitor should print the frequency of the strings being played. The guitar's strings should have the following frequencies:
E - 82.4 Hz
A - 110 Hz
D - 146.8 Hz
G - 196 Hz
B - 246.9 Hz
E - 329.6 Hz

Since the the higher strings have a much lower amplitude signal than the lower strings, it can be tricky to get the frequency detection to work. Amanda's code has a variable called ampThreshold that is the minimum signal amplitude for the Arduino to calculate frequency. For the guitar tuner, the ampThreshold should be high enough that the Arduino calculates the frequency of the higher strings, but also low enough that it does not pick up too much noise from the lower strings. I found that an ampThreshold of 20 works. You have to strum the high strings a bit harder to get the Arduino to pick them up, but the frequency detection works well. You can experiment with other values to get it to work for you. Values ranging from 10 to 30 work okay. For more information on Amanda's algorithm for frequency detection, check out her Instructable: Arduino Frequency Detection.

Step 7: Solder the Chip

Solder the TL082 to the grid-style PC board.

Step 8: Solder the Amplifier and Offset

Solder the resistors for the amplifier and a wire for the output from the amplifier. 

Solder the capacitors and resistors for the DC offset.

Solder wires to the DC offset that will connect to 5V, ground, and A0 on the Arduino. 

Step 9: Solder Power and Input

Solder the red wire on the on/off switch to +VCC (pin 8) on the TL082 chip. Solder the black wire to ground.

Solder the black wire of the other battery snap to -VCC (pin 4) on the TL082 chip and solder the red wire to ground.

Solder the green wire of the audio jack to the positive input of the op amp on the TL082 (pin 3) and the black wire to ground.

Solder the red wire of the power plug to +VCC (pin 8) and the black wire to ground and insert the plug in the Arduino.

Plug the wires for 5V, Ground, and A0 from the DC Offset into the Arduino.

Step 10: Program

Load the following code into the Arduino.

This code contains the frequency detection and controls the LEDs that you will soon add to your tuner.

 * Arduino Guitar Tuner
 * by Nicole Grimwood
 * For more information please visit:
 * 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(){
  //LED pins
  //Beginning LED sequence
  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)<slopeTol){//if slopes are ==
      //record new data and reset time
      slope[index] = newSlope;
      timer[index] = time;
      time = 0;
      if (index == 0){//new max slope just reset
        PORTB |= B00010000;//set pin 12 high
        noMatch = 0;
        index++;//increment index
      else if (abs(timer[0]-timer[index])<timerTol && abs(slope[0]-newSlope)<slopeTol){//if timer duration and slopes match
        //sum timer values
        totalTimer = 0;
        for (byte i=0;i<index;i++){
        period = totalTimer;//set period
        //reset new zero index values to compare with
        timer[0] = timer[index];
        slope[0] = slope[index];
        index = 1;//set index to 1
        PORTB |= B00010000;//set pin 12 high
        noMatch = 0;
      else{//crossing midpoint but not match
        index++;//increment index
        if (index > 9){
    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){
  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){

//Determine the correct frequency and light up 
//the appropriate LED for the string being played 
void stringCheck(){
    correctFrequency = 82.4;
    correctFrequency = 110;
    correctFrequency = 146.8;
    correctFrequency = 196;
    correctFrequency = 246.9;
    correctFrequency = 329.6;

//Compare the frequency input to the correct 
//frequency and light up the appropriate LEDS
void frequencyCheck(){

void allLEDsOff(){

void loop(){
  if (checkMaxAmp>ampThreshold){
    frequency = 38462/float(period);//calculate frequency timer rate/period

Step 11: Create the Front

For my guitar tuner, I chose to laser cut the front of it. I like the look of the white acrylic and the ability to etch the letters and symbols on the front. I have attached a template for the front of the guitar tuner. I used CorelDRAW to create it, but I have also attached it in EPS format.

If you do not have a laser cutter, you can use the normal lid for the enclosure and drill holes into it. Use a 13/64" drill bit and drill six holes for the LEDs indicating which of the six different strings is being tuned and seven holes for the LEDs indicating how sharp or flat the string is. Label the set of six holes with E, A, D, G, B, and E from left to right. Label the middle hole of the set of seven with a triangle pointed toward the hole. Label the rightmost hole with the musical symbol for sharp and the leftmost hole with the musical symbol for flat. 

Step 12: LEDs

Solder LEDs to your matching PC board. Space the LEDs such that they will fit into the holes of your acrylic front piece. An easy way to do this is lay the front piece on top of your PC board and mark the spacings of the holes on your board using a pen. This way, you know exactly where to solder your LEDs. 

Solder a 150 Ohm resistor to the anode of each LED and a wire from that resistor which will go to one of the pins on the Arduino.
I chose red wire for the LEDs indicating whether the string is in tune and green wire for the LEDs that show which string is being played.

Solder the cathodes of the LEDs to ground and solder a black wire to ground. This black wire will connect to the Arduino's ground.

Step 13: Put It Together

Place the front cover of the tuner onto the PC board with the LEDs. 

Connect the wires on the PC board to the Arduino. The following list indicates which LED should be connected to which pin. 

leftmost red LED (most flat)- pin 8
next red LED to the right - pin 9
next red LED to the right - A5
green LED (in tune) - A4
first red LED to the right of the green LED - A3
next red LED to the right - A2
rightmost red LED (most sharp) - A1

Leftmost LED Labeled "E" - pin 2
LED Labeled "A" - pin 3
LED Labeled "D" - pin 4
LED Labeled "G" - pin 5
LED Labeled "B" - pin 6
Rightmost LED Labeled "E" - pin 7

There are also labels on the second image above to help.

The black wire on the PC board should be connected to ground on the Arduino. 

Turn on the tuner and test it out in order to make sure you have your LEDs connected properly.

Step 14: Close It Up

Gently put the front of the tuner onto the front of the enclosure making sure that none of the wires get disconnected.

Screw in the screws provided with the enclosure to fix the front in place.

Step 15: Tune

Plug in your guitar and tune it!

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