Instructable Posted and Final Thoughts

Our Instructable can be found by clicking the Instructable tab in the top right corner of the page or by clicking the menu drop-down button and selecting Instructable.

This project has been a great learning experience for us. It gave us hands-on experience working with signals that we learned how to manipulate in class as well as gave us insight to what Senior Design will be like next year. We encourage all that come across our site to try and build a system like this on your own and gain some practical knowledge.

Revised Circuit Schematic

Since our group has elected to use an audio jack as our input signal for our circuit instead of the microphone with built in amplifying circuit, we have had to revise the circuit schematic we will use. Here is our revised circuit schematic. In this schematic, the audio signal is put through an Op Amp to amplify the signal to 5V peak to peak, then a DC offset circuit so that the signal is centered around 2.5V instead of 0V.


Circuit Schematic

For our guitar tuner, our group elected to utilize an Elegoo Uno, an LCD screen, and a microphone amplifier with adjustable gain. The circuit diagram for our guitar tuner can be seen below.


The microphone we purchased has an Op Amp built in that we can manually adjust the gain to. The microphone will take in the sound played by a guitar, then output a voltage signal that the Elegoo reads and then associates with a fundamental frequency. After associating this signal with a fundamental frequency, the Elegoo associates the frequency with a string and outputs the name of the string on the LCD screen. Below is a picture of our circuit hooked up.


Meeting: 4/13/17


  • Prototype uses a for loop to play notes and display them on LCD screen for testing. Can be seen below:
    • Range of notes is 0-400 Hz
  • Discussed using FFT algorithm to convert signal from an array of voltages to an array of frequencies.
  • We will be referencing this project for converting our input voltages to output frequencies.
  • Our plan for the remainder of the week is to review Eric’s code, it is written in Java for an Arduino, and change it so that it fits our needs.
  • We will regroup Monday afternoon for a few hours and attempt to implement this code. We would like to test the final project with an actual guitar for the presentation.

Learning to Work with Arduino

Over the last few weeks I’ve spent some time trying to learn about Arduino. I began by working to get text to output to a 16×2 LCD screen. Thanks to a wealth of resources out there for Arduino based projects, this wasn’t too hard.

LCD screen showing the team name

Next I wanted to see if I could use a microphone to get an audio signal into the Arduino. One thing to note is that the Arduino analog ports only handle signals between 0 and 5V and a microphone will input both positive and negative values. To fix this you need to build an amplifier circuit with a DC offset and place it between the microphone and Arduino. Here is a video of the sample signal showing on the Arduino serial plotter.

We’re now working to implement code that will identify the fundamental frequency of our signal and output it to the LCD screen. I’ve been looking into a method called the Fast Hartley Transform, a variant on the Fast Fourier Transform, which works only with real data as opposed to real and complex data. More information on the Hartley Transform can be found here:

Arduino FHT – Open Music Labs


Some Basic Concepts

For our EE 421 group project we will be designing a guitar tuner that can determine different strings based on a sound input. There are many parts to this and as we go we will try our best to explain everything in a concise manner. The following post talks about the basic ideas of sound waves along with some other information that may be helpful to know.

A sound wave is caused by a vibration given off by an object moving through some static medium. This medium could be air, water, or anything that allows this wave to pass through it. The vibrations given off by the object, which in our case is going to be the plucking of different guitar strings, creates disturbances in the particles of the medium causing them to move back and forth. These disturbances through the air also create varying fields of high and low pressure that move the particles, which are known as pressure waves. In a sense a sound wave is also a pressure wave. The motion at which the air particles are moving back and forth is called the frequency of the signal.


The standard definition of frequency is the number of occurrences of a repeating event per unit time. In our case the sound wave frequency will be how often the particles of air vibrate when a sound wave from the vibration of the guitar strings passes through the air. A common measurement for frequency is Hertz (Hz). We define a Hertz to be:

1 Hertz = 1 vibration / second

As the sound wave moves through the air each particle has a domino effect on the other particles, meaning that once the first particle begins to vibrate at a certain Hertz it causes the particle right next to it to vibrate at that same Hertz. This continues until there is an obstruction that blocks this from occurring. This chain of particle vibrations is what allows us to hear the sound once the guitar string is plucked. Our eardrum can detect the changes in air pressure caused by the sound/pressure waves emitted from the guitar strings. Humans are capable of detecting sound waves with a wide variety of frequencies, generally from around 20 Hz to 20,000 Hz. Anything above or below that we cannot hear!

The pitch of a sound is directly related to the frequency at which the sound wave is traveling. A high-pitched sound will come from a high frequency sound wave and vice versa, a low pitch sound corresponds to a low frequency sound wave.


Using a guitar for an example, when the bigger, heavier strings are plucked it will vibrate slowly creating a low pitch. When a thinner, lighter string is plucked it will vibrate quickly and give off a higher pitch. Another example of this is when we talk! The sounds that come out of our mouth when we speak are caused by our vocal cords vibrating in our throat. Depending on how much air we force past our vocal cords determines the loudness and pitch of our voice.

The last thing I want to talk about in this post is the tone of a sound, specifically a musical tone since we are going to be using different guitar strings to demonstrate our project. A musical tone consists of many parts, the duration, pitch, intensity, and timbre. We spoke about pitch above, the duration of the tone is how long it lasts, the intensity is how loud the tone is, and timbre is the quality of the sound. Depending on the type of tone you are looking for some of these categories can vary. For example, a simple tone will only have one frequency but can vary in intensity. A complex tone is made up of two or more simple tones and can vary in more than one category.

Differences between pitch, frequency and tone

Pitch is each person’s subjective perception of a sound wave.  Pitch can be classified as high or low depending on the frequency. A high pitch sound wave corresponds to a high frequency sound wave while a low pitch sound wave corresponds to low frequency sound wave. On a guitar with a big heavy string will vibrate slowly and produce a low pitch while on a guitar with a lighter string will vibrate faster and create a high pitch. Sound waves themselves do not have pitch, their oscillations can be measured to obtain a frequency.

Frequency of a wave refers to how often the particles of a medium vibrate when a wave passes through the medium. Frequency is measured in Hertz. Pitch can be determined only in sounds that have a frequency that is clear and stable enough to distinguish from noise. Pitch is closely related to frequency, but the two are not equivalent. Frequency is an objective, scientific attribute that can be measured while pitch is a subjective attribute

Tone refers to the quality of sound. A singer or flautist can produce a perfectly pitched G sharp, but if the tone quality is poor, what results may sound dull or weak. Tone is commonly used by musicians as a synonym for pitch.