Published May 6, 2016 © MIT

Guitar LEDs

Neopixel LEDs are fitted behind the guitar pickups and illuminate with the rhythm of your strumming allowing for a custom and unique design.

IntermediateWork in progress6 hours2,984

Things used in this project

Hardware components

Particle Photon

LM386N-1 OpAmp

Capacitor 10 µF

Breadboard (generic)

Adafruit NeoPixel Digital RGB LED Strip

Jumper wires (generic)

USB Battery Pack - 2200 mAh Capacity - 5V 1A Output

Software apps and online services

Blynk

Hand tools and fabrication machines

Soldering iron (generic)

Phillips Head Screwdriver (Generic)

Wire Strippers (Generic)

Story

Background

My determination for doing this project stemmed from my hobby of guitar playing first and foremost. Second, I love to be creative and make things unique. This has been a project that I had been planning to do for about 6 months, however not this in depth or challenging. However, with the opportunity my MEGR 3171 Instrumentations class presented me to earn extra credit with a project, I thought this would be a great way to link the classroom to my outside hobbies.

Ideally, the project would allow for neopixel LEDs to be inserted behind the pickups of my guitar, linked to my phone, coded via the photon to display whatever color was desired, and ultimately react to the a strumming pattern to turn on and off.

To begin to explain how this can be done, I'll begin by saying that this was the first Internet of Things (IOT) project I have ever attempted so gaining knowledge on the particle photon was the first challenge presented. The particle website has a great beginner's guide to learn all the basics of the particle photon which I used to get started on my way. Here I learned how to set up my photon with the cloud service particle offers and some basic coding techniques. Here is a link to the particle website's beginners guide for photons.

https://docs.particle.io/guide/getting-started/start/photon/

Circuit

After getting my photon up and running, the next step was to develop the circuit to allow the LEDs to work as needed. This turned out to be a very difficult task as I wanted to be able to create a circuit free of any microphones or sound sensing LEDs. In order to achieve this I began my research and after learning of the all capabilities the photon had, I had an idea in mind.

To begin to explain the circuit set up, I will first explain how passive pickup electric guitars are able to work with amplifiers. Essentially what happens is as the strings on the guitar are plucked and begin to vibrate, a signal is generated from the pickups and relayed throughout the guitar, ultimately out through the output jack of the guitar and into the amplifier. The signal that is being relayed is a voltage that remains steady when none of the strings have been plucked and then oscillates as a sine wave as the strings are plucked. This voltage can be read across the positive and negative terminals of the output jack on the guitar when it is connected to an amplifier.

With this knowledge in mind and the capabilities of the photon I had recently discovered, I figured that an op amp could be used to magnify the voltage readings across the output jack of the guitar and send these values to an analog pin of the photon. The reason the voltages needed to be magnified was due to the fact that guitar pickups only output approximately 100 - 400 mV which would be hard for the photon to distinguish. Using an LM386N-1 Audio Amplifier I was able to enhance the voltage reading by a factor of 20.

Coding

Using the Blynk App that was recommended by a friend I was able to record and visualize the values that the op amp was relaying to the A0 pin on the photon. Within the Blynk App a line chart can be made that will take a reading as little as every 25 ms to create a continuous reading of what the analog pin is reading.

Using this chart within the Blynk App, I was able to determine the resting voltage across the output jack of the guitar. With that value, I was able to develop an if else statement, as seen below in the Guitar LEDs code, that would allow the LEDs to know when they should cut on and off. Essentially how that worked is the photon would take multiple readings every millisecond and if a peak voltage was met, the LEDs would know to turn on. I set this peak value at 2200 because the resting voltage reading was that of 2000 on the A0 analog pin and when strummed, the voltage would oscillate between values of 1300 and 2600. This spike could be seen in the Blynk App and that allowed me to determine an appropriate peak voltage that wouldn't set the LEDs off prematurely.

Blynk App reading Voltage Output on Photon Pin A0

The coding was by far the most difficult part of this project as I had no experience in C++ coding before beginning this project. With the help of the blynk website tutorial, http://docs.blynk.cc/, and the neopixel libraries within the photon build website, I was able to learn enough information to get this project up and running. Thankfully, I had a few friends willing to help out along the way as well.

Videos

Example Code using the Adafruit Neopixels

Neopixels lighting up when strummed

Summary

The end result of this project was very cool and I definitely intend to use photons and neopixel LEDs again soon. I now have a guitar that is unique and different than any I've seen. I hope to continue this project by creating multiple patterns and designs as well as wiring them to both pickups to enhance the visual aspect of the project.

The next step for my project will be fitting the circuit to a breadboard capable of being stored within the small cavity available in the back of the guitar. Luckily, I bought a battery pack capable of powering all the parts needed in this project and one that is able to be housed within the electrical cavity of the guitar. This allows the guitar to be mobile while still enjoying the awesome effect of the neopixels.

Code

Guitar LEDs

#define BLYNK_PRINT Serial
#include "blynk/blynk.h"
#include "application.h"
#include "neopixel/neopixel.h"

SYSTEM_MODE(AUTOMATIC);

#define PIXEL_COUNT 4
#define PIXEL_PIN D0
#define PIXEL_TYPE WS2812B

char auth[] = "0c3266c1e6804327975901f9d36be444";

void colorAll(uint32_t c, uint8_t wait);
void colorWipe(uint32_t c, uint8_t wait);
void rainbow(uint8_t wait);
void rainbowCycle(uint8_t wait);
uint32_t Wheel(byte WheelPos);

Adafruit_NeoPixel strip = Adafruit_NeoPixel(PIXEL_COUNT, PIXEL_PIN, PIXEL_TYPE);

int led = D0;
int boardLED = D7;
int pickupVoltage = A0;


//DEFINE A THRESHOLD VOLTAGE, IF THE ANALOG PIN READS OVER THIS VOLTAGE THEN TURN ON THE LIGHTS
// I PICKED 2200 BECAUSE OBSERVING THE GRAPH IN THE BLYNK APP, THE RESTING VOLTAGE IS APPROXIMATELY 2100
int strumThresholdVoltage = 2000;

void setup() {
Serial.begin(9600);
delay(5000); 
Blynk.begin(auth);
pinMode(led,OUTPUT);
digitalWrite(led,LOW);
pinMode(boardLED,OUTPUT);
digitalWrite(boardLED,LOW); 
pinMode(pickupVoltage,INPUT);
}

void loop() {
Blynk.run();

strip.setPixelColor(0, 0, 0, 0);//TURN ALL THE PIXELS OFF
strip.setBrightness(0);
if (maxReading(pickupVoltage,100,1)>strumThresholdVoltage){// IF THE MAX VOLTAGE ON YOUR PIN IS ABOVE THE SPECIFIED THRESHOLD THEN
    strip.setPixelColor(0, 0, 0, 255);//SET THE FIRST PIXEL/LED TO BLUE
    strip.setPixelColor(1, 0, 0, 255);
    strip.setPixelColor(2, 0, 0, 255);
    strip.setPixelColor(3, 0, 0, 255);
    strip.setBrightness(255);
    strip.show();

}
strip.show();

}
// THIS IS THE FUNCTION THAT DETERMINES THE MAXIMUM VOLTAGE ON THE PIN
// IT READS FROM THE PINS MULTIPLE TIMES AND THEN KEEPS THE HIGHEST VOLTAGE
// THE IDEA HERE IS THAT IF YOU POLL THE PIN MULTIPLE TIMES IN RAPID SUCCESSION THEN
// ONE OF THOSE READINGS SHOULD BE THE PEAK VOLTAGE, IF YOU'RE STRUMMING THEN THE
// PEAK VOLTAGE WILL BE HIGHER (HOPEFULL OVER YOUR THRESHOLD DEFINED ABOVE)
int maxReading(int pinNumber,int numberOfMeasurements,int measurementInterval){
    int maxReading = 0;
    int currentReading = 0;
    for (int i=0;i<=numberOfMeasurements;i++){
        currentReading = analogRead(pinNumber);
        if(currentReading>maxReading){
            maxReading= currentReading;
        }
        delay(measurementInterval);
    }
    
    return maxReading;
}

Credits

Corey Childress

1 project • 3 followers

Mechanical Engineering Student UNCC

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Guitar LEDs

Things used in this project

Hardware components

Software apps and online services

Hand tools and fabrication machines

Story

Background

Circuit

Coding

Videos

Summary

Schematics

Circuit Schematic

Circuit

Code

Guitar LEDs

Credits

Corey Childress

Comments

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Guitar LEDs

Guitar LEDs

Things used in this project

Hardware components

Software apps and online services

Hand tools and fabrication machines

Story

Background

Circuit

Coding

Videos

Summary

Schematics

Circuit Schematic

Circuit

Code

Guitar LEDs

Credits

Corey Childress

Comments

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