MSGEQ7 Simple Spectrum Analyzer

Final Assembly

Abstract

Mixed Signal Integration has a cool little chip that has 7 built-in bandpass filters. Run an audio signal through it and you have an instant audio spectrum analyzer! This is a simple spectrum analyzer based on an Arduino. Each of the 5 LEDs represent a single section of the chip’s 7 sections of audio spectrum.

Electronics

Parts used in this project

Parts list:

• (1) – MSGEQ7 (Sparkfun)
• (5) –  LEDs
• (5) – 470Ω Resistors
• (1) – 180kΩ Resistor
• (1) – 22kΩ Resistor
• (1) – 33pF Capacitor (Ceramic)
• (1) – 0.01µF Capacitor (Ceramic)
• (2) – 0.1µF Capacitors (Ceramic)
• (1) – Pushbutton
• (1) – Stripped Audio Cable
• Header Pins
• Jumper Wires
• Adafruit Perma-Prototype Board (or Breadboard)

Schematic:

Source: MSGEQ7 Datasheet

The application example from the MSGEQ7 Datasheet provides the circuit necessary.  The 200k and 33pF are probably the most critical components.  200k is not a E24-value, so I used 180K.   The 33pF shouldn’t be an issue to find.  470 ohms were picked to keep the amount of current flowing through the Arduino I/O pins low.

Firmware

Since there are only 5 LEDs, I decided to make each frequency band adjust the brightness via PWM.  The more energy at each a particular band will result in brighter LEDs.  The code was complied in Eclipse with Arduino-0023 Core on an Uno with a ATmega328.

Code is also available from Pastebin:  MSGEQ7 Simple Spectrum Analyzer

#define msg7RESET 11
#define msg7Strobe 12
#define msg7DCout 0
const int LEDpins[7] = {3,5,5,6,9,9,10};	// there are 5 LEDs and 7 freq bands.  So, repeat LEDs

#define pushButton 2

void setup() {
  // initialize the digital pin as an output.
  // Pin 13 has an LED connected on most Arduino boards:
  for (int x=0; x<7; x++) {
	  pinMode(LEDpins[x], OUTPUT);
  }
  pinMode(msg7RESET, OUTPUT);
  pinMode(msg7Strobe, OUTPUT);

  pinMode(pushButton, INPUT);		// never actually used in this example.
  digitalWrite(pushButton, HIGH);  // Enable internal pull-up
}

void loop() {
	digitalWrite(msg7RESET, HIGH);			// reset the MSGEQ7's counter
	delay(5);
	digitalWrite(msg7RESET, LOW);

	for (int x = 0; x < 7; x++){
		digitalWrite(msg7Strobe, LOW);		// output each DC value for each freq band
		delayMicroseconds(35); // to allow the output to settle
		int spectrumRead = analogRead(msg7DCout);

		int PWMvalue = map(spectrumRead, 0, 1024, 0, 255);  // scale analogRead's value to Write's 255 max
		if (PWMvalue < 50)
			PWMvalue = PWMvalue / 2;		// bit of a noise filter, so the LEDs turn off at low levels

		analogWrite(LEDpins[x], PWMvalue);
		digitalWrite(msg7Strobe, HIGH);
	}
}

Demonstration

YouTube Video showing the light’s action along with some music.  The music was created using GarageBand’s magic instruments.  I liked the groove and how well the lights responded to it.  Enjoy!