Code for the Noise Monitor project in the Arduino for Educators workshop.

ardEdu-noiseMonitor.ino

const int sampleWindow = 50; // Sample window width in mS (50 mS = 20Hz)
unsigned int sample;
int greenLED = 13;
int yellowLED = 12;
int redLED = 11;
void setup() 
{
  pinMode(greenLED, OUTPUT);
  pinMode(yellowLED, OUTPUT);
  pinMode(redLED, OUTPUT);
   Serial.begin(9600);
}
void loop() 
{
   unsigned long startMillis= millis();  // Start of sample window
   unsigned int peakToPeak = 0;   // peak-to-peak level
   unsigned int signalMax = 0;
   unsigned int signalMin = 1024;
   // collect data for 50 mS
   while (millis() - startMillis < sampleWindow)
    {
      sample = analogRead(0);
      if (sample < 1024)  // toss out spurious readings
      {
         if (sample > signalMax)
         {
            signalMax = sample;  // save just the max levels
         }
         else if (sample < signalMin)
         {
            signalMin = sample;  // save just the min levels
         }
      }
  }
  
   peakToPeak = signalMax - signalMin;  // max - min = peak-peak amplitude
  // double volts = (peakToPeak * 5.0) / 1024;  // convert to volts
  // volts = volts *100;
   Serial.println(sample);
   if (sample < 535) {
     digitalWrite(yellowLED, LOW);
     digitalWrite(redLED,LOW);
     digitalWrite(greenLED, HIGH);
   }
   else if (sample > 535 && sample < 800) {
    digitalWrite(redLED, LOW);
    digitalWrite(greenLED, HIGH);
    digitalWrite(yellowLED, HIGH);
    delay(2000);
   }
   if (sample > 800) {
    digitalWrite(greenLED, HIGH);
    digitalWrite(yellowLED, HIGH);
    digitalWrite(redLED, HIGH);
    delay(2000);
   }
}