Voice Loudness Monitor

1// Define constants - these can be tuned to the user's preferences
2#define  sampleWindow 10 // Sample window width in milliseconds (10 ms = 100 Hz)
3#define  LEDtime 1000 //time to keep LED on for when noise goes above threshold
4#define  threshold 40 //mV
5#define QTY_SAMPLES 16 // the number of samples to be averaged
6
7//Define  pins used on the breadboard
8#define MIC_IN A0
9#define LED_LOUD PD2
10#define  LED_QUIET PD3
11#define V_MIC 3.3
12
13//Create global variables
14int sample;
15long  startLED;
16float values[QTY_SAMPLES];
17float sum;
18int index;
19
20
21//  This function takes a rolling average of QTY_SAMPLES
22// The oldest value is removed  from the sum and the newest takes its place in the array. Then the mean of this  array is returned.
23float rollingAverage(float num) {
24  sum -= values[index];
25  values[index] = num;
26  sum += values[index];
27  index++;
28  index = index  % QTY_SAMPLES;
29  return sum / QTY_SAMPLES;
30}
31
32
33//Begin serial output,  initialise pins and set global variables
34void setup()
35{
36  Serial.begin(9600);
37  pinMode(LED_QUIET, OUTPUT);
38  pinMode(LED_LOUD, OUTPUT);
39  pinMode(MIC_IN,  INPUT);
40  float sum = 0;
41  int index = 0;
42}
43
44
45//Sample the signal  amplitude and calculate a rolling average. If the average loudness is too high,  then alert user via LEDs
46void loop()
47{
48
49  // Reset variables
50  int  signalMax = 0;
51  int signalMin = 1024;
52  unsigned long startMillis = millis();  // Set the start of the sample window
53
54  // Record the signal maximum and  minimum over the sample window
55  while (millis() - startMillis < sampleWindow)
56  {
57    sample = analogRead(MIC_IN);
58    if (sample > signalMax)
59    {
60      signalMax = sample;  // save the new maximum
61    }
62    else if (sample  < signalMin)
63    {
64      signalMin = sample;  // save the new minimum
65    }
66  }
67
68  // Convert the signal maximum and minimum into millivolts  from the amplifier
69  float amplitude = signalMax - signalMin;  // This calculates  the peak-to-peak amplitude
70  float millivolts = rollingAverage(amplitude) * V_MIC  / 1.024; // This calls the rolling average function and converts the average amplitude  to millivolts
71  Serial.println(millivolts);
72
73  //Alert the user via the  LEDs if the noise is too loud
74  if (millivolts > threshold) {
75    digitalWrite(LED_LOUD,  HIGH); digitalWrite(LED_QUIET, LOW);
76    startLED = millis();
77  } else if  (millis() - startLED > LEDtime) {
78    digitalWrite(LED_LOUD, LOW); digitalWrite(LED_QUIET,  HIGH);
79  }
80}
81
82//Further work could be converting the millivolts signal  into a Sound Pressure Level (dB SPL), or adding more LEDs to display a noise level  scale<br>