Hi,

It prints the vales from 0 - 1023 but i don’t understand why i dont get any negative values as its a peak to peak output.

``````/****************************************
Example Sound Level Sketch for the
****************************************/

const int sampleWindow = 50; // Sample window width in mS (50 mS = 20Hz)
unsigned int sample;

void setup()
{
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)
{
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) / 1024;  // convert to volts

Serial.println(peakToPeak);
}
``````

How can any value in the range 0 to 5V be negative?

So its not peak-to-peak, its peak?

Is the DC offset 512 then?

Quote from the Article you got the code from:

The output will have a DC bias of VCC/2 so when its perfectly quiet, the voltage will be a steady VCC/2 (1.65v).

So if you power it from 3,3V then with no input you will read 1,65V aka 1,65V / (1024 / 5V) = 337. Max negative peak will be at 0V (that's negative to Vcc/2) aka 0. And the positive peak will be at 3,3V aka 3,3V / (1024 / 5V) = 675.

Im so confused. When i upload it to print volts. it is sitting at 0.23

does the DC bias actually matter?

Have you read the code at all?

``````   peakToPeak = signalMax - signalMin;  // max - min = peak-peak amplitude
double volts = (peakToPeak * 5) / 1024;  // convert to volts

Serial.println(peakToPeak);
``````

So it does not print what it reads directly but the found peak to peak value. And a peak to peak value is always a positive number because we treat is as a absolute value.

One really wonders what prompted this line!

if (sample < 1024) // toss out spurious readings

A reading of 1024 or higher from a 10 bit ADC would be an impressive achievement…