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) { 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) / 30; // convert to volts Serial.println(volts); }