Dangerous Prototypes Open Source Hardware

# Teensy 3.0 @ 96 MHz
# Samples/sec: 2246.69 Avg: 43582.86 Offset: 19.94 P-P noise: 7 St.Dev: 0.944
# Samples/sec: 2245.68 Avg: 43583.17 Offset: 20.25 P-P noise: 8 St.Dev: 0.938
# Samples/sec: 2245.68 Avg: 43583.22 Offset: 20.31 P-P noise: 7 St.Dev: 0.931
# Samples/sec: 2245.68 Avg: 43583.40 Offset: 20.48 P-P noise: 8 St.Dev: 0.940
# Samples/sec: 2246.18 Avg: 43583.25 Offset: 20.33 P-P noise: 8 St.Dev: 0.921

# Teensy 3.0 @ 48 MHz
# Samples/sec: 2236.64 Avg: 43583.83 Offset: 20.92 P-P noise: 9 St.Dev: 1.116
# Samples/sec: 2236.64 Avg: 43583.67 Offset: 20.76 P-P noise: 8 St.Dev: 1.123
# Samples/sec: 2236.14 Avg: 43583.81 Offset: 20.89 P-P noise: 8 St.Dev: 1.117
# Samples/sec: 2236.64 Avg: 43583.73 Offset: 20.81 P-P noise: 10 St.Dev: 1.107

# Teensy 3.0 @ 24 MHz
# Teensy 3.0 ADC test start: 
# Samples/sec: 2156.10 Avg: 43573.35 Offset: 10.44 P-P noise: 7 St.Dev: 0.913
# Samples/sec: 2156.10 Avg: 43573.42 Offset: 10.50 P-P noise: 8 St.Dev: 0.928
# Samples/sec: 2156.10 Avg: 43573.55 Offset: 10.64 P-P noise: 7 St.Dev: 0.927
# Samples/sec: 2156.10 Avg: 43573.44 Offset: 10.52 P-P noise: 7 St.Dev: 0.907
# Samples/sec: 2156.10 Avg: 43573.33 Offset: 10.42 P-P noise: 7 St.Dev: 0.923

// Analog input test for Teensy 3.0    Oct 4 2012 J.Beale
// Setup: https://picasaweb.google.com/109928236040342205185/Electronics#5795546092126071650

    #define VREF (3.266)         // ADC reference voltage (= power supply)
    #define VINPUT (2.171)       // ADC input voltage from resistive divider to VREF
    #define ADCMAX (65535)       // maximum possible reading from ADC
    #define EXPECTED (ADCMAX*(VINPUT/VREF))     // expected ADC reading
    #define SAMPLES (10000)      // how many samples to combine for pp, std.dev statistics

    const int analogInPin = A0;  // Analog input is AIN0 (Teensy3 pin 14, next to LED)
    const int LED1 = 13;         // output LED connected on Arduino digital pin 13

    int sensorValue = 0;        // value read from the ADC input
    long oldT;

    void setup() {    // ==============================================================
      pinMode(LED1,OUTPUT);       // enable digital output for turning on LED indicator
      analogReference(INTERNAL);  // set analog reference to internal ref
      analogReadRes(16);          // Teensy 3.0: set ADC resolution to this many bits
     
      Serial.begin(115200);       // baud rate is ignored with Teensy USB ACM i/o
      digitalWrite(LED1,HIGH);   delay(1000);   // LED on for 1 second
      digitalWrite(LED1,LOW);    delay(3000);   // wait for slow human to get serial capture running
     
      Serial.println("# Teensy 3.0 ADC test start: ");
    } // ==== end setup() ===========

    void loop() {  // ================================================================ 
     
      long datSum = 0;  // reset our accumulated sum of input values to zero
      int sMax = 0;
      int sMin = 65535;
      long n;            // count of how many readings so far
      double x,mean,delta,sumsq,m2,variance,stdev;  // to calculate standard deviation
     
      oldT = millis();   // record start time in milliseconds

      sumsq = 0; // initialize running squared sum of differences
      n = 0;     // have not made any ADC readings yet
      mean = 0; // start off with running mean at zero
      m2 = 0;
     
      for (int i=0;i<SAMPLES;i++) {
        x = analogRead(analogInPin);
//        Serial.println(x,0);
        datSum += x;
        if (x > sMax) sMax = x;
        if (x < sMin) sMin = x;
              // from http://en.wikipedia.org/wiki/Algorithms_for_calculating_variance
        n++;
        delta = x - mean;
        mean += delta/n;
        m2 += (delta * (x - mean));
      } 
      variance = m2/(n-1);  // (n-1):Sample Variance  (n): Population Variance
      stdev = sqrt(variance);  // Calculate standard deviation

      Serial.print("# Samples/sec: ");
      long durT = millis() - oldT;
      float datAvg = (1.0*datSum)/n;
      Serial.print((1000.0*n/durT),2);

      Serial.print(" Avg: ");     Serial.print(datAvg,2);
      Serial.print(" Offset: ");  Serial.print(datAvg - EXPECTED,2);
      Serial.print(" P-P noise: ");  Serial.print(sMax-sMin);
      Serial.print(" St.Dev: ");  Serial.println(stdev,3);
     
//     while (true) {}
    } // end main()  =====================================================