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   1 // sketch_13_04_null_filter_due
   2
   3 const long samplePeriod = 10L; // micro seconds
   4
   5 const int analogInPin = A0;
   6 const int analogOutPin = DAC0;
   7
   8 void setup()
   9 {
  10   // http://www.djerickson.com/arduino/
  11   REG_ADC_MR = (REG_ADC_MR & 0xFFF0FFFF) | 0x00020000;
  12   analogWriteResolution(8);
  13   analogReadResolution(8);
  14 }
  15
  16 void loop()
  17 {
  18   static long lastSampleTime = 0;
  19   long timeNow = micros();
  20   if (timeNow > lastSampleTime + samplePeriod)
  21   {
  22     int raw = analogRead(analogInPin);
  23     analogWrite(analogOutPin, raw);
  24     lastSampleTime = timeNow;
  25   }
  26 }
  27