git.piffa.net Git - arduino/blob - books/ArduinoNextSteps-master/ArduinoNextSteps/sketch_13_05_band_stop_due/sketch_13_05_band_stop_due.ino

   1 // sketch_13_05_band_stop_due
   2
   3 const long samplePeriod = 23L; // micro seconds
   4
   5 const int analogInPin = A0;
   6 const int analogOutPin = DAC0;
   7
   8 // 1000 to 1500 band stop filter
   9 // 44100 Hz sample rate
  10 // http://www.schwietering.com/jayduino/filtuino/index.php?characteristic=bu&passmode=bs&order=1&usesr=usesr&sr=44100&frequencyLow=1000&noteLow=&frequencyHigh=1500&noteHigh=&pw=pw&calctype=float&run=Send
  11
  12 //Band stop butterworth filter order=1 alpha1=0.022675736961451 alpha2=0.034013605442177
  13 class filter
  14 {
  15         public:
  16                 filter()
  17                 {
  18                         v[0]=0.0;
  19                         v[1]=0.0;
  20                 }
  21         private:
  22                 float v[3];
  23         public:
  24                 float step(float x)
  25                 {
  26                         v[0] = v[1];
  27                         v[1] = v[2];
  28                         v[2] = (9.655920584452e-1 * x)
  29                                  + ( -0.9311841169 * v[0])
  30                                  + (  1.9018448769 * v[1]);
  31                         return
  32                                  (v[0] + v[2])
  33                                 - 1.969615 * v[1];
  34                 }
  35 };
  36
  37
  38 filter f;
  39
  40
  41 void setup()
  42 {
  43   // http://www.djerickson.com/arduino/
  44   REG_ADC_MR = (REG_ADC_MR & 0xFFF0FFFF) | 0x00020000;
  45   analogWriteResolution(8);
  46   analogReadResolution(8);
  47 }
  48
  49 void loop()
  50 {
  51   static long lastSampleTime = 0;
  52   long timeNow = micros();
  53   if (timeNow > lastSampleTime + samplePeriod)
  54   {
  55     int raw = analogRead(analogInPin);
  56
  57     float filtered = f.step(raw);
  58
  59     analogWrite(analogOutPin, (int)filtered);
  60     lastSampleTime = timeNow;
  61   }
  62 }