Diff: heartRate/heartRate.cpp

Revision:

0:83277b73a1f8

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/heartRate/heartRate.cpp	Sun Jul 28 08:14:38 2019 +0000
@@ -0,0 +1,112 @@
+
+
+#include "heartRate.h"
+
+int32_t IR_AC_Max = 20;
+int16_t IR_AC_Min = -20;
+
+int16_t IR_AC_Signal_Current = 0;
+int16_t IR_AC_Signal_Previous;
+int16_t IR_AC_Signal_min = 0;
+int16_t IR_AC_Signal_max = 0;
+int16_t IR_Average_Estimated;
+
+int16_t positiveEdge = 0;
+int16_t negativeEdge = 0;
+int32_t ir_avg_reg = 0;
+
+int16_t cbuf[32];
+uint8_t offset = 0;
+
+static const uint16_t FIRCoeffs[12] = {172, 321, 579, 927, 1360, 1858, 2390, 2916, 3391, 3768, 4012, 4096};
+
+//  Heart Rate Monitor functions takes a sample value and the sample number
+//  Returns true if a beat is detected
+//  A running average of four samples is recommended for display on the screen.
+bool checkForBeat(int32_t sample)
+{
+  bool beatDetected = false;
+
+  //  Save current state
+  IR_AC_Signal_Previous = IR_AC_Signal_Current;
+  
+  //This is good to view for debugging
+  //Serial.print("Signal_Current: ");
+  //Serial.println(IR_AC_Signal_Current);
+
+  //  Process next data sample
+  IR_Average_Estimated = averageDCEstimator(&ir_avg_reg, sample);
+  IR_AC_Signal_Current = lowPassFIRFilter(sample - IR_Average_Estimated);
+
+  //  Detect positive zero crossing (rising edge)
+  if ((IR_AC_Signal_Previous < 0) & (IR_AC_Signal_Current >= 0))
+  {
+  
+    IR_AC_Max = IR_AC_Signal_max; //Adjust our AC max and min
+    IR_AC_Min = IR_AC_Signal_min;
+
+    positiveEdge = 1;
+    negativeEdge = 0;
+    IR_AC_Signal_max = 0;
+
+    //if ((IR_AC_Max - IR_AC_Min) > 100 & (IR_AC_Max - IR_AC_Min) < 1000)
+    if ((IR_AC_Max - IR_AC_Min) > 20 & (IR_AC_Max - IR_AC_Min) < 1000)
+    {
+      //Heart beat!!!
+      beatDetected = true;
+    }
+  }
+
+  //  Detect negative zero crossing (falling edge)
+  if ((IR_AC_Signal_Previous > 0) & (IR_AC_Signal_Current <= 0))
+  {
+    positiveEdge = 0;
+    negativeEdge = 1;
+    IR_AC_Signal_min = 0;
+  }
+
+  //  Find Maximum value in positive cycle
+  if (positiveEdge & (IR_AC_Signal_Current > IR_AC_Signal_Previous))
+  {
+    IR_AC_Signal_max = IR_AC_Signal_Current;
+  }
+
+  //  Find Minimum value in negative cycle
+  if (negativeEdge & (IR_AC_Signal_Current < IR_AC_Signal_Previous))
+  {
+    IR_AC_Signal_min = IR_AC_Signal_Current;
+  }
+  
+  return(beatDetected);
+}
+
+//  Average DC Estimator
+int16_t averageDCEstimator(int32_t *p, uint16_t x)
+{
+  *p += ((((long) x << 15) - *p) >> 4);
+  return (*p >> 15);
+}
+
+//  Low Pass FIR Filter
+int16_t lowPassFIRFilter(int16_t din)
+{  
+  cbuf[offset] = din;
+
+  int32_t z = mul16(FIRCoeffs[11], cbuf[(offset - 11) & 0x1F]);
+  
+  for (uint8_t i = 0 ; i < 11 ; i++)
+  {
+    z += mul16(FIRCoeffs[i], cbuf[(offset - i) & 0x1F] + cbuf[(offset - 22 + i) & 0x1F]);
+  }
+
+  offset++;
+  offset %= 32; //Wrap condition
+
+  return(z >> 15);
+}
+
+//  Integer multiplier
+int32_t mul16(int16_t x, int16_t y)
+{
+  return((long)x * (long)y);
+}
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