Diff: pulseSensor.cpp

Revision:

0:16d0c9ce5afb

Child:

1:0053efdb355e

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/pulseSensor.cpp	Sat Jun 04 02:35:48 2016 +0000
@@ -0,0 +1,109 @@
+#include "mbed.h"
+
+AnalogIn pulsePin(dp13);
+DigitalOut led(dp6);
+
+#define SAMPLING 2000.0f  //  Sampling period in micro seconds  2msec
+
+volatile int rate[10];                    // array to hold last ten IBI values
+volatile unsigned long sampleCounter = 0;          // used to determine pulse timing
+volatile unsigned long lastBeatTime = 0;           // used to find IBI
+volatile int P =512;                      // used to find peak in pulse wave, seeded
+volatile int T = 512;                     // used to find trough in pulse wave, seeded
+volatile int thresh = 525;                // used to find instant moment of heart beat, seeded
+volatile int amp = 100;                   // used to hold amplitude of pulse waveform, seeded
+volatile bool firstBeat = true;           // used to seed rate array so we startup with reasonable BPM
+volatile bool secondBeat = false;         // used to seed rate array so we startup with reasonable BPM
+
+// Volatile Variables, used in the interrupt service routine!
+volatile int BPM;                           // int that holds raw Analog in 0. updated every 2mS
+volatile int Signal;                        // holds the incoming raw data
+volatile int IBI = 600;                     // int that holds the time interval between beats! Must be seeded! 
+volatile bool Pulse = false;                // "True" when User's live heartbeat is detected. "False" when not a "live beat". 
+volatile bool QS = false;                   // becomes true when Arduoino finds a beat.
+
+Ticker t2;
+
+// THIS IS THE TICKER INTERRUPT SERVICE ROUTINE. 
+// Ticker makes sure that we take a reading every 2 miliseconds
+void sampling() {                             // triggered every 2 miliseconds
+  Signal = (int)(pulsePin.read()*1023);       // read the Pulse Sensor 
+  sampleCounter += 2;                         // keep track of the time in mS with this variable
+  int N = sampleCounter - lastBeatTime;       // monitor the time since the last beat to avoid noise
+
+    //  find the peak and trough of the pulse wave
+  if(Signal < thresh && N > (IBI/5)*3){       // avoid dichrotic noise by waiting 3/5 of last IBI
+    if (Signal < T){                          // T is the trough
+      T = Signal;                             // keep track of lowest point in pulse wave 
+    }
+  }
+
+  if(Signal > thresh && Signal > P){          // thresh condition helps avoid noise
+    P = Signal;                               // P is the peak
+  }                                           // keep track of highest point in pulse wave
+
+  //  NOW IT'S TIME TO LOOK FOR THE HEART BEAT
+  // signal surges up in value every time there is a pulse
+  if (N > 250){                                   // avoid high frequency noise
+    if ( (Signal > thresh) && (Pulse == false) && (N > (IBI/5)*3) ){        
+      Pulse = true;                               // set the Pulse flag when we think there is a pulse
+      IBI = sampleCounter - lastBeatTime;         // measure time between beats in mS
+      lastBeatTime = sampleCounter;               // keep track of time for next pulse
+
+      if(secondBeat){                        // if this is the second beat, if secondBeat == TRUE
+        secondBeat = false;                  // clear secondBeat flag
+        for(int i=0; i<=9; i++){             // seed the running total to get a realisitic BPM at startup
+          rate[i] = IBI;                      
+        }
+      }
+
+      if(firstBeat){                         // if it's the first time we found a beat, if firstBeat == TRUE
+        firstBeat = false;                   // clear firstBeat flag
+        secondBeat = true;                   // set the second beat flag
+        return;                              // IBI value is unreliable so discard it
+      }
+
+      // keep a running total of the last 10 IBI values
+      unsigned runningTotal = 0;              // clear the runningTotal variable    
+
+      for(int i=0; i<=8; i++){                // shift data in the rate array
+        rate[i] = rate[i+1];                  // and drop the oldest IBI value 
+        runningTotal += rate[i];              // add up the 9 oldest IBI values
+      }
+
+      rate[9] = IBI;                          // add the latest IBI to the rate array
+      runningTotal += rate[9];                // add the latest IBI to runningTotal
+      runningTotal /= 10;                     // average the last 10 IBI values 
+      BPM = 60000/runningTotal;               // how many beats can fit into a minute? that's BPM!
+      QS = true;                              // set Quantified Self flag 
+      // QS FLAG IS NOT CLEARED INSIDE THIS ISR
+      led = 1;
+    }                       
+  }
+
+  if (Signal < thresh && Pulse == true){   // when the values are going down, the beat is over
+    Pulse = false;                         // reset the Pulse flag so we can do it again
+    amp = P - T;                           // get amplitude of the pulse wave
+    thresh = amp/2 + T;                    // set thresh at 50% of the amplitude
+    P = thresh;                            // reset these for next time
+    T = thresh;
+    led = 0;
+  }
+
+  if (N > 2500){                           // if 2.5 seconds go by without a beat
+    thresh = 512;                          // set thresh default
+    P = 512;                               // set P default
+    T = 512;                               // set T default
+    lastBeatTime = sampleCounter;          // bring the lastBeatTime up to date        
+    firstBeat = true;                      // set these to avoid noise
+    secondBeat = false;                    // when we get the heartbeat back
+  }
+
+}
+
+void interruptSetup(){
+    // Initializes Ticker to throw an interrupt every 2mS.
+    t2.attach_us(&sampling, SAMPLING);
+}
+
+