Diff: Interrupt.cpp

Revision:

0:a78b08608d76

Child:

1:171a73d84261

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Interrupt.cpp	Sat Jan 11 12:50:28 2014 +0000
@@ -0,0 +1,98 @@
+
+volatile int rate[10];                    // used to hold last ten IBI values
+volatile unsigned long sampleCounter = 0;          // used to determine pulse timing
+volatile unsigned long lastBeatTime = 0;           // used to find the inter beat interval
+volatile int P =512;                      // used to find peak in pulse wave
+volatile int T = 512;                     // used to find trough in pulse wave
+volatile int thresh = 512;                // used to find instant moment of heart beat
+volatile int amp = 100;                   // used to hold amplitude of pulse waveform
+volatile bool firstBeat = true;        // used to seed rate array so we startup with reasonable BPM
+volatile bool secondBeat = true;       // used to seed rate array so we startup with reasonable BPM
+
+
+void interruptSetup(){     
+  // Initializes Timer2 to throw an interrupt every 2mS.
+  TCCR2A = 0x02;     // DISABLE PWM ON DIGITAL PINS 3 AND 11, AND GO INTO CTC MODE
+  TCCR2B = 0x06;     // DON'T FORCE COMPARE, 256 PRESCALER 
+  OCR2A = 0X7C;      // SET THE TOP OF THE COUNT TO 124 FOR 500Hz SAMPLE RATE
+  TIMSK2 = 0x02;     // ENABLE INTERRUPT ON MATCH BETWEEN TIMER2 AND OCR2A
+  sei();             // MAKE SURE GLOBAL INTERRUPTS ARE ENABLED      
+} 
+
+
+// THIS IS THE TIMER 2 INTERRUPT SERVICE ROUTINE. 
+// Timer 2 makes sure that we take a reading every 2 miliseconds
+ISR(TIMER2_COMPA_vect){                         // triggered when Timer2 counts to 124
+    cli();                                      // disable interrupts while we do this
+    Signal = analogRead(pulsePin);              // 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
+    digitalWrite(blinkPin,HIGH);                // turn on pin 13 LED
+    IBI = sampleCounter - lastBeatTime;         // measure time between beats in mS
+    lastBeatTime = sampleCounter;               // keep track of time for next pulse
+         
+         if(firstBeat){                         // if it's the first time we found a beat, if firstBeat == TRUE
+             firstBeat = false;                 // clear firstBeat flag
+             return;                            // IBI value is unreliable so discard it
+            }   
+         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;                      
+                    }
+            }
+          
+    // keep a running total of the last 10 IBI values
+    word 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
+    }                       
+}
+
+  if (Signal < thresh && Pulse == true){     // when the values are going down, the beat is over
+      digitalWrite(blinkPin,LOW);            // turn off pin 13 LED
+      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;
+     }
+  
+  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 = true;                     // when we get the heartbeat back
+     }
+  
+  sei();                                     // enable interrupts when youre done!
+}// end isr
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