EcgSmartApp - A Low Cost ECG Device

int value=0;  // analog value
int index=1;
byte sntmsg[6];  // vector to send

/* sntmsg
sntmsg is a 6 bytes vector:
1st byte is always 0xFF and it is used as a check
2nd to 6th bytes contain 4 analog values read form the arduino input A0 and converted into 10 bit numbers:

2nd byte: most significant 8 bits of the 1st analog value
3rd byte: least significant 2 bits of the 1st analog value + most significant 6 bits of the 2nd analog value
4th byte: least significant 4 bits of the 2nd analog value + most significant 4 bits of the 3rd analog value
5th byte: least significant 6 bits of the 3rd analog value + most significant 2 bits of the 4th analog value
6th byte: least significant 8 bits of the 4th analog value
*/

void setup() {
  
 sntmsg[0] = 0xFF;  // byte1: check

Serial.begin(9600); // initialization serial
 
noInterrupts();  // interrupts OFF

//set timer1 interrupt at 600 Hz
  TCCR1A = 0;// set entire TCCR1A register to 0
  TCCR1B = 0;// same for TCCR1B
  TCNT1  = 0;//initialize counter value to 0
  // set compare match register for 1hz increments
  OCR1A = 416; // = [(16*10^6) / (600*64)]- 1    (must be <65536)
  // turn on CTC mode
  TCCR1B |= (1 << WGM12);
  // Set CS10 and CS12 bits for 64 prescaler
  TCCR1B |= (1 << CS11) | (1 << CS10);;  
  // enable timer compare interrupt
  TIMSK1 |= (1 << OCIE1A);

  interrupts();  // interrupts ON

}

ISR(TIMER1_COMPA_vect){ //timer1 interrupt 600Hz 

  // read analog value
  value = analogRead(A0);  // read analog value

 switch (index) {

    case 1:

sntmsg[1]= (byte) (value >> 2); // most significant 8 bits of the 1st analog value
sntmsg[2]= (byte) (value << 6); // least significant 2 bits of the 1st analog value
++index;
      break;

    case 2:
    
//most significant 6 bits of the 2nd analog value
bitWrite(sntmsg[2], 5, bitRead(value, 9));
bitWrite(sntmsg[2], 4, bitRead(value, 8));
bitWrite(sntmsg[2], 3, bitRead(value, 7));
bitWrite(sntmsg[2], 2, bitRead(value, 6));
bitWrite(sntmsg[2], 1, bitRead(value, 5));
bitWrite(sntmsg[2], 0, bitRead(value, 4));

sntmsg[3]= (byte) (value << 4); // least significant 4 bits of the 2nd analog value
++index;    
      break;

    case 3:

// most significant 4 bits of the 3rd analog value
bitWrite(sntmsg[3], 3, bitRead(value, 9));
bitWrite(sntmsg[3], 2, bitRead(value, 8));
bitWrite(sntmsg[3], 1, bitRead(value, 7));
bitWrite(sntmsg[3], 0, bitRead(value, 6));

sntmsg[4]= (byte) (value << 2);  // least significant 6 bits of the 3rd analog value
++index;    
      break;

    case 4:

// most significant 2 bits of the 4th analog value
bitWrite(sntmsg[4], 1, bitRead(value, 9));
bitWrite(sntmsg[4], 0, bitRead(value, 8));

sntmsg[5]= (byte) (value); // least significant 8 bits of the 4th analog value
index=1;    

Serial.write(sntmsg,6);  // send value

      break;

  }  // end switch

}  // end timer1 interrupt 600Hz 


void loop() {
}