All project files are on Github:

This project unites the blood pressure monitor and pulse oximeter projects and adds tons of other features.
The first version of the project can be found on Github:

The pulse oximeter is a very useful and affordable medical gadget. It incorporates a quick and easy way of measuring your heart rate as well as calculating the blood oxygen saturation in one go! After having a look inside the Contec CMS50C and CMS50D which are both MSP430-based devices with OLED displays, it quickly became apparent, which one is easier to hack to extract the data.




The CMS50C (the one with the color OLED, available for <15$ on the usual platforms) has a nice line of well accessible and labeled pads, among which is also a UART interface that is streaming all of the useful values such as 7bit photoplethismographic curve data, the "bar graph", the SPO2 and heart rate value, a "beat detection bit" and various diagnostic bits at a sampling rate of 60Hz. An overview over the entire communication protocol can be found here. The serial port settings are a bit unusual: 4800 baud, and EVEN parity, so watch out for that, but other than that it’s a quite clever protocol that is storing all this information in only 5 bytes.



















The most essential connections are GND, TX, RST, the right pin of the trigger pushbutton and Batt. After that you should be able to completely control the thing from a microcontroller and harvest the data.
A code sample for Teensy 3.x is found below:

//sketch for reading the CMS50C pulse oximeter data using a Teensy 3.x

#define TRIG_PULSEOX 3 // has to be pulled to 3.3V to start the CMS50C
#define RST_PULSEOX 15
//vars for pulseOx
char incomingPulseOxbyte;
unsigned int byteCntPulse = 0;
char pulseCurve_PulseOx = 0;
char SPO2;
char HR_PulseOx;
boolean lastBitPulseOx = 0; //the MSB of the heart rate byte is hidden in a different byte - the one that holds the bar graph data
unsigned long pulseOxTrigTmr=0;
unsigned long pulseOxTrigInt=600000; // length of the pulse that triggers the CMS50C
unsigned long pulseOxRstTmr=0;
unsigned long pulseOxRstInt=800000;

boolean triggeredOx = false;
boolean resettedOx = false;

//packet management bytes for the Amarino Android app
char startFlag = 18;
char ack = 19;
char delimiter = 59; //';' in case we use more than 1 channel


void setup() {
  // put your setup code here, to run once:
  Serial1.begin(115200); // Bluetooth port
  Serial3.begin(4800, SERIAL_8E1); // Pulse oximeter CONTEC CMS 50C, annoying fact: it has EVEN PARITY!

   // make the pins outputs:
  pinMode(RST_PULSEOX, OUTPUT);
  pinMode(TRIG_PULSEOX, OUTPUT);
  
  digitalWrite(RST_PULSEOX, HIGH);
  
  
  triggerOx(); //turn on the PulseOx

}

void loop() {

  
  // put your main code here, to run repeatedly:
   //waiting to pull TRIG_PULSEOX LOW again 
  if((micros()-pulseOxTrigTmr)>pulseOxTrigInt && triggeredOx == true){
    digitalWrite(TRIG_PULSEOX, LOW);
    triggeredOx=false;
  }
  

   readPulseOx();

}

void readPulseOx() {
 
  //--------------------Pulse Oximeter data analysis----------------
  if (Serial3.available() > 0) {
    //pulseox data
    incomingPulseOxbyte = Serial3.read();
    if (byteCntPulse == 1) {
      //the second byte contains a 7 bit pulse wave value, Fs=60Hz
      pulseCurve_PulseOx = incomingPulseOxbyte;
      byteCntPulse++;
    } else if (byteCntPulse == 2) {
      //the 0-3rd bits of the third byte is the bar graph value .
      //the 6th bit is bit 7 of the heart rate value!
      if ( bitRead(incomingPulseOxbyte, 6)) {
        //if the heart rate is >= 128, this happens
        lastBitPulseOx = 1;
      } else
        lastBitPulseOx = 0;

      byteCntPulse++; //move on
    } else if (byteCntPulse == 3) {
      //
      if (lastBitPulseOx)
        //if the heart rate is >= 128, this happens
        HR_PulseOx = 128 + incomingPulseOxbyte;
      else
        HR_PulseOx = incomingPulseOxbyte;

      byteCntPulse++;
    } else if (byteCntPulse == 4) {
      //the last byte contains the most important SPO2 value
      SPO2 = incomingPulseOxbyte;
      byteCntPulse = 0; //we're done the data packet has 5 bytes in total
    } else {


      Serial1.print(startFlag);
      Serial1.print("P");
      Serial1.print(delimiter);
      Serial1.print(pulseCurve_PulseOx, DEC); //send the pulse curve value
      Serial1.print(delimiter);
      Serial1.print(HR_PulseOx, DEC); //send the heart rate
      Serial1.print(delimiter);
      Serial1.print(SPO2, DEC); //send SPO2 value!
      Serial1.print(ack);

    }

    //analyze the first byte. it has plenty of information about the data
    //the fourth bit of the first packet byte means "OK signal" if zero, otherwise it stands for "searching too long"
    //the seventh bit of the first byte has to be always set!!!!! (the only byte where this is the case) all other bytes have a bit 7 == 0
    if ( bitRead(incomingPulseOxbyte, 7)) {
      byteCntPulse++;
    }
  }

}

void triggerOx(){
//function to trigger the pulse oximeter button
   digitalWrite(TRIG_PULSEOX,HIGH);
   pulseOxTrigTmr=micros();
   triggeredOx=true;
 }

After ordering the cheapest (wrist-type) blood pressure monitor I could find online (around 10$) to see how it performs in comparison to a “regular one”, I got a nice surprise.




I’ve hooked up a logic analyzer to as many testpoints on its PCB as possible and found out that it has a UART interface on board!! How convenient is that?
This ABP hack has proven to be quite impractical after all, although many people have shown interest in this this project and contacted me as it’s quite useful to have access to your blood pressure data and almost no open source blood pressure monitor projects exist.




 

A sequence of bytes is sent from testpoint “P6” which turns out to be UART TXD @9600 baud 8N1. You can hook up ANY microcontroller to that and harvest the data easily. After a measurement is complete and successful, the device keeps sending the same byte sequence over and over again until powerdown.




This sequence is the one you see on the pictures: 255 – 254 – 008 – x – x – 0 – Syst. RR low byte – Syst. RR high byte – Diast. RR – heart rate.  As you can see the last 4 bytes of the frame is our desired data. For the systolic pressure we seem to require 2 bytes because 255 is apparently not enough. Sad but true 🙂 , then comes the diastolic pressure and finally the heart rate. The frame starts with 3 fixed bytes (255, 254 and 008 in decimal), followed by 2 variable bytes (haven’t figured out what those are for yet) and a zero byte followed by the data.




Throughout the measurement process itself constantly pressure data is streamed via UART. Each data packet begins with a ‘254’ (DEC) byte followed by one “cuff pressure” byte and one byte that represents the pulse oscillation.  Here’s what the data of one measuring cycle looks like if plotted over time:





























2 JST connectors were inserted into the enclosure. The 3 pin one gives you access to GND, the ON/OFF/START button to remotely trigger the device (just has to be pulled to GND) and finally to the TXD pin of the device. The 2 pin one is simply connected to the battery terminals to eliminate the need for batteries and power the thing from an external source.

Just look online for sphyngomanometers of similar appearance if you want to hack one too. This one has “CK” as a logo, but there are models around from different brands that look the same enclosure-wise. The exact model name of this device is “CK-101”




These devices perform reproducible values but you have to make sure to keep your wrist at heart level, as otherwise the values vary extremely. There is also literature that suggests that the wrist-type sphyngomanometers overestimate blood pressure because of distinct anatomical properties of the wrist arteries (https://www.ncbi.nlm.nih.gov/pubmed/15096904).




One application for an automatically triggered wrist sphyngomanometer I can think of is automated sleep measurement because during sleep your wrist is roughly at heart level anyway.

I’ve been experimenting with electrophysiology for some time and therefore the need to better understand the amplifier circuitry arose. I sampled some INA321 instrumentation amplifiers from Texas Instruments and started experimenting. After soldering them to a breakout board you can breadboard them.




The simple setup below can readily be attached to an analog to digital converter of a microcontroller and to 3 skin electrodes wherever you like to attach them 😉




Besides the instrumentation amp (chip on the left) only one additional dual low-noise opamp is used, which implements a buffer for reference voltage and a bessel filter for reducing mains line interference.

Eagle schmatic:




simplestEEG

This experimental setup is a combination of the the 3.3V OLED display setup and the EKG/EMG shield with improved code, which does averaging of 4 RR intervals in order to calculate the heart rate. Also an annoying QRS-beep is added 🙂

//Simple Arduino ECG monitor with SSD1306 OLED display
//Incorporates a simple QRS detection algorithm and heart rate calculation
//the interrupt-based code parts are based on the Olimex approach
//Requires the libraries included below!

#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

//connect the OLED display in the following way:
#define OLED_DC 11
#define OLED_CS 12
#define OLED_CLK 10
#define OLED_MOSI 9
#define OLED_RESET 13
Adafruit_SSD1306 display(OLED_MOSI, OLED_CLK, OLED_DC, OLED_RESET, OLED_CS);

#if (SSD1306_LCDHEIGHT != 64)
#error("Height incorrect, please fix Adafruit_SSD1306.h!");
#endif

#include <compat/deprecated.h>
#include <FlexiTimer2.h>
//http://www.arduino.cc/playground/Main/FlexiTimer2
#include <TimerOne.h>
//http://arduino.cc/playground/Code/Timer1

/*
Erklärung von cbi, sbi, outp und inp
Bei solchen Makros sollte man etwas mehr Klammern spendieren:

#define sbi(ADDRESS,BIT) ((ADDRESS) |= (1<<(BIT)))
#define cbi(ADDRESS,BIT) ((ADDRESS) &= ~(1<<(BIT)))
#define outp(VAL,ADRESS) ((ADRESS) = (VAL))
#define inp(VAL) (VAL)
The outb( ) function provides a C language interface to the machine instruction that writes a byte to an 8 bit I/O port using the I/O address space instead of the memory address space.
*/

// All definitions
#define NUMCHANNELS 6
#define HEADERLEN 4
#define PACKETLEN (NUMCHANNELS * 2 + HEADERLEN + 1)    //6*2+4+1
#define SAMPFREQ 256                   // ADC sampling rate 256
#define TIMER2VAL (1024/(SAMPFREQ))    // Set 256Hz sampling frequency
#define PWM_OUT 9                      // Number of pin used for generating CAL_SIG
#define PWMFREQ 10        //10Hz for Calibration signal             
//#define LED1  13

// Global constants and variables
char const channel_order[]= { 0, 1, 2, 3, 4, 5 };
volatile unsigned char TXBuf[PACKETLEN];  //The transmission packet
volatile unsigned char TXIndex;           //Next byte to write in the transmission packet.
volatile unsigned char CurrentCh;         //Current channel being sampled.

//~~~~~~~~~~
// Functions
//~~~~~~~~~~

/****************************************************/
/*  Function name: Toggle_LED1                      */
/*  Parameters                                      */
/*    Input   :  No                                */
/*    Output  :  No                                 */
/*    Action: Switches-over LED1.                   */
/****************************************************/
//void Toggle_LED1(void){
//
// if((digitalRead(LED1))==HIGH){
//   digitalWrite(LED1,LOW);
//  }
//  else{
//   digitalWrite(LED1,HIGH);
//  }
//}
/****************************************************/
/*  Function name: setup                            */
/*  Parameters                                      */
/*    Input   :  No                                */
/*    Output  :  No                                 */
/*    Action: Initializes all peripherals           */
/****************************************************/
void setup() {

 noInterrupts();  // Disable all interrupts before initialization
 
 // LED1
// pinMode(LED1, OUTPUT);  //Setup LED1 direction
// digitalWrite(LED1,LOW); //Setup LED1 state
 
 //Write packet header and footer
 TXBuf[0] = 0xa5;  //Sync 0
 TXBuf[1] = 0x5a;  //Sync 1
 TXBuf[2] = 2;     //Protocol version
 TXBuf[3] = 0;     //Packet counter
 
 // ADC
 // Timings for sampling of one 10-bit AD-value:
 // XTAL = 16000000MHz
 // prescaler > ((XTAL / 200kHz) = 80 =>
 // prescaler = 128 (ADPS2 = 1, ADPS1 = 1, ADPS0 = 1)
 // ADCYCLE = XTAL / prescaler = 125000Hz or 8 us/cycle
 // 14 (single conversion) cycles = 112 us
 // 26 (1st conversion) cycles = 208 us
 outb(ADMUX, 0);         //Select channel 0
 outb(ADCSRA, ((1<<ADPS2) | (1<<ADPS1)| (1<<ADPS0))); //Prescaler = 128, free running mode = off, interrupts off.
 sbi(ADCSRA, ADIF);  //Reset any pending ADC interrupts  
 sbi(ADCSRA, ADEN);  //Enable the ADC                    
 
 // Serial Port
 outb(UBRR0, 16);              //Set speed to 57600 bps     
 outb(UCSR0B, (1<<TXEN0));     //Enable USART Transmitter.
 
 // Timer1
 // It's used for calibration signal generation: CAL_SIG via PWM.
 // CAL_SIG is used like reference signal when setting-up SHIELD-EKG/EMG's channel gain
 // During normal operation this signal is not required so it can be disabled with uncommenting te row below!
 /*
 pinMode(PWM_OUT, OUTPUT);    //Set PWM_OUT direction
 digitalWrite(PWM_OUT,LOW);   //Set PWM_OUT state
 Timer1.initialize((1000000/(PWMFREQ))); // initialize timer1, and set a 1/10 second period = 10Hz ->freq. of cal signal should be 10-14Hz (schematic)
 Timer1.pwm(PWM_OUT, 512);             // setup pwm on pin 9, 50% duty cycle
 //Timer1.disablePwm(PWM_OUT); // Uncomment if CAL_SIG is not requiered
 */

 // Timer2
 // Timer2 is used for setting ADC sampling frequency.
 
/*****************************************************************
Methods of the FlexiTimer2 library:

FlexiTimer2::set(unsigned long units, double resolution, void (*f)())
    this function sets a time on units time the resolution for the overflow. Each overflow, "f" will be called. "f" has to be declared void with no parameters.
    E.g. units=1, resolution = 1.0/3000 will call f 3000 times per second, whereas it would be called only 1500 times per second when units=2.
FlexiTimer2::set(unsigned long ms, void (*f)())
    this function sets a time on ms (1/1000th of a second) for the overflow. Each overflow, "f" will be called. "f" has to be declared void with no parameters.
    Shorthand for calling the function above with resolution = 0.001.
FlexiTimer2::start()
    enables the interrupt.
FlexiTimer2::stop()
    disables the interrupt.
*******************************************************************/
 FlexiTimer2::set(TIMER2VAL, Timer2_Overflow_ISR); //TIMER2VAL was (1024/(SAMPFREQ)) in ms =4, SAMPLEFREQ was 256
 FlexiTimer2::start();  //enable the Interrupt....
 
 // MCU sleep mode = idle.
 outb(MCUCR,(inp(MCUCR) | (1<<SE)) & (~(1<<SM0) | ~(1<<SM1) | ~(1<<SM2)));
 
 interrupts();  // Enable all interrupts after initialization has been completed
  // by default, we'll generate the high voltage from the 3.3v line internally! (neat!)
  display.begin(SSD1306_SWITCHCAPVCC);
  // init done
 display.clearDisplay();   // clears the screen and buffer
  
  display.setTextSize(1);
  display.setTextColor(WHITE);
  
}
/****************************************************/
/*  Function name: Timer2_Overflow_ISR              */
/*  Parameters                                      */
/*    Input   :  No                                */
/*    Output  :  No                                 */
/*    Action: Determines ADC sampling frequency.    */
/****************************************************/
void Timer2_Overflow_ISR()    //alle 4ms wird das ausgeführt
{
  // Toggle LED1 with ADC sampling frequency /2
  //Toggle_LED1();
 
  CurrentCh = 0;
  // Write header and footer:
  // Increase packet counter (fourth byte in header)
   //Write packet header and footer
 /**********zur Erinnerung: der Header**********
 TXBuf[0] = 0xa5;  //Sync 0
 TXBuf[1] = 0x5a;  //Sync 1
 TXBuf[2] = 2;     //Protocol version
 TXBuf[3] = 0;     //Packet counter
 ***********************************/
 TXBuf[3]++;
  //the whole packet is /6*2+4+1=17byte
  //Get state of switches on PD2..5, if any (last byte in packet).
  TXBuf[2 * NUMCHANNELS + HEADERLEN] = (inp(PIND) >> 2) &0x0F;  //2* NUMCHANNELS, weil jeder CHannel 2 byte hat damit 1024 reinpasst
 
  cbi(UCSR0B, UDRIE0); //Ensure Data Register Empty Interrupt is disabled.
  sbi(ADCSRA, ADIF);   //Reset any pending ADC interrupts
  sbi(ADCSRA, ADIE);   //Enable ADC interrupts. 
  sbi(ADCSRA, ADSC) ;  // Start conversion!!!
  //Next interrupt will be ISR(ADC_vect)
}

/****************************************************/
/*  Function name: ISR(ADC_vect)                    */
/*  Parameters                                      */
/*    Input   :  No                                */
/*    Output  :  No                                 */
/*    Action: Reads ADC's current selected channel  */
/*            and stores its value into TXBuf. When */
/*            TXBuf is full, it starts sending.     */
/****************************************************/
ISR(ADC_vect)
{
 volatile unsigned char i;    //volatile??
 
 i = 2 * CurrentCh + HEADERLEN;  //also wird i auf 4 gesetzt wenn CurrentCh==0 und unten das 5. byte beschrieben,danach TxBuf[4] ([3] ist das letzte vom Header)
 TXBuf[i+1] = inp(ADCL);      //ADC data register LOW byte
 TXBuf[i] = inp(ADCH);        //ADC data register HIGH byte
 CurrentCh++;  
 if (CurrentCh < NUMCHANNELS)
 {
  outb(ADMUX, (channel_order[CurrentCh])); //Select the next channel.
  sbi(ADCSRA, ADSC) ;                   //Start conversion!!! (set ADSC-bit in ADCSRA-Register)
 }
 else
 {
   //this gets executed first....prior to the stuff above
  outb(ADMUX, channel_order[0]);      //Prepare next conversion, on channel 0.
  cbi(ADCSRA, ADIE);    //Disable ADC interrupts to prevent further calls to ISR(ADC_vect). oben hiess es sbi!!!!!!
  outb(UDR0, TXBuf[0]); //Send first Packet's byte: Sync 0
  sbi(UCSR0B, UDRIE0);  //USART Data Register Empty Interrupt Enable
  TXIndex = 1;          //Next interrupt will be ISR(USART_UDRE_vect)
 }
}

/****************************************************/
/*  Function name: ISR(USART_UDRE_vect)             */
/*  Parameters                                      */
/*    Input   :  No                                */
/*    Output  :  No                                 */
/*    Action: Sends remaining part of the Packet.   */
/****************************************************/
ISR(USART_UDRE_vect){
 
 outb(UDR0, TXBuf[TXIndex]);  //Send next byte
 TXIndex++;
 /******hier also***
 ch0hb = TxBuf[4];
 ch0lb = TxBuf[5];
 *******************/

 
 if (TXIndex == PACKETLEN)    //See if we're done with this packet
 {
   cbi(UCSR0B, UDRIE0);    //USART Data Register Empty Interrupt Disable
                              //Next interrupt will be Timer2_Overflow_ISR()
 }
}


//function for fusion of the ADCL and ADCH byte

unsigned int weiterverarbeitung(volatile unsigned char high_byte, volatile unsigned char low_byte)
{
 unsigned int value = ((high_byte&0x0f)*256)+(low_byte);
 return(value);
}

/****************************************************/
/*  Function name: loop                             */
/*  Parameters                                      */
/*    Input   :  last 2 channel bytes of the packet */
/*    Output  :  to display                         */
/*    Action: Draws ECG, detects QRS, calculates HR */
/****************************************************/
unsigned long Start, Finished = 0;
int heart_rate[4];
int heart_rate_avg;
float RR_interval = 0.0;
unsigned int Delay = 2;
unsigned int QRS_counter = 0;
int thisdot = 0;
int prevdot = 0;



void loop() {
 
  //"heart rate"
  display.setCursor(1,52);          
  display.print("heart rate:");
  display.display(); // show it
  
  //show heart rate once per screen
  if(heart_rate_avg<220)
      {
          display.setCursor(80,52);          
          display.print(heart_rate_avg);
          display.display(); // show it

      }
 
  //draw the actual graph: (128 = display width)
  for(int i=0; i<128; i++)
  {
    
    Finished = 0;
    //get the ADC value and scale it to the higth of the display
    unsigned int val = weiterverarbeitung(TXBuf[14],TXBuf[15]);  //using A5 and extracting the last 2 channel bytes out of the packet
    unsigned int y = map (val, 0, 1023, 64, 0);      //oben=0!!
    thisdot = y;
    
    //calculate the graph slope for QRS detection
    //slope can be negative so it has to be an SIGNED int
    int slope = prevdot - thisdot;
    
    //QRS complex detected above a certain threshold
     if (slope >= 8 && Start == 0)
      {
        //QRS Beep, use Pin 6 to not interfere with Timer 2!!
        tone(6, 2000, 50); 
        //start "stop watch"
        Start = millis();   
      }
      else if(slope >= 8 && Start > 0)
    {
      //QRS Beep
      tone(6, 2000, 50); 
      //stop
      Finished = millis();
      //calculate a RR interval
      RR_interval = Finished - Start;
              
      if(RR_interval>=150)  //refractory period, RR-intervals should be longer than this (filter method)
        {
          RR_interval = RR_interval/1000;  //convert to seconds
          heart_rate[QRS_counter] = 60/RR_interval; //collect 4 intervals
          QRS_counter ++;   
          
          //averaging calculation
          if(QRS_counter >= 3){
            for(int j = 0; j<4; j++){
              heart_rate_avg += heart_rate[j];
            }
            heart_rate_avg /= 4;
            QRS_counter = 0;
          }
        }
      //reset Start value for time measurement
      Start = 0;
      
    }
      
    //Draw graph  
    display.drawPixel(i, y, WHITE);
    display.display();
    delay(Delay);
    
    prevdot = thisdot;
    thisdot = 0;
    slope = 0; 
  } 
display.clearDisplay();
 
}

As a medical professional I’ve always been interested in experimenting with biosignals. I’ve made a couple of attempts to build the analog part of a simple ECG amplifier, but encountered some obstacles. Some day I’ve found this well-designed ECG/EMG shield by Olimex which uses an instrumentation amplifier and fits on an Arduino board. It comes with some sample code as well. I was suprised that it uses old C commands such as cbi, sbi, outp() and inp() but I learned a lot while going through the code and understanding it. It was originally written to interface with the ElectricGuru EEG-software via the serial port and processes the input signal of up to 6 of those shields, since they can be stacked together easily.




First of all I wanted to play with the ECG signal and since I had just figured out how to use a KS0108 GLCD, I just combined both to make this neat biofeedback device. One obstacle I came across when trying to connect the LCD to a microcontroller is figuring out which model it is! So take a look at the data sheet or whatever, because there are 3 types of those 20pin displays! The glcd library documentation on contains a table that visualizes the pinouts. Because there are many wires you have to mess around with, I simply soldered a female header on a Proto Shield and hard wired everything.




Another function I wanted to implement is QRS-detection. QRS complexes are those pointed, high spikes in an ECG which represent the electrical activity in the main muscular mass of the heart (myocardium). Their detection is quite easy by measuring the biggest slopes and and can give a more or less reliable representation of one cycle of cardial action. My code calculates the time between 2 detected “heartbeats” (RR interval) and displays that as the heart rate. This has the advantage over averaging a couple of heartbeats that you can directly observe how your heartbeats vary.




Many interestings things can be done with this kind of setup. The next step will be logging the ECG by either writing it to a SD card or sending the data to a PC via bluetooth and logging there (patient insulation from mains powered devices and less disturbing influence from the mains line). This is a very powerful tool for diagnostic purposes. For example arrythmias that occur under certain circumstances can be diagnosed or heart rate variability can be measured, which can give you information on the influence of the autonomic nervous system on cardial action…




Interrupt-based code, modified for use with the glcd:

/**********************************************************/
/* Demo program for:                                      */
/*    Board: SHIELD-EKG/EMG + Olimexino328                */
/*  Manufacture: OLIMEX                                   */
/*  COPYRIGHT (C) 2012                                    */
/*  Designed by:  Penko Todorov Bozhkov                   */
/*   Module Name:   Sketch                                */
/*   File   Name:   ShieldEkgEmgDemo.pde                  */
/*   Revision:  initial                                   */
/*   Date: 01.02.2012                                     */
/*   Built with Arduino C/C++ Compiler, version: 1.0      */

/*EXTENDED BY insanity wolf */

/*This version is for monitoring the signal directly on a KS0108 graphical LCD display*/

/**********************************************************/
/**********************************************************
Purpose of this programme is to give you an easy way to
connect Olimexino328 to ElectricGuru(TM), see:
http://www.realization.org/page/topics/electric_guru.htm
where you'll be able to observe yours own EKG or EMG signal.
It is based on:
***********************************************************
* ModularEEG firmware for one-way transmission, v0.5.4-p2
* Copyright (c) 2002-2003, Joerg Hansmann, Jim Peters, Andreas Robinson
* License: GNU General Public License (GPL) v2
***********************************************************
For proper communication packet format given below have to be supported:
///////////////////////////////////////////////
////////// Packet Format Version 2 ////////////
///////////////////////////////////////////////
// 17-byte packets are transmitted from Olimexino328 at 256Hz,
// using 1 start bit, 8 data bits, 1 stop bit, no parity, 57600 bits per second.

// Minimial transmission speed is 256Hz * sizeof(Olimexino328_packet) * 10 = 43520 bps.

struct Olimexino328_packet
{
  uint8_t    sync0;        // = 0xa5
  uint8_t    sync1;        // = 0x5a
  uint8_t    version;    // = 2 (packet version)
  uint8_t    count;        // packet counter. Increases by 1 each packet.
  uint16_t    data[6];    // 10-bit sample (= 0 - 1023) in big endian (Motorola) format.
  uint8_t    switches;    // State of PD5 to PD2, in bits 3 to 0.
};
*/
/**********************************************************/
#include <glcd.h>
//http://www.arduino.cc/playground/Code/GLCDks0108

#include "fonts/allFonts.h"         // system and arial14 fonts are used
#include "bitmaps/allBitmaps.h"       // all images in the bitmap dir
gText textArea;              // a text area to be defined later in the sketch


#include <compat/deprecated.h>
#include <FlexiTimer2.h>
//http://www.arduino.cc/playground/Main/FlexiTimer2
#include <TimerOne.h>
//http://arduino.cc/playground/Code/Timer1

/*
Erklärung von cbi, sbi, outp und inp
Bei solchen Makros sollte man etwas mehr Klammern spendieren:

#define sbi(ADDRESS,BIT) ((ADDRESS) |= (1<<(BIT)))
#define cbi(ADDRESS,BIT) ((ADDRESS) &= ~(1<<(BIT)))
#define outp(VAL,ADRESS) ((ADRESS) = (VAL))
#define inp(VAL) (VAL)
The outb( ) function provides a C language interface to the machine instruction that writes a byte to an 8 bit I/O port using the I/O address space instead of the memory address space.
*/

// All definitions
#define NUMCHANNELS 6
#define HEADERLEN 4
#define PACKETLEN (NUMCHANNELS * 2 + HEADERLEN + 1)    //6*2+4+1
#define SAMPFREQ 256                   // ADC sampling rate 256
#define TIMER2VAL (1024/(SAMPFREQ))    // Set 256Hz sampling frequency
#define PWM_OUT 9                      // Number of pin used for generating CAL_SIG
#define PWMFREQ 10        //10Hz for Calibration signal             
#define LED1  13

// Global constants and variables
char const channel_order[]= { 0, 1, 2, 3, 4, 5 };
volatile unsigned char TXBuf[PACKETLEN];  //The transmission packet
volatile unsigned char TXIndex;           //Next byte to write in the transmission packet.
volatile unsigned char CurrentCh;         //Current channel being sampled.

//~~~~~~~~~~
// Functions
//~~~~~~~~~~

/****************************************************/
/*  Function name: Toggle_LED1                      */
/*  Parameters                                      */
/*    Input   :  No                                */
/*    Output  :  No                                 */
/*    Action: Switches-over LED1.                   */
/****************************************************/
void Toggle_LED1(void){

 if((digitalRead(LED1))==HIGH){
   digitalWrite(LED1,LOW);
  }
  else{
   digitalWrite(LED1,HIGH);
  }
}

/****************************************************/
/*  Function name: setup                            */
/*  Parameters                                      */
/*    Input   :  No                                */
/*    Output  :  No                                 */
/*    Action: Initializes all peripherals           */
/****************************************************/
void setup() {

 noInterrupts();  // Disable all interrupts before initialization
 
 // LED1
 pinMode(LED1, OUTPUT);  //Setup LED1 direction
 digitalWrite(LED1,LOW); //Setup LED1 state
 
 //Write packet header and footer
 TXBuf[0] = 0xa5;  //Sync 0
 TXBuf[1] = 0x5a;  //Sync 1
 TXBuf[2] = 2;     //Protocol version
 TXBuf[3] = 0;     //Packet counter
 
 // ADC
 // Timings for sampling of one 10-bit AD-value:
 // XTAL = 16000000MHz
 // prescaler > ((XTAL / 200kHz) = 80 =>
 // prescaler = 128 (ADPS2 = 1, ADPS1 = 1, ADPS0 = 1)
 // ADCYCLE = XTAL / prescaler = 125000Hz or 8 us/cycle
 // 14 (single conversion) cycles = 112 us
 // 26 (1st conversion) cycles = 208 us
 outb(ADMUX, 0);         //Select channel 0
 outb(ADCSRA, ((1<<ADPS2) | (1<<ADPS1)| (1<<ADPS0))); //Prescaler = 128, free running mode = off, interrupts off.
 sbi(ADCSRA, ADIF);  //Reset any pending ADC interrupts  
 sbi(ADCSRA, ADEN);  //Enable the ADC                    
 
 // Serial Port
 outb(UBRR0, 16);              //Set speed to 57600 bps     
 outb(UCSR0B, (1<<TXEN0));     //Enable USART Transmitter.
 
 // Timer1
 // It's used for calibration signal generation: CAL_SIG via PWM.
 // CAL_SIG is used like reference signal when setting-up SHIELD-EKG/EMG's channel gain
 // During normal operation this signal is not required so it can be disabled with uncommenting te row below!
 /*
 pinMode(PWM_OUT, OUTPUT);    //Set PWM_OUT direction
 digitalWrite(PWM_OUT,LOW);   //Set PWM_OUT state
 Timer1.initialize((1000000/(PWMFREQ))); // initialize timer1, and set a 1/10 second period = 10Hz ->freq. of cal signal should be 10-14Hz (schematic)
 Timer1.pwm(PWM_OUT, 512);             // setup pwm on pin 9, 50% duty cycle
 //Timer1.disablePwm(PWM_OUT); // Uncomment if CAL_SIG is not requiered
 */

 // Timer2
 // Timer2 is used for setting ADC sampling frequency.
 
/*****************************************************************
Methods of the FlexiTimer2 library:

FlexiTimer2::set(unsigned long units, double resolution, void (*f)())
    this function sets a time on units time the resolution for the overflow. Each overflow, "f" will be called. "f" has to be declared void with no parameters.
    E.g. units=1, resolution = 1.0/3000 will call f 3000 times per second, whereas it would be called only 1500 times per second when units=2.
FlexiTimer2::set(unsigned long ms, void (*f)())
    this function sets a time on ms (1/1000th of a second) for the overflow. Each overflow, "f" will be called. "f" has to be declared void with no parameters.
    Shorthand for calling the function above with resolution = 0.001.
FlexiTimer2::start()
    enables the interrupt.
FlexiTimer2::stop()
    disables the interrupt.
*******************************************************************/
 FlexiTimer2::set(TIMER2VAL, Timer2_Overflow_ISR); //TIMER2VAL was (1024/(SAMPFREQ)) in ms =4, SAMPLEFREQ was 256
 FlexiTimer2::start();  //enable the Interrupt....
 
 // MCU sleep mode = idle.
 outb(MCUCR,(inp(MCUCR) | (1<<SE)) & (~(1<<SM0) | ~(1<<SM1) | ~(1<<SM2)));
 
 interrupts();  // Enable all interrupts after initialization has been completed
 
 GLCD.Init();
 GLCD.SelectFont(System5x7, BLACK); // font for the default text area
}

/****************************************************/
/*  Function name: Timer2_Overflow_ISR              */
/*  Parameters                                      */
/*    Input   :  No                                */
/*    Output  :  No                                 */
/*    Action: Determines ADC sampling frequency.    */
/****************************************************/
void Timer2_Overflow_ISR()    //alle 4ms wird das ausgeführt
{
  // Toggle LED1 with ADC sampling frequency /2
  Toggle_LED1();
 
  CurrentCh = 0;
  // Write header and footer:
  // Increase packet counter (fourth byte in header)
   //Write packet header and footer
 /**********zur Erinnerung: der Header**********
 TXBuf[0] = 0xa5;  //Sync 0
 TXBuf[1] = 0x5a;  //Sync 1
 TXBuf[2] = 2;     //Protocol version
 TXBuf[3] = 0;     //Packet counter
 ***********************************/
 TXBuf[3]++;
  //the whole packet is /6*2+4+1=17byte
  //Get state of switches on PD2..5, if any (last byte in packet).
  TXBuf[2 * NUMCHANNELS + HEADERLEN] = (inp(PIND) >> 2) &0x0F;  //2* NUMCHANNELS, weil jeder CHannel 2 byte hat damit 1024 reinpasst
 
  cbi(UCSR0B, UDRIE0); //Ensure Data Register Empty Interrupt is disabled.
  sbi(ADCSRA, ADIF);   //Reset any pending ADC interrupts
  sbi(ADCSRA, ADIE);   //Enable ADC interrupts.
  sbi(ADCSRA, ADSC) ;  // Start conversion!!!
  //Next interrupt will be ISR(ADC_vect)
}

/****************************************************/
/*  Function name: ISR(ADC_vect)                    */
/*  Parameters                                      */
/*    Input   :  No                                */
/*    Output  :  No                                 */
/*    Action: Reads ADC's current selected channel  */
/*            and stores its value into TXBuf. When */
/*            TXBuf is full, it starts sending.     */
/****************************************************/
ISR(ADC_vect)
{
 volatile unsigned char i;    //volatile??
 
 i = 2 * CurrentCh + HEADERLEN;  //also wird i auf 4 gesetzt wenn CurrentCh==0 und unten das 5. byte beschrieben,danach TxBuf[4] ([3] ist das letzte vom Header)
 TXBuf[i+1] = inp(ADCL);      //ADC data register LOW byte
 TXBuf[i] = inp(ADCH);        //ADC data register HIGH byte
 CurrentCh++;  
 if (CurrentCh < NUMCHANNELS)
 {
  outb(ADMUX, (channel_order[CurrentCh])); //Select the next channel.
  sbi(ADCSRA, ADSC) ;                   //Start conversion!!! (set ADSC-bit in ADCSRA-Register)
 }
 else
 {
   //this gets executed first....prior to the stuff above
  outb(ADMUX, channel_order[0]);      //Prepare next conversion, on channel 0.
  cbi(ADCSRA, ADIE);    //Disable ADC interrupts to prevent further calls to ISR(ADC_vect). oben hiess es sbi!!!!!!
  outb(UDR0, TXBuf[0]); //Send first Packet's byte: Sync 0
  sbi(UCSR0B, UDRIE0);  //USART Data Register Empty Interrupt Enable
  TXIndex = 1;          //Next interrupt will be ISR(USART_UDRE_vect)
 }
}

/****************************************************/
/*  Function name: ISR(USART_UDRE_vect)             */
/*  Parameters                                      */
/*    Input   :  No                                */
/*    Output  :  No                                 */
/*    Action: Sends remaining part of the Packet.   */
/****************************************************/
ISR(USART_UDRE_vect){
 
 outb(UDR0, TXBuf[TXIndex]);  //Send next byte
 TXIndex++;
 /******hier also***
 ch0hb = TxBuf[4];
 ch0lb = TxBuf[5];
 *******************/

 
 if (TXIndex == PACKETLEN)    //See if we're done with this packet
 {
   cbi(UCSR0B, UDRIE0);    //USART Data Register Empty Interrupt Disable
                              //Next interrupt will be Timer2_Overflow_ISR()
 }
}


//function for fusion of the ADCL and ADCH byte

unsigned int weiterverarbeitung(volatile unsigned char high_byte, volatile unsigned char low_byte)
{
 unsigned int value = ((high_byte&0x0f)*256)+(low_byte);
 return(value);
}

/****************************************************/
/*  Function name: loop                             */
/*  Parameters                                      */
/*    Input   :  last 2 channel bytes of the packet */
/*    Output  :  to display                         */
/*    Action: Draws ECG, detects QRS, calculates HR */
/****************************************************/
unsigned long Start, Finished = 0;
float heart_rate = 0.0;
float RR_interval = 0.0;
unsigned int Delay = 9;
int thisdot = 0;
int prevdot = 0;






void loop() {
 

 
  for(int i=0; i<GLCD.Width; i++)
  {
    
    Finished = 0;
    unsigned int val = weiterverarbeitung(TXBuf[14],TXBuf[15]);  //using A5 and extracting the last 2 channel bytes out of the packet
    unsigned int y = map (val, 0, 1023, 64, 0);      //oben=0!!
    thisdot = y;
    
    //slope can be negative so it has to be an SIGNED int
    int slope = prevdot - thisdot;
    
     if (slope >= 8 && Start == 0)
      {
        Start = millis();   
      }
      else if(slope >= 8 && Start > 0)
    {
      
      Finished = millis();
        RR_interval = Finished - Start;
              
      if(RR_interval>=150)  //refractory period
        {
          RR_interval = RR_interval/1000;  //convert to seconds
          heart_rate = 60/RR_interval;    
          
        }

      Start = 0;
      
    }
      
            
          if(heart_rate<220)
              {
              GLCD.CursorToXY(GLCD.CenterX, 2);
              GLCD.print(heart_rate);
        
              }
    
    
    //Draw graph  
    GLCD.SetDot(i,y,BLACK);
    delay(Delay);
    
    prevdot = thisdot;
    thisdot = 0;
    slope = 0;
 
  }
 
 
GLCD.ClearScreen();
 
}

In the code window below you can see the simple version of the code which is only suitable for visualization on the glcd and has an inconstant sampling rate since it reads the ADC from the main loop.

/**********************************************************/
//Simple ECG monitor program 
/**********************************************************/
#include <glcd.h>
//http://www.arduino.cc/playground/Code/GLCDks0108

#include "fonts/allFonts.h"         // system and arial14 fonts are used
#include "bitmaps/allBitmaps.h"       // all images in the bitmap dir
gText textArea;              // a text area to be defined later in the sketch

void setup(){
  GLCD.Init();
  GLCD.SelectFont(System5x7, BLACK); // font for the default text area

}

unsigned long Start, Finished = 0;
float heart_rate = 0.0;
float RR_interval = 0.0;
unsigned int Delay = 9;
int thisdot = 0;
int prevdot = 0;


void loop() {
 
  for(int i=0; i<GLCD.Width; i++)
  {
    
    Finished = 0;
    unsigned int val = analogRead(A5);  //using A5
    unsigned int y = map (val, 0, 1023, 64, 0);      //oben=0!!
    thisdot = y;
    
    //slope can be negative so it has to be an SIGNED int
    int slope = prevdot - thisdot;
    
     if (slope >= 8 && Start == 0)
      {
        Start = millis();   
      }
      else if(slope >= 8 && Start > 0)
    {
      
        Finished = millis();
        RR_interval = Finished - Start;
              
        if(RR_interval>=150)  //refractory period
          {
            RR_interval = RR_interval/1000;  //convert to seconds
            heart_rate = 60/RR_interval;    
            
          }

      Start = 0;
      
    }
      
            
    if(heart_rate<220)
        {
        GLCD.CursorToXY(GLCD.CenterX, 2);
        GLCD.print(heart_rate);
  
        }
     
    //Draw graph  
    GLCD.SetDot(i,y,BLACK);
    delay(Delay);
    
    prevdot = thisdot;
    thisdot = 0;
    slope = 0;
 
  }
 
GLCD.ClearScreen();
 
}

Here is the wiring configuration and the display type I’ve used: