The Graph To My Heardunio

Paul Logston

....... @paullogston

W^3 ... plog.logston.me

TOC

• Intro
• Table of Contents
• EKG Theory (a crash course)
• Olimex Shield + Arduino
• Code for the Olimex Shield
• Python Wrapper (Olimex-EKG-EMG)
• Usage and Comparison to Real Defibrillator
• Live Demo
• Analysis
• Questions & Thank Yous

EKG Theory

Crash Course

EKG Theory

Crash Course

EKG Theory

Crash Course

Building It

• $7 dollar Arduino
• $50 shield
• $20 leads
• $5 red dots
• $82 TOTAL

Writing It

Olimex Shield Output

It streams packets that it builds at SAMPLE_FREQUENCY (125 hz)

//Read the 6 ADC inputs and store current values in Packet
for(CurrentCh=0;CurrentCh<6;CurrentCh++){
  ADC_Value = analogRead(CurrentCh);
  // Write High Byte
  TXBuf[((2*CurrentCh) + HEADERLEN)] = ((unsigned char)((ADC_Value & 0xFF00) >> 8));
  // Write Low Byte
  TXBuf[((2*CurrentCh) + HEADERLEN + 1)] = ((unsigned char)(ADC_Value & 0x00FF));
}

// Send Packet
for(TXIndex=0;TXIndex<17;TXIndex++){
    Serial.write(TXBuf[TXIndex]);
}

Writing It

Olimex Shield Output

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.
  uint8_t       switches;       // State of PD5 to PD2, in bits 3 to 0.
};

Writing It

PySerial

Writing It

PySerial

Writing It

Reading From Serial Port

class PacketStreamReader:
   def __init__(self, serial):
        self._serial = serial

    def _get_next_packet(self):
        byte0, byte1 = 0, 0

        while byte0 != SYNC0 or byte1 != SYNC1:
            # If we don't have enough data to do ALL of the following,
            # return None.
            #   - Move current byte 1 into byte0 position
            #   - Read a new byte into byte1  (1 byte)
            #   - Read the rest of a packet into a buffer (PACKET_SIZE - 2 bytes)
            # We need at least (PACKET_SIZE - 2) + 1 bytes before
            # attempting to get the next packet.
            in_waiting = self._serial.inWaiting()
            if in_waiting < PACKET_SIZE - 1:
                return None
            byte0, byte1 = byte1, self._serial.read()

        buff = bytearray()
        buff.append(ord(byte0))
        buff.append(ord(byte1))
        # read 15 more bytes
        buff.extend(self._serial.read(PACKET_SIZE -2))
        return buff

Writing It

How to we build broken values?

def calculate_values_from_packet_data(data):
   values = []

    for index in range(0, len(data), 2):
        # byte_a is the most significant byte and byte_b is
        # the least significant byte.
        byte_a, byte_b = data[index], data[index + 1]
        val = (byte_a << 8) | byte_b

        # For some reason the data comes in upside down.
        # Flip data around a horizontal axis.
        val = (val - 1024) * -1

        values.append(val)

    return values

Using It

at the command line...

$ exg -p /dev/tty.usbmodem1411

$ exg -f mock-data/nsr.bin

Using It

Compare

[Olimex]

[Lifepak]

Using It

Compare

Using It

Live Demo

Can I get a volunteer?!

Analysis

• Not medical grade. Nothing but course assessment of patient.
• Time drift (1 second per minute)

Thank You

• CPR123 (For the rhythm data)

Interested? More to come in the BOF room

Questions?

Bibliography

[1] Anatomy & Physiology Online - Cardiac conduction system and its relationship with ECG Primal Pictures - 3D Human Anatomy https://www.youtube.com/watch?v=v3b-YhZmQu8

[2] Medical Training and Simulation LLC

[3] http://en.ecgpedia.org/wiki/File:ECGpapier.png

[4] CPR123, https://www.cpr123.com/