Personal Heart Rate Monitor Device

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Personal Heart Rate Monitor Device

• By
• Anthony Shelton, Quintelle Griggs, Jonathan
  Killen, Chan Hauw Ki
• Faculty Advisors
• Dr. James Harden
• Dr. Lori Bruce

2

• More than 2 million people in the U.S. are at
  high risk of having heart attack.
• It would be helpful if there was a way for these
  people to monitor their heart.
• So we have a problem That is the way our
  project focuses on how we can utilize this
  problem and find a solution.

3
Scope

• We know there is device out there that can
  monitor heart rate but
• either big, not portable, and expensive.
• So we need to design a device that not only
  monitor the heart rate for variations, but also
  small, portable, and inexpensive.

4
Objective

• Portability
• To provide a simple device that is easy to carry.
• Weight
• To provide a device that weighs as little as
  possible.
• Size
• To provide a device that is small enough to carry
  without worrying the person that uses the device.
  
• Cost
• The device will cost less than 150 dollar, as it
  is cheap to buy.
• Performance
• Is to maximize speed of detecting heart rate the
  device have to be high speed.

5
Specifications

• 5V
• 10 bits
• 115dB
• 500hrs
• 500
• 3.5 x 5 inches
• lt 150
• 0.18Hz - 160Hz
• Cutoff frequency 0.18Hz
• Cutoff frequency 160Hz
• 500 per second
• 1.39mA _at_ 6 duty cycle

• Input Voltage Range
• Converter Resolutions
• Common Mode Rejection Ratio CMRR
• Battery life
• Amplifier Gain
• Size
• Cost
• Frequency response
• High-Pass Filter
• Low-Pass Filter
• Sampling Rate
• Average Load

6
Requirement for our project

• Includes
• To amplify the signal
• To digitize
• To analyze

• Differential amplifier
• Analog/Digital Converter
• Microprocessor

7
How to

• From Op-Amp to A/D converter
• A Printed Circuit Board PCBs needed to layout
  the chips.
• Microprocessor
• Prefabricated bot-board is used rather than start
  from scratch.

8
Instrumentation Amplifier Stage
Instrumentation Amplifier
A/D Converter
Microprocessor
9
Where to start?

• What we have for input (ECG signal)
• 0 - 5 mV voltage range
• 0.01 - 200 Hz frequency range

• What we need for the A/D converter
• Voltage range from 0 - 2.5V
• Frequency range from 0.18 Hz - 160 Hz
• Common-mode signals and noise rejected

10
Complete Design

• Instrumentation Amplifier

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Instrumentation Amplifier

• MAX 4194

• Common-mode rejection of 115dB
• Isolates EKG differential signal that we want
• Prevents interference from radiated AC (such as
  the lighting in a room)
• Gain of 10

12
What is Inside the Instrumentation Amplifier?

• Two stages of Op-Amps
• All the same Resistor values

Gain 1
Gain 10
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Complete Design

• Patient Reference

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Patient Reference

• It is helpful to reference the signal with
  respect to the patients potential (less
  variation)
• Used values recommended for feedback

Creates stability
Forces the signal to centered around patients
potential
Reference point between voltage sources
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Complete Design

• Filters

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Filters

• High-Pass Filter
• Cutoff frequency of 0.18 Hz

• Low-Pass Filter
• Cutoff frequency of 160 Hz

17
Complete Design

• 5V Voltage Regulator

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5V Voltage Regulator

• MAX 666

• Regulate the voltage needed for the A/D Converter
  and the Microprocessor to operate
• Also, includes a Low Battery Indicator

19
Complete Design

• Second Amplification Stage

20
Amplify more for the A/D

• A/D Converter needs the signal to have a voltage
  range of 2.5V

• Need another Op-Amp with a gain of 50
• Total gain of 10 X 50 500

21
Complete Design

• Stop Interrupt

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Finally, Stop Interrupt

• Used to turn on and off A/D and microP
• Creates a digital signal
• Resistors set our SPS to 500

REF from the A/D
2.5 V
Sleep or Stop signal helps conserve power
23
Voltage over the Capacitor

• Voltage across the capacitor tries to push all
  the way to 5V and down to GND, but gets flipped.

Discharging
Charging

• This creates the digital signal at the output to
  turn the A/D and the microP on and off

24
Speaking of power

• Power Budget
• microP 15mA 100uA
• A/D 4mA 10uA
• 4 Op-Amps 40uA
• Inst. Amp 93uA
• Voltage Reg. 12uA

Min Load about 255uA
Max Load about 19.1mA

• Average Load about 1.39mA _at_ 6 duty cycle

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Possible Battery to use

• Sonnenschein-Lithium
• SL-750
• Max continuous discharge current 20mA
• Small little weight (9 grams)
• With our average load (1.39mA) ? battery life of
  500 hours (just under 21 days)

½ AA Lithium
26
PC Board layout

• Because of MicroSim limitation (30 components in
  layout), we had to split up our design.
• Perfect place to split in the middle.

27
Test Plan

• Analog
• Function Generator
• Three types of waveforms (square, saw-tooth,
  sine)
• MIT wav files
• Now we are ready to create the PC Board layout.

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Requirement for the PCB

• First Follow Rules
• Includes
• Determine the Width of the Traces
• Traces between component (smaller)
• Why??? Low voltage and current.
• Air gap also smaller, 12 mil (1 mil 0.001
  inch)
• Traces between the power source (larger)
• Why ??? High voltage and current
• Air gap bigger, 25 mil

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Requirement Cont.

• Includes
• Traces that runs through a component.
• Must be 12 mil
• Why
• To avoid high heat under the component that cause
  defect.
• Next determining Pads
• rnd-070-030 are use
• .070 diameter of the pad, 70 mil
• .030 diameter of the drill size, 30 mil

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• Why use rnd-070-030
• This is confirm to the machine available.
• Drilling machine have 4 bit size available
• 30 mil 40 mil 60 mil 125 mil
• So since all our device are small, it we chose
  the smallest available 30 mil
• Next determine the footprint
• Differential amplifier and A/D Converter are all
  8-pin SO
• But since we only had 14 SO pin available, the
  14-pin SO are utilize as shortcut only.

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Some tricks to get around MicroSim limitations

• SO8 ? SO14
• Only 2 SO footprints allowed SO14 and SO16
• Assigned pins to use SO14 as SO8

8 7 6 5
1 2 3 4

• Capacitors using Resistor footprint
• Only had surface mount (SMT) footprints for
  resisters R2012 and R3216
• Changed all Capacitors to have Resister footprints

R2012
R3216
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• Next is to determine placement of component
• Since this is important to achieve our
  objectives, placement of the component are very
  important to
• Performance
• Compactness
• Size

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Creating the layout

• Layout Netlist created from each Schematic
• AutoRoute and Netlist Compare make it easy

Stop signal causes interference
More compact
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As for the Bot-board

• Microprocessor have its own board, so there is no
  need to implement one.
• We decided to connect a wire from the implemented
  PCBs to the Microprocessor board.
• This will solve the problem of having two
  different boards.

37
MicroSim PCB Program

• Netlist will be generated from the drawn
  schematic file
• Three files will be generated
• Component layer (Red)
• Top layer
• Solder layer (Blue)
• Bottom layer
• Drill layer (Gray)
• Drill size

38
Prepare for the Milling Machine

• Export DXF files
• 3 layers (Component, Solder, Drill) 3 files

Connects the pad and the trace
39
MicroSim PCB Program

• Why need three file for drilling
• Double-sided PCB

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Test plan

• My test plan mainly concentrate on the defect
  related problem to the chips.
• Major defect fall into three categories
• Problem that related to soldering processes and
  equipment.
• Vender-related problem
• Design-related problem

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Test plan

• First test (Soldering and equipment-related
  problem)
• The supply voltage oscilloscope are tested on
  another device.
• NOTE It also recommended that when soldering the
  chips, 200 C and above will crack the chips if
  not careful.
• Various device are tested for interferences
• Result
• Device selected base on their low interference.
• Conclude everything is in working condition.

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• Second is to test the chips (Vender-related
  problem)
• All the maxim chip are tested on a voltage
  supplier and the output will be measure.
• Result
• All the maxim chips are working correctly. Output
  are measured and there is indeed output from the
  chip.
• Concluded that everything is in working condition.

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• Third test the device (Design-related problem)
• The input of the PCBs are tested with a power
  input, and the output will be shown on a voltage
  measurement instrument.
• Result
• Problem soldering the component to the PC Board.
• Therefore, our test plan could not be carried out.

44
The Use of Maxim 1242 A/D Converter

• Low Power
• Serial Peripheral Interface (SPI)
• SCLK
• CS
• DOUT

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Converter Continued

• 2.7V to 5.25V operation
• Shutdown Mode
• 10-bit output resolution
• Conversion time is 7.5 us

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Code for Converter

• Have offsets for Ports used
• Data Direction Control Register (DDRD) set to 9
• SPI Control Register(SPCR) set to 28
• Status Register set to 29
• Data Shift Register set to 2A

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Code Continued

• Load and Store Accumulators
• Load Double Accumulator to 1050
• Store Accumulator A to Data Direction Control
  Register (DDRD)
• Store Accumulator B to SPI Control Register
  (SPCR)

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Code Continued

• Subroutine
• Store Accumulator A to Data Shift Register to
  start transfer
• Test the MSB in Status Register
• Branch to test the bit
• Load Accumulator A to Data Shift Register(SPDR)
• Start second procedure for transfer
• Use Logical Shift Right Double Accumulator(LSRD)
  Command 5 times
• Return to Subroutine

49
Test Plans

• Use function generator to display waveforms
  square and saw-tooth waves
• Use MIT database to get QRS waveform

50
5 major waves of heartbeat
Photohttp//home.earthlink.net/avdoc/infocntr/ht
rythm/hrecg.htm
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Purpose of Detection Algorithm

• To detect QRS complexes based
• on variations in the signal

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Requirements for Microcontroller Code

• Averaging technique used for rate computation
• User input minimum and maximum heartbeat within
  30 sec. interval
• Setting the alarm

53
Requirements Conted.

• Method for setting detection threshold
• - Detection is done on the
• differentiated EKG ( will monitor
• rate of change in each pair of
• samples)
• - Threshold is set dynamically.
• At start up there is a 5 second interval
• which allows for threshold stabilization.
• - The sample to sample difference is used
• for QRS detection, and the absolute
  
• value of this difference is used to
  
• guarantee a positive value.

54
Requirements Conted.

• Starting and alert sequence
• - Reset button ( initializes the system)
• - Putting the batteries in and putting
• the device on the patient is the
• start up sequence.

55
Variables used in Code

• AVGINT avging. interval over which beats are
  counted
• CLKCNT- count input samples
• CLKST count at beginning of avging. interval
• DATA0 most recent sample
• DATA1 previous data sample
• DEL- difference in successive samples
• STCNT initialization count
• THRESH value of threshold

• QRSCNT- number of qrs complexes
• ALARM set if qrs count is out of range
• QRSMSK count used to mask qrs detection
• AVGDEL- interval delay 15,000
• INTDEL initialization delay 2500
• MINTHR- minimum threshold
• MINCNT minimum heart rate
• MAXCNT maximum heart rate

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Detection Psuedocode

• Initialize MC68HC811 ports
• Clear CLKCNT,CLKST,DATA0,THRESH,QRSCNT(8),ALAR
  M(8),QRSMSK(8)
• STCNT INTDEL 2500
• AVGINT AVGDEL 15000
• getdat STOP
• DATA1 DATA0
• Get NEW SAMPLE FROM A/D converter
• DATA0 SAMPLE
• Increment CLKCNT
• If STCNT ! 0, THEN decrement STCNT
• If AVGINT (CLKCNT-CLKST)
• THEN CLKST CLKCNT and do ALMCHK
• If DATA1 lt DATA0
• THEN DEL DATA0-DATA1
• ELSE DEL
  DATA1-DATA0

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Psuedocode Conted.

• If DEL gt THRESH
• THEN THRESH DEL -1
• If THRESH gt MINTHR
• THEN decay THRESH every 64th sample
• If QRSMSK gt 0
• THEN decrement QRSMSK and go to getdat
• If DEL gt THRESH
• THEN increment QRSCNT and initialize QRSMSK
  to MSKDEL
• .25500 125
• Goto getdat
• ALMCHK If(QRSCNTltMINCNT OR QRSCNT gt MAXCNT) AND
  STCNT0
• THEN set ALARM
• clear QRSCNT
• RTS

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Calculation of a typical DEL caused by a
QRS

• QRS is 5-30mm high
• Duration 0.06 to .10sec
• 5mm 0.5mV
• 1mm 0.1mV
• ½ of the QRS amplitude 13mm(1.3mV)
• ½ of the QRS duration 25ms
• 1.3mV500 650mV
• 1.3/2.5 52
• 52/2 26
• 261024 266 counts
• 25ms/2ms 13 samples
• MAX DEL 266/1321
• Photohttp//home.earthlink.net/avdoc/infocntr/ht
  rythm/hrecg.htm

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Test Plan

• Simulated Waveform
• - simulate the waveform by starting at a
• memory location and use the defined
• constants from the assemblers pseudo
• directives to define data one variable after
• the other. This allows each data sample to
• be defined that is, several for the P-wave,
  
• T-wave, etc. Defining the samples this way
• creates the samples for a single complex.
  There will be some register or memory location to
  keep up with the current location as the data is
  being picked up. The subroutine will sequence
  through it. Once it gets
• to the end, it will start over again. This
  requires a lot of memory.

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TEST PLAN

• Use of the function generator
• - The function generator will provide
• the signal to the A/D converter
• Download EKG waveforms from MIT database

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Summary

• Resistors gt 0.01 18 0.18
• Tantalum (Transistor) gt 1.09 5 5.45
• Ceramic (Capacitor) gt 0.19 10 1.90
• Max 4194 gt 2.88
• Max 1242 gt 10.92
• Max 666 gt 6.83
• Max 4244 gt 4.20
• Max 4240 gt 0.83
• Microprocessor gt 79.00
• TOTAL gt112.19
• Note Our Objective to have less than 150.

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Summary

• Future Implementation
• Person having heart attack could be located using
  GPS.
• Our device will able to send signal to alert care
  giver using BlueTooth Technology.
• Build into any cellular-phone.
• You can download your heart rate and actually
  review your signal right on Personal Computer.
• Software could be come along with the device.
• Dip switch
• Allow users to enter their own Min and Max heart
  rate

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Summary continue

• Issues concerns
• Realistic Constraints
• The operating system of the assembler for the
  compiler is only available for Windows 95/NT. We
  will be using the ECE Department milling machine,
  which has certain specifications that must be met
  for PC Board construction. We will also be
  limited on the life of our battery.
• Engineering Standards
• Our device will comply with the ANSI Medical
  Device Standards Board (MDSB) and the IEEE 1073
  Medical Information Bus standards.

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Summary Continue

• Environmental Implications
• Our device will save battery power by using as
  many low power components as possible and taking
  advantage of shutdown modes of some components.
• Sustainability
• Personal ECG devices will be sustainable because
  there will always be a need to monitor the heart
  rate of people with heart conditions and are
  high-risk for heart attacks.
• Economics
• Our device should be relatively inexpensive so
  that all hospitals will be able to buy it.

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Summary Continue

• Ethical Concerns
• Our device will comply to the IEEE Ethical
  Standards
• Health and Safety
• Product does not shock patient product is
  comfortable to wear
• Our device does not cause any harm to the patient
  and it is comfortable to wear.
• Social Concerns
• The device allows the patient more freedom by
  allowing them to be monitored outside the
  hospital. Also, the product is small enough to be
  discretely worn.

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Summary Continue

• Political
• There are no political concerns for our device.
• Manufacturity
• Since our device will be cheap to manufacture and
  all components are readily available, it will be
  very easy to manufacture.

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Timeline
Deciding Scope for the project Develop idea.
August 24
August 23
Scope and advice from Dr. Lori Bruce
August 24
August 27
CPE Design Worksheet and Charter document due.
August 27
August 30
Assign Individual Part Jonathan Differential
Amplifier Anthony A/D Converter Quintelle
Microprocessor Ki Printed Circuit Board
September 1
September 4
September 4
September 8
Research prices and Information on individual
parts
September 11
September 18
Deciding parts, and ordering part
September 25
September 30
Research for simulator and Debugger for
Microprocessor
October 2
October 10
Slide and prepare for Critical Design Review
October 13
October 16
Simulator found for Microprocessor(Showdow11),
and begin flowchart
October 25
October 30
November 2
November 21
Layout for PCB developed, Flowchart
developed Rough draft due
November 25
November 22
PCB send to lab for developed, Preparing for
final design review, Slide developed
November 27
November 28
70
Final product
Analog Digital
Microprocessor
Belt for the ECG