ecg monitor objective o provide users an economical ecg monitoring device o raise awareness to the...
TRANSCRIPT
ECG Monitor
Objectiveo Provide users an economical ECG
monitoring deviceo Raise awareness to the importance of a
healthy heart and livingo Allow doctors to be updated on patient
health statuso Inform user should there be any
abnormalities in the ECG pulse
ECG Monitor
Program Design Blocks
* Denotes Programming is in progress
*TimeDifference
Calculationsfor 'PQRST'
Receive DataFrom
PIC16F877
ECG AnalogData
Sampling
*Data Storagefor Replay
and FurtherAnalysis
Conversionto Digital
Data
*PerformPoints'PQRST'
Detection
Timer forRequiredsampling
Rate
Transmit Datato Palm PDAby RS-232
Interrupts tohandle PalmCommands
Display Plotson LCDDisplayScreen
ECG Monitor
Circuit Design Blocks
DC ±9VBatterySourceLPF for Anti-
Aliasing &Supply Noise
Removal
1st StageAmplifer
HPF for DCRemoval
2ndStage
Amplifer
ECGAnalogInput
LCD DRIVER DISPLAY
PALM M500 PDAfor Display,
Recording andAnalysis*
RS-232 Interface
MicroChipuControllerPIC16F877
RS-232 Interface
A-to-D8/10bits
Resolution
Ext 32.768KHzCrystal
ECG Monitor
ECG Waveform
A typical example of normal ECG pulses
Analog Interface
Heart pumps blood in opposite directions creating impulses known as dipole moments
Manifests as electrical signals that can be measured throughout body
Analysis can be done to determine heart conditions (not same as pulse)
Analog Interface
Very low levels of signal, down to 0.1mV!
EMI and RFI waves are orders of magnitude larger e.g. 10mV radiated EMI in lab
Industry standard of extracting ECG signals using minimum of 3 probes
Analog Interface
1 probe on each side of heart
3rd probe usually on leg to lower common mode noise – effective impedance of body drops
Shielded interfacing with floating ground topology used
AD620
AD705
MAX292
to PIC ADC
Inputs
AD705Leg Drive
PowerSupply
Analog Interface
Analog Devices AD620 instrumentation amplifier chosen for first stage
Floating ground reference
High CMR >100dB DC to 1MHz
Low bias input current <1fA
Low power consumption
AD620
AD705
MAX292
to PIC ADC
Inputs
AD705Leg Drive
PowerSupply
Analog Interface
Analog Devices AD705 chosen for second stage
Optimized for maximum SNR for specified total gain of 400
Removal of DC on inverting leg
DC level adjustment implemented here
AD620
AD705
MAX292
to PIC ADC
Inputs
AD705Leg Drive
PowerSupply
Analog Interface
Maxim MAX292 8th order Bessel low pass filter for final stage
Bessel filter provides excellent impulse and amplitude response over Butterworth and Chebychev filters etc.
Steep roll off of AC and frequencies higher than 30Hz (specified)
AD620
AD705
MAX292
to PIC ADC
Inputs
AD705Leg Drive
PowerSupply
Analog Interface
Analog Devices AD705 used for leg drive currentEssentially set for floating ground potential (0v)Adheres to international safety standardsBand pass filtered with high frequency pole to prevent parasitic oscillation
AD620
AD705
MAX292
to PIC ADC
Inputs
AD705Leg Drive
PowerSupply
Power Supply
Simple use of 7805/7905 for +/-5vApprox. 10hrs continuous use with 2 9v PP3 Alkaline batteriesSwitching regulators shelved because of lack of time and money :o(Switching regulators provide a cleaner output with noise uncorrelated with the load hence easier to compensate.
Conclusion
Everything should be made as simple as possible, but not any simpler.
- Albert Einstein