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ECG Monitor

ECG Monitor. Objective Provide users an economical ECG monitoring device Raise awareness to the importance of a healthy heart and living Allow doctors to be updated on patient health status Inform user should there be any abnormalities in the ECG pulse. ECG Monitor. Program Design Blocks.

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ECG Monitor

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  1. ECG Monitor • Objective • Provide users an economical ECG monitoring device • Raise awareness to the importance of a healthy heart and living • Allow doctors to be updated on patient health status • Inform user should there be any abnormalities in the ECG pulse

  2. ECG Monitor • Program Design Blocks * Denotes Programming is in progress

  3. ECG Monitor • Circuit Design Blocks

  4. ECG Monitor • ECG Waveform • A typical example of normal ECG pulses

  5. 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)

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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)

  11. Analog Interface • Analog Devices AD705 used for leg drive current • Essentially set for floating ground potential (0v) • Adheres to international safety standards • Band pass filtered with high frequency pole to prevent parasitic oscillation

  12. Power Supply • Simple use of 7805/7905 for +/-5v • Approx. 10hrs continuous use with 2 9v PP3 Alkaline batteries • Switching 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.

  13. Conclusion • Everything should be made as simple as possible, but not any simpler. - Albert Einstein

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