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

ECG Monitor Program Design Blocks * Denotes Programming is in progress

ECG Monitor Circuit Design Blocks

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 3 rd probe usually on leg to lower common mode noise – effective impedance of body drops Shielded interfacing with floating ground topology used

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

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

Analog Interface Maxim MAX292 8 th 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)

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

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.

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