hi
I'm thinking about designing a portable ecg unit, but i'm affraid about 2 or 3 dummie's things (after reading i'm still confused btw)0:
1: Two lead or 3lead testprobe?? 2: If i can use 2 leads for test purposes, wher i must place it in my chest??? 3: why if i put leads on the two corners of my chest even, i only recover a 60 hz amplified and homogeneous signal at the output of the ad8237 ( i followed the schema of the datasheet btw, except that i put 3.3V !!)
Am i doing something bad putting the AI to work at 3.3 ? or there's some constipation against me each time i use more than 3 opamps in a board?
has any one got code for LPC3128 to help me start?
> 1: Two lead or 3lead testprobe??
Three leads are essential, two differential inputs, and an indifferent electrode (base potential) to cancel the potential difference between body and the ECG amplifier. When your ECG device is "floating", ie. battery-driven stand alone (or wireless), you may apply two leads.
> i only recover a 60 hz amplified and homogeneous signal at the output of the ad8237
Power line noise is much greater than ECG voltage (around 1mV at body surface). Your ECG device should have filter to suppress power line noise.
> i followed the schema of the datasheet btw, except that i put 3.3V !!
This schema? www.analog.com/.../AD8237.pdf Figure 77. AD8327 in ECG
How did you implement "patent protection" black box on the schema? There comes a filter network, bandpass from around 0.67 to 40 Hz on standard ECG equipment.
You may add digital filter after the amplifier, like these articles.
Heart-Rate and EKG Monitor Using the MS430FG439 - TI www.ti.com/.../slaa280a.pdf
ECG Front-End Design is Simplified with MicroConverter - Analog Devices www.analog.com/.../ecg.html
I've copied my post on TI MSP430 forum, here. It'll also give you some suggestions.
ECG:MSP430FG439 e2e.ti.com/.../100464.aspx
The boards on the ECG appnotes are designed to pick up differential voltage from fingers on both hands. Usually, the axis of heart inclines from the center line of body. This inclination makes the differential voltage at both hands, caused by the heart electrical activity (ie. ECG). Some people, however, has straightly-positioned heart. Thin and tall shape often has this heart position. In this case, the differential voltage at both hands are reduced. Attach a wire to one of the electrode, and pick up the voltage of foot and hand.
Another consideration is contamination of electrical activity of muscles (EMG: electromyogram). EMG generates much higher voltage (around 100mV) than ECG (around 1mV). To relax the arm muscles, the testee sits in front of a desk, and places both elbows on the desk. And (s)he touches to the electrodes on the desk softly.
Tsuneo