ecg machine using PIC micro controller

[tolessblue]

hello
i am trying to build an ecg machine using PIC microcontroller. i have previously worked with microcontrollers...but I am not getting the ecg right. I will be very grateful if anyone can help or introduce some sites where I can get information.

 

[andre_luis]

Right here on Edaboard forum you can find many threads discussing questions regarding to this subject, however you need specify exactly what is the problem you are undergoing.



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[doraemon]

Hello!

I did quite a lot of medical devices. I think the most tricky part is the analog circuit.
(But maybe I say that because I know digital better). Once you managed to get a decent
analog signal (i.e. that fits within the bounds of your CPU input range), then the rest is
just a matter of programming and displaying / storing / sending.

ECG is somewhat easy because the electric signal you get from heart is in the mV range.
(EEG is a lot more difficult since it's in the microvolt range and therefore quite noisy).

Have fun!

Dora.

 

[andre_luis]

I did quite a lot of medical devices. I think the most tricky part is the analog circuit.

You´re absolutely right. ECG professional circuits are quite complex, featuring a lot of tasks, such as suppressing transient voltages, 60Hz and 35-40 Hz noise elimination, DC decoupling; and all this for each one lead. We can find some designs which also performs an algebraic combination of some leads even on analog circuits.



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[D.A.(Tony)Stewart]

Common mode rejection can be a great challenge, if you only rely on the InstrumentAmp. Often RF can be converted from a CM noise into a differential signal since it is beyond the BW where CMRR is useful, so RF suppression methods must be used such as ferrite Baluns and RF cap.

The other most common noise is galvanic skin response of the electrode interface where skin chemistry with electrodes creates a natural battery voltage modulated by motion, thus selection of materials must follow the best practises.

As with any signal conditioner, the optimum channel filter matches the signal spectrum, which must be well understood to reject noise to gain the highest SNR. In addition, deep notch AC filters are often included to reduce any residual differential hum from the large CM Electric field of AC line noise in a high impedance input.

Shielding, Filtering and CM rejection with single point floating ground reference leads and isoating digital noise from the analog are the challenge to measuring high impedance signals.

Any SMPS used for DC power will be a great source of interference including stray capacitive coupling of AC modulated RF switching noise in the SMPS. So isolation of DC CM noise is a huge requirement.