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About a week ago I had an idea to build a computer EKG using the computer's mic input as a signal input. One of the most complete tutorials I found on the internet was this one (that is applicable on ECGs also). Here is a view of the circuit: enter image description here

The first part is an AD602AN amplifier (very common on EKG circuit). All the other op-amps are filters:

-first: 60hz noise cutter

-second: galvanic current (from the skin) cutter

-third:I don't know if it is necessary for an EKG(see link for more info)

-fourth: I think its something related to gain adjustment

-fifth: again, a 60Hz noise cutter

I have some questions:

  • Is there any useful changes on the circuit given that it was primarily built for an EEG, not ECG?

-In case I want to "skip" some filter in the circuit, can I add a switch that will make the signal pass through the filter or directly to the next filter(alternator) without any kind on loss?

-Any recommendations al all?

Thanks

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  • \$\begingroup\$ You'll need more gain, maybe by a factor 10 to 50 \$\endgroup\$ – Scott Seidman Sep 2 '15 at 0:49
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    \$\begingroup\$ Be extremely careful how you power this, since you'll be connecting it via low-impedance terminals to someone's chest. Batteries would be safer than a line-powered supply, and would reduce the 60Hz noise as well. \$\endgroup\$ – Daniel Griscom Sep 2 '15 at 1:23
  • \$\begingroup\$ Isolation, isolation, isolation \$\endgroup\$ – Matt Young Oct 2 '15 at 18:51
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I that think you need to add a driven right leg circuit at the first for patient safety and protection to bypass the excessive current in case of contact with live wire. Also for proper reproduction of waveforms on PC make sure to isolate your analog ground and your controller ground.

Also for Ecg, gain of around 10000 is enough.You can split this gain between two stages to avoid saturation and add a 60hz notch filter between the two.

Eg. stage1 amplifier(Instrumentation amp)----notch filter------stage2 amplifier.

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