3 / 12 lead ecg

Electrocardiogram, or electrocardiograph??

Electrocardiogram: buy an appropriate electrocardiograph, connect the leads per the instructions, start the recording also per the instructions...

Electrocardiograph: study FDA regulations for such equipment for several years...

You could try the other side of google:

Have Fun! Rich

OTOH, if it is for your own personal use, sits in a plastic box and runs only off a 6V battery or less, and you strictly refuse to connect the device to any external devices except maybe via optical fibre cable, and there is 100kOhm in series with each electrode, then it is a lot safer than, say, working on your own mains wiring or bulding a valve (tube) amplifier.

That is, of course, assuming that your heart does not actually have something wrong with it, in which case (regardless of technical issues) it might be more important to get a piece of equipment that your doctor will immediately trust and be willing to use the results to take any necessary action.

Chris

I did a lot of searching around on google but seems most of the designs I pulled up for ECG are for a single lead configurations.

I am looking to design a electrocardiograph with a 3 lead configuration. Is multiplexing the signals the way to do this?

Thanks for any leads! :)

-Mike

Need more information. You need three channels and you must sample each in turn - then send it somewhere for display or storeage etc.

snipped-for-privacy@yahoo.com snipped-for-privacy@yahoo.com posted to sci.electronics.design:

In general, no. No reasonable advantage. Please understand you are looking for microvolt to millivolt signals in a tens to hundreds of millivolt noisy environment. Conversion time is not an issue, the signals are slow (bandwitdh of interest is less than 20 Hz). Also there are serious requirements for device safety, overload protections, and more. Learn how some of the original units were built many years ago by searching patents.

The way I understand it, just use two leads in a differential mode, and put the third lead somewhere out of the circuit, kind of like a common-mode null point.

Good Luck! Rich

If Googling fails you on this, try your library for books on biomedical instrumentation. I have a biomed text (actually a pair of books) that covers it in some detail, not only the basics of the amplifiers but the reasons for the multiple leads, and where they are normally attached.

Cheers, Tom

Medical background:

If you've never done this, a tutorial:

Actual schematics might be somewhere on the web, the ones I designed I can unfortunately not share. Multiplexing is normally not done but you must send the signals across an isolated barrier. That is no small feat at all since you have to fulfill 601-1 breakdown requirements. Personally I would never design anything below defibrillator-proof grade. After the design it's off to the UL lab for cert and for a newbie that can be like a dentist visit for a quadruple root canal.

You also have to transfer isolated power to the amps on what we call the "patient side". The return signals are usually transferred using the chopper frequency of that power path as a carrier.

Of course you could also multiplex in many ways, for example by giving each lead signal its own carrier, time slot, whatever. But generally that's not done and you'll end up with as many signals on the system side as you have leads. Of course then you could multiplex those if, for example, you absolutely wanted to squeeze them into a PC via the soundcard.

On Wed, 12 Sep 2007 22:07:57 GMT in sci.electronics.design, Joerg wrote,

Like, with a AC transformer?

Nope, you'd have some problems maintaining leakage limits and the noise would kill your signals. It's happening at tens of kHz, usually.

If that defibrillator shock comes along you don't want a lot of capacitance between patient side and the rest of the world. It could be deadly.