Do-it-yourself EEG, EKG, and EMG • Hacker News Board

Re: Do-it-yourself EEG, EKG, and EMG

#41

Post by gwu78 » Mon, Nov 18, 2013, 4:06 AM UTC

aestra wrote: post #33

gwu78 wrote: post #25

Most difficult part of "personal EEG" going forward seems to be the pasting of the electrodes to the front and back of the scalp and the chest. In hospital, someone else does that for you.

EEG is an electroencephalography and measures electrical activity of the brain. Why would you put the electrodes on your chest for that? I've had a few EEGs and there was never any on the chest. Proper placement would seem to be an issue.

You are right. The proper acronym is ECG.

I guess you've never had a polysomnography. There are electrodes placed on the scalp, chest and leg.

Re: Do-it-yourself EEG, EKG, and EMG

#42

Post by cybp » Mon, Nov 25, 2013, 1:25 AM UTC

neurotech1 wrote: post #40

cybp wrote: post #19

Earlier quoted context omitted.

You are incorrect. This circuit can potentially apply unsafe currents across the patient. A standard medical biopotential measurement circuit will have single-point failure protection to prevent conditions like this. This is required by standards like EC11, EC13, and 60601. Those systems are extremely safe. Most hobbyist designs, like the one in this article, do not have such protection. Indeed, for this particular c…

Your talking potentially "unsafe" vs somewhat likely hazard. Most of the "danger" comes from poor isolation. The skin resistance is too high for EEG to cause major problems. I realize the actual standards have requirements that are detailed and somewhat strict. The difference is that ECG has sensors that can directly put current through the path to the heart so the risk is higher if there is a worse-case ESD latchup.…

Skin resistance is quite low. You are thinking skin-electrode impedance. That is generally high enough to be safe, but with modern electrodes and luck, it can get somewhat low too. 5v 1k 5mA would not be unreasonable.

Re: Do-it-yourself EEG, EKG, and EMG

#43

Post by cybp » Mon, Nov 25, 2013, 1:32 AM UTC

MichaelSalib wrote: post #35

pmelendez wrote: post #27

Earlier quoted context omitted.

Do you know any hobbyist design that can be built safely?

Sure. Have your entire kit powered by a AA batteries. Any connection to the outside world should be either radio-only (wifi/bluetooth) or optical. That way, there's no electrical path that can carry current from a device that's plugged into the wall to your body. In the worst case, you'll have a pair of AA batteries tied to your body, which should be a negligible risk.

AA batteries are a negligible risk when you touch metal with skin. That resistance is very high. Resistance inside your body is much lower -- 100 ohms is typical. If you were to get 0.5v between you arms, you could get unsafe currents.

With electrodes, the current can be /much/ greater than touching metal wires with a finger. Single-digit kilo ohms is typical. The big ECG paddles are tens of ohms, probably.

Another way to think about it -- have you ever felt even a 24v battery? No. Now You know that 9v tingling on your tongue? That's saliva and a tiny contact area. Now think of a large patch of engineered electrolyte can do.

Re: Do-it-yourself EEG, EKG, and EMG

#44

Post by benbojangles » Tue, Nov 26, 2013, 8:57 AM UTC

alphaoverlord wrote: post #38

benbojangles wrote: post #12

I have been working with EKG on and off for ten years. I helped with this briefly: http://www.neozap.com/freeECG.htm I would love it if someone could produce a more 'rounded' piece of software. I really love my 12-lead ECG machine I got for £10. It prints using thermal paper, and has an audio output that I put into the laptop mic input. It's not dangerous at all so you shouldn't be afraid. Sticky electrodes can be ha…

That's really cool. Where did you get your ECG machine? I'd be interested in getting one if its that cheap.

good old ebay. It is a Nihon Kohden machine. comes in a brown briefcase. It's old enough not to have an lcd screen, but with the output going into a laptop, it is possible to record your ecg readout. sticky electrodes are by Ambu blue (x50 for £5 on ebay).