Minimal ECG using an Arduino and Xoscillo | Hacker News Reader

Minimal ECG using an Arduino and Xoscillo

codinglab.blogspot.be

55 pointsJare21 comments

That's an absolutely phenomenal trace... Obviously he's working under somewhat idealized noise conditions (as he described), but that trace is _cleaner_ than what we get out of the portable ECG monitors we carry in the back of ambulances (it also has much higher resolution). These are monitors have a price tag that you'd be more familiar with on a new car...

Don't get me wrong, I'm well aware that there's a big gap between some wires in a breadboard and a ruggedized, battle tested 12-lead. I'm not complaining about the cost of our Lifepacks; rather I'm ust blown away at how great that trace looks with such rudimentary equipment.

I'm gonna have to 'borrow' some electrodes from the station and give this a shot myself...

Hi, I'm glad to hear that, I'll be happy to help if you plan to build one!

As for the idealized conditions, if I gently pass my finger on my laptop's aluminum case I can feel the 50hz hum, so that is why I have to unplug it to get that signal, it may be a laptop's issue. I will check with a desktop and post my results.

That sounds a lot like your laptop's chassis might be hot instead of grounded. Possibly an issue with the wiring in your house?

50hz is pretty easy to knock our with a simple RC low pass filter. That should make a difference but it will probably attenuate the signal so you will need an instrumentation amp.

2 hours later... Ahh commercial grade design and massive BOM.

Great work at keeping it simple :)

Thanks! I am using an instrumentation amp indeed. As for the 50hz, I think I'm getting that noise just because my laptop is not grounded properly, no biggie

Probably right. Be careful!

I had a Chinese clone Lenovo charger a while ago. There was 50v floating AC on the chassis when supposedly open circuit (!). Zapped myself on any metal part I touched.

Fake one was dismantled for study and appeared to be missing most of the components. Tracing the circuit found a 1k resistor between live/hot and the ring on the PSU connector (laptop chassis DC ground). Turns out I was basically turning it into a voltage divider by touching it and was a the mercy of my quite high skin resistance :)

Replaced with a genuine Lenovo one immediately resulting in no random minor electrocutions!

(So that's where that hum comes from. Been wondering for a long time.)

Which lead was the picture from? That biphasic morphology of the T wave is a little unusual. Do you have an older ECG to compare it to?

Yes i noticed that too, I thought it could be because I put the leads where ever I felt like.

I am using 3 electrodes, the reference one (ground), was on my right thigh, the other two were, one where my right chest meets the shoulder and the other one on my left side at the level where the floating ribs are...

I placed them in non standard positions so that is why i may be getting funny values... But I agree that lower lobe is not in any ECG I have checked so far... I may go to the doctor to double check..

That's close enough to the standard Lead II. A biphasic T wave in that lead is technically abnormal, but there are a number of benign causes. Certainly wouldn't hurt to check in with your doctor though (and you get to tell him a cool story of how you discovered it)

Hey! Thanks for letting me know! I'll try to get a real ECG as soon as I can... I hope that negative lobe is just an artifact :) Thanks again, and if you need help building one please let me know I'll be happy to help!

I'm good enough to follow along a diagram and build stuff I find online, but have no real clue as to the electronics.

Given I have a neglected arduino kicking about and a paramedic I could probably get some electrodes from how far removed is this kit from knocking up a very basic 'brain controller'?

I've often fancied feeding some 'thoughts' into Ableton for some synth tweaking fun.

[edit] thought I should actually do some searching on the subject and I just found the openEEG project which has some info in that direction.

Yeah, another thing to try is to connect it to my head to see what I get.. I'd need to increase the gain a bit though

I am assuming you do the A/D conversion with the electronic board, and then treat the digital signal with the Arduino?

How difficult would it be to wire your A/D conversion unit to do USB? Then any laptop, or even a smart phone could do the UI part. Or am I missing something?

The arduino has an ADC conversor and sends it with no posprocessing at all to the PC. This could be easily used with a smart phone indeed, in fact that is my next step :)

I hadn't realised arduino came,or could have an option ADC. This is really cool. Thanks!

There's prior art on that one... (using the microphone input as a ADC, sending power to the preamp via the headphone output)

http://web.eecs.umich.edu/~prabal/projects/hijack/

Great work! This is why I come here :)

I built a pulse oximeter as my final year project at university and have been rather obsessed with medical electronics since.

I've always wondered if it's possible to build your own ultrasound sensor. Rather complicated devices though.

Is it still good practice to have opto-isolators on anything that you're wiring up to your body?

I would DEFINITELY use opto-isolators (my EEG BCI had them) and would always run the ECG on a laptop with its AC adapter _unplugged_. Do you really want to risk even a small chance of electrocution?

this would be a cool school science lab experiment

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