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So I found out they sell lil single/three/???-lead EKG modules for a few dollars and decided to grab one of them. Only problem is the electrodes on this thing are Red, Green, and Yellow, and don't have any marking to tell me where they go. I got conflicting answers looking it up on the internet, too. How do I know which is which, and out of curiosity what happens if you place them in the wrong spot?
Last edited by Diff (2019-09-15 14:49:30)
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I've never tried putting them in the wrong spot, but I think it just won't read correctly.
Correct placement (according to the instructions that came with mine) is red at the 2nd intercostal space, right side of the sternum (aortic-ish area); yellow at the 2nd intercostal space, left side of the sternum (pulmonic-ish area); green at the 5th intercostal space, mid-clavicular line (apex/PMI area).
So which module are we talking about and what lead cable?
I thought what I'd do was, I'd pretend I was one of those rap guys' girlfriends.
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On my HealForce device green electrode is the "data", signals from red and yellow are presumably used to filter out mains interference I guess? So if I place them as on the pictures in the Internets, red on right arm, yellow on left arm, green on left leg (not on the limbs themselves, obviously, under the collar bones and on the stomach below the ribs), I get a rough equivalent of aVF.
P.S. "leads" /= "electrodes". Originally, a "lead" is the voltage between a pair of electrodes. With "augmented leads" and precordial leads one of the electrodes is "calculated", thus a "lead" can be thought of as a projection of the voltage vector to a specific direction.
Last edited by thewyrdguy (2019-09-15 20:03:47)
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So which module are we talking about and what lead cable?
The AD8232, and the cable is this one.
Correct placement (according to the instructions that came with mine) is red at the 2nd intercostal space, right side of the sternum (aortic-ish area); yellow at the 2nd intercostal space, left side of the sternum (pulmonic-ish area); green at the 5th intercostal space, mid-clavicular line (apex/PMI area).
On my HealForce device green electrode is the "data", signals from red and yellow are presumably used to filter out mains interference I guess? So if I place them as on the pictures in the Internets, red on right arm, yellow on left arm, green on left leg (not on the limbs themselves, obviously, under the collar bones and on the stomach below the ribs), I get a rough equivalent of aVF.
Ah cool so it does sound like I was more or less right, just with the green one being a little far away from where it should have been. I'll give it another shot, thanks!
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The AD8232, and the cable is this one.
In this particular case, red goes on the right, green on the left, yellow on the "right leg".
Since these leads don't correspond to the leads in the SparkFun tutorial, the only way to figure it out was to use a multimeter to test continuity between the leads and the labeled headers on the board.
Last edited by paperpenguin (2019-09-16 07:11:34)
I thought what I'd do was, I'd pretend I was one of those rap guys' girlfriends.
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Diff wrote:The AD8232, and the cable is this one.
In this particular case, red goes on the right, green on the left, yellow on the "right leg".
https://i.imgur.com/giKWSgT.png
Since these leads don't correspond to the leads in the SparkFun tutorial, the only way to figure it out was to use a multimeter to test continuity between the leads and the labeled headers on the board.
In that case I was all kinds of off and I'm amazed it got so close to looking like an EKG lol
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Basically any placement would get you _something_. Reading AD8232 datasheet, place electrodes connected to -IN and +IN (pins 2 and 3) the way you want to get your lead, and the one connected to RLD (pin 5) some way off of both. -IN and +IN on the arms will get you lead I, +IN on the PMI and -IN anywhere else - approximation of V4.
It's speculation, but I am pretty sure this is how it actually works.
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I gave it a try again this morning, sadly I wasn't able to get anything out of any orientation. I knew these electrodes weren't reusable but I was hoping they'd last for 2 rounds lol. Basically just got pure noise out of it, sometimes with a spike for my heartbeat. Kinda regretting not doing much recording last time. Anywhere I can get these pretty cheap? Do they make reusable ones?
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Basically any placement would get you _something_. Reading AD8232 datasheet, place electrodes connected to -IN and +IN (pins 2 and 3) the way you want to get your lead, and the one connected to RLD (pin 5) some way off of both. -IN and +IN on the arms will get you lead I, +IN on the PMI and -IN anywhere else - approximation of V4.
It's speculation, but I am pretty sure this is how it actually works.
Hardly anyone uses the AD8232 on its own, the vast majority buys a breakout board (usually a knock-off clone of the SparkFun design), which offers a 3.5mm TRS jack option, and 3 through-holes for soldering your own leads.
I gave it a try again this morning, sadly I wasn't able to get anything out of any orientation. I knew these electrodes weren't reusable but I was hoping they'd last for 2 rounds lol. Basically just got pure noise out of it, sometimes with a spike for my heartbeat. Kinda regretting not doing much recording last time. Anywhere I can get these pretty cheap? Do they make reusable ones?
I ordered a 50-pack of disposables off of AliExpress before AliExpress started removing them en-masse. I'm sure there are still plenty of options on eBay.
Reusable ones do exist, in the suction-cup variety (although you would need to supply your own gel and live with hickeys), and in the TENS-style sticky pads (though the "nipples" on them are sometimes smaller than what most snap leads require so they may not be compatible. Do you even need to ask how I know this?)
I thought what I'd do was, I'd pretend I was one of those rap guys' girlfriends.
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Amazon has several kinds of quality ones you can buy in packs. I got a couple packs of 50 of 3M ones.
Got the electrodes in late last night, been playing with placement but I'm still getting crazy amounts of noise, although for a brief moment last night I got a perfectly clear signal like everyone's showing off online. Is it possible my roommate's fridge is throwing it off? If I wear headphones I can hear his fridge so that made me wonder if it's screaming in the EKG's ears as well.
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Might be just messy power out your outlets or EMF noise in your apartment. Back at my old place, any attempt to get analog readings out my Arduinos was noisy as all hell, even on laptop battery. Now that I moved to my new place with better wiring and fewer brown-outs and such, it's a much cleaner signal, with only slight noise detectable in some parts of the room.
As an aside, are you using a breadboard? In which case, can ya try not to? Sometimes the breadboards can act as antennas and pick up stuff you wouldn't get otherwise.
I thought what I'd do was, I'd pretend I was one of those rap guys' girlfriends.
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I could have sworn I left something here.