Hi welcome to Teardown! Tuesday We've got an exciting one for you today. It's an AED an automatic external defibrillator. This one's called the Samaritan pad and these are of course designed to shock your heart and restart it if you have a heart attack. Fantastic! Thank you very much! - Why George Miska for sending want this one into the mailbag a long, long time ago.

sorry I've only just got around to it and he this is a fully working one. but tada it is missing the battery pack. George Actually it is expired apparently. So this was the battery pack that was in there.

A whole bunch of Ci12 3 Lithium primaries in there I'm just your ultra sonically welded together. Got some hot melt in there as well to keep him together. presumably they were, you know, shrink packaged up or something like that and they were sitting inside here. Um, of course it's a basically a single-use type device is our primary type things.

This is actually one of these, like public access devices where you're like might leave them in a public location, in a building, or you know, some other area or something like that. And if somebody's having a heart attack, then so goes the theory. a Joe average hence the name. The Samaritan there a Good Samaritan comes up Joe average and uses this thing to hopefully attach to somebody having a heart attack.

But these ones designed for such use are fully automatic so you really can't kill you know, like a live person. if they've just fainted or something like that, they very smart. They automatically monitor the heart first to make sure and then they give these LED indicators here and it's got voice prompting as well. So this one's only got two buttons power and shock here and you turn it on and then it'll voice prop you whether or not it's an adult or a child because adults will have a different energy level.

A shock energy level around about this one's about 150 to 200 joules, but some of these can go up to 300 or 350. Jules I've read this one in particular sets 50 joules for a child, so lower energy about. you know 1/4 the energy of an adult and we've got our two pads here. It shows you exactly where to put the pads on the person if every if it doesn't detect a you know a heartbeat and everything else or an erratic heartbeat it decides whether or not to shock person.

It'll say stand back and press the shock button boom and it will I shock them with a biphasic waveform. And here's a look at the waveform around about 10 milliseconds or something like that. It's called biphasic because Go! It's positive first and negative. Older devices from you know, a few decades back didn't do this.

They had a mono phasic one where it only went positive and shock to you. but the newer models like these ones use a biphasic pulse like that. And for those playing along at home, this is the heart Sign Samaritan Pad Sam 300 P manufactured by Heart Sign Technologies Limited in their island. I'm basically Belfast in the United Kingdom So hi to all me Irish Viewers to be sure like to be sure and there's the instructions on the back on how to use it.

turn it on, remove the pads, place the pads on the bare chest stone clear if advised, Press shock button. As I said, it's got voice prompting so it'll have like a pre-recorded voice chip. One of those vocoder type chips are pre-recorded in there and if needed begin CPR So I think it only like has one go at it or something like that. Anyway, certainly with the Lithium primary batteries, this wouldn't be although you can actually get new pads for it.

I Think Anyway, these were expiring 2017 so I don't know why this one expired because it says December 2016 but George said that this one had expired. So here's your pads. Jeez, the person wouldn't want to be. Well, they are in a hurry aren't they? How do you? How do these bloody pads come out of here? Oh there we go.

Hey, you just rip it. So yep, Oh yes, yes, there we go. So you just get that. you rip it.

Bingo. These are your two hard pads. There you go. I Presume they've got a sticky.

yep and then a sticky adhesive thing. Yep, you peel it off. Yep, that's it. hit.

Mmm, hang on. Whoa. that smells no ice that would have a a specific dielectric you know constant to get you know, like to actually allow the current to pass and things like that. So they'd be specially designed pads.

so you got two of those. Whip off, put them on the person I Know here we go. It tells you this one must go here. This one must go here.

So there you go. You've got to get them around the right way. presumably it's not gonna work at all. It won't.

It might detect it if you've got a month back to front. Maybe I Don't know. but yeah, there you go. Polarity.

It's pretty easy. I mean average Joe could come along and and you know I've worked these things on I think and this one does actually come with a port on here. Check it out. and it actually came with a cable that you plug in USB cable so you can actually monitor it.

There is like another version of the model from this manufacturer that has like an LCD display and that you can get. They're actually the cardiac waveform and everything else. But yeah. so I don't know why you maybe you can use this to mana to the heart anyway? hmm and this one's actually reusable.

You can actually just whip out the pad and the battery so you can just buy these and that's quite neat. Innit I Like that so you know You don't have to just buy an entirely new machine. Guess these go for about twelve. This particular model goes for about twelve hundred US dollars and it is a current model so you can still buy it.

so I don't know. You might pay an extra hundred or two hundred bucks for the pads and the battery pack or something, but certainly cheaper than buying a good one anyway. You know we say you're on the eevblog, don't turn it on, take it apart. You certainly wouldn't go taking one of these puppies apart if it was powered up and or if you powered it up recently because the we're gonna see a big-ass capacitor bank in here.

which of course I stores the high energy pulse up to 200 joules as I said for an adult and 50 joules for a child. So maybe whether or not they I don't know whether or not they control the energy coming from one capacitor bank. or maybe they have - not entirely sure we'll find out, but that's we. Expect to find a big capacitor bank in there, electronic switching of course, and maybe some inductors to control the you know, to take the edge off the pulse or something.

And now we are we done taking out all there. Yeah, there's probably clips on here anyway. let's check it out and there'll be a some micro or some description and wouldn't be surprised. It wouldn't surprise me if part of its potted.

Maybe our IP 56 rating, but you know these things have to be quite rugged. It'll be designed to be thrown around and all sorts of stuff, so our shock and vibration and moisture ingress and things like that should be. Well, at least on the high voltage parts of it should be handled fairly well. So um, I like the little pogo pins on there anyway.

hang on, try and pry it open. Here we go. It was just stuck with age. Tada.

Oh, we're in like Flynn Look at, that isn't that lovely. I was wrong about the potty though. There is no pot in and there's our capacitor bank. We've got five caps.

They could be in series, perhaps giving higher voltage. We'll check out the specs we've got our look at. There's our switching MOSFETs presumably their MOSFETs Let's yeah, it's interesting. It's all the one board, so it's not not very complex at all.

Let's wiggle these off and get right in there and I'll show you all the individual parts. Bingo. oops. Check it out.

I Pulled the entire connector off the off the bare pins down there for the battery. oops. It looks like the whole board is just kind of lifts out. except for a yeah.

We got ourselves the ribbon cable. There we go. which goes down to the yeah. We've got ourselves a speaker.

uh yet. double-sided load. not a huge amount on the back. there.

we've got some Elf resistors you know, I'm AM Elfa bit of a Mel fanboy and of course the high voltage stuff. There's our Dyers. look now you can automate instantly. see they've got a diode across each cap that's to prevent, and you can see that the caps are all in series.

Look at that. So there's a reason there's a diet across each cap like that is because when you charge up caps in series like that and you discharge them, you don't want any differences in the capacitors to cause one capacitor to actually reverse charge because then it could well explode and the magic smoke escapes. And you don't want your defibrillator exploding because it'll cause somebody else to have a heart attack. and there won't be a second defibrillator around to resuscitate them.

So yeah, there you go. You can see the ground plane all under there. all the digital stuff now cuz we're generating high current pulses down in here, you know? So this is all ground plane around here. That's all for.

The digital stuff is actually, well take a look at those, but that's a that's a fair beefy amount of digital goodness down in there, but it's not a huge amount to the energy section at all. Got a couple of big ass relays in here. Looks like we're gonna transformer in the note that's an inductor. No.

I Thought that was a transformer for a second, but one interesting thing is that they've got a backup battery. What does the backup battery for? Well look I See a watch crystal down in there? 32.7 kicks 8 kilohertz. That'll be an RTC chip. Why have they got an RTC in this thing? I Can only presume that it actually records the time and date of when the incident actually happened, in which case.

Well, it's You Know, it may not be that the date will be accurate, but the time may not be accurate because it presumably sent the factory or whoever installed it in the location. But the the thing with these is that they can sit there for years and the drift. unless you have a really Schmick crystal in their temperature control. or TC EXO or something that's going to drift like, you know, like a couple of minutes a year.

It could be even worse than that actually with temperature extremes and things like that. So yeah. hmm. Anyway, look labeled Sternum Apex Beauty and this is a 2007 vintage.

thank you very much. Cornell DubLi Affair or you Cornell DubLi A Fanboys There you go. 600 Mike 400 volts working and made in the United States of America Awesome! If you haven't heard about Cornell do Glia. They are yeah, top Shelf capacitor brand.

So maybe they would have maybe specifically characterizing for the purpose? maybe not. They're probably I don't know. You could go look up the part number and just not the shelf one probably. But anyway, they do all have an individual sticker on them.

So does that mean that there are qualified part? I Don't know about the requirements? Well, I can tell you that the requirements to get one of these designed and produced and certified for manufacture and public use would be ridiculous amount of red tape to actually do this. So maybe the parts in here need to be qualified for this particular use. I Don't know. is anyone in the medical electronics field can tell us if these would have been a you know, a qualified certified part for using defibrillators? Let us know.

And if you don't know anything about one volts, reverse on an electrolytic capacitor is going to potentially do some damage to them. So having a single diet across them limiting to under one volt Bob's your uncle? Guess we should actually read the user manual for this thing. It actually shows that it can do like three pulses here by looks of 150 joules, hundred fifty, and then 200. So here's your one shock and then weights presumably weights 120.

Second: CPR pause so give him a shock, then I Guess you're supposed to give him CPR and then shock him again. One interesting part on the PCB here is look like here's the string. Okay, so all the caps are in series like this. Okay, they're 400 working volts each.

so one two, three four five. We've got 2,000 volts maximum for our capacitor bank here at what was it? Six hundred Mike and you'll notice that the trace comes across here. Cap Plus and Cap Minus. So they're actually this isn't connected to anything except this would be maybe part of the production test jig or something like that would be my guess.

And they've got some. Looks like it's some test stickers on here. They're gone through the testing process, so they might put that down to a bed of nails or something like that, and then they test across the capacitor beam directly. Okay, so what we've got here is the charging circuitry.

the high-voltage step up, because hey, this thing has to be charged to, well, somewhere over a thousand volts. Something like that. It's a 2,000 volt maximum pack here. I Think it's like normally 1500 volts or something like that.

Our battery is straight into our input terminals here. So this is on the primary side of the transformer. I've obviously got a switching transistor here I'm surprised that's just flapping around in the breeze, you know. I'm not a fan of Tio2 20s just flapping around in the breeze.

and we've got a 10 turn trimmer. thank you very much. There's no y gunk on that - why stick that down? So I Don't know if somebody's tweaked that at the factory or not. Anyway, low impedance path switching the primary of the transformer here, the then it a boost up on the secondary and use it to charge the capacitor bank.

So that's obviously the location you want it from a low impedance point of view. So I don't know how long it takes to charge this thing up to 200 joules. and if I hold this up to the light, we can see through the board here and you can see the ground plane actually goes from primary to secondary over there. So this is not an isolation transformer.

Oh and there's our MOSFET on the back of the board by the way directly on the battery terminal. Look at that straight over to the secondary side and this sense circuit here with these high value protection resistors that's actually sensing the voltage to read across the capacitor bank. So these resistors are obviously providing most of the voltage drop across there. and this isn't So this only needs to be like a low voltage our amplification and that's actually a fairly common technique dropping the voltage across some to high value resistors.

There it's technique to what's used inside these high voltage differential probes. If you don't know, you might be familiar with these things. You might think that there's some ways being proprietary isolation transformer technology in there and stuff like that. Know if you want me to do a No? I've always wanted to do a teardown a reverse engineering of one of these and oh let me know if you want me to do it and you'll find it's a similar thing.

It's basically high value dropper resistors in here. Actually, you know this is like a hundred one division ratio up to you know what? is it? Yeah, plus minus seven hundred volts and 700 volts common mode. but there's actually no transformer isolation inside this thing. And the inductor that we've got in here looks like it's going to be in series with the output and in series with the patient under test Part P UT But patient under test.

There you go. You're a part if you connected up to this thing putz. Hmm. Anyway, the inductor is going to be in series just to like limit the energy that's being dumped to you, limit the rise time of the pulse that's going into you now.

curiously. I'm In pre older architectures that weren't intelligent like this, they'll just dumb and less use capacitor relay and like and inductor switching. They would have the inductor in series to actually create the mono phasic waveform, but with the new biphasic stuff and all super intelligent and timed and everything else, it's like, yeah, operates slightly differently, but I believe, but it's still going to limit. You know, you don't want that capacitor bank being dumped boom via an instant low impedance straight to the body, so you do want to control, so they've obviously got a choice in doctor in there.

You'll notice on the back side of that inductor there's two diodes in series missing here, so that's rather interesting. They would have been used to clamp any back EMF from that inductor presumably. but yeah, they decided not to not to fit those. There's a couple of missing capacitors over here, don't know what's going on there, but yeah, they're the only.

These two are obviously mission why they've got to there is because diodes can. Actually what they can do is they can fail short. So like as in a short circuit. That's typical failure mode for a diode.

So if you've got one just across there, especially in high voltage high energy stuff like this, if it shorts out, it's gonna could ruin your day. But if you've got two of them, then one then the other can take over. and bingo, you know it's not a problem really. So that's not an uncommon technique on our high reliability stuff, which presumably this thing has to meet.

there is reliability standards and things like that. So which is why I'm surprised that you know none of the high voltage stuff is actually got any pot in and there's a couple of things flapping around in the breeze here. you know, vibration. Although this one's like this one's designed to sit stationary in like a you know, an emergency break glass kind of situation, it's not designed to, you know, be out in the field with ambulance officers and things like that.

But yeah, you know, I'm probably like there's no silastic anywhere holding anything down or pot in or anything like that, but still, it's You know? it's obviously good enough. Let's take a look at the main power packages. There's actually three of these babies here. this one this one and this one over here.

And these aren't just regular up MOSFETs these are our IGBT superfast twelve hundred volt transistors designed for you know, really high fast high-energy switching and no surprises for finding those puppies in there at all. And the other two packages in that little Bank there aren't transistors there. these are actually SCR 30 TPS Towers once again from International Rectifier. No one hung low.

Rubbish. You know, a medical-grade device like this and Scr is kind of makes sense here because what Nessie are does of course might have to a fundamentals Friday on them is that once you trigger them on the gate then they stay latched on and they will deliver with all the state on until in this case deliver the energy from the capacitor bank through to the hut, the person under test and so the wrestler. so once triggered the rest of the circuitry can like fail and it doesn't matter, this baby is still gonna stay latched on until it until the Energy's bled away and the voltage threshold is you know, over it's done. So yeah, SCR makes sense and they're twelve hundred volt packages.

but even though is a small fry compared to the Big Daddy over here which is doing all the business, thank you very much. I'm an exorcist Cs20 22 Murphy No, it's an Mo if one that is. Anyway, in this fantastic ISO plus I-4 package and the reason it's called ISO Plus if you can, maybe you can see it. There's a hugely wide pin spacing.

there's two pins over here close together and then massive pin space in here. Oh Flip it over. There it is. There's the massive spacing across there and that's how they get the twenty two hundred volts isolation of this baby.

I Mean this is a serious bit of kit and that's a phase control theory stir any kind of otherwise known as an SCR Let's not get into the differences, but yeah, Cyrus de ser same thing works the same way. once you latch those things on BAM they're staying on until the voltage drops down to bugger-all Now please excuse the crudity. if the model I didn't have time to build it to scale or to paint it. this is the Dave Caird reverse engineer in addition and I've just done a little bit of reverse engineering problem.

maybe not a hundred percent, but it's going to be close enough for the purposes of today's experiment and adjust the basically the charging of the capacitor bank and the discharging to the sternum and the apex positive and negative terminals on here so let's have a look. We've got our cell C6 Cr123 batteries over here obviously I've got a couple of MOSFETs driving the transformer and of course that transformer. There is that one there. So there's our battery input right there and that's one of the MOSFET and the other MOSFET is on the bottom there.

So they're just driving the primary of that transformer. There's a current sense resistor that's that baby. there. 68 milliamps and the secondary of the transformer has just got WAP Eva one diode which is missing or three in series like this and that just charges the capacitor bank up.

And as we've mentioned before, we've got now five big main storage caps 600 mic, 400 volts each in series with their reverse protection diodes on there to stop them. We're charging in Reverse sense and limiting the voltage to under a volt to keep the electrolyte safe inside. The things: Because anything over a bolt a volt cannot damage a little electrolytic capacitors. Now, our output from the cap.

here. it charges up. Okay, so when you first power it on, it'll obviously start this up. They'll charge up the capacitor bank ready to do a discharge.

How long that takes to charge up? I Don't know. there could be other detection stuff in here and anyway, we're not going to. Actually, there are various. There is another tap point coming off the capacitor bank as well, which goes off to an amplifier anyway, as there are.

there are sensing amplifiers directly on the apex and the sternum terminals here, so they just go off to all the control circuitry, etc. Anyway, as soon as you turn on the power, it charges up the capacitor bank and then it's ready for action. Now it's not going to discharge until such time. and as these two Scr's turned on here to go and the relay to go out to the sternum, or these Igbts turn on or these Scrs here turn on, so obviously these would all be switched off in the normal state, that relays it be off so you'd be relay isolated.

There's the two relays there, so you'd be completely safe. The big excess SCR is that one there and the big inductor here. The big storage inductor is that puppy that we've seen in there. And then we've got the the TPS SCR that ones on the other side here and two other TPS scr's which are identical are those two there.

and the Igbts as we've seen are those two on the front there and the two relays and the two terminals. and there's the other sense one on which I haven't drawn that it comes off the main capacitor being here. Okay, so this is what I think happens when you actually press that shock button. We've got our charge stored on our capacitors here.

it's going to go out here and first of all, it needs to be a positive peak. Okay, so our sternum is the positive terminal, our apex is the negative terminal here. So obviously it's not going to be shuttered down here. it's going to go through the inductor.

And of course, that's going to limit the inrush current to the patient under test the pot. And then these two SC are going to turn on. the relay is going to switch on and Bingo. It's going to go out the sternum, through the poor little dude here like this, and through the dude and then out, oh please, excuse the Trudy this through the eye, into the apex terminal.

and then where does it has to go? Well, they have to turn this relay on of course. and then they have to turn this SCO on here. So Bingo like that. So current flows through the poor schmuck like that.

And now you can probably see why. we need a big beast to kilovolt isolated thyristors. Here is because look, it's directly across the capacitor banker there. so which you know has a maximum of 400 volts times five to Kilovolt.

So you need a matching to Kilovolt Now Syrustey in here. and likewise for this little stubborn network across earth. Arista Here, you need that to Kilovolt rated Cap there as well. But this might come into effect when we go to the negative.

So now we have to actually produce our negative poles. But we haven't actually dissipated all the energy in our capacitor because there is no second capacitor bank in here. No second storage element in order to give us that negative shock pulse, a biphasic response that we actually need. Sure, this inductor is going to charge up.

There's going to be some magnetic field in that inductor, but you know it. Just look at this. you know it's tiny compared to the any energy storage in these five caps. A little tiny magnetic field in there, so that's not going to do the business.

So now we need to reroute this so we can use the rest of the energy in our capacitor bank to shock them in the other direction. Let's give it a go. So, I've got some charge still in our capacitor? It's still going to be positive and negative here, so we need to flip it around. So what do we do? Okay, we've got our little dude here again and he's getting shocked like this.

What can we do now? I'm not sure if they'll realize, actually switch off at this point and then switch back on. They don't necessarily have to I Suspect they may not because the waveform travels directly Negative. So the relays would probably switch on. But what happens is that these two Scrs here they turn off.

Okay, so and then they switch on the IGBTs here. So that current so well. let's draw it Okay, realize on through the IGBT like this and then through here and this Scr turns off. it was on before.

but we go to our capacitor bank now. What haven't we switched on yet? Bingo! Our big excess Scr slash thyristor up here. Okay, the capacitor bank is now through here like that. So now we've got the positive here and the negative actually here because this is negative of the capacitor that was opposite to what we had before.

We had the positive Sterman his sternum here and then the apex was at the negative. So Bingo! we've now swapped it over and we shocked them in the other direction. Current is now flowing this direction instead of that direction like it was before. Too easy.

And you'll note also that this TPS SCR down here isn't as highly rated as the this one up here because we're now at a lower voltage because we're on the negative part of our waveform. It's a lower voltage, lower energy shock. So therefore, this SCR doesn't need to handle as high a voltage as this Ex's one did with the huge monster pin space in. so here it is that one is not nearly as high rated as that one with its monster pin pitch on there.

It's two kilovolt isolation. And likewise, these two TPS they don't have to handle the same as well. Bite you. Also note that the inductor here there's going to be some back EMF in that, and they did actually put two diodes in series on the back there as we've noted before, but they haven't populated and so clearly.

Well, they don't care about because these SCR s are switched off so it's not a problem for the patient. it's just a matter of our voltage rating for the two TPS parts in series there. But anyway, that's it. And of course, in this case, this snubber network here is probably doing something as well.

You'll note the two different value resistors in series with those diodes there, so it's probably operating in the negative side like that. So there you go and hopefully our little putt here is revived. That's a plan anyway. Boy, you're just going to Cpr, So there you go I Hope you enjoyed that too.

Look inside the Samaritan pad. AED automatic external defibrillator and thank you very much George for sending this puppy in. It's really quite interesting and it's You know it's a reasonable design I Just would have expected a bit more mechanical robustness in there, but as I said, that's you know it's not really fulfilled. Use: It's designed for locking in a cab, Litton cabinet and or you know, storing like in an office environment or something.

You know a lot of officers will have one of these and you might have somebody who's you know done half a day's training on how to use them or you know, or a couple of people something like that and well, you hope it's not one person and then that's the person that has a heart attack. Anyway, these things are pretty foolproof because there's a voice prompt and everything like that. and yeah, by the way, all the voice I didn't look at the voice stuff. there might be a voice chip in there Oh Yep, there it was hiding under the label.

exactly what I suspected it's the classic chip quarter is d4 double Oh four series have been bought out by various companies over the years anyway. I don't know, but yet that's still the anything single chip voice recorder. your pre program in the voices in there and then this one's an Sbir control. but you know there are Dumber ones that you can just you know, like five different playback messages or whatever and you just stroke the pin and boom it plays it back.

so too easy. and there's some more analog II goodness and stuff down in there since amps and you know things like that. Maybe I'll post some high res teardown photos of this puppy as I do with most tear downs, but if you're interested then you can maybe take a look at that. But anyway I hope you enjoyed that teardown.

Thank you very much George for sending that in if you want to discuss it. links down below if you like that. big thumbs up and all that sort of jazz. Yes, it does help with the search engine rankings and you know Google foo and things like that YouTube through catch You next time has an ECG function as well and we took a look at some of the circuitry last time and what some people wanted me to play with this.

So okay, let's see if we can actually get some ECG data out of this. There we go.