- Parker has a new update to the Jeep Bluetooth Radio Mod. To level shift the Bluetooth audio to what the TDA7340S expects, Parker is going to build a differential opamp. The Bluetooth audio adapter has a 50mV DC offset and a 1.9V Pk-Pk at max volume where the TDA7429L is expecting a 4.65V DC offset with a 800mV Pk-Pk. See Figure 1.
- Stephen has a crazy idea to make the “ultimate” inexpensive resistor standard. His plan is to use a big array of resistors that are in parallel/series. He hopes that statistically it will swamp out the tolerance. Stephen will use different manufactures to swamp out batch issues. Next week we should have some analysis on this project done.
- Analog-EETimes article: Why the zero-ohm resistor?
- NASA Wants SpacePoop Hackers. Reminds Parker of this Apollo 10 radio transcription. See page 416.
- New Bluetooth 5 spec is out. Key updates to Bluetooth 5 include longer range, faster speed, and larger broadcast message capacity.
- Samsung exploding battery update.
Special thanks to whixr over at Tymkrs for the intro and outro!
About The Hosts
Parker Dillmann is MacroFab's Co-Founder, and Lead ECE with backgrounds in Embedded System Design, and Digital Signal Processing. He got his start in 2005 by hacking Nintendo consoles into portable gaming units. He also runs the blog, longhornengineer.com, where he posts his personal projects, technical guides, and appnotes about board layout design and components. Parker graduated with a BS in Electrical and Computer Engineering from the University of Texas.
Stephen Kraig began his electronics career by building musical oriented circuits in 2003. Stephen is an avid guitar player and, in his down time, manufactures audio electronics including guitar amplifiers, pedals, and pro audio gear. Stephen graduated with a BS in Electrical Engineering from Texas A&M University.
Host 2 00:10
Hello, and welcome to the macro fab engineering podcast. We are your hosts, Parker, Noma and Steven Craig. And this is episode 45. Yep. Alright, so continuing on from last week, we did Jeep radio. Yeah. I think last time I said I was going to actually measure the signals and stuff that comes off the radio. Off the chip. I did that.
Host 3 00:33
Yeah. And you actually last week you had actually found the right chip
Host 2 00:37
Found the right chip? Yep. The TDA 742 Nine L. So the interesting thing is in that effects loop that that goes out to a capacitor and comes back. Yep. The voltage levels there are very interesting. It's a 4.65 volt DC offsets.
Host 3 00:56
Which audio signal Yeah. Which is kind of like half scale. Yeah,
Host 2 00:59
Half. That's half. It's a little bit higher than half the rail. Yeah. And it's an 800 millivolt Peak Peak audio signal. Yeah, that's
Host 3 01:08
Kind of weird. Yeah. It's kind of weird. I've
Host 2 01:09
Basically figured that out by inputting into the chip a one kilohertz, what sine wave, and then just measured what that was. Read until you got distortion, right? Yep. Until I got distortion. And that was the the wave. So that's all fine and good. Except the problem is the Bluetooth audio adapter is designed to be plugged in through speakers. So it's only got like a 50 millivolt DC offset, which is probably just like, you know, measuring, you know, measuring offsets, right, and then it's got a 1.9 volt peak peak at max volume. Yeah, yeah. So that they're kind of not compatible. Because if you pump that into that chip, it's nothing's gonna work. You actually don't get anything. Cuz you just overload the hell out of it. No, it's below the DC offset. Oh, okay. I got you. Yeah. Yeah. So Stephen, helped me design basically a differential op amp setup. Yeah, you
Host 3 02:02
Get to get get into the analog world. Yeah.
Host 2 02:05
So I don't know what's up African us, it seems that I can just use pretty much whatever, since it's, you know, under 44 kilohertz, and
Host 3 02:14
Well, yes. Yes. The answer is, is in general, yes. In other words, you don't have to go out and buy like a crazy audio op amp, because old op amps. Right. You know, I told Parker, a to 072 to 082, or an any lm 3558.
Host 2 02:35
We don't need power. You know, that's like the it's like the 7805 of the op amp world.
Host 3 02:42
Oh, yeah. Or a 741? Do not use a 741. They are garbage. Yep. Yeah. So like any Jelly Bean audio op amp will do or not even audio, but like just low noise. When doing audio stuff, it doesn't hurt to get a J fet input just because the noise is low. Net. So really, if you're looking for audio stuff, start by saying is it a J FET? Input, and you're probably going to get a good op amp from that.
Host 2 03:09
So people out there on Twitter, tweet me at Longhorn engineer, what op amps should I use for this thing? But yeah, so it's like it's got a basically a feedback loop, basically, make sure has, you know, basically will cut the waveform in half. So from you know, 1.9 volt to 100, millivolts, you're probably around 850 millivolts. If we do just straight half, but that's fine. Yeah. And then do the DC offset, we're putting in on the non inverting side of the op amp, a DC offset with a voltage divider, basically divide the rail in half,
Host 3 03:47
Right. So what happens is you raise the output by your your DC offset. Now you're putting your audio signal into the inverting side, or you are inverting it, but it doesn't matter doesn't matter. So you're good? No. So basically, you're adding a DC offset, and your signal which is cut in half, which it is important to note for people who don't know, cutting it is still gain. Yeah, it's just a game less of less than one less than unity less than
Host 2 04:17
Oh, yeah, there's a sad word for you
Host 3 04:23
Know, but it's still considered gain.
Host 2 04:25
Yes, it is. Yeah, that's all I have on that.
Host 3 04:30
Cool. So, so I had a thought earlier this week. Oh, this thought Yeah. Well, okay, so So I was this. I've actually had this thought a long time ago, but it but it kind of came back to me. And I proposed it to Parker and he's like, why don't you do it? Like, oh, God,
Host 2 04:47
I just want to see it built. Well, okay, so
Host 3 04:49
Here's the thing, if you take resistor standard, in other words, you can purchase these ultra expensive boxes that have a resistor in it. That is an exact resistor and I hold
Host 2 05:03
It up and it's just like one carbon film resistor. But it's like been measured perfectly to be that that resistance maybe
Host 3 05:09
You never know, although the temperature coefficient would probably be all over the damn place. Yeah. So So okay, so these, these resistor standards exist, where you can buy like a 10k resistor, and you put your multimeter on it, and you can calibrate it to 10k.
Host 2 05:26
Yeah, how many digits your, your multimeter goes to, right, right, and you can
Host 3 05:30
Get them down to almost any precision level you want. But I have a thought that if you take, let's say, you take, you wanna, you wanna whatever resistor, you can, you can parallel and series resistors such that the cumulative addition and parallelisation, or however you say, it makes them that value. Yep. But if you, if you do it properly, you can actually use tolerance components such that they all stack together and you get a tighter tolerance component. In other words, if you take two resistors in parallel, and you put those in series with two other resistors in parallel, all the same value, you get a resistor whose cumulative resistance is that resistance. In other words, for
Host 2 06:23
You basically wash trying to wash out any manufacturing tolerances, right,
Host 3 06:28
So my thought was, what if we make a board? That is a big matrix? of tons of resistors?
Host 2 06:36
Oh, 805 by 10? Cakes? Yeah, right. Like, I'm talking hundreds, maybe even
Host 3 06:40
1000s of resistors that all equal the value of that resistor? In other words, like, if you take a say 1000 100k resistors. And you series and parallel them such that they're all 100k. Can you make a resistor standard yourself? Basically?
Host 2 06:59
Yeah. Um, I thought it was really cool idea. I really want you to make this thing just for like a thought experiment. Yeah. I think next week, we need come back and like, do the math on this. Yeah. And there's got to be like a limit as this as you grow. Because exponential since it's a diminishing return. Yeah, you get diminishing returns because at this this, this grid will grow exponentially in resistor size of when does how many units you get to get to a point where, like the next resistor, you only gain like point oh, one ohm. tighter tolerance will Okay, so here's the thing, and what's acceptable as tight tolerance?
Host 3 07:38
Well, what's crazy about it, okay, so when when manufacturers make resistors, and they put some kind of tolerance value, one 510 20, whatever percentage tolerance on there, they, that doesn't necessarily mean that is equally distributed across the entire batch that they make correct. So if you pull all of these resistors, from a single real, and a real is coming, what 510 k depends on Yeah, so if you pull all the resistors from one reel, you will not get an accurate result. Because that whole reel might be off of its value by how much flow? 2%? Exactly. So my thought was, if I have a matrix, a hole, like, let's, let's just pretend 10 rows, and 10 columns, if I make every single row to be a resistor, from a different manufacturer, can I smear the results across all of it such that I get, in general, a Gaussian result. And that way, with a certain percentage of confidence, let's say 5%, or I'm sorry, 95% confidence, we can agree that it's within the value that I asked for, I want to do those counts, because I think it sounds like
Host 2 08:51
Fun, I think you're gonna also need to add in the resistance of the traces in between,
Host 3 08:55
I was thinking about Yeah, that was and then
Host 2 08:57
I noticed, like 10 ounce copper, yeah. Also, resistance of the fillets, because that's gonna be important. Once you get to a certain insane size, the solder will have a slightly different resistance.
Host 3 09:12
Well, and if you put your multimeter leads onto it, you need to know how much those add with either pressure contact, or how do you actually connect to this board to measure the resistance?
Host 2 09:24
No. And also I'm thinking is if you're trying to make something super precise for measuring this stuff, because too, this is something that's not even on the sheet. So yeah, yeah, secret secret stuff is when you have two dissimilar metals, you get a voltage difference between those two That's correct. So if you have the solder like sack through a five and then Enough, enough plated copper, what kind of voltage difference do you get there? Which will you will be able that does that wash out over this entire, ginormous border? doesn't doesn't not? Or doesn't, does it? Does it even matter? I don't know.
Host 3 10:06
So all said and done, I don't think we even have the gear to be able to know. Like, theoretically we could we could have fun with it.
Host 2 10:16
I'll see if I can score a six digit multimeter
Host 3 10:20
Ooh, yeah. This is this is a good project to do that for. Yep.
Host 2 10:24
Build this and then and then like, Get A Six segment on like loan or something. So okay, cool. Maybe someone in Houston's got one that we can borrow?
Host 3 10:34
Maybe? Well, I'm not sure there's I don't know. Wait, okay. Correct me if I'm wrong. Oh, 603 components, chip components, especially resistors are the most bang for your buck, right? Yes, they are. Because Oh, four Oh, tubes are more expensive, because their size and weight of fives are more expensive because of their size. Because they have more material. Right? So Oh, 603. If you're wondering that you get the best price breaks for those? Yes. So I'll probably do this. Oh, 603. And I will let however many columns and rows in the matrix. define how large the board is? So in general, how ridiculous I feel like getting with this.
Host 2 11:21
Yeah, I really want you to make like a 16 by 16 inch panel. That's all it'd be like three real resistors
Host 3 11:27
Oh my god, that board would be so expensive. And our production manager would hate.
Host 2 11:35
Especially if you were like, Hey, that resistor is backwards.
Host 3 11:39
I'm gonna make all of them just random rotations. Oh, man. So yeah, that's that's what I've been kind of thinking about this.
Host 2 11:49
I can't wait to see it. Hopefully next year, I think we should have like graphs and crap
Host 3 11:54
Next week. I wonder if there's a way to automate dip tray so I don't have to place
Host 2 11:59
100,000 people. There is just my little scripts.
Host 3 12:05
Eagle. Eye might have to do it in Eagle just so I don't have to do part by part. Yep.
Host 2 12:16
Yeah, cuz I think you'd have to write the script yourself. Because I don't think there's like a offsets copy offset script. You know, I shouldn't wait a script
Host 3 12:24
Way that this actually dip Trace has an auto REPLACE function. And if I just so think about this, if it's just, oh, 603 components, and I make a square board and I tell it to auto place, it's probably going to place them in a matrix.
Host 2 12:43
You know, what you should do is, is I'll give you some some software's like, like open source broadcaster, and we can record your desktop as you do this. Yeah, we should totally do that. Yeah. And see how frustrating or not frustrating this? Well, I'm
Host 3 12:59
Sure as hell not gonna place a few 1000 resistors by No, let's let's do that. That sounds
Host 2 13:05
Awesome. Yeah. Awesome. Cool. Okay, and then I guess on to RFO. That sounds great. Okay, so the first one is a analog e Times article. Why the zero ohm resistor? Oh, yeah, I saw this. That's cool. Um, I think this would be a really good topic just to blog about because Why do you use a zero resistor?
Host 3 13:28
Okay, I have some interesting interesting things about zero ohm resistors. Because I've used a ton of them in the past. zero ohm resistors. Here's what's what I feel is awesome about them. They're cheap. Yes. And so when you're making a prototype, and you're, you know, either you don't have a lot of time to make the prototype or you're just unsure about certain functions of a chip or whatever, blah, blah, blah. It doesn't cost any extra to lay down pads on a board. Yep. And then mark them as Do not place. Yep. So if you have pads that are there on the board, and you need to short it, solder in a zero ohm resistor. I did that on so many chips, where it was like, oh, I want to try this function. I'm not really sure what it's going to do to my circuit. I just saw her and a zero ohm resistor or even even if I wasn't sure if I needed a pull up or a pull down I could put in both packages and then and then that and it all man it saved my ass a lot. I've
Host 2 14:29
Used zero ohms for doing FCC CE testing. Yeah, so basically for whenever a connector went to the outside world, I'd put all in series zero ohms so that if I needed to put in a ferrite bead Yeah, all I do is hot air the old one off, and you'll put the ferrite bead on like at the the facility I'm doing the testing and then BAM done and then I just have to update the the Bill of Material materials at the end of the day, right And that saved our baking a couple times with a with a Rs 45 communication stuff.
Host 3 15:06
And even if you were to put zero ohm resistors, across almost all your nets, it still is cheap. Yeah. And for prototyping, it is so worth it. When you when you finally get your prototype done, then you go back, you roll the revision on your board and you cut out whatever zeros you don't need anymore. Honestly, I feel like that's why they exist. Yep.
Host 2 15:28
And, um, I've also seen a lot of people use them for doing a one sided PCBs. Yeah. So instead of doing a through hole, like jumper, you can just have a surface mount jumper.
Host 3 15:41
Yeah, as long as your trace fits between the pads, the but if you use like an o 805.
Host 2 15:45
Yeah, most of the time, you can get a couple you can probably get to 10 mils underneath there. Sure. Yeah. Yeah, you
Host 3 15:51
Got a lot space. You could do do a bit of sneaking. But yeah, you could get in there. Yeah. Now here's the thing. That's interesting. Zero 80. Go look at the datasheet for a zero ohm resistor. It has a wattage rating. Yes.
Host 2 16:03
And they have a wattage and a tolerance. That's.
Host 3 16:07
That's true. Yeah. And it starts to bog
Host 2 16:09
Minus 10%. On zero.
Host 3 16:12
Exactly. So it was funny. I was looking at that for I think the SSPs. I was using some zero resistors in some places. And it was like, What's the difference between an 8/8 watt and a quarter watt, zero ohm resistor? It all it all is based on the fact that they're not actually zero. ohms? Correct? Well,
Host 2 16:33
If they weren't actually zero ohms, we've somehow figured out through Quantum Lee tunnel electrons through this device to the other end.
Host 3 16:41
Are you just super cool it?
Host 2 16:43
Right? When when you get like quantum tunneling the electrons through?
Host 3 16:50
No, so it's it's annoying, but you have to actually consider that. Yeah. Because you, you technically can burn up a zero
Host 1 16:59
Ohm resistor. That'd be a lot of power.
Host 3 17:03
It would have to be an enormous amount. But you know what? I pictured the SSPs. could do it. Probably the super simple power supply for those who don't
Host 2 17:10
Know, yeah, we haven't worked on a thing in a long time. Yeah, totally bad for that project. Yeah. Anyways, cool. Article, post link. second article. This was on Hackaday. And it's a NASA wants space poop packers? I know. Yep. Yeah, he said, What, but it's to design a system that will move waste away from the human body, where it cannot cause infection. But while you're in a spacesuit, and so this is designed so that you can be in a spacesuit for multiple days, say on Mars. Okay. And where you you know, you don't have a you can't set up a porter John outside. It's a space diaper. US fancy space diaper?
Host 3 17:53
Well, I mean, it's NASA. So it's a super expensive space. Yes. So
Host 2 17:57
It has to operate in zero gravity and also has to operate under normal gravity. It has to operate under for 5g which is reentry into the earth. It's interesting, because the only the only going to reward the person who comes up with the idea for with 30k. It's pretty inexpensive.
Host 3 18:18
Well, I mean, maybe they're, maybe they're reaching out to, I guess the base that that is willing to work for. You know, some people, you know, for a lot of a lot of the engineering base 30k might be a whole lot of money. But for NASA, that's nothing. Yeah.
Host 2 18:33
Well, that's that's what the typical engineer, it's like half half of your salary.
Host 3 18:38
Yeah, for an intro. Yeah, right. Right. For strapping engineer, I
Host 2 18:41
Didn't come up with that idea in six months, and prototype it and fund it. That might be worth it. Oh, absolutely.
Host 3 18:48
No 30 case not. We're not I'm not trying to say that it's a small amount of money. No, no, no, that but for NASA, it is.
Host 2 18:55
But it reminds me of a sexy really funny reminded me of the Apollo 10 transcripts. And it was really funny, because I was actually going through the comments on Hackaday. And it reminded someone else and they actually posted the link to the transcript. Oh, yeah. So I printed it out. Oh, great. He made my work easy. So apparently, Apollo 10 was the one where they went around the moon. Right. And then it came back and it was I think Apollo 10 was actually the was Apollo 10. Maybe Apollo 13. I think Apollo 10 was the one the farthest humans ever actually gone away from Earth. Oh, because they rounded farther away on the other side of the moon. But it might have been Apollo 13, though, because they had all those technical issues.
Host 3 19:36
Well, 13 was where they were trying their best to use the gravity of the moon. Yeah, so maybe it was then
Host 2 19:41
That maybe we're searching anyways. That's besides the point. There's a transcript of they're there. All three of them are talking on the in the lunar module. Yeah, or the command module, which is the cone one. Yeah. And the the there's just like Like, this is like a transcript from from NASA here actually here in Houston. And oh, who did it? Who did? What? What? Who did it? Where did that come from? Give me a napkin quick. There's a follow through the air, and then there's at the bottom of the page is confidential. Amazing. And then like it goes on, it says, I didn't do it. It ain't one of mine. I don't think it's one of my neither. Mine was a little more sticky than that. I'll throw that away. Oh, and then one guy goes, God Almighty.
Host 3 20:41
All three of them. Not me. It was
Host 2 20:45
Someone Someone had to, you know, poop. Yeah, up in space, there's a lot of challenges. It's gonna be the most expensive for how expensive it is to get stuff into space. That's the most expensive waste material ever. Oh, that's awesome. I'll be interesting to see who
Host 3 21:10
Comes up with this idea. So where's it gonna be at the r&d ideas on
Host 2 21:15
Hackaday? No, it's on NASA. today. We're just reporting on their content. Oh,
Host 3 21:19
Okay. I gotcha. Yeah. So you can go you can go get more information on NASA. Yeah, I'll
Host 2 21:23
Post a link to that. There was a new blue through spec that came out. Okay. I didn't even know it was coming out. Because they just came out with Bluetooth, four, le four 4.1, or whatever it was, it was called Bluetooth five. The general rundown is has long range, faster speed, and larger Broadcast messaging capability. So it's like, it's just it's better to for Yeah, just better, better. Everything.
Host 3 21:50
Right. Well, do you know what the range is now?
Host 2 21:54
No idea. Awesome. Yeah. According to the News, the news
Host 3 22:01
Is longer. That's all you need to know.
Host 2 22:05
And then another important one is the explodey. Samsung batteries that are catching people on fire. And, you know, all that crazy stuff that was bought two months ago, something like that. Yeah. So these guys actually took apart a Note seven, and actually did a failure analysis. Who are these guys? Um, instrumental.ai. Okay. As these guys, I didn't see a name. Maybe I didn't look hard enough. Those guys, those guys. They basically took one apart and actually measured like the space the battery had. Yeah, and their phone was only two months old. And it had already taken up and already swelled, all the Z depth. And they're in their battery. So I got a quote here is the ceiling is what they call this. So it's like, you have the x and y, which are the width and length of the battery. And then the height is called the ceiling. Okay. And so they usually say is a cell phone, or for any lithium batteries, you want about 10% ceiling. Because as the battery ages, it swells. When they took them apart. It was only two months old. It had 0% ceiling. It was already just compressed. It's already compressing that battery. Yeah. And yeah, so
Host 3 23:24
You just say efficient use of space efficient use of space. Yeah.
Host 2 23:29
And they had it actually the, there's interesting is they had the aluminum chassis of this phone is actually has a battery area that's actually milled out just for the battery to protect it. But they made the horses too small and that so you can swell into the sides as well. And that's how it happened. That's how that's what does
Host 3 23:49
You know what I see this becoming? I don't know what happened at at UT. But at a&m, we had an ethics class. Yep. It was ethics for engineers. Yep. And what we what we did was we took I don't know a couple, handful of examples, maybe five,
Host 2 24:05
Something like that. And what the space shuttle Challenger Yep. And yes, several. Yeah, they were every single one of those same.
Host 3 24:13
Yeah, probably. I think we had one about it was a skyscraper in New York. Yeah, if a certain hurricane came by then it could fall down. There was only one guy in the entire world who knew that it could do that. Oh, yeah. What does he do? So I could see this becoming one of those textbook examples. Yeah, you have a battery and it's inside of this component. And you're the guy who knows that what do you do? Yeah, you know?
Host 2 24:39
Well, yeah, but least there's closure on that. I think Samsung is actually doing the right thing. They're recalling every single one of them and they shut down that entire line.
Host 3 24:49
Yeah. Just to replace it with Well,
Host 2 24:53
I think they said that the note line is done. Yeah, the notes done they're gonna make something Yeah, the part call like the Winder the bottom,
Host 3 25:02
That Trapper Keeper. Lisa Frank bottles it has like unicorns and tigers and multicolored. Ah, no. So how was it? Shoot? Oh, no, no, I can't remember the the the. I was in my ethics class. It was one of those. It was an automotive company that measured the like how much it cost if a person that loses their life as Ford was at Ford where the Ford Pinto Yeah, right. Yeah, they measured how much it was for like an appendage.
Host 2 25:37
Oh, I think that's actually GM. Was it? Yeah, Ford was because it was the the Ford was the exploding Pintos gas tanks. Right, right. Yeah. And they figured out that, like a human life is worth X amount. Yeah. And they're like, Okay, it's a couple million dollars to pay out. You know, and we had to do that, like, 10 times a year, right? Or cost, you know, you know, 200 million to do the recall. Right. Right. And they ended up just, you know, not recalling.
Host 3 26:08
Exactly, because they were willing to pay off whatever. Medical bills are. Dead. It's not a medical bill.
Host 2 26:15
I don't know if anyone's actually paid died in a Pinto accident, but maybe they have.
Host 3 26:20
But but but the Samsung thing is a bit different. Because it had it was so front and center. Like there was no option but to recall everything.
Host 2 26:33
Well, he said, I guess the right thing would have been do more testing to figure this out. But, but
Host 3 26:38
But, you know, like every, like college level class where they talk about batteries from here on out, just gonna be like, make sure you have enough room for that battery. Yeah, you know, cuz it'll swell. Yeah, it'll
Host 2 26:49
Swell. Battery engineering. Yeah. Interesting. Yep. And so next week, you're gonna have a super special podcast. I really hope we're working really, really, really hard to get this. It's actually we're hoping it's gonna be videocast now we're gonna do it. So it's gonna be podcast, but also have video. Look later. Yep. I'm really hoping that we can pull it off. We're trying really hard to get done.
Host 3 27:18
And you make it sound like we work really, really hard.
Host 2 27:20
I'm actually working my ass off and get
Host 3 27:23
This thing next week working now. It's gonna be good when we were pushing for this. Make sure you you stay tuned for it. It's gonna
Host 2 27:30
Be asked. Yeah, so that'd be episode 46. Probably several sections after that, too. Yeah, yeah. So that was this episode of The McWrap engineering podcast episode. 45. Yeah, we're your hosts Parker Dawn and Steven Craig better guys. Take it easy.
Transcribed by https://otter.ai