Is there a way to macgyver measuring a voltage without a multimeter? Is macgyvering even a word? Parker and Stephen discuss this for well too long.
A custom, open source, DIY multimeter? Parker and Stephen go down the rabbit hole of putting down design requirements and what open source means.
Is lead forming components a lost art? What specifications of a solar panel is important for an embedded system? Find out more on this weeks episode!
PART 2 : Is there a macgyver way to measure voltage without a multimeter?
Interesting EE homework question
Parker is an Electrical Engineer with backgrounds in Embedded System Design and Digital Signal Processing. He got his start in 2005 by hacking Nintendo consoles into portable gaming units. The following year he designed and produced an Atari 2600 video mod to allow the Atari to display a crisp, RF fuzz free picture on newer TVs. Over a thousand Atari video mods where produced by Parker from 2006 to 2011 and the mod is still made by other enthusiasts in the Atari community.
In 2006, Parker enrolled at The University of Texas at Austin as a Petroleum Engineer. After realizing electronics was his passion he switched majors in 2007 to Electrical and Computer Engineering. Following his previous background in making the Atari 2600 video mod, Parker decided to take more board layout classes and circuit design classes. Other areas of study include robotics, microcontroller theory and design, FPGA development with VHDL and Verilog, and image and signal processing with DSPs. In 2010, Parker won a Ti sponsored Launchpad programming and design contest that was held by the IEEE CS chapter at the University. Parker graduated with a BS in Electrical and Computer Engineering in the Spring of 2012.
In the Summer of 2012, Parker was hired on as an Electrical Engineer at Dynamic Perception to design and prototype new electronic products. Here, Parker learned about full product development cycles and honed his board layout skills. Seeing the difficulties in managing operations and FCC/CE compliance testing, Parker thought there had to be a better way for small electronic companies to get their product out in customer's hands.
Parker also runs the blog, longhornengineer.com, where he posts his personal projects, technical guides, and appnotes about board layout design and components.
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.
Special thanks to whixr over at Tymkrs for the intro and outro!
Welcome to the Mac fab engineering podcast, a weekly show about all things engineering, DIY projects, manufacturing industry news, and engineers that took chemistry one on one sometime in their college career. Where are your host, electrical engineers, Parker, Dolan and Steven Craig. This is episode 326. Before we jump into his podcast McWrap is hiring, we're always hiring. But we haven't positioned for a test engineer level three. So that's like a senior level test engineer position. Go to macro fab.com/jobs. Go apply. There's a couple of engineering there's a almost every single position is hiring at Microsoft right now.
You all are Yeah, like you said, you're hiring all the time. I've checked every once in a while just to see like how you guys are doing and there's just, there's always new positions. So yeah, just out of curiosity, what does a test engineer do at macro fab?
So a test level three will do not not really testing things. They they test the tests that customers give us validation. Some development work, depending on the customer managing third parties for like third party engineering firms are they are
they like setting up and adjusting test jigs and things that like if a customer has something like they're the person who makes sure that it works?
Yeah, so they might be a test engineer. Level three might be also in like the new product introduction meetings, as like a lead. For make, like giving advice to customers about testing, that kind of stuff that's doing designed for testing DFT work. Kind of like what my current job is, I guess right now, at macro fab.
I feel like throughout the time, your time at macro fab, you've worked every one of these, even if it's not like your actual position, you know that
that's true. And then in our Twitch chat, gadget junkie, who is one of our software developers that macro fab, is saying software developers are also hiring. So if you go to macro fab.com/jobs Everything is there go apply. We've had podcasts before where we talked about like the HR pit of doom. We don't have that at macro fab. Like if you are actually applying for like an engineering position. I'll probably be the one that's looking at your resumes first. And also interviewing you
watch out party you're gonna have like 5000 emails.
I hope so. I hope so. And a lot of the a lot of the jobs are remote too. So you don't have to be in Houston, Texas. Now for tests engineer level three, that's probably going to be a Houston, Texas location. So you're gonna have to like live in Texas for that one.
Out of curiosity, how many software devs do you have now? You probably have a big team, right?
Oh, let's see. Let me check. Gadget junkie
it's just spit it over. 20 right now over 20 Wow, cool there. Yeah.
So that's probably not like, if you include like the product team is probably way more net to. That's getting what's our official number at right now.
Like headcount, you're over 100 Right. Yeah. Yeah,
I think we're at 179 right now. According to our Slack,
main channel. 179 people well, yeah. Targeting 30 by 30 software devs by the end of this year. Well, you guys are grown.
Yeah, it's it's getting insane. Okay, on with the podcast episode. So last week, we talked about this Reddit post about discussing a way to MacGyver a way to measure voltage without a multimeter our Slack channel or public Slack channel had a lot of good suggestions and like, kind of like almost went down like history lane of like, devices that measure voltage. The biggest problem with a lot of those devices was you have to do a lot of experimentation to actually like get a number like yet to calibrate them. Um, or you'd have to have like, precise ways of like measuring distances. Like this is what we're talking about with like forces, like we like if you use the fraction of like water or something like that. The margin of error would require you to have something very precise to measure
Well, or, or in building a device, you have to have something that's precise to build the device itself.
Yeah, yeah. At lathe or a, or a
milling machine, or scale, or scales for weighing materials, and yeah,
that was, that was one of our first ideas was using a scale and then measuring like electromagnetic force. And the problem with that is you then you need a scale is actually an easy thing that I can balance being would be pretty easy to make. On the on the flip side, that though, is having precision weights to use that beam scale doesn't really work out?
You know, I think we should revisit the stipulations of this, this question, because we I feel like as we were talking about it last week, we were like, creating stipulations as we did it. As we were going Yeah, as we were going but but just sort of remembering where we were it kind of like it started with this question of like, how do you MacGyver a way to measure voltage, and then it ended up being like, desert island kind of thing you like you're stranded on an island, and there is something that has a voltage on it, and you want to measure that. So if you were stranded on an island, and you had just like, what's kind of around you? How do you measure voltage? The one thing that we said we were we would allow was, what a pint glass right? Well, it was just like a cleaner a container. Yeah, of unknown volume, right? Well,
so it's not really we were allowing a container, it was more of a rule on using the least amount of things and the least amount of measuring tools possible, right? And you don't have any available like precision ways to make things. Right. So that's kind of like the rule set is, minimize how many tools you would need, minimize how many measuring ways the be like a micrometer or a multimeter, a calipers, stuff like that, a scale, the least amount of tools you can get away with. Yeah. And so we, so Steve, and I kind of came up with this idea of as really Stephens idea of using electrolysis, to basically generate hydrogen, and then back calculate the current involved. And I thought that was such a brilliant idea that I actually went down and started writing that like, Okay, how do you what kind of formulas do you need to make this thing actually work. And then what kind of tools and measuring devices would require to make this work. And that was where Steven said, a pint glass, anything that you haven't known volume of. And the great thing about most containers in the world nowadays, is the volume is printed on it, because they have to sell by the volume of liquid that's in them. So like, I have a mineral water container here, and it says 12 fluid ounces, 355 milliliters. So if you're on a desert island, the good chance there's trash, human trash is everywhere on this planet. And you can probably find a container that you know, the volume of and this is one thing we talked about after the podcast was you can't derive voltage knowing nothing. In terms of like measuring something, you have to be able to measure something is what we basically boiled down to, like you can't, you have to be able to have one thing measured. Regardless of you know, any of the variable constants or anything like that, or the equations, you have to be able to measure one thing to get to another thing. And knowing just volume. You can I think get most of the way there with the voltage. And well, in a watch, we have to have a watch too.
So we have two measurement tools. Yeah, we have two tools,
one yet to have a known volume container. And then two is a watch. And then you should be able to calculate the voltage using electrolysis basically for for, because basically what you're doing is you're calculating the hydrogen
content. And there's a little bit of assumptions that go into this as well. So yeah, there
are some some assumptions. Yeah. So like the first one is, let's just say you have distilled water. So you and you can distill water fairly easily by just cooking the water off and then collecting the water vapor. I think you said a palm leaf, a banana, so adamant about that is that like an a, from a movie or something?
I don't know. Like, it just came to mind, like banana leaves are really big. So you just drape a banana leaf over some kind of pot that you're boiling. And then it'll condense on the backside of the banana leaf and roll off into whatever jar you want. So you can do some desert island distillation pretty easily. Okay, okay. So it could be a palm, it's just banana leaves are big and flat and easy to work with. Okay.
So that's my first assumption was you have to make distilled water, because it makes the equations a lot easier in terms of like figuring out basically, how much voltage you need is required. So I found a website, because we are not chemists on this podcast. So if you are a chemist out there, go, and we say something wrong. Come complain to us in our Slack channel correct.com/slack. Or on Twitter, too, you can complain to us, too. They're doing our best here as electrical engineers.
We know the zappy part, the all the rest of this stuff is magic.
Yeah. But we do know as engineers, electrical engineers, current times time gives us cool alms. Okay. So that's our first step, because Because chemists like to work in moles of things, which is a really weird concept. Which I had to refresh myself on what a mole was. I still don't really remember anymore. Besides it being like a furry little animal that likes to dig in the ground, right?
I'd say a certain quantity of very little animals that dig in the ground, right?
Yes, certain quantity, yes. But the bridge between, like moles, and electrons is this thing called coulomb, which is just a unit of charge. And so using that there was this nice website that Purdue, the chemistry department at Purdue has the has a lot of different equations about hydrolysis, and how our electoral electrolysis, I should say, and how it all the different how all the different formulas interact with each other, basically, unfortunately, there wasn't one where the inputs was time and volume gives you voltage. So we had to make one up,
or well, there's a little bit more to it than you. There's, there's further stages beyond that. Yes, yes.
So the first thing is, let's go, let's go to the volume route. So if you know your volume, let's go and find kulambu. Right. So if you have unknown volume, how much unknown volume of we're gonna say hydrogen gas, okay, because that's what we're making. We're making a known volume of hydrogen gas with electrolysis. If you haven't known volume, how much coulomb of charge, charge are you need. So it's basically boils down to volume times one mole of hydrogen, or h2, divided by 22.4 liters, which is such a weird number because it's a constant, which is the standard pressure or standard temperature pressure of one mole of any gas is 20.4 liters, which is kind of crazy to think about. And times basically how much electrons it takes to make or how many, basically the ratio between electrons to hydrogen h2 molecules, which is two electrons per h2 molecule. Then times like this conversion to Faraday, which is one Faraday per one mole of electrons, which is that's a mole electrons. There's just like finding think about too, but it's canvas. It's a quantity of stuff, right? It's a quantity of stuff. And then you convert Faraday into coulomb ohms, which is nine 6485 coulomb per Faraday. And that gives you coulomb. So now we have an equation it goes from volt volume of hydrogen. Basically we're using the formula for electrolysis which is four electrons in plus four moles molecules of water, h2o yields us. Two hydrogen twos. And four What was that hydroxide, right?
Oh, yeah. Oh h minus. Yeah.
Oh h minus hydroxide. Which I first looked at that and said hydrogen oxide and seems like nuts that right? Technically, it's correct.
Rusty water, Rusty water.
But so that's that's where you get the relationship. This is like chemistry one on one like day to class. It feels like right now trying to remember all this stuff. It what
it is, for me is chemistry where I'm one on one day to where I'm like, Oh, God, this, I have to know this.
You have to know this. And this is a thing when you were in school, you're like, I'm never going to use this ever as let's go engineer. Guess what? Today is the day of reckoning.
Oh my gosh, I'm still getting a C on the exam. See for coulomb, that's right. Oh, no, I got lower. Lower Casey's not capital. Casey's,
Casey's.
Alright, so that gives us volume to cool alarms. Now we need to bring in the what was it? I'm looking at my notes real quick. Blah, blah, blah. Where is current comm current is ohms law, we know that one. That was straightforward equals current times are flipping around voltage divided by resistance equals our current. And so now we have and then we use the relationship between current times time equals coulomb now, so plug all that in together, do a little arranging of all the all the unknowns to one side. And then what we want to know on the other side, we get volt, voltage equals the volume times 8,614.73. I basically combined all the known constants and stuff into one number times the resistance in ohms divided by the time it took for this to happen. So how long did it take you to make that volume of hydrogen basically, right gives you volts. So the only thing that we don't know now is ohms.
Yeah, the resistance of the wall? You can't,
and you can't measure it, because then you would have a multimeter
Yeah, right. Right. Well, okay, so and this is where some of the, I guess the there's a little bit of assumptions that go on here. And also, this MacGyver guy just knows all of these equations and knows a lot of just like baseline things like constants and things of that sort. So well, yeah, he's smart, he's smart. So we're just, we're allowing infinite knowledge in this. So the thing is, I did a handful of calculations on finding the resistance of water. I did it two ways, if it were to be distilled water and if it were to be saltwater, and the part of the that there's some assumptions in here is you have to know the volume of what you're passing your current through. And the assumptions was basically parking I just Parker had a Topo Chico bottle. And he was like this, it's this. So I made just some basic assumptions about the length and width of it. And the reason I was okay with doing assumptions on this is I changed the volume after I had calculated with my assumptions, I changed the volume to see the impact on the resistance values, and it has an impact but not so much so that I like yeah, sure there's some error in there, but it's I'm not gonna worry about it if I got a Topo Chico bottle off by three or four centimeters, like the the gross resistance value of the water in it is will be plenty good enough. So, for distilled water, the resistivity of distilled water is 18.2 mega ohms centimeters. And if you calculate that out with my assumptions on the on this bottle that you would be passing current through, you end up with a total resistance of about two point or 24.1 mega ohm So pretty high resistance in something like that. But instead of filling the bottle with distilled water, you do sea water, which seawater has a average resistivity of about 20 Ohm centimeter. So not 18 mega ohms centimeters, 20 ohms centimeters, you end up with a total resistance in the bottle of something around 1.84 kilo ohms. And that's a lot more reasonable like it could be done with with the distilled water, you just be there to take a lever, right? So let's go with the seawater and just make it go Zippy fast. So 1.84k, is what I came up with.
Interesting, because what you could do is you can do the spark gap test and figure out how energetic it is and figure out if you want to use salt water or distilled water.
That's true. Yeah, well, yeah, cuz you don't know what the voltage is, you don't know if it's going to take forever, or if it's just going to explode the second
when we put those leads in the water. Cooler, because that's that. What we should do is write out that ohm calculation with those variables, like the basis of the volume calculation of the whatever container you have. Yeah. And then because it probably also depends on how close the leads are together, or does it?
Yeah, it's making the assumption that the leads are at the end of a cylinder effectively,
okay. Oh, so like cylinders, like long ways, then.
Yeah, hotdog style. Okay. Okay.
So we probably should have like, a probably like, because I'm going to actually draft this up into a blog post, yeah, probably won't make the macro reblog. But definitely might
do your own personal opinion. And then
put in like, here's a diagram of our container with all the variables that you'd have to measure. And then what I want to do is actually, like, figure out what that tolerance is, because that's where most of our errors is going to come from is that own calculation, and then figure out what the error generated in becomes and figure out how that ends up impacting our voltage.
I think if you wanted to get really fancy, instead of doing a volume calculation, if you just assume that you have the sea available, that is, in effect, an infinite volume, right? If you just took two, two leads, and put them some distance apart in the ocean and applied current through it, you would get some kind of current distribution that flowed between the two. The problem is, you don't have the capture, you don't know the distance between the two leads, right? And so how do you calculate the resistance between those two leads?
And the author, you have to have something that captures it?
Yeah, yeah, no, it's right. So in other words, if they were, if they were, the leads were two inches apart, and you you had your capture thing. It would just capture all the all the hydrogen that comes off
of it. Yeah. I wonder how much that current falls off. And so let's say you had a, a bathtub of saltwater, at this point, a big container, you know, and then you took, let's say, you had a jar, you put it on, I'm trying to figure out how you build this thing, okay. And you put the jar in the water, and you bring it up. And so that, like, you know, it creates a suction. So holds the water above the above the surface, and then you put your leads underneath it. Yeah. So that any gas generated between leads goes into the jar? Yeah. Okay. What is the resistance between those two leads that point?
Yeah, you start getting into some calculus problems now. Because you have to, you have to, you have to do a much more like interesting volumetric calculation, as opposed to like a standard, like cylindrical resistor calculation with resistivity.
Well, the thing is, though, is what I'm getting at here is there's a fall off the where it doesn't matter anymore, right? Where the error of your total volume or total space, I guess just falls off. There's a limit, right? It's the limit problem. Yeah. So it falls off eventually. Well, as I
was saying, like it's a calculus problem. It's like a three dimensional problem where you have to look at like, the current is going to flow. Least Resistance between the wires, right? And then yeah, be some distribution around that. Yeah. And now we're getting into some really complex stuff. Yeah.
So what's gonna be interesting is could you have just done a straight line between them and is that good enough?
Well, the answer is there will be some error. What is that error? I don't know. You know, is that like, 20% of the real value is at 98% of the real value? I'm not sure.
Yeah, that's gonna be the interesting thing is if you just because you can just look up like, the straight line distance and water, both salt water or whatever, for resistance. Is that close enough? Like?
I mean, you could, you could, okay, the thing is you could, the equation for resistance in a in a in a thing is, you know, it involves you resistivity involves the length of whatever the resistance is, it involves the surface area of it. So if you think of like a cylinder with length, you could collapse the radius of your resistor, and just keep making it smaller, but keep the length the same. And get some you know, as you do that your your resistance would drop, but you'd get closer to your straight line. Basically,
your resistance should go up. Hang on.
Yeah, yeah. Sorry, you resistance should go up as your surface area goes. Down. Yes. Correct. Because this area is, is in the denominator. So yeah, it should go up as you go to. thinner and thinner, have a lot back.
Interesting. Not the run, you got sudden that spreadsheet over so I can take a look at at the calculations and actually like do some testing?
Yeah, I mean, it'd be fun to actually like, probe some water and see what resistance we get, you know?
Yeah. And I want to see like, is there a simpler way? Can you just like, assume that's just gonna go straight shot through?
Well, I think one thing you could do is, you know, you have your bottle, I think you'd mentioned this earlier, like, strip end of whatever, wire, however, you're connecting this, and put that down at the bottom of your bottle, and put your other conductor right at the top of your bottle. And now you you effectively have a cylinder with connections on top and bottom here.
You still got to capture that though. The I'm still trying to visualize how you cap do you have to capture all the gas to
read, but couldn't you? Okay, so fill that with your water and then put that under water, your path would still be through the bottle through the volume in the bottle. So I guess that's a practical way of limiting it.
Because what I was thinking is you could have the bottle upside down full of liquid, right underwater, too. And then you put your two electrodes really close to each other at the entrance of it. Well, but
what Okay, so what if I'm adding stipulations here? What if you had two bottles, one for capturing and one for generating?
And maybe I'm just trying to think of like, again, does the if you have the the anode and cathode close together? Does it matter that how big your container is at that point? Or where it's at?
Oh, no, no, no, no, no, it wouldn't. It wouldn't. And that's Yeah. And that's sort of what I was saying earlier. Like, if you just stuck some leads in the ocean and pass current through it, it's gonna happen. But it's hard to calculate the
the resistance then. It's not impossible. It's hard.
What's interesting is, this leads us to our next question here, which was an interesting electrical engineering homework question that it was on Reddit. I think last week, and it's a let me I'll post this. I'll post the link in our live chat real quick. Oh, and bro kabhi. Smith. Sorry, I'm gonna change topics back. reverse gear right now is Robbie Smith says, would there be some way to connect a unknown voltage to a motor and try to gauge voltage by rpms? Yes, you could do that. But one, you need the voltage to rpm output chart for that motor. And then to you need a device to measure the RPM. And I one is what we
said you'd have a watch.
Yeah, you'd have a watch. But so I guess you could probably try to estimate how fast it's rotating at. But then you need the chart to figure that out. And I actually have not seen like a while I've looked at motors, I have not seen a like a DC motor like voltage to out RPM output. Usually they have a rated voltage and then what the RPM output is at that voltage. There's no sliding chart for that.
Yeah. For one voltage, yeah, they're
intended for one. Yeah, they have one rated voltage usually. I haven't seen a chart for one every awesome. There was cuz then that would be pretty easy. Yeah. So like, open up a drill, power drill trash that you found and pull its electrical motor out.
There's there's all kinds of interesting trash on this desert island. Yeah. Which, by the way, quick, quick tangent. I love this desert island thing. I kind of think that maybe in the future, we should have more desert island questions where it's like you're stranded on a desert island. And you need to know the beta decay of this particular radioactive thing. How do you find that?
How do you find out?
Yeah, they even even like, Okay, you have to measure something more simple. Like, you know, we've been doing Yeah, something. Some other thing that's simple like, I that would be fun.
Yeah. Yeah, again, the only problem with that one broke Harvey Smith is is you don't know the relationship between voltage and RPM output?
Unless you did I get well, I guess the
one you know, you know, zero is zero rpm. And then you know, whatever stamped on the motor usually, I get?
Well, the thing about it is maybe you plug it up to this random voltage choice, and it turns at its intended RPM, you then know what the voltage is? Yeah, you get just lucky. Yeah. Yeah, I'm on this desert island, and there's 24 volts here. It's perfect.
The I'd love like, unless I'm completely wrong about motor PDF, like data sheets having that chart in it. I just never seen one. So I wonder if I should after after this podcast, I actually go grab a DC motor. And like my part Ben and look it up and see if I can find a chart like that. And like its datasheet? Because that'd be cool.
You know, one of the hard things about measuring the resistance of water, if you just wanted to, say put two leads in the water and just know the resistance in between them is you would have to you would have to know how far apart they are. You'd have to measure that.
Yeah. That's what I'm saying is like, how close can you guesstimate and actually affect the overall breeding basically? Right? Like, can you get away with a tape measure?
Oh, probably.
So, you know, you're the best you're going to do is at that point of 16th of an inch, right? I guess technically, it was half that. So you actually would have 130 seconds. So Oh, six to five inches. Anyways, back to what we were getting that is there someone posted a human potato hybrid is their username on on Reddit, posted a homework question. Uh, basically, it's like a grid of resistors. And finding, if you were, if you were take your multimeter and probe each node, what resistance would you get? And I liked this question a lot, because it really relates to what I do a lot is in circuit testing. The
last week, we were talking about that classic homework assignment. I didn't talk about on the podcast we're talking about in the pregame, but that classic one of the resistor ladder, the infinite resistor ladder, that resistor ladder,
which is very similar to measuring the resistance between two points in like saltwater. Yeah, yeah. except that instead of a resistor network, it is the resistance between all the discrete atoms in that entire grid? Because, again, what happens is, there's a limit to the formula, right? It averages out. Well, not average output limits out.
Well, yeah, there is a discrete value. Discrete limit. Yeah. So this homework assignment, it's actually I really liked this one, because it totally flips everything on its head. And it's it's just goofy. It's just a regular like, homework problem, but I've never seen it asked this way. What this way most other way. Yeah, that's the other way where it's like, here's the value of every single resistor in this equation, or in this circuit. It's like, what's the parallel combination of all of them or like what's, you know, blah, blah, blah. In this one, it says, You don't know the value of each discrete resistor. It just says when you probe across this, your meter reads this and when you probe across this other one, it reads that and then you have to go and back calculate the resistor. That's super cool. And that's actually useful if you ask me.
Yeah, it's actually what I was saying earlier is it's, it's in circuit testing. Yeah. So if you have this network of resistors. And so yeah, sure, you could D solder each one and to measure each one individually, or you do it this way, and then save you a bunch of work. I like some Excel formulas that give you the answer.
Yeah, right. Well, I mean, and this has five resistors. And you get five measurements. So you can just make a network of equations and back calculate the resistance of each one of these. But what I really like about this is, what it what it kind of trains is, for things like circuit testing, and doing failure analysis, and, you know, finding problems on boards. one skill that I think is really useful is being able to just guesstimate with your gut, what you should be reading when you measure something in circuit. Sometimes you get lucky and you're like, oh, this resistor should be 100k. And your meter reads 100k. But
oh, but because it's hooked up to like the high impedance of like an op amp Pomona.
Right. Right. But you don't always get that lucky. So no, it's
always gonna be the value or lower.
Yeah, right. Right. Right.
If you're getting the value, if you're getting higher than the value, something's wrong.
Well, I mean, that's a good gut check, right? Yeah. Yeah. So I don't know. They just I, why were we reminiscing, there was something about the infinite resistor ladder broke? Because
one of the it's like, one of those Bs questions that like, that professors asked, Did like blow your mind? And that's one of those, like, Intro to limits, too. Yeah. Because the whole thing with limits is like when one number goes to one part of the equation goes forever, because infinity, right, or it goes to 01 number is doing that thing. So what happens to the other things in the equation, like the outputs? Yeah. And so it's one of those like, introduction of limits in electrical engineering, I guess. But like, everyone has that question, or very similar question.
And I've seen it asked a bunch of different ways. In fact, if I remember, right, maybe it was Dave Jones, maybe it was someone else who was talking about it, where instead of a resistor ladder, which you think has like a left and a right direction, but it doesn't have a y direction? What if it was like an infinite sheet of resistors?
That yeah, that's the one that I had in college. Yeah, well, and that one starts to
get a little bit more practical. Because if you, if you take your probes and you stick it in to any two points on like, a piece of foam, what resistance you're going to get, if you think of collapsing that piece of foam to an infinitely thin sheet of resistors. Yeah, sure. There's some applications with that. But that whole like string of resistors out there, just to get you to do some math tricks to find that R is equal to two R or whatever. Like that. It's like, come on.
Again, it becomes we just applied that same rationality to measuring the resistance in water. It's the same kind of idea. Oh, of
course. Yeah. Yeah. And now Now you're in a third dimension as well.
My big thing with that is, would what were the resistor was our over to our right.
For the ended up being for the infinite ladder? Infinite grid? Yeah. And I don't remember it depends on Yeah, depends on some, some of some of these questions are like infinite Voltage dividers, some of them are, like, the traditional ladder, some of them are like squares of resistors. It depends on which one you're talking about. It
really depends. It's one of those, I should take a look at it and figure out, you know, if you just took our right, like, it's usually it's between like the, you're probing, like, right across to one resistor. And but there's this whole network of resistors I can't remember how the what the answer was to it anymore. But like, how close if you just put our what's the error there? Like a straight shot? Because that's probably the answer to our like, putting too, you know, wires into like the ocean, and knowing and knowing the resistance, but no, it's yeah, it's very similar. Can you just go What's the error between just using
straight to Google what's the resistance of the ocean?
From the top, North Pole to the South Pole.
Yeah. Mitigating the resistance of the wires you have to carry too. Plug in your probes into their
No, just use for wire. Oh, yeah,
you have wires
I wonder
if you now nevermind, I'm not gonna I'm not gonna go down that route. It's it's not the easiest thing to calculate what the resistance of the ocean?
Well, the accuracy depends on where you put the probes that exactly.
But if you have a predefined volume of water, it becomes a lot easier. Okay,
I just want to I want I need to do some research. I wonder how important that actually becomes, though. Like, if you make the distance really short. Does that matter? Can you just treat it as a straight shot? Like, what's the fall off?
You? Oh, yeah, there's,
there's a there's a nucleus cloud around here of current that passes through. And that falls off? Okay. When does that fall off? Become? 10% 15%? You know, a 1%?
How about this, how about this, this might be the easiest way of thinking about it. Let's just say you took whatever wire you had, whatever gauge and you clip it, and it's just a flat beats just cut and, and you put those cut ends some distance apart from each other. If you just consider the the radius of the wire as a straight shot, the radius, the other one, it's just a cylinder in between the two, you could calculate that very easily. And just like assume that there's no fringing. It doesn't like go outside of that cylinder. It's just a straight shot.
So you're trying to you're trying to calculate the exact number. So try to do we really, like I guess at the end is weird. I guess we'd never input a tolerance on our voltage, though, that we're trying to find.
No, no, no, no, this voltage is very explicitly like it is one value is one, there's no tolerance on this magic voltage on this island.
So no, that's the thing is like what I think one thing we have to figure out is, what are we going to consider is good enough on our voltage number, like half a volt, that's good enough or USB voltage, right? If we're trying to charge our phone on a desert island, and we need to know if this voltage source is somewhere within five volts, so we can plug our phone in safely, then all we care about is plus minus five volts point five volts, I should say. And then knowing that you can figure out how loosely you can be on your own image on your calculation.
I'm sure the way we're doing this is very loosey goosey. Like, we're not there's no precision in what we're doing here. You know,
you know, let's, let's go with that. Let's go with this. This scenario. You're trying to charge your phone, and easy plus minus half a volt for USB standard.
So how much era can you stand at every step? Oh,
5.25 volt to 4.75 volts is your range you need to hit then. And let's just assume your volume, you're going to hit your volume number Perfect. Let's just assume that's because basically, the moment it bubbles out of your container is that's when you stop your watch. So you hit your volume plus, we'll just assume that you're perfect on that. And you're perfect on hitting your stopwatch at the right time to what would your tolerance on your well, we're not gonna calculate this with five minutes. Let's do this podcast button. For next week. We're going to stretch out this topic
that multi week here.
What is the tolerance on the image and needs to be and then you can figure out like, can you just get away with just doing a straight shot and saltwater?
Well, okay, so let's
calculation for basically, a infinite, like you're doing a calculation for, yeah, a big container, calculate that, and then just do the straight shot really close together and see, would that difference in image cause more than half a volt deviation.
So let's just let's go back to the value that I had calculated for seawater, which was 1.8k. If you only have five volts across 1.8k, you're getting somewhere in the range of 2.7 milliamps. How long would it take at 2.7 million?
Well, you're you're using that the ends of bottles and then
just back up like I'm getting at is just I'm trying to like just get an idea of like, how long would it take longer? Probably a very long time
part of your long talk. Yeah, but that's why I'm saying this, put the bleeds really close together, drop that resistance down to like 2030 ohms. And let it rip.
Let it rip. I love it. I mean, technically, you could make it whatever resistance you want. If you have the ability to control the distance, maybe not whatever you want, you'd have to measure the salt and yeah, it starts to Yes, I'll get I'll get closer it starts to get crazier. Right?
Yeah. Okay, that's next week, we'll come back with that with a tolerance on your own image and how close you would actually have to get
it so many ways. I feel like this is such a roundabout way of figuring this out.
But its uses so little tools. Yeah,
I've been fun. I'm having a good time but it's also like real gotta be a better way.
The only real tool we're using is a stop isn't watch the time it well and
our pint glass or leader or whatever it was
that honestly that I think I think that could be any size. And I'm, I'm assuming because we haven't calculated yet on what the the tolerance on our image would have to be like could just sticking two wires in like a coke bottle upside down? So it's like half an inch apart? Is it going to be safe to assume that the resistance is going to be a straight shot so you don't have to do any crazy calculations on the on the image? Yes, there's like straight shot saltwater. You know, what is it like? I can't remember it was like 20 What was the straight shot of the straight shot distilled water was like 50k per centimeter. So of like normal, they call it normal distilled, which didn't make any sense. But like distilled water that you could make it in your house by boiling it and then condensing it on a banana leaf.
Example it's got to be a banana leaf did Gabi banana leaf what is the radius of say 20 gauge wire? I'm gonna see I'm I'm already I'm already thinking about
figuring this out.
point eight, one to eight millimeters. Perfect. All right. Yeah. Well, I guess we'll we'll we'll think about this more and figure it out.
Yeah. Yeah, now we have a tolerance. That's actually what we should have came up with like last week. So you need this problem solving. Yeah, so you need to charge you need keep your phone charged because you're on a desert island. And you need to be able to call the Coast Guard or
who may be able to call for higher precision tools. Yeah, higher precision tools.
So so we're assuming Well, I guess doesn't have to be a cellphone basically, we want to have you we need to make sure that this voltage is safe enough to plug a USB device into probably your phone to keep it charged or like your phone's dead. So you need to charge it up. Yeah. And you'd like you open up this warehouse and there's like a ginormous like, wall of plugs that just says random voltage at the top figure out what you got figured out which one to plug into.
I liked that yeah, you have to test all of them and then figure it out. Yeah,
this is very like Monkey Island click point adventure puzzle I think that's gonna wrap up this part. I think so too. So that was the macro fab engineering podcast we're your hosts Parker Dolman and Steven
Gregg later everyone take it easy
thank you yes, you our listener for downloading and listening to our podcast if you have a cool idea, project or topic or comments about our chemistry abilities. Let Steven and I know Tweet us at Mac fab at Longhorn engineer or at analog ng or emails that podcast at macro fed.com Also check out our Slack channel. You can find it at macro app.com/slack And check us out on Twitch is twitch.tv/macro Fab 6pm Central time on Tuesdays.
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