MacroFab Engineering Podcast #283
MacroFab Engineering Podcast #283
Hail to the signal switcher! On this episode, Parker wraps up his prep work for the Extra-Life Charity stream and Stephen discusses switching signals.
Why is estimating a projects completion time feel like it takes more work then the actual project? Estimating Project Time, the quest of management.
Our Spider-sense is tingling... OH that is actually a man-made zombie spider crawling up my leg. Who thought that would be a good idea? WHO!?!
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 macro fat engineering podcast where your hosts Parker, Dolman, and Steven Gregg, this is episode 283. And we'll get close that 300 number.
So at the end of last week's podcast, Parker threw out a question to everyone that was just basically. Oh, it was along the lines of if you could design a custom multimeter, what would it what it? What would it look like and what would it be? And I thought it'd be fun to kind of gig on that idea, this episode and talk about a multimeter. Because so so Parker's been kind of dreaming big for some test equipment, I think
dreaming small, but in a big way.
You know, it's the mecca of imaging parties, when we make an idea, it usually starts out big, and then it either fails or gets shrunk down enough to the point where it's functional. Right? achievable, achievable, achievable, reasonable, reasonable, mildly reasonable,
reasonably achievable,
just past the threshold of achievable. So I thought it'd be fun to talk about a custom multimeter, to kind of meet the idea of Parker's new fleet of test equipment,
macro test equipment, TM, macro boxes, rocker boxes, actually, I have no idea of what we would ever call Actually, the thing is, if we, if we ever did a multimeter, it'd be called the macro meter. Of course, it was of course, right? Remember, the macro amp?
Oh, yeah, we have the macro amp. We will, you've been kind of dreaming up the macro supply. Right.
Macro supply? That's actually I thought we were going to talk about because I've been working more on that multimeters actually something that could be more community driven, I think. Because we are going to try to open source as much as we can on this project. I think
it would be fun to make it just reasonable enough such that anyone could build one. But but but good enough that you could use it in industry.
Yeah, and good enough for industry. Open source stuff. But I think the big thing is clamping down on the specifications and its functionality early. And if someone wants more, guess what it's open source, learn, adapt, overcome and make a pull request.
GitHub, good luck.
Good luck.
Well, okay, and so what's funny is, basically what I've written down on our notes to kind of talk about today is those specifications is, is just, let's start hammering out, let's, let's, let's duke it out and figure out like, what is a generic multimeter that will work for most applications, that doesn't just break the bank and make this a massive project that won't ever happen. Alright, so I think
before we even dive into specifications, like, what is the use case? For this first? Yeah,
like why why even do this? Like, what's
the whole point here? Yeah, why? What? What are the use cases? So my use case where I want out of this is, I need a multimeter, that fits into a one U rackmount. Case. So that is 17 inches wide, which is that's pretty large, but about eight inches deep. One and three quarters inch tall? is that's the outside dimension of the box. So inside slightly smaller than that, but
we'll end the rack face is 19 inches. Yeah, well, that's
what the ears Yeah, the ears, your ears are 19 wide. And then all the hookups are in the back of the of the meter, no hookups to the front, because this is designed to go into rack mount and be hooked up to other test equipment. It is not. It is not designed for an operator to be plugging stuff into this thing. It's for a computer to talk to it and go get me the acquisition of that of the reading right now. And then it gets it I think a little screen on the front that just lets you know what the meter is doing at the time might be useful. And maybe if we design the small enough we can put like 234 into one of these one you racks. So because it's 17 inches wide, you got a lot of real estate in these in these cases. Especially if we're not designing crazy have, like a like a multimeter nowadays is like, you know, it's like a playing card deck of cards. It's like, okay, we can fit a lot deck of cards into one of these racks. So that's that's what I'm getting at now and four specifications, voltage readings, that kind of stuff. It handles, I guess we'll get there. But if handles what your handheld multimeter can handle, it's pretty much what it needs to do.
So your your use case is perhaps a little bit different than what people might have been thinking when when we originally said custom multimeter. But I think your use case is actually really great in this situation. Because if you step outside your use case, and you're, you start thinking about designing a multimeter that somebody can use on their bench to, you know, probe around something, just go buy one, right? Yes, this custom multimeter I think solves a few issues, or maybe not even issues, but it scratches a niche, shall we say, to have a decent way to gather data, talk in a very simple way to a computer and log that data somehow, right? And, and that's sort of what you're getting at as opposed to like, if you want to get a handheld multimeter that does that, that's great. And you can pull that off. But then like, you end up getting into the Raspberry Pi issue of where like, you have one thing with 15 different cables around it. And it requires setup every single time you want to set it up. And in a production environment, that's not as desirable. So if you could have something that's like a rack mount case, that just is easy to plug into your testbed, and then run some kind of script that pulls everything that seems ideal in this situation.
That's what I'm going for. It's not three play. It's not a benchtop model. It's not a desktop or a handheld model. It's it's a it's a module. It's a multimeter module. And there are a couple of companies that make these like Keithley and a couple others. But frankly, those are little expensive. As a little, they're like north of seven grand, which is like okay, Parker, you're gonna be spending a lot of time designing something you're designed time's worth money and stuff like Yeah, and
it does that times free. Right?
Exactly. But that's also one of those. It's learning. I've never designed a multimeter before. And so I want to try doing it.
Well, and okay, so it's application, its end application is to be in service, testing customer gear, or customers products. And so when it comes down to the specifications, it's totally worth keeping that in mind. Like, at the end of the day, this just goes into service testing people's equipment. So basically, it specification should just cater to what the what, what the average customer's device is going to go through. Correct. So in other words, let's stay away from education's let's this this thing doesn't need to be able to read 40,000 volts. Yeah, if it needs a read, if I need to be able to read something like that, then I'm going to go buy the $8,000. Keithley, to do so. It'll be very custom. Yeah, yeah. But if
so the idea here is to make a rack mount $10 Harbor Freight meter for more than $10.
But that talks digitally to your computer and makes talk to the aggregator.
And yeah, there's more than what the $10 multimeter from Harbor Freight we're going to be doing. But that's that's the functionality. I think we're poor, we need more digital precision, of course.
Well, and I was mentioning this to park earlier, you know, something that I would I would find useful at a contract manufacturers say I had a few of these rackmount multimeters just lying around. And a new customer comes up and says hey, I've got a product, we're almost done with the with the test procedure. But we were hoping to work with our contract manufacturer to figure things out, and they say, Hey, what gear Do you have? You could provide a spec sheet and say, Hey, I have this rack mount multimeter that makes all of this test procedure a lot simpler does this work for you just just hand them a one sheet little, hey, here's my meters.
And I think one thing about doing this as an open source project allows other people who are developing their own products, they can look at this project as a way to incorporate into their own test procedures as well.
Right, right. And you know, it's it's,
they can go and develop their own test procedures and not have to go buy the $8,000 keathley they can go build their own and go do it for I don't know what a couple 100 bucks maybe? We don't know yet actually honestly No idea what this price is going to be. It can be $10,000. When we're all done. Yeah, I hopefully it's under. So price point is, I can buy two siglent, digital multimeters, throw them into a three rack case for like 800 to $900. That's with like banana jacks. So like bass, I'll take some pictures, but like banana Jacks may see coming from the inside the case, going into the front of the meters, and then the wires going up around the meters into plugs into the back. And then the backs cut out with where the meters are, like bolted to the back of the case. I can do that for like 800 $900. So technically, we have to beat that price point. For two channels, which I think it should be doable.
I like the idea that if it's open source, and someone doesn't like some aspect about it, like you mentioned earlier, no jacks on the front jacks on the back. Well, it's open source. So if you want jacks on the front, cut some holes on the front, stick them on there and wire a man and
yeah, do a request for you know, Jack in front design. No, that's totally what it is, is if someone wants to make a, a front mount version or wants to add more physical buttons to it, sure, just make a pull request when we get to that point.
Well, I'm also excited about this, not necessarily because it's a new project. That is fun. But but but more that it is kind of it ties into a larger group of other things that we've have been talking about, like some power supply stuff, but also digital communication, like talking Skippy over to these devices and actually controlling them. So let's talk about, let's talk about some of the specifications that we think we might need out of this. So first of all, guaranteed it's a multimeter. Where it's going to need DC voltage reading, like that's just a guaranteed, right. That's the first thing. Yeah. So what kind of range would we expect from our average client?
The the highest I've ever had to measure off a client product was 300 volts. And that's getting up there.
Yeah, I think I think you could, you could probably have it do less than that. And you would cover it's still
the best. Oh, yeah. The next one after that. It's like 48. Right, right. Most, most readings are zero to three and a half. 3.3 volts. Basically. There's some five some twelves Yeah,
some 20 fours.
A couple, maybe 20. And then it goes, there's 148 that I know of. And then after that's 300. It's so like what's a normal meter? Like grab a multimeter? And what is its top DC voltage range?
My my Harbor Freight hits? 1000.
Yeah, let me I've got a I should have got a lot of socks. We were talking about this. I have a Beckman 310 which was my grandfather's. This is my this is my domain family heirloom by the way. It goes up to 1500.
Yeah, I'm looking at the specs for the fluke 87, which is sort of like the de facto standard. And that's 1000 DC. But so it's 1000 AC as well. So yeah, so
yeah, let's say 1000 volt DC, is what a handheld model can do. When
all said and done, like having wider DC voltage range. It doesn't have a huge impact on the design to have a wider DC voltage range. To my knowledge, some one of the biggest things that impacts is just your safety clearances and things like that when designing things or choosing what wires you use. So yeah, I think I think up to 1000 volt DC is would cover basically everyone if you need something outside of that. It's super custom.
Yeah, what is like most of your cables, or your probes are what cat three 1000 volt? Yep, rated? Yeah. So if you make your front end able to survive 1000 volts. That's kind of that's probably why that number gets picked. Yeah, yeah, I think I think that I'm wondering if these probes that are in this bag from this, Beckman are 1500 volt rated. I'm looking real quick. You know, well, he's saying they don't have they don't have a cat rating or anything on
that They're good luck. Good luck. They're
just hard plastic. Yeah, they got the got the Beckman logo on No, that's good.
I forgot to mention at the at the beginning I found an article. It's just a fun article about the electronics and meter design. And it's it's pretty basic. But it this is
the electronic design in a very inexpensive meter. Well,
honestly, if you're a student in college, or if you're learning electronics, and you're looking at voltmeter versus ammeter, and you're wondering how that actually gets accomplished, this is a really great article, and we'll post it up on the on the blog post for this. For this episode, go check it out. If you're curious about how all of that gets done. This is the basically steps through every setting you would have. And then at the end of the article, you have a functional multimeter. Maybe not the world's greatest, but you'll have something that does what it needs to do. So yeah, I think I think 1000 volt DC range will cover everything. Cool. So I'm actually writing this down. So we can write a little spec sheet and and have a design goal or target of sorts.
Accuracy. This one's tough. This is like, for me, it's like good enough, because I don't No one asks me how good my meters are, right?
Yeah, well, and accuracy is kind of loaded that word when it comes to all of this. Because well, okay, accuracy versus precision, like, if I measure a thing 100 times am I gonna measure that thing exactly the same every single time? That's precision, right? But if, if we're talking about accuracy, well, if we're talking about absolute accuracy, like how close are we to reality with each measurement, right? So it would depend on on the range, because you don't need like microvolt precision when you're reading 1000 volts, right? Correct. So you know what, I think? If you're alright, with it, I would like to, I would like to shelf accuracy for the moment, because what I think what will happen is that the design will end up dictating what the accuracy is, because of to later on, we will probably run into designs that utilize specific chips, and then we can choose between them. And those will let us dictate what the accuracy is.
So one thing on accuracy. And this might be resolution as well. What does afford, like when you look at the meters, you see like three and a half, four and a half, five and a half digits. Yeah. How does that play into this?
Well, it's, you know, it's also, that's, that's a bit confusing, too. There's a handful of articles about that, that I was I was looking to link to one just to give people an idea on it. Whenever you see,
to me, that just means how many decimal places it goes to, is that come the right idea?
It's well, but it's interconnected also with whatever you're looking at, because if you're looking at 1000 volts, it's not going to like say you have a four and a half digit. It's not going to show 1000 volts point 00 zeros. Yeah,
so you it's how many digits of precision you just have. So if you're if you're a four and a half digits, at 1000 volts, the best you can do is 1000. point x. Well, the best you can show best as you can show Yes. 1000 point X you're in.
That's That's how many digits you're displaying on a screen effectively.
Well, that but not it? Well, it's not just that, because remember, this thing doesn't have a screen. So it's just how, what its effective resolution and accuracy is that whatever range you're at, which I guess is next thing is range.
Yeah, sure, like a four and a half digit. multimeter can display full four full digits, and then a half digit after that. So you basically get four.
Yeah, so a 1000 volts, a four and a half digit would show 1,000.5 or 1,000.0. Or,
actually, basically it just shows does basically just don't consider the decimal. It shows you 1000
Right. Yes.
So well. Okay, so that is a question. How many digits Would would you think would be needed on this? I think four and a half to five and a half would be totally reasonable.
Yeah, four and a half to five and a half is plenty fine for what we're going to be using this meter for.
Yeah, because it Once again, if you need anything like way outside the edges, you then this isn't the meter for you, you would purchase something purpose built for that. So like six or seven or even eight and a half digit multimeters. Like if you're making precision things that need to read down that low, buy the thing that's right for that. Don't don't rely on something that we decide to read that that low. Okay, so here, here's, here's another function that is divisive between people auto range or manual range.
I hate on arranging. Granted, I've only owned cheap meters. So I do know, nice, and I have used nice meters that have decent autoranging. For this device, you know, what raise you should be measuring. This is not a testing or valid, this is not even, I shouldn't say not for testing, because that's what this is for. This is not for experimentation. When you're experimenting with a circuit, you might have an idea of what the range of that signal you want to read is. But honestly, you could be anything. Schroeder signal, you don't know what it is. So you measure it.
You know, I liked the idea of not having auto range. Because like you said, you should know what you're going you're reading before you're going into it. That's the whole purpose of this thing. And if it's outside that range, that's actually a problem that it doesn't need to switch to a different range. It needs to say like, Oh, I'm not in my test boundaries.
Yes. Again, this is would be open source. So if someone wanted to write an auto range function, because that would probably be in mostly software for it to automatically switch between its ranges. So that will could be in software. Someone can make a pull request and add that functionality into it. But yeah, that's, oh, my meters are not autoranging. So
I think I think that's reasonable. My meter right now that I use daily is not autoranging. And yeah, I've never, I've never been upset because it doesn't have that.
upset.
I would say the Rangers that are really slow, and they suck because that and they're annoying.
Yes. That's the problem is bad. autoranging is terrible, almost borderline unusable. But on top of that, though, is you have to make sure. Let's say we'd I would say we have to design the hardware portion of it. So that if someone does implement autoranging, that it can do so safely.
Yeah, like switching input resistance or whatever.
Yeah, make sure that it can be done safely.
Right. Right. So design for it, but don't implement it.
Well, on the software side, yeah. Right. But that's just a safety thing. Making sure basically while it because what if you are testing something and you go, okay, set the range to blah, and it was the wrong range?
So I guess there just need to be, I mean, you have to have saved checks on the on this on the software side, because this thing, it's just going to do what the software tells it right?
Well, so think about your multimeter that you have that's in your hand, if you hook it up to a high voltage input or a high voltage source, and you would go the controls around on your multimeter. It doesn't explode in your hand. At least it shouldn't. Well, honestly,
that's one of the reasons why most multimeters have current reading as a whole separate Jack, you have to move that Yes. Especially you can't swing the arm through. No, that's
true. That's an RS would have the same this meter would have the same thing.
Sure, but somewhat, right, because that's a hardware protection that is a physical mechanical protection against these kinds of things. That's actually
one thing we will get to when we get to DC AC current on here is I have an idea of for that. But that's the thing with auto ranging or switching ranges is if you're in the low voltage range by accident because you gave the meter the wrong command. You don't want it to explode. So it needs to be able to safely be in the wrong range.
Right, right, right. If you're expecting low voltage and you plug it into high voltage, that's not a problem.
That is not a problem, right? That your monitor does that when you hold
I also really liked the idea that if this, if this meter becomes something that is, you know, a mainstay, say, for macro fabric or anyone else, I like the idea of being able to create cable harnesses that are test harnesses, where you plug them into the back of that, and then you have a dedicated test, plug on your, on your array of boards or whatever. And then you could just plug it in and run your script. That's, that's, I've been trying to go that way more often with my designs, as opposed to like telling people get 15 of these cables, and six of these and then plug them in this way. Like that's super annoying. Cool. So yeah, let's talk about let's talk about AC voltage. Do you want this thing to read AC voltage at all?
It's one of those. I, we probably never have to do it. I've actually don't think I've ever had that for a customer. But it's a multimeter. It probably probably should do that, at least in some form. And I think most meters go up to 600 volt AC. So that's probably what we have to be designed for.
Yeah, the biggest thing when it comes to AC voltage isn't necessarily does it do it? Or does it not? It's more about how it does it? Like, you probably see, in fact, I bet you um, Trump pulling up a picture. Yeah, if you pull up a picture of a fluke 87 It has some words right after fluke 87 It says true RMS multimeter. It's such a big deal that they silkscreen it to the front of their meters, to have true RMS,
and on this screen, this meter is yellow.
They don't need to, it's pretty bold. But having true RMS in your meter is a big deal. And I guarantee you, your low $10 guys are not reading True RMS. True RMS, it takes a lot more work, it takes more expensive circuitry on the input. So there's, there's sort of like three grades, I think there's actually four, but I'm gonna call it three, there's no AC measurement whatsoever, then there's like, average ish AC measurement. And then there's true honest to God, RMS, the fourth one, there's another RMS measurement in there as well, that's not as good as true RMS. But effectively, most of your like $10. cheapo multimeters, they're expecting to see a pure sine wave. And they'll give you the correct reading for a pure sine wave and nothing else. Everything else they will read incorrectly. Now 99% of the done, you know, what are you? What's, what's the one AC signal that you're reading for with a multimeter? Your infinite power out your wall? Yeah, your mains? Right? So, you know, you're typically just trying to read, is it there? Or is it not kind of thing. So, you know, I don't know how much it matters. Because if you if you want to get more accurate, you're gonna put it on a scope. And you're going to look at it on a scope and get get some some much more accurate readings. So I can sort of take it or leave it when it comes to AC and I agree like, even me working an audio company that works with AC signals 100% of the time, like I never have to read them I never have like, or if I ever have to read their amplitude, it's done on the scope. So I don't know. It's difficult because you're not going to a technician is not going to take your rackmount meter out to a three phase motor and hook it up and try to read amplitudes on a three phase motor and hope that it's true RMS right?
Well, let's make it true RMS so we can silkscreen True RMS on it.
It's sort of true RMS conditionally True RMS, only for sideways. So to be honest, if you get rid of AC voltage, it actually makes the design a bit simpler. So, but it is a multimeter. So probably should be able to do it.
Yeah, well, I think we will have to start looking at when we actually start doing the design stuff and figure out that's something we want to add then. Because the next part, which is DC, AC current is also like, well, if you're not doing AC voltage and you're not going to do AC current as well.
Right, right. Well, if you don't do current at all, then you save yourself some some heartache. Let's put it that way. If you just do a DC voltage, it ends up just being a voltage reading device. Like yeah, that does not have to be very minimal specs.
Good dc, dc AC current scope is go.
Yes. Okay, so if we wanted to add DC current, which I think is reasonable.
Oh, it's going to have to have it yeah.
What What kind of range? Would you would you need on something like that? 10? Amp minimal? Okay. So do you have some clients that require that?
Oh, yeah, there's some stuff I've measured that's like, up in the 15 amps easy. Okay. Okay. A lot, a lot of lighting, a lot of power supply design stuff, where you're loading stuff down with through a programmable load. Got and you need to verify that you're pulling that much power.
Well, okay, so if you want AC voltage, then you have to have AC current. And if you or other way around, right, yeah.
Well, I don't I can take anything AC, I can take it or leave it. Honestly. I think we should. I think we should design it in there. Because it is a multimeter.
Yeah, yeah.
And for the range 10 amp seems to be like the minimal what meters can do. More is going to be better, of course, on the on the range. And then for accuracy slash resolution. You know, micro amps.
I would love that.
Yeah, it is. So
you do a lot of micro amps. Say if I was reading a five volt signal, and I could read down to four digits are four decimal places. So hundreds of micro amps, or micro volts. Either one of those, that would be that would be killer.
Well, if it's a four and a half digit, you'd only get three decimal places.
Yeah, I'm just saying that would be killer. And, and actually craft like brings up a kind of a funny point. In addition to silkscreening True RMS on the front of something, you could say extremely low burden in all caps on on a thing. And that that is sort of a buzzword, right? Low low burden being the like the amount of voltage that's generated due to putting current through a, a, an ammeter. So
that high impedance basically,
yeah, I don't know. Like, that's, I think we're getting edge KC there. I think we're getting a little too far into the weeds on that. So I would say let's dodge that. So okay, DC, 1010 amps, DC, AC current or higher?
I think we should start looking at the components. The thing is, I think most banana cables are 10 amp rated. So it might be one of those. We can design it. And then if someone wants more, they they design different connector on it. That kind of stuff. Yeah, so I would say 10 amps is probably good. spot for it.
Sure. Yeah. Okay, yeah, I think I think that covers it.
So below, so four and a half or five and a half digit from a zero to 10 amp range. And I'd like to be able to measure micro amps with with the meter. So
okay, I think that adds a little bit of complexity. But yep, no worries.
Yeah, I think the cigarettes I'm currently using, they go down to six that have a 600 Micro ramp range. And I think that's I can't remember, I don't have the PDF here. But that's not the lowest it can read. That's just the range zero to 600 micro amps. And then whatever its resolution is, is your deviations inside of there, of course, right. But that's what I like it to do. So one thing that I have never really used before is for wire current measurements. So I've never used it before. I'm assuming what that how that works is because it uses four wires from your meter is two wires, our sense wires that read, I want to guess the voltage at those two points that you're picking up and so then it can it can calibrate out the drop from the wires from your meter to your D UT.
That's because that's how that works. Yeah, that's correct. And that only works. If your cents wires are the same length, right? Because you want them to both basically be equal. We're in resistance. So yeah, I think having four wire on that given that this is a test environment, I think four wires is required on this.
Yeah, I would say that's a requirement as well. Yeah.
And that that's for resistance measurement as well. Yes. That might that might be a stretch goal,
stretch goal? Or are we just, again, I've only done really preliminary research on some of this stuff. So
so so craft labs says, Hi, power, amp and speakers for Super continuity testing mode, which I love the idea. I would love one that just shakes the walls whenever you have a continuity, right. So you can have your music
on really loud. And ya
know, however, I think that kind of defeats the purpose of this thing being like a dedicated test bench. Like, once again, with continuity mode, you would use your handheld for that.
Yeah. Now, it will have a cartoony mode, because that's something we test a lot of.
But it wouldn't necessarily need to beep.
No, it doesn't actually anything it should not be.
That might be annoying.
And then resistance measurements on a percent. And diode testing. Which is similar to the katooni measurements.
So all the basics,
really, yeah. All the basics. Yep. Which is what we what we talked about last week, but in more detail this time. Yeah.
Okay, so how about communication? I guess this is just USB over to a computer, USB over
to computer. And I'm going to implement what I've been doing on my test equipment, which is Skippy, I found that's really, really useful. And it's a universal style of communication to test equipment. So you could easily integrate this meter into pretty much anything else. Any other test environment fairly easily. So craft lab is saying a counter. I've never used a counter for test equipments.
You know, I have but it's been really specific situations. And I feel like if you need a counter, you could probably implement that in software. It would not be anywhere near as accurate as hardware. But But yes, you could do that in software.
So for me, communication is strictly USB. I see some mentions of Ethernet. Because Skippy can go over TCP. Guess what? Make a pull request at it.
Just USB for rev 0.1.
Well, for what I'm going to be excited for just have USB, but if someone wants to add Ethernet, they are totally welcome to add Ethernet to it. Yeah. Remember, this is so much this is a project for Steve and I to learn about multimeter design. And also for y'all to learn about multimeter design. This is not a product for y'all to buy off the shelf. I think that's what people need to realize about this project, too. This is not something that someone's going to go to Mac fab.com and buy this thing this is not what this is for this is for you to learn and expand your knowledge base.
I do like the idea of Ethernet though. Especially especially if it was Power over Ethernet and it just all ran entirely off of one Gable that'd be tight.
You added then yeah, maybe I don't know. So remember remember how much board real estate we have in this
includes you have unlimited basically. Oh sure. It's huge. Yeah.
So if someone wants to add it, they can easily add it cool.
So how about powering the meter? It needs to be isolated right?
Yeah, it has to be isolated. So 120 volt AC in honestly, probably a a they make these 120 volt two AC DC output isolated blocks that are panel mount Yeah. nother they panel mount into your chassis. I'm probably would use one of those. Yeah, just to make design easier. Sure. Can we make it cheaper doing something like a our own solution on the board? or, or a wall wart or something like that probably. This is one of those. It's an isolated part. I wish I had that we talked about this before and Pacus, long, long, long time ago,
it was an IEC inlet that had a isolated SNPs in it. That that just you chose the output voltage and however much current Yeah, I know, I know what you're talking. Yeah.
Yeah, I wish I had the part number on hand. But we I would I want to use one of those, or probably will, yeah. And what we can do is, if we have multiple of these inside your chassis, you could just have one of those, and it goes to each one. And so that's true. If we treat it that way. Do we want each of those banks to also be isolated? Probably right.
Yeah, probably like, I would just treat each one as independent.
So you'd have to have multiple of these blocks in on the back of your meter, and multiple AC inputs,
or just one AC input and distribute to each one of these power supplies. Well,
so the isolated that that block that goes on the back the plug that's got the isolated DC power supply built into it. That's only isolated. But if you daisy chain that two different units inside your? No, that's what I'm saying. Those aren't isolated. Just
you could always just not use the one that's integrated into the IEC inlet. Just use separate, isolated supplies. That's probably these Yeah. So
what we should do then, is, if we're going to support multiple these boards inside of rack, then each board has to accept 120 volt AC? Or do we accept a DC voltage, and it's isolated on the board? Because that way, that way, we can be the board's become a country?
Agnostic,
agnostic, yes. Because then you can put in whatever AC front end you want, depending on what country what hurts what frequency, what Well, that's the same thing. What voltage, you know, I'd like to see that instead of saying it has to be 120 volt AC, or having to design a 120 volt AC to 240 volts switcher, or are where the switches up, I'd like to keep that part as a separate thing.
You could do
the 120 volt or the wall to DC as its own module, that's that's on the back, and then you just have a DC to DC, isolated regulator on each board. That could work. And that would be a lot easier to design, I think. Because then you wouldn't have to worry about the wall stuff. And you can get a UL rated part that's got all the certifications and stuff for that. And then if someone wants to use it in some other country that's got 240 volts and 50 hertz or something crazy like that, they can easily do
crazy. I love that. Yeah, that would that would make it easy, you know, in another solution is to have one board that connects to AC on the back, somewhere in the back of the rack that you populate however many power supplies you want in it. So if you only have one populate one power supply, and then it just delivers whatever voltage it spits out, if you have to populate, to, you know
what, and then there's also a way think about is, if if you did the other way with the boards accepted Dc, then you could populate it into a backplane style, you could change the form factor of the board itself to be a backplane style. And then you could slot these into a backplane. Yeah, so you can either design an AC module board that's got isolated outputs old DC, or Yeah, I like having the DC isolated on the boards themselves. Because then that kind of self contains each unit. You don't have to. You don't have to have anything else to make multiple these boards inside of inside of a rack.
Yeah, I think I think I lean that way. Although I do I do like the at the idea of a card edge kind of thing. That just adds complexity that's unnecessary. Well, that's
if someone wants to make a cartridge version they can. Sure. And so we'll just have an isolated DC DC converter on each board. Yeah, yeah. And that makes it makes it easier to make that a module that you can multiply into a rack. Yeah,
it's an individual thing. It stands alone. Yeah. Cool, I dig it. So, okay, so how about the enclosure, you already kind of mentioned it just a 19 inch or a 17 inch rack. One you high, and you said about eight inches deep, which is a pretty stock rack. That's what he's let us buy off the shelf.
Exactly. Now, it can be any form factor anyone really wants. So, things to think about is we need mounting holes. For sure. Now,
do what you just not going to duct tape your stuff down to the board or the enclosure.
So the thing but think about the mounting holes is do we ground these boards to the chassis or not?
Oh, I see what you.
So does does the through holes have exposed copper so you can clamp these you can screw these down into the chassis?
Well, okay, so 100% The whole chassis gets grounded to earth ground or at the IEC for safety reasons that's required. I think you could leave the meters floating. In fact, that's probably preferable. Yeah. Cuz
they're isolated. Yeah,
they're isolated. So float them that way you can, you can do all the multimeter tricks with them.
Right? Yes. Yeah. So this should be floating. Yeah. So you're mounting holes need to be isolated?
Completely? Yeah. Yeah. Or, like banana Jacks go through the chassis, like they don't bolt to the chassis.
Correct? Yeah. Yeah, so the meter itself needs to be floating. And then the mounting holes themselves are isolated, meaning that we don't require a specific type of mounting, meaning that you can use metal screws if you want. Oh, right. Yeah, you don't have to use plastic standoffs.
Right, the whole board is designed not to not to ignore the mounting holes. Yeah. Yeah, that makes sense.
Okay. One thing that we didn't talk about communication, is, I do want to put the capability built into the board to have a screen on it, just so that the operator or, or when you're programming, yours, your setup, you know what the meter is doing. He doesn't need to send live updates or anything like that to it. Certainly someone could, because it's gonna be open source, and you can change the firmware, the firmware, but I want to be like, it's in voltage mode in this range. That's like what I care about, Oh, you don't even want to display the value. You can though, you totally can just that's only a firmware. So having a way to hook up a screen is going to be part of this first iteration. And I'm thinking just a standard, you know, like, 16 by two character display. So having that capability of having that kind of screen hook up. That's whatever that protocol is the four bit or eight bit parallel. Yeah, to screen. We'll probably use the four bit style though because that's way less pins and honestly, though, that's just so you know, what the media is doing?
That's, that's really useful for development of the test software.
That's the thing. It's, it's for development purposes. And if someone wants to actually turn that into, it's actually spitting out what it's reading. Go right ahead. Yeah. Now the big thing safety because within certain limits, the sink should not kill you.
Well, okay, so it's connecting two mains. So there's there's mains fuses for for that side, but all the inputs are fused or need to be fused as well correct.
And on but on the the in the design that I want to do the AC side is kind of taken care of safety wise in terms of the isolated block that's spitting out DC voltage. And so that goes into the meters, the meter boards and then that goes to a DC isolation voltage. And then so the boards themselves will need to have protection from that DC voltage side, right. So probably a fuse, and then a couple diodes.
Yeah, and on most cheapo multimeters you see a 200 milliamp fuse and a 10 amp fuse for different current range.
Yes. Now, I've really liked how the sequence of setup, they are one because most meters have two ports for amps, they have a 10 amp, and then a Milla amp micro amp range, the sevens got one. Now, I don't know if it's switching different inputs or how it's handling that, but that's how I'd like to set it up it, it only has this port is amperage. And actually I'll go in farther is we kind of I kind of alluded to this, when we're talking about voltage and current and you brought up, you usually have two different ports, because it depends on where you're just swinging the dial on your meter. This thing doesn't have a dial. So we don't need to do that. We can have one input, and then a common plus the two more for if we do four wire. And so and then it just voltage to current. Yeah. So when you say I want to take a current reading, it just switches to that current, that proper setup and in on the hardware. Okay. Yeah, because we shouldn't need a dedicated pin or dedicated banana jack for that. It should just be that pin. So you limit how many Bennett Jacks you have on the back? So you're talking about just for? Yeah, just for this sequence got five, what's the other one for?
Well, you you have the four for four wire, and then you have the current the 10? amp current? Yes, yes,
yes. Correct. Yeah. Yeah. Well, I'm thinking is you have the four. But the voltage can also do current because why couldn't it?
Well, that's that's just the one thing that I was, like, if somebody was was writing their test procedure, and they accidentally switch current instead of voltage. That's when you could run into from, you know, that's the way
you would just blow a fuse right away. You are right, we shouldn't do that
we should get short for. Yeah, so five, five would be more ideal, although I like the idea of four. Because once you have your wires connected, you don't have to switch things around, especially if it's on the backside of a wreck. But yeah, but but we got to remember back to the original concept of this. This is a test a piece of test gear for a test situation, if you know you're going to be doing current, you're going to set this thing up and plug it in for current and you're going to leave it that way.
Well, so the thing is, it will have what I want to do on the also on the inside is all the jacks are disconnected on powerup.
Oh, they're all like really connected. Yeah, they're
all really connect. So you can actually technically disconnect everything if you want to. And so that's why I was thinking you can get away with just four to four cents and then 244 cents wire and then your common or your reference, it actually starts becoming more like an oscilloscope and that way.
I don't know, I think I might stick with five and and just make it dummy proof.
But the thing is, if you have five, it doesn't stop anyone from plugging the plug into the wrong spot. And then turning it on and then it just dumps a bunch of current through setup and because the wires are set up in voltage what the play with it, I think I think it's would be a good idea to we can get easily get due for just four. And that way you just have one common. Though, if someone can make a good argument of why we need five. I'd love to hear it. Okay. Why would why would we need a dedicated banana Jack, if we could basically connect the bandanna jack to either the voltage side of the front end or the current side of the front end? Why do we need to make them separate?
I think we might have wrongly
obvious reason why. Or is that?
No, nevermind. Go ahead.
That'd be because that's the thing is I'm thinking these are not even connected all the time. They're really connected.
Would you ever need to do both voltage and current? And if so, would you just use the second one?
You would have to use a multimeter. So you'd have to use the second one because you're going through the same common.
Yeah, my bed you right? Yeah, no, you're totally right. Yep. Okay.
All right. So what 55 minutes, so I found an IC that might work for them. us. It's the H Why 3131 Bye Hi Kondik iconic, something like that.
Hi, Khan technology.
And digital, it has actually made a Arduino shield based on this chip, I got one on, we're just talking to these test drive this stuff. Now their hardware design only goes up to like 50 volts, stuff like that. But that's, that's all the front end work and resistor divider stuff that we've got to develop. Now, the only thing is I haven't dealt gone too far into the datasheet yet, but I do not think it can do for wire. Because it's not really designed this chip is mostly for handheld multimeters. You know, it's not for a benchtop model, which would have the sense wires.
So I think this is just a goofy thing. But But I think I found a typo in this datasheet for it, because I was reading it earlier. And I was like, Okay, well what kind of what kind of power does it get powered off of. And if you go to their page where it says supply voltage, it says typical is 3.6 volts, the maximum is 3.6 plus 50, millivolts. And the minimum is 3.6 minus 50. millivolts. So, according to this datasheet, you have 100 millivolt window to hit the supply voltage perfectly for this thing. I'm pretty sure this thing can actually be powered off at 3.3 volts. And that supply range is supposed to be like, I don't know, 3.0 minus 50. millivolts. That's you have a Yeah, you. But like, if you read this, it's like, holy crap, I gotta be super accurate on my art supplies. Well, I
mean, it is a digital multimeter. So
it demands perfection. Yeah, so this looks like one of those all in one packages, that just kind of gets the job done. Right? It
doesn't do everything. But does most of the stuff that we were talking about. And adding a little bit more stuff, we can probably get to do more. The only thing is I don't think it does do the four wire. Honestly, though, you would do two of these chips. And then you could do for wire. Because the fourth wire that you're just measuring
voltage and current.
Yeah. So 10. So yeah, two chips you could do for wire? Because you'd basically you need to melt because two multimeters could do for wire if they don't have if they don't technically support for wire.
Yeah. This thing also does Gosh, what is it? 50,000 count or something? Yeah, it is a 5000? Oh, yeah. The Hy 3130 Does 5000 Count, which is pretty low. But the the one year caught calling out the 3131 does 50,000 count? So that should get us decent enough accuracy for what we're going for here?
I thought the count was speed.
No. There's like a whole thing that's like, all the
specifications. You're right, two meters higher counts provide better resolution for certain measurements, right? Okay. See, this is why I wanted is, this is why I want to design one because I had no idea how at the time,
I'm going to post this. This is actually a post on a Digi key forum. But it calls out all the different specifications of a multimeter multimeter. And description of it like resolution range display counts, those kinds of things. Like display counts. If you have a 50,000 count meter, it will read, say 49.999 Before switching over to 50 volts. Gotcha. And at that point, it'll read 50.00. So it it's also depend it also gives an idea of how many digits it'll show on a screen, whereas a 5000 count will show much fewer, like 5000 count will show five zero.
Yeah. Cool. So one more thing. Yeah. Before we go is last week we talked a little about like, if we wanted to do a Python stream and introduction to Python for like hardware engineers on a stream, and everyone was like Yes. So we need to schedule that. When should we do that?
Well, let's let's throw it out there and if anyone wants to be a part of that, so I So let's give a quick description of what we're talking about, like this is
this is not how to program Python. No,
this is using Python for Well,
what I'm thinking of is like, installing Python on like a Windows box. Yeah, like a quick tutorial on how to make that work, setting up an IDE, real quick, we're probably going to use PI charm. And even though I don't use nearly like, this is going to be a learning experience for me too, because I only have somewhat of a developer background for Python. Because there's way more than that IDE can do besides being a really fancy text editor, right? Setting that kind of stuff up making sure that stuff runs write a little script in Python, this is not going to be like an introduction of how to write Python. So you know, teaching syntax is not what this is for. But then on the other side is setting up a Arduino to respond and basically making a computer program talk to an embedded system over a comport with Python on one end, and Arduino C language on the other end. I think we can easily do that in probably an hour or two.
Yeah, that sounds probably more like two. Okay, so if you're interested in that, I would say let's get on let's get some more conversation going on the Slack channel and start proposing dates for that. So if you're not on this lecture already, come and join up netfabb.com What slash slack. Yeah.
And then I will try to record it, because we'll probably do a Hangout with Steven and I, and then we'll have both live streaming of course. And then I'll record the live stream as a VOD I think Twitch because video on demand, whatever. And then throw that on YouTube. Cool. No editing though. So it's gonna be like a two hour slog of tech issues.
So we'll find we'll find out, you know, for the community if I don't know a Saturday night is better than say a Wednesday night.
Yeah. So yeah, just make a poll on the Slack channel. Cool.
So yeah, join up and let us know if you want to be a part of that. Yep.
So that was the macro engineering podcast. We're your hosts Parker Dolman
and Steven Gregg. Later everyone take it easy
Thank you. Yes, you our listener for downloading our podcast if you have a cool idea, project or topic, or a really cool idea for this multimedia project. Let Steven I know Tweet us at Mac fab at Longhorn engineer or analog EMG or email or email us at podcasts at Mack fed.com. You think after like five years of doing this, I could speak well know. Also check out our Slack channel. You can find it at Mac fab.com/slack
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