- DSO138 Oscilloscope
- Comes as a kit (just through hole) but can be purchased assembled
- The “true” version can be had for ~$30
- Counterfeit versions exist for $4
- Open Source Firmware!
- Analog bandwidth: 0 – 200KHz
- Sampling rate: 1Msps max
- Sensitivity: 10mV/Div – 5V/Div
- Sensitivity error: < 5%
- Vertical resolution: 12-bit
- Timebase: 10us/Div – 500s/Div
- Record length: 1024 points
- Built-in 1KHz/3.3V test signal
- Waveform frozen (HOLD) function available Save/recall waveform
- In short – it’ll getcha through college
- DSO138 Oscilloscope
- Pinheck REV 8 is routed
- Finishing silkscreen after the podcast
- Placing an order for prototypes this week!
- Switched from standard SD card to microSD card
- Next board is the I2S Audio Amp
- Working with the TAS5755MEVM
- So far it kinda works
- Need to generate a clock for it?
- Pinheck REV 8 is routed
- Making A Classic Chip From Discretes
- Apple says sorry
- iPhone Batteries and Performance
- Zapp from the Slack Channel asks “If my MCU has internal pullups on an IO why would they recommend additional pull up resistors externally?”
- MacroFab Hiring!
- Apply here
Visit our Slack Channel and join the conversation in between episodes!
Special thanks to whixr over at Tymkrs for the intro and outro!
About The Hosts
Parker Dillmann is MacroFab's Co-Founder, and Lead ECE with backgrounds in Embedded System Design, and Digital Signal Processing. He got his start in 2005 by hacking Nintendo consoles into portable gaming units. He also runs the blog, longhornengineer.com, where he posts his personal projects, technical guides, and appnotes about board layout design and components. Parker graduated with a BS in Electrical and Computer Engineering from the University of Texas.
Stephen Kraig began his electronics career by building musical oriented circuits in 2003. Stephen is an avid guitar player and, in his down time, manufactures audio electronics including guitar amplifiers, pedals, and pro audio gear. Stephen graduated with a BS in Electrical Engineering from Texas A&M University.
Host 3 00:11
Hello, and welcome to the macro fab engineering podcast. We are your hosts, Steven Craig and Parker. Dohmen.
Host 2 00:16
This is episode 101. Yeah, and we're finally back from vacation. Yeah,
Host 3 00:25
It is now. 2018. So we've been doing this for is it? I'm checking my phone three years, five years. I can't remember a long time.
Host 2 00:34
100 divided by 56 or 101 5656. Is it 5362 52? Weeks? Yeah,
Host 3 00:43
It's 52. Okay, yeah, we're engineers. We don't we don't pay attention to things like time and dates and years, because that's all just like details, right? It's
Host 2 00:50
More times expandable and compressible, and moldable and stretchable. And something like that. Depends on how fast you're going. Yes.
Host 3 00:57
So it's all so I guess in this episode, where we'll talk about the 2018 projects that we're going to start this year, but not finished
Host 2 01:05
Finish, and then actually finish one. I was actually gonna bring up some projects that we did in 2016 as well. Oh, wow.
Host 3 01:11
They haven't finished yet. We haven't finished. Okay. Yeah. Okay. Because I think we finished, like, I know of maybe two that we finished like your
Host 2 01:18
Synth. Yeah. And then we finished? No, we got a couple projects that we finished. Okay. You have a list of cuz I can't like, you know what, that would have been a really good topic is to talk about what did it what did it next week? Well, we finished okay, no, oh, open projects of the map. We the ones that we accept
Host 3 01:35
Host 2 01:37
Knows a while ago we did it was it was in November,
Host 3 01:39
Host 2 01:40
No, we did it when you finished a synth. And we're like looking at these parts. I completely already forgot that.
Host 3 01:44
That's and and all the listeners are like, yep, cuz they don't have the listeners don't get to actively put their fingers on the projects that we work on, like, like we do. But we just don't actively put the finger on our own projects. They just sit there and wait. And we apologize. collect dust. Yeah.
Host 2 02:00
I actually found a super simple power supply.
Host 3 02:03
Well, I mean, it's a giant brick. It's hard to miss. Well,
Host 2 02:07
He had bought a quarter inch dust on it. Yeah, yeah. Yeah, we got
Host 3 02:11
It. That's funny, too, because it was that we got that one to the point where it's effectively working. Yeah. I mean, I had it on a bench doing things, you know. So I guess we never really just connected the digital to the analog side, analog need some some? Well, I guess both sides sort of need some more work. It would need short of another spin. But in terms of the prototype, like, we asked it to put power out and it power did that. Yeah. And it did it in the way that I wanted it to. Yeah, that's,
Host 2 02:39
I think, well, I want to make that one of the first projects we go and finish. Oh,
Host 3 02:47
That's a that's a beefy project. Yeah. Go all the way back to Episode One and finish that project. Yes.
Host 2 02:54
So we need a budget Iris. Yeah.
Host 3 02:57
Give us some money to fix this. So we don't have to bankroll it ourselves. Yeah.
Host 2 03:02
So the thing is, though, most of the money's already been spent on it. And just sitting in a box.
Host 3 03:07
We got a bunch of transformers. We got a big case for it's
Host 2 03:11
All in all the budget is in those transformers. Yeah. Yeah. It's like 150 bucks and transformers. And
Host 3 03:17
We got two, two of them. Yeah. And they're monstrous. Yeah, like the size of your head. Yeah, yeah, they're big.
Host 2 03:23
What we call those donut transformers. Yeah, donuts. toroidal. Turtles, but donuts better done. Transformers. That was the that was the name of the podcast. Probably that episode. Yep. Okay, so Steven. Yeah, I'm transitioning. Actual topics for this podcast
Host 3 03:42
Segue. Except not a segue. Now. It's just a brute force. Yep. Okay. So kind of over the break, the Christmas New Year's break. I was out on vacation but had plenty of time to just kind of like browse and I kind of did the thing where I just look at like, what's out there. And I found a pretty cool little, I guess, I guess you could call it a project. It's weird. Sort of doesn't fit as a project in my mind, but an oscilloscope a really inexpensive oscilloscope called the D SW. Oh 138. Okay, now this is a little oscilloscope kit that you can build sort of all are the old like Heathkit kind of thing where you get like a whole package and it's just everything's right there to build it. And and most of the listeners not I shouldn't say most but but I bet listeners have seen this before because it's incredibly inexpensive way to get a scope that actually works.
Host 2 04:35
You go on eBay and search for oscilloscope and select lowest price first and this pops up. Okay.
Host 3 04:41
Actually, before we even go into this, let's let's do a quick little game. This is an oscilloscope one channel and I'll give you that much information. It's one channel oscilloscope it does basically what your benchtop would do. Just not as well. If you go to eBay, guess how much you would see it for I mean, I saw that I looked okay. Okay, I didn't know. So you could find it for $4 a sample once. Yeah, four bucks.
Host 2 05:10
He says $30 Here. Oh,
Host 3 05:12
Okay. Okay. But so I sort of jumping the gun here is, let me let me talk about this scope for a second. Because I just think this is funny, I don't actually have one, nor have I even ordered one. I may do it one day, I don't know, I just I saw it. And I was like, this is a really interesting thing that has popped up because the the true version, and I put that in quotes can be had for 30 bucks. So what I mean by that is the whole board everything, you get this whole scope, which is, I don't know, it's got a bunch of bugs and assemblages, it is, but it's not the through hole parts. Okay, so it has a couple of surface mount slapped on there, and then a bag of through hole parts. So you basically get to learn to solder through hole parts, which, you know, that's like, it's like a solder kit, or like learn to solder kit. But it's kind of I don't know, if there's other better options for the if this is like just buy the assembled version, it's a couple dollars more for like $33, you get a symbol Dan, you know, acrylic case or something like that. Regardless, let me tell you the specs on this. It has a bandwidth of 200 kilohertz, which, okay, that's fine for most simple projects. It has a sample rate of one mega sample per second.
Host 2 06:22
That's not too bad. No, no, I
Host 3 06:23
Mean, for simple stuff. It, that's plenty. It has decent range, it goes 10 millivolt per division to five volt per division.
Host 2 06:32
I like how I most of the LDMOS that I use for my projects. They're ripple is under 10 millivolts. So this couldn't measure the ripple on my power supplies. Well, or
Host 3 06:43
You just see the peaks of the ripple. Yeah, yeah. So it's not, it's not incredibly sensitive. It's got 12 bit resolution, which funnily enough, that's actually better than a lot of like desktop. Yeah, guys, mainly because they're way faster. So they do eight bit resolution, and much faster. But regardless, it's 12 bit, that's cool. It will go 10 microseconds all the way to 502nd time base, so you can have this thing like take minutes of data, even though it only has a recording length of 1024 points. So basically, if you want to take like a couple points of DC across 500
Host 2 07:20
On like an 80 Mega 328 P, or some 80 Mega eight bit processor, these are like wouldn't typical eight bit stuff
Host 3 07:28
Wouldn't surprise me, I don't actually I don't actually know off the top of my head. So it does have open source firmware. Okay, cool. So if you want to, if you want to take their firmware and change the graphics, or if you want to go and change, like the colors of traces, or whatever, or even write your own firmware, your own custom front end for this thing, go for it you that's fully open. So it's like, it's a really, really simplistic scope. But if you're just looking at little signals on a breadboard or something, it works great. In my mind, what this actually works really fantastic for is like, Is it their test? Yeah, you could just plug into something. If you see something on the screen, you know that there's a signal there. And to be honest, even though that's really simplistic, you'd have no idea how useful that actually is.
Host 2 08:13
Well, it's like the most time you use a multimeter for is for continuous metering. Right.
Host 3 08:18
Right. Yeah. So, you know, a lot of people think that you get these scopes to look at like, AI diagrams for speeds on USB. No, you know, the time you're just looking. Yes, there's a signal on this. Yes, this is, you know, you're just passing signals. Most of
Host 2 08:31
Them I'll use my scope for like, I'll you because most times with it. I just looked at analog stuff. Yeah. Right. Because if you're put this way, if you're doing digital stuff, you don't want to scope.
Host 3 08:44
Well, yeah, if you're trying to decode digital stuff, yeah.
Host 2 08:48
Well, yeah, if you're looking at digital stuff, you don't want a scope. You want a a logic analyzer,
Host 3 08:54
Right? Unless you're unless there's something like you're getting runt pulses, or weird shaped like curved pulses. Yeah. Okay, if you're getting weird stuff like that, but at that point, you're probably not getting any data. What's exactly yeah, I
Host 2 09:07
Know I can see you using it's got like if you're trying to measure overshoot, or undershoot or roll off on your clock speed, but for most projects, you're not getting into that speed range where those become a problem. Like 100 You're talking like I diagrams for like, you know, doing qualm modem stuff and carrier signals, like you're not doing that with an Arduino?
Host 3 09:32
No, no, no, no. And you're probably not doing that on your home bench either. No. Yeah. So, so this thing ain't gonna do that.
Host 2 09:39
Yeah, but what I'm saying is, if you're just doing Arduino stuff, something like the DSO 138 for your scope, and then use like a, you know, open bench logic analyzer, which is like 50 bucks. And that's under $100. You have a basic lab to do pretty much anything that Arduino can do.
Host 3 10:01
Oh, yeah, absolutely. Even even a pie? Yeah, you could you could, this is good enough for that. That was actually one of the points I was gonna bring up with. This is like for 30 bucks, you can get a scope that'll get you this this scope would get you through college. Oh, yeah.
Host 2 10:15
Oh yeah, it would.
Host 3 10:15
Yeah. So let's let's put it that way. It's that advanced. Yep. You know, so for or colleges that devalue. So regardless, what's funny about it is for 30 bucks, you would think that this would be kind of like the only scope out there, there is a counterfeit version of this scope. That's the $4 one. So it's like, why counterfeit, something that's already super cheap already. It was,
Host 2 10:42
How do we get to $44? I have no idea. Maybe it's actually a real one. And they just stole it. That could be.
Host 3 10:51
But like, there's websites that don't show you like, you know, look for this writing on the PCB and look for this kind of sticker. And like, the true one has this kind of font or something like that. Like, there's ways to tell that there's counterfeit of this. And I, you know, I haven't researched it enough. I know that there's kind of it's I don't know, if the counterfeits work well or not, they might be the exact same thing. They're probably the exactly same thing. Yeah, they probably are. So the the other thing that's kind of cool about this is the whole screen is on a pin header. So if you get the soldering kit, you can actually omit the pin header and put in like a ribbon cable, such that you could mount the screen to anything. I see what you're going for it this. So you could put this anywhere, really. So you're gonna make this a display for a synthesizer. That was the original idea.
Host 2 11:40
Yeah, it could be it's a 30, you'd have a $30, basic customizable VU meter, and signal, what they call waveform. What's that term? It's an older, it's like a wrong time when you had really old like the, like scopes that you had, were actually had round displays frown tubes. Okay. And they had something that was called a waveform. Viewer, I want to say what it was, and it was more of a lower end scope. Hmm. Basically was a scope that was like fixed to look at one specific, you know, channel and stuff.
Host 3 12:14
Oh, yeah. You could probably make it a whole lot cheaper. Yeah, doing it. So
Host 2 12:17
Yeah, it was basically you plug the signal in, and it would just look at whatever you're like that one specific frequency it's looking for.
Host 3 12:24
Right, gotcha. Yeah. So yeah, I mean, this. This could be something cool like that. Yep.
Host 2 12:31
I think it's cool idea. Yeah. So what you've been up to burger, so the pin heck. And I know I said I wasn't going to mention this until it was done. It's actually all routed now. Finally, how long did that take you? Oh, man, six hours to finish it up. And the hardest thing was like resisting going back and rerouting old stuff. Oh, yeah. Cuz you can get caught up in that. Yeah. And I was like, I'm only gonna change the minimal I can change. And I think so I said last time, too. So all that's left is silkscreen now, um, cuz I added some fuses and stuff, had to put documentation on the board and all that good stuff and make sure like the silkscreen is not underneath a part because you can't read it. But yeah, everything is looking pretty good on it. We changed over from the standard SD card size to a micro SD card size, finally, okay, that was like pulling teeth because everyone knew. So like, against that. I'm like, Guys, micro SD 2018 2018. Guys, come on. Yeah. What's that thing? It's like, if your argument starts with its year x, it's not a valid argument.
Host 3 13:41
So basically, you get the cleanup and polish lift to do.
Host 2 13:44
Yeah, a couple choices. Probably just looking at them. And I'll be like, oh, what? That one doesn't look as pretty. I'll nudge it a couple mills. Yeah, yeah. Yeah, it's in that phase now. So I'll probably order the I think we're ordering four boards this week. Okay. And those are some pricey prototypes.
Host 3 14:00
Yeah. So in a couple weeks, you get to test Yeah, everything worked out for it's a Ford GT RC passes. DRC that's best. Yeah, that probably feels good.
Host 2 14:10
Yeah, you know what's really funny though, is like I pretty much know what like when I'm routing outs like I know what 816 Mills is because just the routing that we use so I know what six Mills looks like. And so I like I think I had to just like two traces afterwards. Nice. Yeah, cuz it like one got a little too close to a via it was like a mill off and like, but then I got just like, that I just nudged the mill and moved everything else. Oh,
Host 3 14:39
That must have been nice. Yes, it was it was it. Was it snappy or did it have to like think
Host 2 14:43
It was pretty snappy. Cool. It wasn't too bad. Yeah, cuz it gets annoying
Host 3 14:47
If you if you ever use push shove, and you actually like bump the mouse and has to think about the everything and then you're like, ah, Ctrl Z. Yeah,
Host 2 14:58
That's I didn't have to rethink Yeah. Yeah, exactly. Yeah, you're not I haven't tried is if you do a push route and you did a CTRL Z, would it reroutes?
Host 3 15:06
I haven't tried that yet reroute all the other traces? Well, yeah. So
Host 2 15:09
If you push route it and push them all away, and you control z, it should remove that trace and push everything back to where it was it yes,
Host 3 15:17
It should, because it should consider a push change as one one operation. Yeah. Yeah, I wonder if it does or not? Cuz that would be really bad. If it didn't. Yeah,
Host 2 15:27
I gotta try that out. Yeah, yeah. Um, so after this board, after we order it, I gotta start working on the I to s audio amp. And so I talked about the slot two times three times ago, something like that, the Ta s 5755 M, which is a 70 watt, I two s. Chip from TI. So I start playing with because I got the evaluation board. And so I hooked it up to the Raspberry Pi, and got that all running and it mostly worked. What is what is that it was really staticky. So I think in some settings wrong, or I based at the play with it, or might be the evaluation boards busted? Because I wasn't using it in like a non standard configuration. Oh, yeah. So I'll fix it.
Host 3 16:17
Basically, I'm gonna have to rip data to that.
Host 2 16:21
It's at 48 kilohertz. Okay. So well, times your size, plus whatever
Host 3 16:27
Extras. You have. You have, you know, yeah, eight bits plus your acknowledge and all that crap. Yep. Okay. So pretty fast. Yeah,
Host 2 16:36
It's, it's some it's had the PI has built in hardware
Host 3 16:40
That does that. So you don't even have to worry about it, you know, send that crap. And it goes, yep. Okay,
Host 2 16:44
The big problem I think we're gonna run into is the Raspberry Pi doesn't output a master PCM. Clock. Most I says don't require it, they just have their own. That's like their sampling rate, the 44 point whatever kilohertz or 48 kilohertz or whatever, kind of like the motor here has its own. Its own master clock. The motors are recording interface. Yeah. So it has its own master clock, it doesn't get that signal from the computer. But this amplifier to increase flexibility, a lot of the higher end ones, you need to generate the master clock for it. And so I don't know if that's something I needed. I can I just put a 48 kilohertz clock on it and call it good, or what I think that might have been part of the staticky problem at the try it I'm gonna put it in a standard configuration according to like the evaluation PDF. And hopefully, if it works, well, then I'm I know it's something I set up wrong. And like, the Raspberry Pi site or something, just need to spend some time on it. Yeah, I basically just threw it together with some jumpers in like, 20 minutes and a beer and tried it. And I'm like, it worked it just like so.
Host 3 17:57
Yeah, sounds like you got something wrong.
Host 2 17:59
Yeah, something's wrong on that. But it's least at work. At least you can hear audio and song. So it's playing Doom. Doom, OSD. Oh, the new Doom new. Yeah, correct. Yeah, it's fine. The new Doom? Well, that's all static calls. Yeah. That might have been blowing the speaker out or something.
Host 3 18:18
It's possible. Cool. All right, on to the RFO
Host 2 18:22
On the LFO. So this is what I was bringing up earlier about previous projects was on Hackaday. There was a guy who made a classic chip from discretes. All them like awesome. I'm like, oh, Steven has made op amps before. Oh, yeah, just exactly the same way. It's a board with you know, the standard 400 mil dip with pins and stuff. But he made a MC 1466 voltage regulator, which is a obsolete voltage regulator for one of his lambda adjustable power supplies. Okay. So yeah, it's kind
Host 3 18:59
Of a, you know, if you go through all the trouble of making a device seems like you would pick one that's like, more flashy than a voltage regulator. But well, how does he did it? I
Host 2 19:09
Guess, yeah, his voltage regulator in power supply was broken. I think it was like a reference voltage or something. Okay. I didn't read his article too much. I was more interested in like how he did it, which is he got the schematic or that's got he got the datasheet for the part. And then it had the breakout of what it would be like the block diagram with all the transistors and stuff. And he basically replicated that. That's cool. And it worked. I don't know if he's done a lot of testing on like, how close it is to the original, but, but going farther back into the archives is when you did that op amp. Mm hmm.
Host 3 19:46
That was a project we finished. Yes,
Host 2 19:48
It is one but then we we had another open ended one and we haven't started it yet. Okay. It was the 555 timer, all discrete. My timer. And the i Our idea was you just keep stacking boards.
Host 3 20:01
Oh, yeah, you have this big huge stack. Yeah. So
Host 2 20:03
You have a stack of PCBs that are all interconnected to fit all the parts? Yep. What's that is to you? Like, we need to build a, I guess it's not discrete. But if you just plop like a little tiny CPLD on it, and then tell it to be a five, timer program that in Verilog
Host 3 20:21
That actually, so they kind of I looked this up the other the other day reminds me if you remember proto bricks, we had the guy from proto bricks on, we're like, that the actual bricks themselves weren't really the chip. Yeah, just kind of plug in and tell the computer to do that. Whatever that function. Yeah, yeah. Kind of. It's sort of that that mentality. Yeah. But everybody pretty funny. There is that we talked about a while ago, but there is that that big 555 kit you can buy? And yeah, yeah, six inches by 10 inches is huge. Yep. And you build a discreet five by five. But from what I think Dave Jones did a video on, I think, if I remember, right, it has most of the functionality of a 555 but not all. So it'll do like, I don't remember there's there's three configurations for 555. There's the one shot, a stable and the Mano stable or something. Yeah. And I think it may not do one of those. I can't remember exactly how it works. Regardless. Yeah, that would be fun, because I think you can do it all with, like 39 Oh, fours and sixes. I think you can
Host 2 21:24
Pull it all off with that. And a couple resistors and caps because because
Host 3 21:27
A 555 timer is like a what? It's a it's a it's a stack of three 5k resistors. Yep, in there. And those feed to two Schmitt triggers. Yep. And then those do some other stuff back on the back end. So it's like, I think it's it's almost all transistors. Yeah, effectively. Yeah.
Host 2 21:46
That should be doable. might not fit in, you know, the DIP package size. But this guy he made the board actually just bigger. Yeah. And so it fit the same package, but like overhang it had a muffin top of a PCB.
Host 3 22:01
Okay, it was bigger than the standard dip size. Yeah, yeah. I tried really hard when I did those discrete op amps to make them dip size. They were just slightly bigger. We could but they had to be because of the pin headers. Yep. I originally, I wanted them to just plug into a regular socket. And that took some fancy. There was some sneaky sneaky traces on that so you could
Host 2 22:21
Get going in between resistors and stuff. pads
Host 3 22:25
Or like you know you have a SOT 23 transistor Oh, and sneaking diagonally between pads and stuff. There's there was a bit of that. Sneaky, sneak cranky.
Host 2 22:35
Okay, so next topic is. Apple says sorry.
Host 3 22:40
So what do they say? And sorry for?
Host 2 22:44
So this is the thing. I wish. This is on, you know, how everyone when they upgrade their operating system on their iPhone, it gets
Host 3 22:54
Slower? Oh, well, yeah. Yeah. Because Apple commands it to be slower.
Host 2 23:00
So this is what Apple said that when you upgrade the iOS, your phone, it's it's not specific to just the new iOS is your phone's battery just degrades, and they have smart monitoring. And so it won't like it won't pull as hard as you're bad on your battery when your batteries are a load of crap. So like they'll basically instead of, you know, pulling X juice, they'll pull y juice and so downclock your processor. And so, to fix this, they're offering a discount on battery replacements. So it's not unlike free batteries discount, there's a discount. Thanks apple. It's like a $50 replacement. It's like $30 you say 20 bucks,
Host 3 23:44
Say yeah, okay, but you still have to give them money for them purposefully slowing down your yes device. Just make my battery life worthless. Just let it run the regular speed. And, you know, is their software update can't be that magical that it burns that much more juice? Really can't.
Host 2 24:05
Oh, maybe it's apple juice. Hey,
Host 3 24:11
That was bad.
Host 2 24:17
But they say this affects like iPhone sixes and nothing before. But I clearly remember like my friends having like iPhone threes. And then like the new iOS update comes out and like, the phone is unusable.
Host 3 24:31
I mean, the mothership sends down the stop working command and things happen. Yep.
Host 2 24:37
Yeah. And I know MacBooks do the same thing. So it's not just iPhones. But hey, they at least said sorry for one thing. Well, he go
Host 3 24:46
Do they offer discounts on MacBooks? No, it was just iPhone $15,000 down to 14,000. No, something like that. Oh,
Host 2 24:55
Okay. This is for iPhones. Well, now So the next one is a question from I'm really good at those aren't your fantastic
Host 3 25:04
Looks? We've said everything we need to say,
Host 2 25:09
Well, none of us own Apple devices. So,
Host 3 25:12
No. So it doesn't. Yeah. Android doesn't slow down. I mean, it will. It does. But it's like, nature just makes it slow down, you know, nature. Yeah, I mean, yeah, all the the hardware just gives up eventually.
Host 2 25:27
I like how this nature just takes us course. That's right. Yeah. Okay, what's next? So zap from the Slack channel, asks, If my MCU has internal pull ups on an IO? Why would they recommend additional pull up? resistors? externally? Hmm, so this is a really good question. That's a good question. So soon.
Host 3 25:49
Yeah. Okay, so I have two things that come to mind immediately, as why so well, okay. So there's sort of three things here. If your circuit can get away with using their internal pull ups, and you've tested using their internal pull ups, go ahead and use them? What the hell? Why not. I mean, if it works, it works. A lot of times, those internal pull ups don't have a lot of protection around them. And they're usually really, really light. Yeah, they use a massive resistor there. And so depending on what other load is attached to that line, it may not be enough to work properly, especially if you have a really heavy load on that line, potentially. And the thing is, the more chips you stack on that line, the heavier the load getting up work. Yeah. So depending on your requirements for your load, you might need a, I guess what they call a stiffer pull up, or like one that effectively allows more stronger juice to flow through,
Host 2 26:49
Or apple juice, stronger, stronger, or lower, valuable, right?
Host 3 26:53
Now, here's the thing. And in fact, it was funny, I was gonna, I was gonna bring this up, maybe we'll talk about this in a in a future podcast. In fact, we probably will, I wanted to do a topic on like, what resistor to use where and when that would be a fun topic. But the thing is, the value of the resistor used for a pull up can have a pretty large impact on the timing, and the curve of a pulse going up or down based off of the load capacitance. Yep. So once again, that internal pull up, it's most of the time, they're super light, they're not, you know, there's there's a thing called Miller capacitance, which is basically the inherent parasitic capacitance on the input of every chip. And if you put a bunch of chips there that can be you know, that can get worse. Or if you push it far away from its driving chip, that can make it even worse. So you can get those runt pulses and those bad pulses we were talking about earlier, when we're talking about the oscilloscope. So all of these kind of stackup to most of the time, it's better to spend the extra point oh, one cent and put a resistor there that you know, is heftier than what's inside the chip.
Host 2 27:59
Yeah, and most time it just boils down to they're just generally weaker. Yep. there anything that's got touched the outside world, they're not going to be powerful enough to override, like a, a ESD event. Or, like, let's say you press a button and your your fingers got a lot of that means how phones capacitive touch phones work is your body has quite a bit of capacitance to it. And so if you touch a button that's hooked up to it, just in the pull up is just a, you know, internal internal guy, he might not have enough juice to recover fast enough.
Host 3 28:35
Right, right. Yeah. And that's, that's one of the key words fast enough, because of the capacitance of your body or whatever job you're giving it. Other chips might spring back to life faster than your MCU. And it might get confused, because you know, it's looking at things it shouldn't be looking at. And
Host 2 28:51
Another one to think about is, it's not even about this, it's about white when you this is all steady state stuff in operations. When you first turn your device on, those pull ups are not enabled. That's right, because that's a part of your that's part of your initialization code of your MCU is to boot in order to turn those, those resistors on,
Host 3 29:16
Right. But but good code would turn those on before it needs them. Yeah. But
Host 2 29:20
If you have a device that turns on faster than your MCU, and it's also looking for the state of these pins. Yeah. Then like let's say an I squared C device.
Host 3 29:31
Yeah, right. The speed of light is usually fast enough, you know, so put it put your own resistor, your own dedicated resistor there, and you can be pretty sure that it's going to get pulled up as fast as your power supply comes up.
Host 2 29:42
Yeah. The important one, think about this is like a FPGA. So FPGAs code from the flash. And that takes a couple seconds while your support glue circuitry like let's say a 595 shift register is now looking at You know, it's input plot pin. And in those three seconds, if that line is just floating, it's going between your 3.3 or whatever your rail is by 3.3 volts of use and 55595 and zero and so it's getting just garbage data in and then, you know, maybe randomly latches and displays some garbage on your, whatever you're driving like LEDs or whatever. Yep. So if you put if you pulled those, those clock pins high or low, then you basically fix that problem.
Host 3 30:31
I've actually had a situation where I had a 595 on a board. And if you touched the VI, five, five, not even the pins, the body of the 555, it was enough to yank the latch pin 595 Sorry, yeah, you're right. 595 my bed. But my pull up wasn't, wasn't strong enough. And so I could manually latch my 559 touching it. And it would make I had controlling a bunch of relays. So would make the relays just go nuts. And it was probably not very good for things because it would go from, you know, zero current to like two amps, like right away. And yeah, making my powers like, cry bloody murder,
Host 2 31:10
But oh, yeah, digital circuitry is probably freaking out. Oh, yeah. Yeah, yeah, it
Host 3 31:13
Was probably going all over the place. And all I had to do is solder resistor on there, and it fixed it, you know? Mm hmm. So those are the
Host 2 31:20
Best fixes. When you solder one part on like, yeah, like a bypass cap. That fixes
Host 3 31:25
The problem. A lot of times, that's what it's like in digital world. Yep. It's just, Oh, I forgot this one thing, or it's not beefy enough, or
Host 2 31:33
Yeah, it's usually noise. When the digital realm noise is your enemy. Yep. So it's a funny thing. It's like an analog world. You can live with some noise.
Host 3 31:44
You have to Yeah, you have to know
Host 2 31:47
What's like the like old analog radios, you could like, you know, just because you're slightly off on the tuner, you can still make out what the person saying. But if you have a digital radio, if it doesn't get that packet, it's gone. That yeah, yeah. Yeah. Well, it
Host 3 32:07
Has a whole lot less side band. coverage. Coverage. Yep. Yeah. Yeah.
Host 2 32:11
So interesting stuff. So I think we know what you glass.
Host 3 32:17
I'm about to take the last sip of some homebrew that I made over the over Christmas here. I got a little bit more Parker.
Host 2 32:24
I'd say. Oh, I
Host 3 32:25
Love this glass. Yeah, that's not to take a picture. This glass is the glass from from my wedding.
Host 2 32:31
So it's as Lauren and Steven established 2015. That's got a velociraptor.
Host 3 32:36
Yeah, we made we made custom pint glasses because we had our wedding at the Dallas Science Museum. And I was like, Can we put a dinosaur on our blank glasses? My wife was like, oh, hell, yeah. She she's a trooper. That's for sure.
Host 2 32:50
Huh? Cheers. Cheers. 101101 To New Year. So we're almost at
Host 3 32:56
Host 2 32:59
Well, yes, but we it would be 52 So 104 episodes will be three years Zack Yeah, so we got to do the Star Wars Episode. And then episode 100. And then the New Year episode, which we just did, and then the two year anniversary, all at the same time? Well, in like,
Host 3 33:22
Two months. Yeah. One small package.
Host 2 33:24
Yeah. So cool. So see you next week for episode 102. Right cuz that's coming up. Right.
Host 3 33:32
That's That's our new exit. Yeah. Guys, guess what? There's another episode next week. Yep. Okay, so that was the macro web engineering podcast. We were your hosts, Stephen, Greg and Parker Dohmen. Take it easy guys later.
Host 2 33:55
Thank you. Yes, you are listener for downloading our show. If you have a cool idea, project or topic or beer that you want Steven and I to discuss or drink. Tweet us at Mac crab. Email us at podcast at Mac fan calm or get with Irish to ship us the beer. Also, check out our Slack channel. If you're not subscribed to the podcast yet, click that subscribe button. That way you get the latest episode right when it releases and please review us on iTunes. It helps the show stay visible and helps new listeners find us. We also have a position open on our software development team and opening for a production engineer. Check out those links
Transcribed by https://otter.ai