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Forseti posted:Yeah it's a bit to toggle them. PLL_D2_CLK is actually the master clock for the SoC divided by two. Even though it says 160MHz there, I'm not sure that's actually true if you set the SoC to run at 240MHz (160MHz is the default speed and it's just an option in the build config). It does look inconsistently translated. This part is (wrongly I think) calling APLL_CLK as 'analog PLL' and the clock part is calling it 'audio PLL' . Looking at what it can go to, it does look solely intended for clocking the I2S audio. Why don't you want to use it? It seems like the preferred clock to use and you would only use the PLL_D2_CLK (main PLL clock/2)+divider if you didn't have power budget to run the other one. I think the intent of the extra configuration on the audio PLL (in the clock module, not the I2S module) is so that you can make the audio PLL frequency match the desired audio clock without having to divide it down inside the I2S peripheral.
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Feb 26, 2021 20:30
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Foxfire_ posted:It does look inconsistently translated. This part is (wrongly I think) calling APLL_CLK as 'analog PLL' and the clock part is calling it 'audio PLL' . Looking at what it can go to, it does look solely intended for clocking the I2S audio. It's not so much that I don't want to use it (and honestly it's probably what I'll ultimately use because it's more stable anyway), I'm just stubborn about wanting to understand things. I've never been good at accepting "I don't understand why this doesn't work but this alternate thing does, so whatever". Your proposed explanation makes sense though and kind of what I felt like I was missing. Like there was some reason not to that more experienced people probably knew about that just wasn't explicitly stated. I also somehow missed that there was a clock called the Audio PLL because the APLL is listed separately and before it in the section "Reset and Clocks"  Tha Manual posted:4.2.4.4 APLL_SCLK Source Also Tha Manual posted:4.2.7 Audio PLL
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Feb 26, 2021 21:03
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ante posted:Half the developers at Espressif are from the Netherlands lol Well poo poo, most of them probably speak English better than I do then 
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Feb 26, 2021 21:07
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Question time!~ I've been wearing a respirator mask in the workshop most days now and people understandably have a hard time hearing me. I've worked around this by getting a personal voice amplifier unit off of Amazon and tucking a lapel mic inside the respirator, with the cable coming out through the rubber seal by my face. It works, but it also sucks to have to deal with the cord and also keep the amp clipped to my belt or otherwise on my person. I have been entertaining the idea of replacing one of the two cartridges on my respirator with a 3D-printed one that would ideally be a self-contained mic-amp-and-speaker assembly. I'd have to mod my respirator a bit, but it'd be great if I could just clip the unit into one of the holes on the mask and have it rebroadcast my voice from inside it. Was playing around with something like this idea:    I don't know, just roughing it out. Ideally I'd like to stuff a small LiPo battery in there that I can recharge through a port on the body of the thing, maybe a volume knob too. Any recommendations for hardware with a small footprint that would work well for this? I started looking at microphone amp boards but most of them are not set up to output directly to a speaker from what I'm seeing, and the ones that are are pretty big. Setting aside the fact that it might impact the performance of the respirator, which I can deal with, is this just an impractical idea in general?
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Feb 27, 2021 21:41
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Hey everyone, noob here looking to ask some questions that (hopefully) aren't annoying. I used to be a computer engineering student (and took CompTIA and stuff), but shifted over to philosophy (which is now my full-time gig). Despite that, I've always remained interested in hardware and technology, but never pursued it in much depth. I'm very into old tech and understanding the developments of the technology (I suppose naturally because I'm overly familiar with computability and history of computability [esp. in logical and mathematical applications]). As a hobby I'd like to get into electronics and want to find out what prerequisites might be required and/or if I'm looking in the right areas. As of now, I've been reading Art of Electronics (second edition) and I've been enjoying it so far. It is a little bit complicated at times and skins over the physics side of things, but I guess that isn't necessary for most people going into the field. As some interested in the more fundamental (physical) aspects of electronics, are there any resources people would suggest? Is Art of Electronics something I should stick with? Thanks!
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Feb 27, 2021 21:50
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RadicalTranslation posted:Hey everyone, noob here looking to ask some questions that (hopefully) aren't annoying. RadicalTranslation posted:I used to be a computer engineering student (and took CompTIA and stuff), but shifted over to philosophy (which is now my full-time gig). Despite that, I've always remained interested in hardware and technology, but never pursued it in much depth. I don't think there's anything wrong with just starting to read every book you can find on the subject, sticking with the ones that interest you and shelving the ones that are less interesting, possibly for later and possibly to never pick up again. The Art of Electronics is a classic for a reason, but it's breezy and informal, and it's primarily a circuits book. On the physics side, there are a few different places to go and a lot of resources online. I don't know where you want to start, but the first discussions of electronic devices I read were in the second half of Knight's Physics for Scientists and Engineers, which includes both an introduction to electromagnetism and a brief introduction to circuits, including AC circuits and phasors. After that comes semiconductor device physics and I can't recommend any specific book on that subject but there are a lot available and a lot of resources online. It may be worthwhile to have a project in mind, and this thread is probably a good place to discuss these projects. If you're interested in the physics behind basic components, you can absolutely start by just building things like capacitors, inductors, resistors, and transformers and measuring them with an LCR meter or building simple circuits with them. If you're interested in device physics, the projects get more complicated fast but it's still possible to build things like cat's whisker detectors without getting too far off into "playing with arsenic solutions in the kitchen" territory.
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Feb 28, 2021 00:13
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Stack Machine posted:I don't think there's anything wrong with just starting to read every book you can find on the subject, sticking with the ones that interest you and shelving the ones that are less interesting, possibly for later and possibly to never pick up again. The Art of Electronics is a classic for a reason, but it's breezy and informal, and it's primarily a circuits book. On the physics side, there are a few different places to go and a lot of resources online. I don't know where you want to start, but the first discussions of electronic devices I read were in the second half of Knight's Physics for Scientists and Engineers, which includes both an introduction to electromagnetism and a brief introduction to circuits, including AC circuits and phasors. After that comes semiconductor device physics and I can't recommend any specific book on that subject but there are a lot available and a lot of resources online. Hey thanks so much for the response. I think your advice of trying to start building your own stuff is a great suggestion, and I might as well try out building a resistor and just learn as I go. I don't suppose you have any suggestions where I need to go to figure out what to buy, etc?
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Feb 28, 2021 00:34
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RadicalTranslation posted:Hey thanks so much for the response. I think your advice of trying to start building your own stuff is a great suggestion, and I might as well try out building a resistor and just learn as I go. I don't suppose you have any suggestions where I need to go to figure out what to buy, etc? Building a resistor probably isn't going to be especially interesting, they're basically a long and/or thin wire. If audio interests you at all, it might be fun to build a 2-way speaker with a crossover circuit. There'll be tons of info out there and you can roll your own inductor which is pretty much the only passive device that people actually make custom sometimes. Probably go with a sealed cabinet doing this for the first time because you don't really have to design that. Edit: Audio also has the benefit of being a really slow signal that you can easily see with something like an oscilloscope program that uses a sound card, which would let you see how the performance change as you vary things like capacitance and inductance as well as hear it Forseti fucked around with this message at 00:54 on Feb 28, 2021 |
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Feb 28, 2021 00:46
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You can recreate the discovery of the LED with a bench power supply, a needle, and a chunk of silicon carbide, that's fun to do. Just kinda poke around on the chunk with the needle in a dark room until you see a dim yellow glow. ...okay it actually sounds incredibly boring when I describe it but I love that kinda poo poo 
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Feb 28, 2021 02:24
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RadicalTranslation posted:Hey thanks so much for the response. I think your advice of trying to start building your own stuff is a great suggestion, and I might as well try out building a resistor and just learn as I go. I don't suppose you have any suggestions where I need to go to figure out what to buy, etc? One piece of advice I followed from earlier in the thread was to read hackaday and some other sites I haven't kept up with to see other people's projects: https://hackaday.com/. Dangerous prototypes, too, but they don't post as much: http://dangerousprototypes.com/blog/. Youtube has also taken off as a platform to watch folks do little electronics projects. A lot of people do their projects open source so you can recreate them or do a modified version for yourself if you want to. When I started reading this thread the most complicated thing I'd done was to make a binary counter with flip flops in a computer architecture class that had a little hands on section at the end and most of my electronics know how was from Physics II with electricity and magnetism which mostly focused on the Kirchhoff's laws. Now I've soldered up a bunch of little arduino projects and planned out a lot more that are just taking forever to finish or that I've dropped (I never figured out the supercaps thing I was doing). For parts I've often bought multipacks of various things like resistors where you get 20+ of a bunch of different values, dupont wire, tiny nuts and bolts, LEDs, etc. It sort of depends what projects I'm doing. I also have a dozen microcontrollers of different flavors around as well as some little lcd and oled displays. Voltage buck/boost converters are good for some projects involving different power requirements (I've done a couple of things with 9 or 12V motors and 5V controllers, and used them on my 24V 3d printer to use some 12V fans). I wouldn't buy more than you need unless it's something really basic like a component multipack. You'll probably want a couple of breadboards and eventually you might solder your first projects onto protoboard (unless you get a custom PCB made which is very cheap these days, but I've done a lot of my one-offs onto protoboard). Ultimately I think that finding a project will determine what you want to buy to complete it. Sometimes it's worth paying a little premium to get the parts faster because I've definitely had my interest in some projects wane while I waited for cheap parts to show up a month or more later from ebay.
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Feb 28, 2021 02:25
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RadicalTranslation posted:Hey everyone, noob here looking to ask some questions that (hopefully) aren't annoying. I meant to say in my earlier post that these are good questions and I'm probably more worried about scaring you off with frightening enthusiasm that you are worried about annoying people in this thread. Forseti posted:Building a resistor probably isn't going to be especially interesting, they're basically a long and/or thin wire. Or by putting some pencil lead in some alligator clips, or by filling in squares on graph paper with pencil marks and touching it with meter probes... It's not much but it's a great way to see the geometric reasons behind rules like the formulae for parallel/series resistances. If that gets boring you can always start trying to measure the amount of heat your resistor is generating by using it to heat up water... I'm not saying it has to be what you do first, but it's fascinating enough that I was definitely just stabbing graph paper with meter probes (turns out similar-looking pencil marks are really inconsistent in terms of resistivity, but they're at least in the right order of magnitude.) Stack Machine fucked around with this message at 03:21 on Feb 28, 2021 |
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Feb 28, 2021 02:34
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RadicalTranslation posted:Hey everyone, noob here looking to ask some questions that (hopefully) aren't annoying. This sounds a lot like my situation and where i’m coming from- interested in electronics but being a blacksmith/machinist with a single 100-level college circuits class under my belt, interested in the fundamentals and historical/pioneering aspects of electronics, etc. i can’t point you to much resource-wise, but maybe my own take on it is useful? i wrote up a few of the projects i’ve been working on over the past year or so for a CC project roundup thread, specifically: - redesigning an electro therapy medical quackery device from the 1860s to use modern materials; - designing printable trimmer capacitors because i couldn’t source my own while living in the woods; -building my own century+-old radio emission detector based on a gugliemo marconi original post: https://forums.somethingawful.com/showthread.php?noseen=1&threadid=3946255&pagenumber=6&perpage=40#post511119124 my approach to this, as a hobby i’m taking at my own pace, is to do a lot of deep research to find weird little niches that really catch my interest, and which are accessible to me given my skills and resources. b/c of the artisan metalworking background this tends to be either primitive dead-end curiosities from the pre-radio age, or areas that are particularly bound up in something physical, like capacitors, RF stuff, weird chemical battery designs, etc. i approach stuff as an engineering/fabrication challenge, and that motivates me to do more technical (and lets be honest, drier) research and self-education. i couldn’t sit through this stuff in school but i love learning in a broader sense, so i put myself in the position where i’m actually enthusiastic about The Fundamentals. that said, i still don’t really know poo poo by the encyclopedic standards of this thread’s posters. but i’ve had fun along the way and picked up some cool skills, so heck. Ambrose Burnside fucked around with this message at 03:52 on Feb 28, 2021 |
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Feb 28, 2021 03:45
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Has anyone actually made the first transistor again? I feel like it should be reasonably possible using eBay materials and handtools, and it would be fun to put it onto a transistor tester and characterise it
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Feb 28, 2021 03:50
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ante posted:Has anyone actually made the first transistor again? i actually rounded up the materials (some big juicy germanium whisker diodes ready to have their Ge blocks yanked) and dug up some old research papers on em but never got around to anything there, partially b/c the current-pulse “forming” step wasnt well-documented from the sources i had and would prolly involve a lot of destructive ooopsies, but mostly b/c my brain is bigger than my hands, so to speak, when it comes to project ideas it’s absolutely viable tho, apparently early on after it’s discovery making your own was actually fairly common and hobbyist-accessible. i’ve seen one or two modern successful hobbyist attempts, prolly shoulda looked into those for the forming info Ambrose Burnside fucked around with this message at 03:58 on Feb 28, 2021 |
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Feb 28, 2021 03:56
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Stack Machine posted:Or by putting some pencil lead in some alligator clips, or by filling in squares on graph paper with pencil marks and touching it with meter probes... It's not much but it's a great way to see the geometric reasons behind rules like the formulae for parallel/series resistances. If that gets boring you can always start trying to measure the amount of heat your resistor is generating by using it to heat up water... I'm not saying it has to be what you do first, but it's fascinating enough that I was definitely just stabbing graph paper with meter probes (turns out similar-looking pencil marks are really inconsistent in terms of resistivity, but they're at least in the right order of magnitude.) Good point, I wasn't really being fair. I guess I never really found it interesting personally because the geometric reasons already make sense to me and I grasp that particular concept easily. My mind's mode has always been highly intuitive and I was always terrible at doing proofs in math. I had a hard time enumerating the small steps to get from point A to point B because I'd be stuck on "What do you mean prove it, it's obviously true  "
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Feb 28, 2021 16:10
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Does anyone have an opinion on cheap oscilloscopes? I'm a power EE and somehow never touched a soldering iron after high school, but I got into electronics during the first lockdown last year and things developed into a long term (years to never) project. I'm mostly loving around getting a feel for microcontrollers now and want to look at the signals, and the prices for oscilloscopes seem almost funny. What's so expensive about them? High frequency DACs couldn't be that expensive, and the rest is just software? The cheap Chinese ones seem more reasonably priced and from what I gather they're mostly lying about the maximum frequency and sample memory. Is it a problem? I don't expect to work with more than a MHz for talking to things, how much more do you need to solve everyday problems?
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Mar 1, 2021 00:10
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Get a 4-channel Rigol, and yeah, it should last you many years to come. But also, adjust your expectations on specialist test gear - The Rigols are "mindblowingly cheap", not "reasonably priced". Even 5-10 years ago, you'd expect to fork over $10k for a decent Tektronics scope with the same specs.
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Mar 1, 2021 00:49
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Knitting Beetles posted:Does anyone have an opinion on cheap oscilloscopes? ebay is your friend. most oscilloscopes are power than you need. Buy cheap first and if it doesnt suit you buy more expensice Ferdinand the Bull fucked around with this message at 01:26 on Mar 1, 2021 |
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Mar 1, 2021 01:05
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I would recommend not getting a vintage scope without digital storage
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Mar 1, 2021 02:05
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Nothing is inherently super expensive in a scope, but volumes sold are small + they have more engineering effort to make the analog parts have wide bandwidth without distorting stuff. For basic scope, get one of Rigol 1054Z, Siglent SDS1104X-U, or SDS1104X-E at ascending levels of $ for niceness. The main thing the Siglent ones have over the Rigol is convenience stuff like better USB handling, more memory for zooming, more trigger options, and more display configuration. Don't get an ebay analog scope. The only advantage to that is cheaper bandwidth you probably won't need at the expense of every quality-of-life feature
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Mar 1, 2021 02:21
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Knitting Beetles posted:Does anyone have an opinion on cheap oscilloscopes? My strongest opinion re oscilloscopes is whatever you do don't get the low-end Hantek USB thing. It doesn’t do triggering in hardware and the USB interface isn't fast enough for it to sample continuously so it just grabs blocks of samples unpredictably. If you want to use it to look at a one-time transient event you have a good chance of just not capturing it. It also doesn't have many hardware options for front-end attenuation so you get really limited resolution for low signal levels, unless you put the probe in X1 mode and suffer the 10X higher equivalent capacitance. I like the form factor but if you want a USB-only scope you aren't going to pay any less for it than something with the same performance with its own user interface. I don't really have much beyond this. The used market is great since obsolete nice scopes perform as well as new low-end scopes and are built like expensive things instead of cheap things (metal casings, easier to service, etc.) Analog oscilloscopes have a lot of charm, but like the bad Hantek, can't really handle signals that aren't periodic. That said, a friend and colleague of mine uses a Tek 535 at home. It's a work of art that also happens to be a functional piece of test equipment (with 10MHz bandwidth, so good enough for any SMPS at least).
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Mar 1, 2021 02:28
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If you only need to look at digital signals, a cheap logic analyzer like this will work, in combination with PulseView software. As ante and Foxfire said, if you want to look at analog signals, This Rigol is a good bet. You can unlock additional features using cheat codes.
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Mar 1, 2021 02:49
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From what I've heard, the 1054z just comes unlocked now.
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Mar 1, 2021 02:52
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If any newbie is looking for a scope and doesn't know what they need and $400 is in the budget, the Rigol 1054 is the obvious and only choice.
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Mar 1, 2021 03:11
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Harvey Baldman posted:Question time!~ Your question seems to have been overlooked so far, but I don't really have any good advice. Are you sure you can comfortably breathe with just one filter while working? I could imagine it being possible to shrink everything into a small enough package to mount elsewhere on the mask while staying within a hobbyist's budget. 3D print a front cover from your favorite Star Wars/Mortal Kombat character, add some voice manipulation, Bob's your uncle.
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Mar 1, 2021 04:47
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Yeah, I would avoid any cartridge-based solution, it's a very tidy way to go about it but I strongly suspect you won't be willing to use a single filter cartridge for long, halving all the inlet + filter surface areas will make breathing much more physically-arduous and you'll get tired very quickly- and it might be impossible to draw enough air comfortably if you're exerting yourself. Try pulling a cartridge and blocking its port with a cork or cap or some sort, and doing what you normally do for a good half-hour or so- this'll give you a pretty good idea of how much of a non-starter that approach may be. There's no other good inside:outside interface aside from the cartridges, of course, which is its own problem. You'll probably have to put a hole in the mask for a wire passthrough here, and modified PPE may or may not be acceptable in your workplace. Another problem is the lack of real estate for adding electronics. I would consider hiding the batteries + controller somewhere other than the facepiece of the mask- for example, maybe a small unit that clips onto the mask straps or something low-profile stuck to the strap pad for the back of your head, if it's that kind of mask? That'll make running wires fairly painless b/c it'll still all be built off the mask, you won't have an awkward belt unit or sth. Some sort of ad-hoc network for linking different parts of the system wirelessly would be ideal wrt not modifying the mask, but that'll mean a significantly larger amount of circuitry inside the mouthpiece itself, which has essentially zero Project Space to begin with, plus everything'll need its own batteries and etc. e: actually, I think I have a better solution for this: avoid any sort of modifications to the mask or mics inside the mouthpiece by just using a throat mic for the pickup + a simple portable amp/speaker dealie for broadcasting. Throat mics are already the go-to mic pickup for people who have to wear masks while staying in constant communication, like pilots, soldiers, firefighters etc. The unit has nothing to do with the mask at all, you could build the speaker into the front of the project box and keep it in a shirt pocket with the speaker facing outwards. I can't promise you people won't make fun of how you sound tho Ambrose Burnside fucked around with this message at 05:32 on Mar 1, 2021 |
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Mar 1, 2021 05:23
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Ambrose Burnside posted:I can't promise you people won't make fun of how you sound tho
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Mar 1, 2021 06:31
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Found some pictures of an old motor controller I pulled apart, years ago This strategy is usually, uh, not done by machines, I'd wager
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Mar 1, 2021 09:33
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Thanks for the advice, the "old analog scope from ebay" was out anyway because I hated those fuckers at university. What's the use of 4 channels instead of 2? The electronic youtubers all have these big honking 4 channel scopes but I've never seen them use all 4 except for reviews. Spending a couple of hundred is okay, I guess I'm spoiled by how incredibly cheap the hobby is otherwise.
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Mar 1, 2021 09:46
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Knitting Beetles posted:Thanks for the advice, the "old analog scope from ebay" was out anyway because I hated those fuckers at university. What's the use of 4 channels instead of 2? The electronic youtubers all have these big honking 4 channel scopes but I've never seen them use all 4 except for reviews. EEVBlog talked about 2 vs. 4 channel scopes a while ago, and recommended 4-channel because you're definitely going need 3/4 channels eventually (I wind up using them all the time actually) and you'll barely ever need the higher bandwidth you'd get from a 2-channel scope at the same price.
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Mar 1, 2021 09:54
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I always recommend 4 instead of 2 for the basic reason that one of the channels will always be your trigger. So you'll set channel 1 as your trigger, on the slowest waveform. Channel 2 will show your signal of interest. But... What if you need to compare two signals? You'll hit the limits of a 2-channel really quickly. It's possible to do everything with only two by probing, saving, and then probing the next one, but it's like a million times harder.
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Mar 1, 2021 10:03
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I have an Agilent 54622d that I love, but it's an older digital scope with a CRT so it's huge compared to modern scopes. You also have to be prepared to fix things on a 20 year old scope (e.g. the battery backup). It's 2 channel but it has a dedicated trigger input on the back. It's also a mixed signal so I have a 16-bit logic sniffer in place of the extra two channels which is a pretty nice trade IMO. I camped eBay for a couple months and got it for ~$150 but there's actually one on there right now that looks pretty nice for ~$230 shipped: https://www.ebay.com/itm/Agilent-HP-Keysight-54622D-Mixed-Signal-Oscilloscope/353174448527 I mostly like it because I used an older HP (who spun off their test eq into Agilent which became Keysight) at my first job so I'm familiar with and love the interface. Someone on eBay sells the digital input "pod" for ~$50 so that's an expense too to actually use the sniffer. So that's an option, but realistically the Rigol is a much safer choice for not much more.
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Mar 1, 2021 15:34
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Even if 95% of the time, you only need one channel, and 4% of the time, you need 2 channels, that 1% of the time that you need more, you NEED them.
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Mar 1, 2021 15:46
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I also have the Rigol with the built-in in logic analyser... I wouldn't bother. I've used it a handful of times, but it's worse than that $5 dedicated one from China
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Mar 1, 2021 16:27
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Harvey Baldman posted:Question time!~ It would be more modification and lack amplification but I was thinking someone should make a respirator for our modern helltimes with a passive radiator (e.g. https://www.amazon.com/AOSHIKE-loudspeaker-Vibrating-Diaphragm-Replacement/dp/B01MZ1N98J). On the plus side, once added to the design I would think it would be cheap to produce at scale and it wouldn't require batteries! Hell, it might even improve the performance somewhat as a heavy sigh or something could be buffered by the diaphragm's suspension and reduce the changes of lifting the seal to escape. Might also improve the comfort of the device as I would think it would help reduce the felt resistance on inhale and exhale. Typing that last bit just made me think it might be better for your design too actually, if you made it into a cartridge like you're saying, maybe the buffering capability would help compensate comfort wise for only having one filter, which I agree with posters above, sounds like it would suck a lot otherwise. I do think you'd probably need a purpose built radiator though or at least find a place with more options. The cheap ones I find on amazon seem to be more for adding boomy bass to bluetooth speakers and as such are probably much higher mass than you'd want for voice.
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Mar 1, 2021 17:44
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Knitting Beetles posted:What's the use of 4 channels instead of 2? Past actual examples from me: - Was troubleshooting a soft-start circuit for ramping up current on a load. I had channels on gate & drain of a FET, and two more reading voltages across a current sense resistor. - Watching SDA and SCK on a serial bus, plus a GPIO to trigger a capture - Watching hall sensor outputs and motor winding voltages when troubleshooting a BLDC controller (and really wanted a 6 channel scope for this, 4 is already making due)
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Mar 1, 2021 19:32
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I've got a MOSFET question. So I'm switching a 4A load, and I'm comparing three different MOSFETs. It has been more than a decade since my Transistors 2 class, and I don't think I did that well. Here's one:  It turns on slowly, and with a short enough enough pulse, it doesn't even turn on all the way. Total trash. According to my fuzzy memory reading the datasheet, here's a much better one:  Yeah, I'll buy that. Edges are faster, it has time to fully turn on. Not shown, but these are much more consistent from device to device than the previous ones, too. Okay, and here's an even better one:  Yikes! What the hell happened? Notice I had to change the vertical scale to capture all the ringing, too. For the last one, I selected for high Ids(on) (obviously), a reasonable VT, and really low Qg, but clearly I'm missing something. ante fucked around with this message at 05:02 on Mar 3, 2021 |
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Mar 3, 2021 04:58
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ante posted:Okay, and here's an even better one: You know how inductor voltage is L*di/dt? You have a 4A current and when you turn off your FET, very quickly you have zero current so you get that mad overshoot from parasitic inductance in the wire to your load or whatever. It doesn't have to be much inductance because it's a lot of current and the low Qg means it switches very quickly. You can slow down the FET gate by putting a little resistance in series with it and that'll help by making that turn-off event slower. You can also put some capacitance between the drain and ground to slow that edge down. Both of these hurt efficiency and burn a little more power in the FET. If you have a long cable or something else increasing the inductance on your load, putting the FET closer to the load will help too. Stack Machine fucked around with this message at 05:56 on Mar 3, 2021 |
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Mar 3, 2021 05:15
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Stack Machine posted:You know how inductor voltage is L*di/dt? You have a 4A current and when you turn off your FET, very quickly you have zero current so you get that mad overshoot from parasitic inductance in the wire to your load or whatever. It doesn't have to be much inductance because it's a lot of current and the low Qg means it switches very quickly. You can slow down the FET gate by putting a little resistance in series with it and that'll help by making that turn-off event slower. You can also put some capacitance between the drain and ground to slow that edge down. Both of these hurt efficiency and burn a little more power in the FET. If you have a long cable or something else increasing the inductance on your load, putting the FET closer to the load will help too. Yeah, I understand that I'm dumping my (effectively) huge output inductor's energy right back into my MOSFETs on turn-off. I've "solved" this issue on previous designs by using a series gate resistor to slow down the turn-off, and a drain-to-VCC diode to snub the peaks. It's fine. It's still not ideal. The question more is, how do I select better MOSFETs for my system? You can see my three wildly different results, but the second one (a good result) is not really that different from the third one (a bad result), based on what I think are important parameters, and that's what I'm missing. For reference, MOSFET #2 is a VBE1615 with a Qgs of 10nC, while MOSFET #3 is an IPD096N08N3 with a Qgs of 9nC. So obviously there's something going on.
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Mar 3, 2021 06:52
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I'm bad at MOSFETs, but don't you have to charge the gate-drain as well? VBE1615: Q_gs ~= 10nC, Q_gd ~= 12nC IPD096N08N3: Q_gs ~=9nC, Q_gd ~= 5nC Scope V_ds, V_gs, and I_ds? V_ds doesn't start dropping until after all Q_gs charge has been added and doesn't finish until Q_gd is added. The threshold voltages on those parts are also different (2V vs 2.8V), so they'll start doing stuff at different times too Also, turn off cares about body diode characteristics. Foxfire_ fucked around with this message at 07:56 on Mar 3, 2021 |
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Mar 3, 2021 07:51
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