EEVblog Q&A #1 Announcement - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: November 01, 2013, 03:52:55 am
content: Submit your questions for the first EEVblog Q&A video, either in the youtube comments, blog website, or forum thead here:DO NOT comment on this video, this is for Q&A questions only. If you do I'll delete it, and probably ban your arse for being an idiot who can't follow simple rules.

author: mamalala
author_rank: Unknown
timestamp: November 01, 2013, 04:09:35 am
content: Now that you have a JBC soldering station, what do you think about the importance to be able to adjust the temperature, and why?Is a tight control loop preferable to an adjustable temperature?What about "regular" irons and their arangement of heater/tip/sensor? Do you think they are capable of a tight temp control, compared to the arrangement that modern station use? (i.e.: all that in a small area of the exchangebake tip-cartrigde)Greetings,Chris

author: rexxar
author_rank: Frequent Contributor
timestamp: November 01, 2013, 04:17:57 am
content: You showed Sagan hanging out in your new component cabinet a while back (and posted some pictures on twitter). Can we see that? How do you sort your components, E24 series sorted by magnitude or? Do you keep an inventory, or is that too tedious?

author: TNb
author_rank: Regular Contributor
timestamp: November 01, 2013, 04:23:25 am
content: Hi! Always wanted to ask you one thing(sorry if question is kinda long):I am student and now I have two possibilities to continue my study - study software programming(I mean in depth) or study electronics(in depth too, microprocessors VLSI and other complex stuff). I'm struggling about it since software programming is easy for me, have no problems with that, but it's boring as shit, I'm tired of doing it. Electronics is harder for me, but it also much more interesting.But the question really is - how likely it is to get a good job in electronics field?I mean in software programming there are a lot of positions to work and you can also freelance, but I don't see a lot of companies offering place for VLSI designer or VHDL programmer or anything at all. And needless to say there is no freelance for it.I just want to do the stuff I like in my life, but I'm scared to be out on the street with no money because of that or end up working as a stupid clerk and hating every second of my workday.So questions are:how likely it is to get a good(!) job in electronics field?and how should find it? I found almost nothing on job offering sites(at least in Europe).Thanks!

author: aalbri
author_rank: Contributor
timestamp: November 01, 2013, 04:25:30 am
content: Hey Dave.I just finished my BSEE. Could you talk about how to gain enough experience to get a good electronic development job? I come from a poor family and never got to mess with electronics til I was at university, but I really love it. My biggest problem is figuring out what to focus on (software, circuit theory, etc).

author: iceisfun
author_rank: Regular Contributor
timestamp: November 01, 2013, 04:29:22 am
content: Hi DaveCan you talk about the most important mathematics of electronics, there is a ton of stuff to learn and maybe you know some of the best books?

author: Scutarius
author_rank: Regular Contributor
timestamp: November 01, 2013, 04:35:02 am
content: What's up with the power supply project? still working on it?What about the new uCurrent version, it is going to be cheaper?What is, approximately, the total amount of money you have on equipment? from 3d printers, oscilloscopes to multimeters.for what company would you consider to move to the states and live there for a while?What about making your own company and making custom products for companies(like IDEO)? is that feasible, for a living, in Australia?Is there any project that you really want to work on but simply would take months of work and leave the EEVBlog?is there any new micro-something gadget coming up?Thank you

author: tiofilo75
author_rank: Contributor
timestamp: November 01, 2013, 04:47:26 am
content: Hi Dave, I just wanted to ask for your opinion on whether its a good idea to start my career by pursuing an RF technician position after earning my E.E degree or go for an RF engineering position right of the bat. Not sure if that makes any sense. I have about a year left in college and I was thinking that I would like to start from the bottom where I can troubleshoot components to get a better idea of how they function and get my hands dirty before I move onto an actual engineering position. Thanks.

author: Rutger
author_rank: Regular Contributor
timestamp: November 01, 2013, 04:52:15 am
content: What do you think electronics is going to look like in the next 10-20 years? Any predictions?

author: Strada916
author_rank: Frequent Contributor
timestamp: November 01, 2013, 04:54:02 am
content: What would be your advice to anyone who would like to start their own yt/podcast channel? What are some of your own goals in eevblog, did you think you would get this far? Can this type of business/hobby be sustainable in years tocome?

author: Goophy629
author_rank: Contributor
timestamp: November 01, 2013, 04:55:52 am
content: so a possible repeated question, the uSupply again, any info regarding the progress of the project? Thanks

author: Whales
author_rank: Super Contributor
timestamp: November 01, 2013, 04:56:36 am
content: It is part of the culture of some electronic suppliers to rebrand or replace popular parts with duplicates (fakes) -- but I understand this is only uncommonly a bad thing, as it provides a price buffer against availability change and often the non-genuine parts are just as good, or good enough for it not to matter. Do you buy your parts strictly from reputable resellers, or do you embrace the culture of ordering anything with the right part number off eBay? XOR is there a good place in-between?If a young hobbyist came to you in Sydney and asked if they could borrow books off you, would you oblige?

author: mtc2629
author_rank: Contributor
timestamp: November 01, 2013, 05:18:37 am
content: what is the eev corporate tower or where ever you work at and the dumpster dive videos when is that and isn't that stealing

author: opablo
author_rank: Regular Contributor
timestamp: November 01, 2013, 05:38:08 am
content: I heard you may be designing a new version of the uCurrent....Do you find this construction design interesting for such a project ?http://blog.spitzenpfeil.org/wordpress/wp-content/uploads/2013/05/IMGP7653.jpgon the back there's a cr2032 socket... I think that's quite a neat design for a device like the uCurrent...

author: asgard
author_rank: Regular Contributor
timestamp: November 01, 2013, 05:39:59 am
content: Hi Dave,What would you say is a good short list of things to consider when transitioning and learning to do 4-layer board design? Do you think that Eagle will do the job anywhere as well as Altium, where moderate-sized devices are concerned? What is the best way to prepare the design files for panellizing and/or pick+place, or is the board shop likely to do that for you?J.R. from the Mt. Shasta area

author: iWalrus
author_rank: Newbie
timestamp: November 01, 2013, 05:44:51 am
content: Hi Dave,What are your thoughts on butane gas powered irons?I do have a cheap one (from Jaycar cat TS1111) for use in the field, and find it quite handy to have in my toolbox. It saves me time finding power for an electric one, and it heats up and cools down rather quickly. I find myself using it even at my lab bench where i could be using a mains iron. The downside to this iron is the exhaust port, that i constantly manage to blow across my fingers (ouch) or occasionally into the enclosure of the device I'm trying to repair. My next question comes from this; I want to get a decent one. Can you recommend a good gas iron? do you believe such a thing exists? could you maybe in the future do a video on gas irons?One more question: I want to start doing microcontroller development. Currently I mess around with PICAXE chips, but that's entry level stuff, and quite slow (compared to other chips out there). For a novice (i have moderate programming experience with Java) where should I start?Cheers,Walrus.

author: jeremy
author_rank: Super Contributor
timestamp: November 01, 2013, 05:56:39 am
content: Why aren't there any good USB based oscilloscopes for a reasonable price? Surely if you can buy a 4 channel DS1000Z for $1k (which has USB and ethernet mind you), you should be able to buy the same thing minus the screen and controls for less?I'm serious! Is there something I'm missing?

author: apelly
author_rank: Unknown
timestamp: November 01, 2013, 06:10:44 am
content: What are the chances of an eevblog wiki? I understand there is associated admin overhead, but some of the long threads here, as well as some topics which are quite dispersed, would really benefit from a method for community consolidation.It was just pointed out to me that there is indeed a wiki already. There's nothing like looking like a dick in public hey?Anyway, the wiki looks hardly used. What are the chances of adjusting divs upper_section or main_menu on the forum to include a link to eevblog.com and the wiki?

author: casper.bang
author_rank: Frequent Contributor
timestamp: November 01, 2013, 06:17:59 am
content: For several years, I worked from home with an Atlantic between me and my colleague?s/boss. Working from home can be super nice but also have its drawbacks, particular when it comes to delivery and time management - procrastination, feature creep and other excuses not to finish what one is working on, kicks in several times a day! Finishing something is hard work and the artist in us will always claim our work is never truly finished!I now know the status of the uSupply, that I should not necessarily expect a Fundamental Friday (but do expect a Sagan Monday) and that we should not ask too many questions about it - but this can be a little confusing to a new audience. Considering 1 finished project is usually beneficial to 10 unfinished in so many ways, have you tried adopting a GTD, Scrum board or similar method, to follow through on the structure I feel you would like to have, but appears to fail at implementing? Was MM, FF etc. an attempt at time-slotting your time and have you since abandoned this but kept the names?

author: Orpheus
author_rank: Regular Contributor
timestamp: November 01, 2013, 06:38:05 am
content: I've read (and will review again) your posts on what software you use, but I have a specific question: which packages are the best for "pop-ups"? I have always been perversely fascinated by those, but have never done them. I plan to start a (non-competing) channel that is likely to be revision-heavy

author: M0BSW
author_rank: Frequent Contributor
timestamp: November 01, 2013, 07:06:38 am
content: My question Dave, Is there a defined way for fault finding , such a order in which way things should be checked, a fault finding chart for example like switch it on power yes or no, then it branches off to the next question, depending which answer. that type of thing. part of me is thinking this is a stupid question, however I really don't know, so thought I'd ask.Q2 if you have the time can we have more repair videos, as this is the type of electronics most of us end up doingPaul

author: Unknown
author_rank: Unknown
timestamp: November 01, 2013, 09:12:53 am
content: Is there any ultra low cost solution where to stock a large number of electronic components?? DIY should be a good option to consider?

author: Ericho
author_rank: Regular Contributor
timestamp: November 01, 2013, 10:29:39 am
content: Hi Dave,Q1 How do I match a PNP and NPN transistor ? for example a 2N3904 and a 2n3906Q2 are you still using your IET DE-5000 and what is your opinion of it after some use ?Kind reg

author: Jon86
author_rank: Frequent Contributor
timestamp: November 01, 2013, 10:50:20 am
content: As an electronics student, do you think there are any concepts or utilities that I should learn before I go on to degree-level education to make my life easier? Say for example learning how to use an FPGA or the basics of designing an RF PCB?

author: tarrryan
author_rank: Newbie
timestamp: November 01, 2013, 11:38:00 am
content: Hello Dave,I have a younger cousin about nine years old who has displayed a keen interest in electronics, I have taught him ohm's law which he can remember easily enough and also do maths in binary/BCD like it was a written number, It only took half an hour to explain the idea behind binary/BCD before he was asking me for math problems to solve! Up till now i have only seen him a few times a year from from January ill see him on a frequent basis.So my question is how would you personally go about teaching someone as young as him the basics of resistance, current and voltage? I have been trying to think of my own ways but every source of input is more than welcome.The little blighter is very curious and eager to learn, who known maybe we have a British version of Dave in the making!Thankyou very muchRyan Tarr

author: uwe
author_rank: Newbie
timestamp: November 01, 2013, 11:56:57 am
content: Hi Dave,what is the state of the Rigol DP832?- Do you know, if it there is a new, fixed batch of them around?- Is there something in the same price range and capability you know of?Thanks in advanceUweP.S. i know my name is unpronounceable for native english speakers.P.S.2. and i love your show, keep it running forever

author: madshaman
author_rank: Frequent Contributor
timestamp: November 01, 2013, 12:14:33 pm
content: Hello Dave,I remember watching one of your videos where you talk about supporting the original designer by purchasing their product instead of knockoff which copies that design.If someone releases their designs to the public in the interests of education, do you feel that this would have a significant impact on the sales of their product (given that, with enough effort, someone else could always copy the design from the product itself)?Do you have any personal experience with this kind of situation?Thanks in advance from Canada,madshaman

author: greatal
author_rank: Newbie
timestamp: November 01, 2013, 12:41:42 pm
content: Hi DaveWould you please post some videos about immigration from 5V TTL logic to 3.3 or 1.8 TTL for those people use to work around arduino AVRs and other 5v TTL devices driver boards like L297 stepper driver level shifters or Dot matrix/charter LCDs …?I know there are too many solutions but actually they don’t speak about benefits and cost around these solution some issues like power consumptions and heat dissipation cost and …There to many solution like voltage dividers transistors MOSFET and FETS or diode solutions … and some good site like this link but there is no good answer.http://elinux.org/RPi_GPIO_Interface_CircuitsIt need some good tips like you fantastic video over PCB design for manufacturing

author: nitro2k01
author_rank: Frequent Contributor
timestamp: November 01, 2013, 01:47:33 pm
content: Now that you're a family man, I'm wondering how that affects your work as a vlogger. We only get to see what ends up on tape. How much time a week do you get to spend in the lab? Which times of the day do you typically spend there? Usual 9-5, late nights, etc? How much time do you spend in the lab on things that are not directly related to video making, such as side projects or just general hacking?

author: ivan747
author_rank: Super Contributor
timestamp: November 01, 2013, 01:49:17 pm
content: Hey Dave, I am doing the obligatory introduction everybody else is doing:I've been following the EEVBLog for probably 400 episodes. A lot has changed, so I was wondering, can you do a new EEVBlog lab tour video like you did on episode sixty-something? You know, a full tour.Greetings from Dominican Republic.-Ivan Veloz (veh-loss)

author: 8163jb
author_rank: Contributor
timestamp: November 01, 2013, 03:58:22 pm
content: Hi Dave, I'm a bit of a beginner and my bench is sadly lacking (due to the fact I'm still in school and do not have enough money to buy stuff), what, second to a soldering iron, do you think the most important tool is and what should I invest my money in first? I say second to a soldering iron because I have just recently bought myself a Hakko fx-888D and so do not need onecheers!

author: Jope
author_rank: Regular Contributor
timestamp: November 01, 2013, 07:11:48 pm
content: What are your main interests/hobbies besides electronics?

author: jeroent
author_rank: Newbie
timestamp: November 01, 2013, 07:17:22 pm
content: Hi Dave.Can you do a video how a compression F connector actually works inside? There are many videos on Youtube, but it's not clear to me how the shielding connection works. Perhaps you could take one apart to show us?

author: tsmith35
author_rank: Frequent Contributor
timestamp: November 01, 2013, 07:34:27 pm
content: Two questions:1) How do you store your millions of components (you must have many) in such a way that is both space-saving and usable?2) What the heck do you do for fun (besides work on electronics)? Besides that, it would be fun to see "A Day in the Life of Dave".Okay, I guess that's technically two questions + an implied question...

author: EvilGeniusSkis
author_rank: Regular Contributor
timestamp: November 01, 2013, 09:09:07 pm
content: Have you done a video/series on how you make your videos and if not would you consider it? I want to start making videos and anytime I try I always end up looking like a complete idiot.

author: dentaku
author_rank: Frequent Contributor
timestamp: November 01, 2013, 11:37:21 pm
content: Do you have any favorite methods for quickly finding good datasheets?Finding datasheets for unknown components is always annoying for people like me who find old parts that I don't even know what they're called. Inductors are the most mysterious parts on most PCBs because there seems to be no standard way of labeling them.Glass diodes are also very difficult to read PLUS sometimes the numbers on them end up not showing up in any search engine.

author: kizzap
author_rank: Unknown
timestamp: November 02, 2013, 01:15:42 am
content: I'd really love to hear some industry stories...As an EE in the working field, what was the hardest problem that you ever worked on, one that was giving you the right royal run-around, and how did you end up resolving the issue? I.e. was it a simple obvious solution, or did it involve a lot of work.-kizzap

author: Excavatoree
author_rank: Frequent Contributor
timestamp: November 02, 2013, 01:17:53 am
content: I'll preface my question with a blurb to try to better explain what I mean.As a child, I experimented with very basic electrical projects, and I built electronic projects using the ubiquitous xxx in 1 kits with the spring terminals. I never applied myself to electronics as much as you did, but I always had an interest. I was also interested in other things, under the broad category of automotive. I took vocational electronics in Secondary School, and went on to University. After graduation, I could have chosen a path of electronics engineering, but instead I chose the School bus factory, which lead to my work in the construction equipment industry. My knowledge of electronics has helped, and I get to "dabble in it" on occasion, but I realize I've chosen a different path than you.Sorry for the long blurb, but the question is simply, were there any other career paths that you considered, or did you always know you would be an electronics engineer?

author: rsjsouza
author_rank: Super Contributor
timestamp: November 02, 2013, 02:46:49 am
content: Being a "man of the media" these days and heavily involved in generating and producing content, how is your typical day shared between the work on "pure" electronics, concoction of new ideas and "heavy duty" media production? Also, was it difficult to mentally cross the line from the traditional job to being self sufficient by producing the blog?Quick background: in my career I had multiple roles that involved development and technical media/marketing simultaneously, and I only got comfortable in these multiple transitions with time. I am curious to know how you deal with that.

author: braintree
author_rank: Newbie
timestamp: November 02, 2013, 07:02:03 am
content: How do plasma balls work?I know this is probably a simple question & there are surely answers alll over the internets, so I understand if you skip it.That said, I would be fricken stoked if you explained it. I reckon you'd do a better job than some pompous fathead.

author: michi42
author_rank: Newbie
timestamp: November 02, 2013, 08:04:48 am
content: Hi,how did this suface voltmeter work you had in the electrostatic shielding bags episode? Was ist some sort of charge amplifer / integrator? That would explain the funny "reset" button.I built a rotary voltmeter "field mill" myself that overcomes this problems.Keep up Blogging

author: scott216
author_rank: Regular Contributor
timestamp: November 03, 2013, 03:27:39 am
content: I'd like to learn more about the best practices for schematic layout. I'd like to start putting some of my projects on Github for others to see and I'd like the schematics to look like they were well laid out and followed some accepted best practices.

author: griffo666
author_rank: Newbie
timestamp: November 03, 2013, 04:21:04 am
content: Hi...Great show...I am a beginner and using arduino..I know how much you hate cheap oscilloscopes but is it possible to use the dso scope or some other small cheap scope. for simple viewing of wave forms on an arduino board ..Just to see the output pwm for example...Thanks and keep the videos coming

author: VK5RC
author_rank: Unknown
timestamp: November 03, 2013, 12:18:07 pm
content: Hi,Some questions that are currently bugging me.Is there a simple way to calculate the value of a NTC thermistor used to reduce inrush current in power supplies?Is there a sensible way to store all the cables, power, DC, jumper and coax? How do they do it in big labs?Again great series, ThanksRob

author: SeanB
author_rank: Super Contributor
timestamp: November 03, 2013, 01:53:24 pm
content: Datasheets for the NTC inrush limiters are available from the vendors, and these have a range of currents they recommend for operation. Typically you use a single unit of around 5R or 10R for a running current from around 1-5A, and a lower value one for higher. Just remember that in use they do run quite hot, so must be not touching anything flammable and must be able to dissipate the heat generated, typically you also leave the leads at full length. during mounting.As to cable storage you can use clothes hangers, tie hangers or any number and variety of hanging hooks available from the local hardware store. in your case in Australia/NZ Bunnings or B&Q.

author: hammy
author_rank: Unknown
timestamp: November 04, 2013, 04:56:54 pm
content: @SeanBYou are doing the answers in this Q&A thread?If you answer them all Dave has no reason to make a video.Sorry, couldn't resist!

author: SeanB
author_rank: Super Contributor
timestamp: November 04, 2013, 06:03:02 pm
content: Plenty for Dave to make a video of still, just a quick answer to save time. I give a seat of pants answer that works most of the time, Dave will give the design criteria.

author: idolstar
author_rank: Newbie
timestamp: November 04, 2013, 06:50:18 pm
content: My question is:What are the biggest mistakes you see in beginners, and how can they (we) avoid them?(It's probably a video on its own, which maybe you already made, I have not seen them all yet. Maybe there is one thing you want to pound into our collective skulls?)

author: Rory
author_rank: Frequent Contributor
timestamp: November 04, 2013, 09:30:47 pm
content: What kind of EE- type video would you personally like to see, to complement what you put out? Any particular subject or style of video? Is there something you could do, but just don't have the time or inclination?

author: mrbyte
author_rank: Newbie
timestamp: November 04, 2013, 09:45:40 pm
content: Hi Dave,My question is how do you get into the industry?I have a degree in computer science (which did include some electronics modules), and I also have a top grade electronics a-level. I love electronics and I would like to get into the industry, especially if I could be self-employed.How easy would this be and what would I have to do to achieve it? I always tinker about with electronics at home as I love it and it would be great to get paid to do it too!Thanks for all your videos by the way, I watch every episode and always end up learning something

author: vaualbus
author_rank: Frequent Contributor
timestamp: November 04, 2013, 09:51:06 pm
content: I want to do a question a little bit difficult.How to make voltage controllable variable gain amplifier.Basicly I'm developing an analog function generator and I've to deal with the amplitude controlling.I don't want to use potentiometer but only digital data then converto into a voltage from a dac.Best regards, wish to have a replay. Alberto.

author: Ronald1962
author_rank: Contributor
timestamp: November 04, 2013, 09:55:05 pm
content: Hi Dave,here are my questions (filtered out of so many...):1. What is the actual status of the µsupply?2. Could you please teach us a little more regarding the advanced usage of a scope?( I guess my scope could do much more than I know now...)3. Can you tell /teach us more in the audio direction?(design an test etc.)Thank you very much in advance!!!RegardsRonald

author: josko
author_rank: Newbie
timestamp: November 04, 2013, 11:04:00 pm
content: Hello I have these two questions:First questionCould you do analysis of novice hardware designs?I mean I have done decent hardware design in my bachelors thesis - it was digital oscilloscope with beefy FPGA and despite the fact that it is fully working I am aware that there could be many design flaws and I think many people starting in electronics design could learn from mistakes in these designs.There's link to forum post about my design if you were interested:https://www.eevblog.com/forum/projects/opensource-fpga-dev-kit-with-dsologic-analyzer-module/Second question:Quote from: TNb on November 01, 2013, 04:23:25 amVirtually the same question as cited question above.. Although I have already chosen hardware/embedded systems path.But I have the same concern.. In Europe (or at least where I study) with software you can find well paid job virtually anywhere especially web and mobile application development where I easily had student part-time offers for maybe 6-10€ per hour or more.Now that I have made my way to hardware through my bachelors thesis (digital oscilloscope) I have applied for part time in big semiconductor company (I don't want to specify - piss that it's ONSemi), in particulary ASIC development (standard cells) but I already see it's paid significantly less (3-4€ per hour for student part timer).After long interviews that covered digital and analog hardare principles I got to say that I am bit disappointed - it is much less development than I have expected.. at least what concerns standart cells it is over processed corporate work.I mean what I do is that I get some specifications in some format and I generate HDL views with some Perl scripts, no development what so ever, nothing just dull process over and over and even if I develop something it is more regarded to scripts than actual hardware. I don't know if that's just for part timers.. Or it is regular in corporate design? I have say that my thesis was many times more interesting and really hardware concerned.

author: BobC
author_rank: Unknown
timestamp: November 08, 2013, 04:55:47 am
content: Got a fun one for you Dave! It's more of a problem than a question, but it involves everything: Mechanical, electro-mechanical, electro-chemical, electronic, and software, all in a single real-world problem.At work we built a board to drive brushed DC gearmotors to raise and lower a load. We fed the PWM output of an ATmega328P (in "Phase Correct" PWM mode, of course) through some glue logic to a MOSFET H-bridge driver chip and then on to the MOSFET H-bridge and the motor. To keep things simple, the main 28V supply provides power not only to the H-bridge and motor, but also to the electronics (at +5V and 3.3V) via an on-board buck switcher module (+5V out) and a 3.3V linear regulator. The system had been operating reliably for weeks.I wanted to show how a DC motor is self-braking when the input is shorted. So for an initial demo I used a battery and a SPDT switch, which when thrown would remove one side of the the battery and short the motor. It worked like a charm: The load descended extremely slowly.For the next demo, I wanted to show that the H-Bridge would perform a similar function, that when the H-Bridge and all the other electronics was turned off while the motor was lowering a load at full speed, the MOSFET body diodes would become forward-biased, shorting the motor like the switch did and again causing the large braking effect. I have done similar demos several times over the years, always with ooohs and ahhs as the inherent safety of the system was demonstrated.So while the motor was lowering a load at full-speed (which was still fairly slow due to the gearmotor's 60:1 transmission ratio and a 2:1 pulley ratio), I removed power from the system. And much to my trouser-soiling surprise, the motor RPMs shot up and the load came crashing down!Now, this wouldn't be so bad if I had been using a toy motor at my desk. No, I was using a powerful gearmotor that itself weighed 15 kg, hooked up to a 350 kg load, powered by a pair of 12V AGM marine batteries in series, just as I had with the SPDT switch demo. The thud truly made the earth move.Fortunately, nothing was damaged: Not the board, not the gearmotor, not the load, and not the concrete slab the load landed on.So what happened? Why didn't my load descend slowly, like it did with the switch? What can be done to make it work how I expected it to?I think I've figured out the basics of what went on, but I'm afraid to test it (that last thud raised more than eyebrows). I'd really like to see you sleuth your way through the problem and solution before I try anything. All the above happened just last week, and I'm still a bit shaken by it. Literally.Thanks,-BobC“It could be that the purpose of your life is only to serve as a warning to others.” - Ashleigh Brilliant

author: boccafriend
author_rank: Newbie
timestamp: November 08, 2013, 06:38:27 am
content: Hello,What is the best electronics toy/learning kit for an 8year old?I also had a Tandy 50-in-1 kit so many years ago....is this still the way to go?Thanks.

author: BobC
author_rank: Unknown
timestamp: November 10, 2013, 08:38:18 pm
content: Here are some of the parts I think I've figured out regarding the problem posed in my prior post about the Big Thud:The ATmega PWM in "Phase Correct" PWM mode outputs clean DC at PWM values of 0 and 255, meaning at 0 the H-bridge is off, and at 255 it is in full-on conduction (well, two of its legs are).We use a GPIO pin to set the motor direction at the MOSFET driver chip, giving us the equivalent PWM range of -255 to +255, where zero in each direction has the H-bridge in the same state (no legs are on).One important thing I forgot to mention in the original post is that our gearmotors have built-in friction brakes that are normally engaged, and need DC applied to release them and permit the motor to rotate. The DC comes from a second PWM directly driving a MOSFET. So removing external power SHOULD have engaged the friction brakes!Clearly, removing external power did NOT remove power from the system. And the only other power source is the now motor with a 350 kg load attached. We expect a motor to become a generator under these circumstances.But how did this power get to the brakes?And why/how was the polarity correct? Why didn't the system get fried by reverse voltage from the motor?There is only one possible answer: The H-bridge served as a bridge rectifier, routing power to the supply bus instead of cleanly shorting the motor.When external power was removed, the motor became a generator and immediately started powering the system. And because the logic power supplies took power from the same bus as the H-bridge motor power, those supplies never lost their input power, and the processor never stopped running. Which means it's state of driving downward is still active, and prevented power being removed from the friction brakes!So, current was still flowing through the motor: Shouldn't this have slowed the descent? Well, it probably did, a little, but not obviously enough to matter.OK then, if there wasn't enough current for significant dynamic motor braking, why didn't the voltage climb high enough to damage any circuitry?There are two key pieces of data I don't (yet) have: 1) What is the current through the motor when its input is shorted with a 350 kg load applied? 2) What is the voltage on the open motor output with a 350 kg load applied? In other heavy-load systems, I've seen shorted motor currents of several hundred amps (but zero volts), and open circuit voltages of hundreds of volts (but zero amps).Our system was somewhere between these two extremes.The first element to fry would/should have been the buck switcher module. While we were using it with an input of 28V, it was rated up to 42V, and would probably survive 50V or higher for the few seconds it took for the load to fall to the floor.Releasing the friction brakes takes about 3 amps at 12V, and the PWM to the MOSFET was set for a 43% duty cycle, for an average current draw of 1.3 amps at 28V. The logic supplies pull under 100ma from the 28V bus, and so aren't as important a load as the friction brakes.Bottom line, TWO things had to go wrong for the load to crash to the floor: The motor wasn't shorted, and power wasn't removed from the friction brakes. If either of these had happened, the load would not have come crashing down.What did we do wrong?First, there were no diodes present to block reverse current from the motor to the 28V bus. These diodes would go between the 28V supply and the H-bridge. Oh yes, they were present in the initial design, but we INTENTIONALLY removed them when someone noticed we could recover power from the system by doing regenerative braking during descent. And that effect was in full evidence when going down at full speed: The current on the 28V supply bus was indeed reversed, and we were supplying current back to the supply (which had other large loads). But the regenerative braking didn't permit nearly as much current to flow as would a true shorting of the motor leads.Second, why didn't the H-bridge short the motor? Remember, two of the legs were in full conduction during the descent, and that didn't change when the supply was disconnected (because the electronics driving it never had power removed). When a MOSFET is on, the body diode essentially "goes away" because its forward voltage drop is never reached, so it can't be driven into conduction. The only available current path was to the supply bus, not shorting the motor.What's the fix? Well, what if we never remove external power? While that sounds impractical, it turns out that adding an internal pair of AGM batteries (only slightly larger than motorcycle batteries) can provide enough power for our system under all required operational scenarios. The external 28V bus is attached to a heavy-duty battery charger instead of directly to the system. Instead of a peak current draw of 60A and a reverse current of 10A, the external supply now sees a load current that can't exceed the charger's draw limit of 7A.But isn't that a kluge? Yup, it sure is, but it does have other benefits (such as independent operation). What's the REAL fix?One key flaw is the ability of the motor (in generator mode) to power the friction brakes. If the friction brakes had engaged, everything would have come to a safe and immediate halt. The friction brakes would engage if power to its MOSFET were removed, or the MOSFET itself were turned off. Which means a related flaw is the motor being able to power the electronics.If we gave up regenerative braking, the solution would be to insert the blocking diodes mentioned earlier. But now that we are using internal batteries for primary power, regenerative braking allows us to meet our operational requirements using smaller batteries than we would need otherwise.Are we in a "Catch 22"? We haven't yet found a simple or elegant way to ensure the motor can't power the brakes or electronics and still keep regenerative braking. There are lots of complex approaches that use reverse current sensors and relays, but they add complexity and cost (more than the batteries and charger did), and may reduce overall reliability (new failure modes).What do you think the right approach should be?(Yes, I've wandered a bit from the intent of this thread. But it's still a question, so *technically* it can still go in this thread. Please don't banish me!)

author: Dave Pye
author_rank: Newbie
timestamp: November 13, 2013, 03:49:08 pm
content: Hi Dave,looking through the posts, the general theme seems to be the thirst for knowledge. How can I learn? What's the best way? Etc. Etc..So before I ask my question let me give you a brief background about me (But I'm just one of many)Just like you, I caught the electronics bug when I was young. I bought magazines, built gadgets and generally played with things. But I never really understood what was going on.I gave up when I was about 18 years old, out of frustration more than anything else. Then one day (just this year), I came across this Aussie bloke whilst browsing the internet. His name was Colin Mitchell (Remember him?). Anyway, just for old times sake I thought I'd take a look at what he had to say.It was an eureka moment, for the very first time I understood how a transistor worked. That was it, I was off the blocks and running, the electronics bug was back - And no stopping it this time. That was 37 years after I had gave up on the subject.So my question is:-Why don't you do more tutorials? I love them. Can't get enough.

author: Kjelt
author_rank: Super Contributor
timestamp: November 14, 2013, 08:37:13 pm
content: Quote from: VK5RC on November 03, 2013, 12:18:07 pmNot very simple, see page 6 to 9 :http://dkc1.digikey.com/us/en/tod/Ametherm/NTC/NTC.html

author: iwasz
author_rank: Contributor
timestamp: November 18, 2013, 10:24:25 am
content: HiWould you consider making some videos about High-speed digital (PCB) design and signal integrity? This seems to be some mystical topic and a very few videos on YT are available. You know topics like ringing, reflections, crosstalk, mutual capacitance, mutual impedance and so on. Regs!

author: pa7
author_rank: Newbie
timestamp: November 29, 2013, 09:51:19 am
content: Hi, Dave! I enjoyed all the videos on th uSupply and I learned a lot form all of them, but what happend with that project? What is it's current status? Is there going to be a continuation on it? Thank you for what you are doing! Helps me learn a lot.