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Fooley posted:I think I'm finally ready to order a microcontroller and get started on my costume, I just want to make sure I'm starting at a good point. Anything you play around with at first should work fine off 5V. That's supplied by the USB cord plugged into the board and will be able to handle LEDs and small piezo speakers.
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Mar 16, 2011 01:44
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http://www.heathkit.nu/heathkit_nu_IG-18.html I just picked up one of these for $35. It's functional, though the negative banana jack/binding post on the square wave is missing. My crappy multimeter reads about 350mV at what's supposed to be 1V RMS, but that could be either my meter or the fact that it uses archaic dBm(600). Frequency is almost dead on, maybe 0.2% error. Now to get the $95 tubes-missing Tek 547 that was right next to it...
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Mar 16, 2011 19:06
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sixide posted:http://www.heathkit.nu/heathkit_nu_IG-18.html Your crappy multimeter doesn't support true RMS, that value is only correct if it's a perfect sinewave.
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Mar 17, 2011 06:23
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ante posted:Your crappy multimeter doesn't support true RMS, that value is only correct if it's a perfect sinewave. The sine oscillator uses feedback through a notch filter, so it should be pretty close to pure. Probably, the bias trim pot needs to be adjusted.
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Mar 17, 2011 17:23
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Reposting from the softwaresupermegaawesomeultrathread. I'm looking for easy-to-use and preferably free electronics design software to help me out with my studies. We just started using Altium Designer at Uni but I can't afford to buy the thing and nobody has a copy. I'm not really looking to simulate circuits right now, just designing them.
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Mar 18, 2011 00:33
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Would Eagle fit the bill? http://www.cadsoftusa.com/
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Mar 18, 2011 00:46
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I think that'll be perfect. Thank you.
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Mar 18, 2011 00:55
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Eagle has a few limitations, but it has the benefit of being fairly well accepted. I'm really not a fan of the 12 in^2, 2-layer limitation should you upgrade to the $50 piece of software, not to mention the single-page schematic capture which also plagues the evaluation version. KiCad isn't limited at all, but has the usual baggage of a linux->windows port. Though, it's pretty much the same baggage that any CAD software has (arcane interface, sluggish, etc.). If you ever plan on simulating circuits, LTSpice is the only way to go (for free). It's also an acceptable schematic editor without any limits.
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Mar 18, 2011 01:03
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I don't know, I've tried to use KiCad several times, and trying to actually do PCB layout is a freaking nightmare in that thing. Eagle has some problems but holy hell is KiCad awful for actual layout work. Even the simplest tasks take 50 extra steps, and the most bizarre combination of right-click menus and control keys and 'modes' to do every little action (even just grouping/moving/rotating objects) you will ever see. Seriously, just trying to place and route a board with like a dozen resistors, caps, and transistors, and I was going insane.
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Mar 19, 2011 04:47
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Slanderer posted:So, I need help identifying a mystery component on a very old circuit schematic. That's an adjustable DC bias supply. It's drawn as batteries like that because it's floating (not grounded on either end). I can't say whether it would actually have been built using batteries at the time, but there's little reason to do so now. Just use a power transformer with low capacitance (split-bobbin) and an adjustable regulator circuit. My guess is the integrator needs to be biased in some way, you can see the polarity reverses every time the main relay does (changing directions?). Unfortunately there's no indication what sort of voltage range is needed.
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Mar 19, 2011 05:04
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semi-related: if you are in the USA and curious to have a [cheap] radiation detector, this place just dropped an email on me with Mueller tube kits for not very much- http://www.goldmine-elec.com/ Two notes: 1) these units are Mueller-tube buzzers, so they can't really "tell" you anything other than a relative radiation level. One has a counter on it but without being calibrated, it cannot accurately tell you the mrads/hr level. 2) these kits aren't radiation-hardened, so they're not good at all for higher levels, under any circumstances. The IC's will start acting weird, when you LEAST want them to. They are for elementary-school science class stuff, do not bet your life on them working perfectly.
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Mar 19, 2011 09:42
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I'm really surprised the kit can run off a 9V battery, those tubes were designed for a ~300V bias. (fake edit: I suppose that's why the schematic shows what seems to be a simple boost converter) You can also grab a 10-pack of the tubes on ebay for $75 (vs. $25 per unit). Either price looks to be a steal relative to new GM tubes.
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Mar 19, 2011 09:56
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Hell yeah gonna protect myself from negligible amounts of radiation. *dies after touching terminals of live geiger tube*
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Mar 19, 2011 20:36
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Does anyone know of any good literature on building a ac-dc power supply? I mean, most of it is straightforward, but certain things are hard to find info about, such as where ato place fuses and what types to use, how it should be grounded (ie, how the grounded AC wire might be used), and how to do current limiting. I mean, the art of electronics has a pretty good chapter on power supplies, but it's hard to find anything about constructing circuits that run directly from line voltage.
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Mar 19, 2011 23:48
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Quick question for those with a deeper understanding of electronics that I... I have a number of network devices (switch, 2 routers, usb drive/nas, etc) that all seem to run on 12v or 5v power bricks. Would it make any sense for me to take an old computer power supply and turn it into a power octopus for these devices? My thinking is at 70-80% efficiency, it would be better regulated/consistent, and it would save a few watts in waste heat from each of the power bricks (which may not be switching). Is this hyper-sperg-focus, or would it be worth the hour soldering and cutting (my wrists)?
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Mar 20, 2011 00:28
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edmund745 posted:semi-related: if you are in the USA and curious to have a [cheap] radiation detector, this place just dropped an email on me with Mueller tube kits for not very much- Before the whole Japan thing, I was actually thinking of building a USB-connected Geiger counter. I've had no luck finding a GM tube in Canada and I bet shipping/customs duty from the US would be murder. And may get me onto a watch list, I don't know.
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Mar 20, 2011 00:30
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Slanderer posted:Does anyone know of any good literature on building a ac-dc power supply? I mean, most of it is straightforward, but certain things are hard to find info about, such as where ato place fuses and what types to use, how it should be grounded (ie, how the grounded AC wire might be used), and how to do current limiting. I mean, the art of electronics has a pretty good chapter on power supplies, but it's hard to find anything about constructing circuits that run directly from line voltage. Generally fuses are placed on the primary side of your transformer(s). You could certainly use them to protect other parts of the power supply as well. Mains ground is attached to the chassis grounding lug. One of your transformer secondary taps becomes your circuit "ground". If circuit ground is connected to mains ground, it usually seems to be through a capacitor. I'm currently building a +/- 70Vdc 60W power supply. I've come to realize that unless you have special requirements, a CotS power pack or a simple IC-based regulator is the way to go. Power supply components are expensive and there are hundreds of potential pitfalls. I'm waiting on some interconnects and a few passives to begin construction of my linear regulator and I have serious doubts about its real-world stability. Even fixed-voltage regulators can have problems with proper regulation across the full range of potential loads. I've never seen a book about power supply design, but Google has served me quite well. The various techniques aren't always explained well, but looking at the myriad power supply schematics present is good enough. You can usually figure out what they were trying to do and how it works, then decide if you need it.
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Mar 20, 2011 02:06
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Just find a switching controller IC that fits the bill then build to the recommended layout(s) in the datasheet.
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Mar 20, 2011 08:28
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Heh, not an option, really. Going linear, since it's easier to get a mix of high current and low noise/ripple without as careful component selection. Not saying switching regulators ain't a goddamn modern marvel, and that I don't love them for making designs that are efficient---it's just that they are somewhat more complicated; not to mention, SMPS design is a true bitch.
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Mar 20, 2011 09:34
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Speaking of AC-DC supplies, the LT1083 datasheet has a nice schematic for a regulated linear high power supply using SCR rectifiers to reduce the input voltage: This looks like it would blend some of the advantages of SMPS+linear output stage without the overhead of doing SMPS design. Obviously the rectified waveform will be pretty distorted so it looks like extensive filters are needed.
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Mar 20, 2011 20:32
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longview posted:Speaking of AC-DC supplies, the LT1083 datasheet has a nice schematic for a regulated linear high power supply using SCR rectifiers to reduce the input voltage: SCR rectifiers are a pretty good compromise between linear and true switching power supplies, but usually in order to keep ripple current/voltage and crest factors to reasonable levels, you need very large inductors and capacitors. Like in that schematic, just the transformer would be quite large, and then the 1mH inductor and 50mF capacitor. That thing would weigh probably 20 pounds or more, whereas with a switchmode it would be less than 5 pounds.
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Mar 20, 2011 23:11
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Please stop saying SCR rectfiers.
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Mar 20, 2011 23:58
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the wizards beard posted:Please stop saying SCR rectfiers. A rectifier is a type of circuit. A rectifier built with SCRs is a SCR rectifier 
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Mar 21, 2011 00:37
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For those of you that have used Altium Designer before, is there any way that I can simulate the ammount of light hitting a photodiode so I can sort my useless circuit out? That's all I need.
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Mar 21, 2011 03:07
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ANIME AKBAR posted:That thing would weigh probably 20 pounds or more, whereas with a switchmode it would be less than 5 pounds. I'd make that monstrosity with 5+ LM317s in parallel. gently caress efficiency I want ripple rejection.
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Mar 21, 2011 03:29
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sixide posted:I'm pretty sure either a linear or switching regulated supply is going to get 90% of their weight from the transformer and 9% from any large filter capacitors/inductors. You're probably talking about a 2-3 pound 30 dollar choke for 1mH @ 7.5 amps DC. The power transformer, which I'm guessing could be a mislabeled F-259U, is 7.5 pounds and 50 bucks. What kills you is the magnetics are operating at 60hz rather than tens of kilohertz. 50,000uF of low-ESR high-ripple caps will not be cheap, another 20 bucks at least for bottom-of-the-barrel caps. Rescue Toaster fucked around with this message at 06:42 on Mar 21, 2011 |
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Mar 21, 2011 06:40
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Not disputing that a 7.5A power supply is going to weigh a ton, but I don't see a SMPS weighing 25% of what that SCR-based supply does when it still needs a similar amount of heavy poo poo to do the job. A 300 VA transformer doesn't get significantly lighter just by using a lower secondary voltage.
sixide fucked around with this message at 07:33 on Mar 21, 2011 |
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Mar 21, 2011 07:30
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sixide posted:I'm pretty sure either a linear or switching regulated supply is going to get 90% of their weight from the transformer and 9% from any large filter capacitors/inductors. sixide posted:A 300 VA transformer doesn't get significantly lighter just by using a lower secondary voltage. It does when you make it out of ferrite, design it well, and operate it at 100KHz or more...
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Mar 22, 2011 00:32
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Even in a flyback converter as you describe, you need a mains transformer. Right? That weight doesn't go away. Feel free to tear me a new one if I'm completely full of poo poo (not unlikely), but I don't think chopping up 120 straight from the wall is accepted practice.
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Mar 22, 2011 01:33
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sixide posted:Even in a flyback converter as you describe, you need a mains transformer. Right? That weight doesn't go away. That actually is how modern switchers do it. Rectify the 120v right away, then chop it up at hundreds of kilohertz and send it through a transformer, then rectify again. That's why your laptop adapter is so tiny.
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Mar 22, 2011 01:38
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And why a 600 watt PC power supply does not have a 10-15 pound 600VA toroid in it.
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Mar 22, 2011 02:09
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Mill Town posted:That actually is how modern switchers do it. Rectify the 120v right away, then chop it up at hundreds of kilohertz and send it through a transformer, then rectify again. That's why your laptop adapter is so tiny. Consider me enlightened, both on SMPSes and why HAMs/power companies hate switching power supplies so much.
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Mar 22, 2011 02:21
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sixide posted:Consider me enlightened, both on SMPSes and why HAMs/power companies hate switching power supplies so much. Eh, the EMI issue can be dealt with. But yeah a lot of the time it's nicer to get a huge linear supply and not worry about it. Now florescent lights, on the other hand....
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Mar 22, 2011 03:14
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As far as the power company is concerned, modern SMPS are vastly superior to linear supplies because they can have a power factor very close to 1, while linear supplies usually have pretty terrible power factor unless they are choke input (very rare). That is to say, a good SMPS appears as little more than a resistor/heater load to the power company, while 'linear' power supplies, from the power company's view, are a nonlinear mess. SMPS can certainly cause noise problems depending on the situation though.
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Mar 22, 2011 04:20
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I've never used a rail-to-rail opamp before. I have a design with an op-amp acting as a buffer, 0-10V in and 0-10V out. I would like to use a single-supply rail-to-rail op-amp (LMC7101). The board has 3.3V and 5V rails. Can I use a charge pump to double to 5V rail to power the opamp? I feel like I should generate a voltage slightly higher than 10V (quadruple 3.3V?) and use a zener to regulate the output. Am I just being afraid of rail-to-rail? I'm considering using a micropower direct 5V to 12V power module as an alternative. It is more expensive, but I know it will work.
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Mar 22, 2011 18:00
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Zaxxon posted:ok writing tutorials is hard, and I'm not necessarily the best writer but here is the start, I'm gonna do it in 3 parts, first the programmer, then the software setup (I have to do some research to make sure my linux info is correct.) Then the actual boards and programming process. Been a month since you posted the first part of this and no follow-up yet. I have to say the first part is kinda confusing, I was hoping the rest would help explain. A friend of mine has given me a PIC 18F4620-I/P chip, so I might try PIC, although th book I bought is all about Arduino. Need to find somewhere in UK/Europe that sells them at a decent price.
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Mar 22, 2011 20:04
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Keep in mind that most "rail to rail" opamps will go maybe 50-100mV within the supply rails under no load (when loaded a bit it may become worse). Very nice ones will do 10mV. But if you absolutely need it to work down to the rails, then you need dual supplies with a little headroom.
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Mar 22, 2011 20:07
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Fat Turkey posted:the book I bought is all about Arduino. Need to find somewhere in UK/Europe that sells them at a decent price. See: "Europe"  http://arduino.cc/en/Main/Buy
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Mar 22, 2011 20:13
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Gonna crosspost this from the "Tell me about engineering" thread since I know there are a lot of EE's in here... Aaaaah I don't know what to do...I know I shouldn't be complaining to be in a position like this but I'm so torn haha... I now have 2 offers for summer internships. 1 is at a company that does integrated circuit design with a focus on DRAM design. It would pay $13.00/hour, with the upside being that it is in my hometown, so I can live at home and not pay rent. On the flipside, I was just offered an internship at XCel Energy, for $17.00/hour with the potential for continuing work during the school year 10-20 hours per week as a Power System Protection Engineer Intern. I feel like whatever I choose now is gonna define my career path (as one guy put it, I've gotta choose which side of the decimal point I want to be on). If I choose the circuit design job it'll be much harder for me to move to power in the future, and vice versa. I'm at a sort of crossroads and don't know which way to go. I will say that I have more of an interest in circuit design. I like tinkering with electronics and soldering and building projects, but then some say don't make your hobby your career unless you want to end up hating it. Can anyone comment on the job outlook of either? Power is always going to be here...I also had something of an interest in working in a nuclear power plant, so the XCel job would help a lot in moving in that direction.
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Mar 22, 2011 22:53
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I'm trying to order some male to female single pin connectors. Just something I can connect to a pin on a microprocessor board, then plug the other end into the breadboard. Any idea's on what to search for? (and maybe an aussie source for them) Since it's so general I just can't seem to find them. Thanks!
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Mar 23, 2011 05:13
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