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Fristly, the arduino thread is this: https://forums.somethingawful.com/showthread.php?threadid=3505424 There is a great deal of overlap between people posting in these threads, but atleast software questions is more suited for that thread. To give a walkthrough of how Id approach one of your ideas: Tuning the radio antenna First, an idea or a purpose for your build - you're well set there. Two, breaking the idea down into cause and effect logical blocks. Firstly, you will have some type of sensor reacting to the rotation of the antenna. Secondly, you'll have an output responding to the first sensor, in your case perhaps a light turns on and a speaker plays a sound. Between those you'll have some wires and some glue logic Thirdly, brainstorm hardware with price and purpose that fits your needs. For the sensor, Id suggest a Hall effect sensor and a little magnet glued to a outrigger on the antenna, somewhere the audience cant see. When the antenna turns into the correct position, the magnet moves near the hall effect sensor, which is read by the controller (perhaps an Arduino). For the lights/sound, a LED and a speaker with perhaps a driver depending on desired volume. Fourth, find suitable components - ask here, buy from digikey or whatever or a local hackerspace. Fifth, breadboard prototype. A breadboard is this. A quick and dirty way to test a (low-power) circuit. You can plug the components in and test hardware/software. Then it gets a little fuzzy. You might transfer to a Veroboard / stripboard (soldering, yay!) or for more complicated stuff, get a PCB made - either DYI (chemicals) or China (takes a little knowledge). As rawrr mentions, kits are an option. Some starter kits are pretty solidly made with good documentation and explanation - others are a pile of components and a PCB, good luck! The official Arduino starter kit is expensive (100$) but comes with a book, some components and directions to get started. If you can find it cheaper or a knockoff, its a place to start.
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Dec 15, 2017 20:40
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chitoryu12 posted:Well, I have specific objectives in mind but I don't plan on actually constructing them for about a year. I'd like for my skills and knowledge in electronics to be more than just learning how to do each individual thing I want to do, so I'd like to have a breadboard for my first hands-on experimenting and some useless little projects to solder together first like simple lights or motors. I figured a kit would be a good way to get the really basic equipment and practice cheaply before buying things meant for specific projects and accidentally ruining them. Ah, the joys of China and electronics. Dinky electronics are incredibly cheap from China - a few dollars shipped. The guideline I've heard when ordering is to order 3 of something you need 1 of. One that wont work on arrival, one to fumble and blow up, one to actually do the thing.
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Dec 15, 2017 20:43
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Generic fuel tank senders are pretty cheap too, and have well documented resistance to tank level charts: https://www.amazon.com/Bosch-SP0F000013-Fuel-Level-Sender/dp/B00VAGA19S/
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Dec 15, 2017 20:50
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chitoryu12 posted:Well, I have specific objectives in mind but I don't plan on actually constructing them for about a year. I'd like for my skills and knowledge in electronics to be more than just learning how to do each individual thing I want to do, so I'd like to have a breadboard for my first hands-on experimenting and some useless little projects to solder together first like simple lights or motors. I figured a kit would be a good way to get the really basic equipment and practice cheaply before buying things meant for specific projects and accidentally ruining them. The thing is, hooking up lights or motors won't really teach you the skills to implement a hall effect sensor; most of the challenge with arduino projects is integrating your various devices both in the hardware and software sense. The tutorials you'll get with your kits will more or less be "connect these pins to those pins, download the program, press a button to upload it to arduino". If you're set on starting with a kit first, I'd recommend that you prioritize documentation over the value or number of parts in the kit. Electronic components are ridiculously cheap, especially for jelly bean parts. As in, less than a dollar cheap for most things. Also, if you don't know what you don't know, don't underestimate the amount of time your project may take. That's why I'm suggesting you jump right away into applications, because you'll inevitably need to take detours to learn other things on the way, whether that's soldering, programming, or figuring out how to keep your project powered.
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Dec 15, 2017 22:21
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chitoryu12 posted:Some Stuff Instead of making these things fake, real parts will really work. Fuel tank: Just install a float switch, like a real tank. A real generator also has a port at the bottom to let fuel into the carb. If you use a real fuel tank, then you can just open that port when you're done and the fuel will come out. Fuse: JUST USE A FUSE. You have two contacts that need to conduct power between them. This is the definition of a switch already; why go through getting a "fake" fuse and a separate mechanical switch? Pull-start systems in real small motors pull a shaft with magnets mounted to it. This is hall-effect gold. You could even determine if they're pulling "hard enough" by how fast the shaft turns. For the "pops the fuse if it's hooked up wrong" you could just use a 5V light bulb and put 12V on it. There are even 5v lamps that are kinda fuse-like if you want to make them replace the fuse. Otherwise, you can have a small circuit breaker that you overcurrent, and the require the actors to reset the breaker. If you have the chassis of a radio where the dial still works, then yeah, mounting a sensor so it triggers when the pointer is in the right place is a good bet. As far as kits, I like the Sparkfun Inventor's Kit. Throw a couple of hall sensors and a relay shield in with your order and you'll be interacting with the real world in no time.
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Dec 15, 2017 22:29
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One of the reasons I wanted to use a fake fuse for my puzzle was to idiot-proof it from the audience. There’s no concerns about a fuse being broken and failing to work or someone having trouble inserting it correctly because they’ve never done it before, because just having the item inside (broken or not) will press on the switch and complete the puzzle.
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Dec 16, 2017 00:46
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Using an actual fuse to close a circuit would be way more reliable than some sort of hidden switch system.
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Dec 16, 2017 02:02
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chitoryu12 posted:One of the reasons I wanted to use a fake fuse for my puzzle was to idiot-proof it from the audience. There’s no concerns about a fuse being broken and failing to work or someone having trouble inserting it correctly because they’ve never done it before, because just having the item inside (broken or not) will press on the switch and complete the puzzle. Fuseholder and a piece of copper pipe, then. This is already a VERY ambitious project. Go with very, very, very simple first, and then fix the things that break or don't work in practice. "idiot-proofing" fuses is something we've been doing for a couple hundred years at this point, and they're pretty much idiot-proof now. The more you can leverage stuff that already exists and works, the better. Don't re-invent some way of figuring out whether there's liquid in something and how to get it out: this problem is solved in a commercial gas tank with petcock. Plus, inserting a real fuse in a real fuseholder that's obviously real is a much more immersive and convincing experience. If they're then pulling on the starting cord from an actual (dead) generator instead of some paper maché box with blinkenlites, that much the better.
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Dec 16, 2017 03:33
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Ne Cede Malis posted:Overall your design looks fine I think. I bought a hot air station and was planning on getting the PCBs and trying to do these boards myself. That said, there's like 100 people who want to buy copies of this loving thing, so if I can figure out an economical way of having a fab house actually do the assembly I'd be 100% up for that. I have never ordered a PCB of meaningful scope - the only time I did was from OSH Park. OSH Park lets me upload my .brd files without me having to figure out how to generate gerbers that make sense, so I figured I'd go for that, but I'm entirely open to suggestions. Is having this stuff assembled likely to cost $texas? Do I have to do anything different to my files to clearly direct what needs to go where? I only added the "CUT OUT" text because OSH Park suggested it. It's drawn on my board Outline layer right now, and when I uploaded the files to them for review it did look like they were going to properly cut that hole out. Adding the drills as well is a smart idea, though - I'll do that.
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Dec 16, 2017 07:29
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Check out Macrofab. Good people and not an arm and a leg. They have an online quote system and you can talk to them and whatever
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Dec 16, 2017 08:48
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I would suggest using a large high voltage fuse so it is harder for the players to lose it
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Dec 16, 2017 08:52
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I might use a cartridge fuse like this, commonly used for residential A/C. Two tips: You might want to hack up a fuse and replace its guts with a “secret” resistor because players will try to cheat by bridging the contacts with metal objects. If you do use a big fuse and big, exposed contacts, you will be using low voltage, obviously. Still, some people are squeamish about that and I played a room once where an insulated glove was provided for such people.
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Dec 16, 2017 09:02
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Platystemon posted:I might use a cartridge fuse like this, commonly used for residential A/C. I like both of these ideas. There are a number of "finger safe fuse holders" by many manufacturers. We still don't know what the budget is for this project, but hopefully it's not basement-level. Custom-fabbing enclosures to look like things isn't cheap. Even getting wrecked equipment isn't that cheap, and modifying it well is very labor-intensive.
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Dec 16, 2017 16:32
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I had initially decided on a fake fuse because of my experience with escape rooms (which this project is incorporating some aspects of with the puzzles, albeit on a simpler level). There's a room in Brooklyn that simulates corporate burglary, and they try to use realistic task-based steps instead of solving overt puzzles. One of those involved opening up a wall box that had a large circuit board inside and bridging connectors with wires, which would actually complete or break a circuit to activate or deactivate things in the environment. There was a sense of trepidation as I did the task because the circuit board was actually a full and complex circuit board, and I wasn't sure if it was just a dummy sitting in the wall or if it was actually part of the room's systems and I could gently caress up the game if I wasn't careful. I have the feeling that having players manipulate a real electrical system would cause the same level of worry. Another room I did in Orlando had a similar fuse puzzle to what I'm proposing, but they did it with a crafted prop fuse and a hidden switch or magnetic sensor to open a hatch nearby when inserted.
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Dec 16, 2017 17:46
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I want to switch a 36 VDC, 750 mA load with 3.3 V logic. It seems to me that this thing http://www.mouser.com/ds/2/205/LCB710-22935.pdf is absolutely perfect for my needs. Datasheet claims it can switch up to 60 V at 1 A, only needs 1.2 V at 1 mA to power its LED, and it'll only dissipate 1/3W at the load I'm putting through it. I don't particularly care about switching speed. Is there some drawback to this thing that I'm missing? Being able to switch a 60V circuit using only 1.2V with an on resistance of 0.6 ohms seems too good to be true.
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Dec 16, 2017 18:47
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nobody- posted:I want to switch a 36 VDC, 750 mA load with 3.3 V logic. It's much more expensive than a mosfet that would do the job just as well if you didn't need the isolation. Given that it's a opto device, it needs a fair amount of current to turn on, rather than the basically zero current going into the gate. Related to this, you'll need an external resistor to control current. .6 ohms isn't particularly good, you could do about an order of magnitude better with a mosfet. This, along with the packaging constraints from being an opto device are whats limiting it to only 1a. You've noted that the switching speed isn't great. None of these are deal killers.
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Dec 16, 2017 20:24
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nobody- posted:I want to switch a 36 VDC, 750 mA load with 3.3 V logic. The P-channel FET that I just used only has an RDSon of 0.0069Ohm at VGS = -10 V ... 600mohms is a LOT. I'm running 48V and 60A through mine, though. If you want an optoisolator, and can drive it effectively (2mA is pretty high draw compared to a FET), then it works fine? It's nothing special.
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Dec 16, 2017 20:27
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Is there a thread-recommended resource for FETs? Like, I want to have [high/low] side switching of [5/12/24/80/120AC] volts using [3.3, 5, 12] volt logic with a PWM frequency of [0,200,2k,50k] Hz, and it needs to be [through-hole, surface-mount, TO-220 heatsink]. Then just go and find the currently recommended FET.
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Dec 16, 2017 22:10
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Aurium posted:It's much more expensive than a mosfet that would do the job just as well if you didn't need the isolation. Thanks. I was under the impression that there aren't really any FETs that could switch 36V with a gate voltage of just 3.3V.
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Dec 16, 2017 22:26
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Harvey Baldman posted:I bought a hot air station and was planning on getting the PCBs and trying to do these boards myself. That said, there's like 100 people who want to buy copies of this loving thing, so if I can figure out an economical way of having a fab house actually do the assembly I'd be 100% up for that. I have never ordered a PCB of meaningful scope - the only time I did was from OSH Park. OSH Park lets me upload my .brd files without me having to figure out how to generate gerbers that make sense, so I figured I'd go for that, but I'm entirely open to suggestions. Is having this stuff assembled likely to cost $texas? Do I have to do anything different to my files to clearly direct what needs to go where? OSH Park is great. It’s highly automated but I’d guess theres still a human who at least glances at a panel before going into production to catch things like the cut outs. Ive used other prototype services where its all scripted and things like this can get overlooked. Hobbyist PCB assembly is still somewhat expensive but its definitely becoming more and more accessible to the general public. The cheapest one I’ve seen so far is seeed studios fusion pcba services. For something like this it’d probably run $1500-2000 + the cost of your BOM. You can get a quote online by uploading your files and BOM. As long as your reference designators match the board and the BOM and you have pin 1 marked the fab house should be able to place everything correctly. Good fabricators will ask you to clarify if theres anything ambiguous. If you were going to actually manufacture ~100 of these I would strongly recommend doing it on one PCB to save costs and assembly time.
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Dec 17, 2017 00:06
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Is there a solid state equivalent of a SPDT relay? I'm looking to control two ~1000W heaters independently with TRAICs, and it'd be ideal if there's a way to hardwire it such that it'd be impossible for both heaters to be on at the same time.
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Dec 17, 2017 18:51
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rawrr posted:Is there a solid state equivalent of a SPDT relay? I'm looking to control two ~1000W heaters independently with TRAICs, and it'd be ideal if there's a way to hardwire it such that it'd be impossible for both heaters to be on at the same time. This is a common concern in motor control circuits. A motor controller is way overkill for this application, but maybe you can find something basic in that realm. If nothing else, you can make this yourself out of FETs acting as logic, but it may not guarantee break-before-make.
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Dec 18, 2017 00:17
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rawrr posted:Is there a solid state equivalent of a SPDT relay? I'm looking to control two ~1000W heaters independently with TRAICs, and it'd be ideal if there's a way to hardwire it such that it'd be impossible for both heaters to be on at the same time. Why do you want solid state? At that wattage, I'd go for a relay. Do you need frequent switching or something?
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Dec 18, 2017 05:33
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I am assuming he is using the triacs to do power modulation by chopping the waveform. You have a few options: Control-logic lockout on your triac gates, which would be the cheapest and easiest as you are switching the triacs anyway. Mechanical spdt relay, you can increase reliability and component life for the relay by never switching while loaded. Thermal switch lockout, with temp safeties on the opposite coil cutting out the other supply. Actually I recommend that last one as an overall safety if this project is going to be operating unattended at any point.
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Dec 18, 2017 05:57
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You could do a relay and a TRIAC if you need to vary it. If you put the TRIAC north of the relay you only need one to modulate both.
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Dec 18, 2017 09:27
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I do plan to have thermal cutoffs for overtemperature protection and a SPST mechanical relay that shuts everything down for if/when the triac fails short. I did find this: https://www.homemade-circuits.com/triac-spdt-relay-circuit/ But it seems to me like a combination of making sure the firmware is written in a robust way (i.e. a call to turn on triac 1 is a wrapper method that turns triac 2 off if on and vice versa) and some sort of control-logic lockout is the best compromise. Or maybe it just seems the most intuitive to me. Needing only one triac to modulate both is a neat idea actually, but I think if I valued longevity over BOM cost, having two triacs to share the load would give them longer service lives.
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Dec 18, 2017 20:01
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ate all the Oreos posted:e: Wait wouldn't it have to be unpolarized, because when the low FET is on it would pull HS down to ground and HB would be at VDD, but when the high FET is on then HS would rise to Vin and HB would still be at VDD? Or is there something I'm missing that's not reverse-biasing the polarized cap somehow? When the bottom switch is on, the capacitor is pulled to ground and is charged to VDD. When the bottom switch turns off and the top switch turns on, the bottom of the capacitor now sits at VIN and the top is VDD+VIN (roughly, in this circuit). The diode keeps the capacitor from discharging to VDD (because it is now higher than VDD and the diode is reverse-biased) and can now supply the top FET with enough voltage to fully turn it on (until it discharges the capacitor). I've used a 1uF polarized cap for this many times on a breadboard, put the negative side on the drain/source junction of the FETs. Make sure to choose a capacitor that is small enough to be charged up fully while the bottom switch is on, but large enough to supply the required gate current for long enough while the top switch is on, or else you'll put the FET into its linear region and waste power and create more heat. For large FETs they can consume quite a bit of current, enough to discharge the capacitor just enough. ArchNemesis fucked around with this message at 20:47 on Dec 18, 2017 |
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Dec 18, 2017 20:31
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Op amp wizards: I've got two signals at around 80VDC and I'm planning on running them to an LT1016 acting as a comparator through a voltage divider to get the signals below ten volts or so. Does that sound reasonable? I only ask because some op amps seem to cause a physical revulsion with some analog people, but I don't really know how to spec them other than speed and voltage levels. I'd like to detect signals crossing in under a microsecond or so, and that looks extremely possible.
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Dec 18, 2017 21:30
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ante posted:Op amp wizards: What you are looking for is high common-mode rejection ratio CMRR, something like this http://www.analog.com/media/en/technical-documentation/data-sheets/AD8479.PDF would work fine (you can also use just resistors and a normal op-amp, depending on how accurate you want to be).
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Dec 18, 2017 21:57
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Is there a reason why you can't use an actual comparator?
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Dec 18, 2017 22:02
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Well since the LT1016 is a comparator, you can use it just fine. It does have limits on the inputs at +/- 5V, so just make sure your signals, at peak value, don't exceed that voltage. So a voltage divider is fine.
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Dec 18, 2017 22:09
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ArchNemesis posted:Well since the LT1016 is a comparator, you can use it just fine. It does have limits on the inputs at +/- 5V, so just make sure your signals, at peak value, don't exceed that voltage. So a voltage divider is fine. Ah yeah I saw "op-amp" in the original post and followed your link to another op-amp so I got a bit mixed up. I am curious about it more in general though. I thought "don't use an op-amp as a comparator" was a pretty normal rule of thumb, since they don't have hysteresis and generally aren't designed to slew between the rails real fast, but you were recommending one so now I'm wondering if there's another reason - do they not make comparators with that high a voltage tolerance or something? Is the slew rate and lack of hysteresis not actually as big a deal as I always assumed?
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Dec 18, 2017 22:27
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You can always use an op-amp as a comparator, the hysteresis comes from the resistor in the feedback loop that shifts the threshold when the output goes to either rail. Purpose-built comparators are usually faster, and are designed to swing rail-to-rail, which not all op-amps are. The signal levels in question were pretty high so I was referring more to the concept of common-mode rejection. Any higher in voltage and it may be easier to deal with the signals as differential signals, then operate on that lower-voltage output. Depends on the particular application.
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Dec 18, 2017 22:42
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Thanks for the discussion, all. Yeah, my op amp/comparator education is over six years old at this point and very much disused. This gives me some more starting points for reading I have to do to brush up. Coincidentally, this gap in my comfort levels has cost me at least one job offer, recently!
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Dec 18, 2017 23:17
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I flubbed the op-amp questions in my google interview too
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Dec 18, 2017 23:49
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I assume comparators are generally cheaper than rail-to-rail op amps so that might be a reason for that rule of thumb?
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Dec 19, 2017 08:36
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Splode posted:I assume comparators are generally cheaper than rail-to-rail op amps so that might be a reason for that rule of thumb? They also tend to have better slew rates, and since they're designed to spend all their time at the rails they tend have a better recovery time moving away from the rail after being saturated. LT has a pretty good and short paper. http://www.analog.com/media/en/training-seminars/tutorials/MT-084.pdf nobody- posted:Thanks. I was under the impression that there aren't really any FETs that could switch 36V with a gate voltage of just 3.3V. It's easy to choose the wrong part, because the the obvious spec isn't want you actually want to use. If you have threshold voltage of ~3v(common enough) it sounds like it's a good choice for a 3.3v circuit, when absolutely isn't. For a 3.3v circuit you want a threshold voltage of around 1-2v. I like the IRLZ44. It's <$2 in one off, rated at 60v 50a. At a gate voltage of 5v it has a rds on of .028ohms. It'll be slightly worse at 3.3, say around .050 ohms. There's even cheaper out there, as 50a is definitely overkill for your application. But I tend to just buy a bunch of one thing so I can build with what I have on hand.
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Dec 20, 2017 05:32
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You can't use all opamps as a general purpose comparator because some high performance opamps have anti-parallel diodes across the inputs - remember that typically opamps operate with no voltage differential on the inputs. Normally that will be specified in the data sheet either in text or as an equivalent input schematic (see the LTC2057 for example). It'll still mostly work but the input impedance will be highly non-linear. The LT1990 is also a pretty good choice for high voltage differential sensing, annoyingly it's not rail-rail out and kind of slow. For a discrete solution with dividers that would be fine, but for an accurate solution you'd need a low offset voltage comparator and very good resistor matching. Making it fast could also be an issue due to the high value resistors you'd likely have to use (this also seems to be an issue with some of the IC solutions). Adding a feed-forward capacitor across the top resistor in each divider would speed up the AC response but it'll require some careful thought - if one of the signals suddenly changed rapidly that could drive enough current through the capacitor into the comparator to destroy it. There's other clever ways of doing it like floating a voltage/current converter referenced off a fixed high voltage reference and capturing that current at ground potential. I've mostly seen it done in some of LTCs high side current sensor ICs so not sure how easy it would be to implement discretely.
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Dec 20, 2017 17:48
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I have a potential need to monitor voltages in a battery pack. The pack voltage is 144v nominal (185v peak) and there are 10 taps along the way. What is the normal, automated way to do this? (ie not sticking a volt meter in the taps).
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Dec 21, 2017 15:52
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 I successfully built my first ever breadboard circuit last night! I don’t have a multimeter to check yet, but is there a noticeable voltage drop or resistance difference between the power rail and the conducting strips the LED and resistor were plugged into? I also built this circuit to connect the Arduino to the power rails first and the LED was significantly dimmer.
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Dec 21, 2017 16:00
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