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Jonny 290 posted:I have a type K thermocouple and a MAX31855 interface board with screw terminals for the thermocouple. Is it okay if I cut the thermocouple wires to length and strip them and use these terminals? Assuming so, didn't want to ruin a thermocouple. You can cut it down, the main thing that'll gently caress up your thermocouple is soldering it / otherwise affecting the junctions.
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Oct 29, 2012 18:40
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 So i bought one of these for a project, it's 4mm wide. I didn't really think about how tiny it would be till it got here and now i need to connect it up. Am i just going to have to solder very carefully (i haven't soldered for a while and i sucked when i last did it) or are there connectors that small?
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Oct 29, 2012 18:45
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Thanks for thermocouple help. We have screw terminals on the prefabbed amplifier board, so I'll trim and clamp in there, no solder.Loving Africa Chaps posted:
Hmm, 4mm wide....those are some tiny pins. This one might be tough if you're inexperienced at soldering. I'm pretty good and I'd definitely be breaking out the magnifying glass.
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Oct 29, 2012 18:55
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Jonny 290 posted:Thanks for thermocouple help. We have screw terminals on the prefabbed amplifier board, so I'll trim and clamp in there, no solder. I've seen some videos of people soldering surface mount stuff. Would similar techniques be worth a try? Think i'm going to practice on some card or something first and am definitely going to need a better iron then the £5 i have in the toolbox.
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Oct 29, 2012 19:04
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Loving Africa Chaps posted:I've seen some videos of people soldering surface mount stuff. Would similar techniques be worth a try? Think i'm going to practice on some card or something first and am definitely going to need a better iron then the £5 i have in the toolbox. What is it and are you just attaching to those 3 holes at the end? If that's the case, it probably isn't too bad.
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Oct 29, 2012 19:46
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movax posted:
It's a video camera and those three holes at the +,- and composite video terminal.
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Oct 29, 2012 19:48
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Loving Africa Chaps posted:It's a video camera and those three holes at the +,- and composite video terminal. I think you'll be OK with a decent tip, high-gauge solid wire (properly strain relieved) and some flux to make sure solder only flows where you want it too.
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Oct 29, 2012 19:50
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How impractical would it be to make a wireless power surface that would cover a few square feet and only have to provide enough power to drive a few LEDs or maaaaybe a device requiring no more than a couple hundred mA? Possibly multiple such devices simultaneously, but never that much (nebulous requirement, I know.) Efficiency doesn't really matter. Also, if such a thing were within the realm of possibility, what sort of range would it have? Would 1/8" be too far? 1/16"? The idea is to have a (large-ish, no more than 2'x3') surface upon which I can place multiple arbitrarily-located objects which have LEDs or whatever in them.
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Oct 29, 2012 21:04
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Bad Munki posted:How impractical would it be to make a wireless power surface that would cover a few square feet and only have to provide enough power to drive a few LEDs or maaaaybe a device requiring no more than a couple hundred mA? Possibly multiple such devices simultaneously, but never that much (nebulous requirement, I know.) Efficiency doesn't really matter. I'm not up on the physics of this stuff (since it often operates in the near-field condition, which is weird), but I'd imagine the larger your transmitter, the more power it would require. Unless you're receivers were tuned with a high Q, then it would probably be pretty inefficient. I think the optimal condition would be two identical planar antenna parallel to each other, but that's just a guess. I know there is the "Powermat" brand out there that has surfaces that can charge multiple devices, but I don't know if they'd use one big transmitter spanning the surface, or multiple smaller ones, or what.
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Oct 29, 2012 21:13
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Multiple smaller ones would work just fine, as long as I can put them more or less up against each other. Efficiency isn't really an issue, as long as it's not a physical hazard to anyone using it. Obviously I don't want to be running at 15A to drive a single 20mA LED, but I can't imagine it'd be that bad. I guess worst-case scenario would be 1-inch square pads in a grid over the whole space. That'd work well enough, although it'd be nice to be able to place the objects off-grid.
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Oct 29, 2012 21:19
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Bad Munki posted:Multiple smaller ones would work just fine, as long as I can put them more or less up against each other. Efficiency isn't really an issue, as long as it's not a physical hazard to anyone using it. Obviously I don't want to be running at 15A to drive a single 20mA LED, but I can't imagine it'd be that bad. I honestly have no idea whether devices are starting to use resonant inductive coupling (as opposed to regular, plain inductive coupling), but here is a working example of the former: https://www.youtube.com/watch?v=SSgo_N-5JOg Inductive coupling is gonna be simpler, since you're essentially building an inductive heating element for your transmitter (a planar half-transformer wound in a tight spiral), with smaller planar elements wound for the loads. All I know about that is that at higher frequencies, you're gonna start bleeding power from the skin effect if you use normal wire. Luckily, you probably won't be approaching high enough power for this to matter. EDIT: The only suggestion I can make for resonant coupling is to keep everything stable. Make you're coil using coated magnet wire, if possible (depending on the required power), and then fix it in place with superglue or lacquer or whatever---changing the coil geometry will affect the inductance, and thus the resonsant frequency. Maybe include an additional adjustable capacitor in the transmitter, so you can make tuning adjustments over time (if required). For the receivers, the same issue with the wires applies, so those need to be fixed as well. You might also want to encapsulate the whole receiver assembly, so that the parasitic capacitance caused by someone touching it doesn't detune it. Slanderer fucked around with this message at 21:34 on Oct 29, 2012 |
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Oct 29, 2012 21:30
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I remember a couple years back someone did a senior project in which they turned the entire surface of a cornhole platform into a wireless power pad. Then they put little gizmos inside the bean bags with some simple electronics that basically allowed them to automatically determine where the bag landed (roughly). IIRC the whole thing took several tens of watts to power about one square meter of area, but doubt the bean bags required more than a few milliwatts of power. To get a rough estimate of efficiency, you need to know your kQ factor (k being coupling coefficient, Q being quality factor of the two resonant elements). As a general rule of thumb, if kQ is greater than 0.1, then you can get about 1% efficiency. Otherwise it will be less than 1%. Been a long time since I did the math myself. ANIME AKBAR fucked around with this message at 13:41 on Oct 30, 2012 |
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Oct 30, 2012 03:49
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Slanderer posted:I know there is the "Powermat" brand out there that has surfaces that can charge multiple devices, but I don't know if they'd use one big transmitter spanning the surface, or multiple smaller ones, or what. If I were going to homebrew something like that I would buy some of the inductive pucks and receiver backs for the Palm Pre; it's designed to run on a standard high-power USB charger. It must have been designed halfway decently, since it could charge the phone relatively quickly as compared to plugging it straight in.
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Oct 30, 2012 06:36
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Can anyone recommend a reputable place to get a tip set for Hakko irons? Going to pick up one of these soon. http://adafruit.com/products/303 I know I will want a small chisel tip at least. There seem to be a lot of sets on ebay but I don't know what to look for as far as them not being a piece of crap. Gotten burned on security bits etc before.
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Oct 30, 2012 23:48
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Techni-tool certainly has them, but they're expensive. Incidentally, there are cheaper places to get that Hakko solder station than Adafruit.
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Oct 31, 2012 00:05
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Amazon has the solder station $10 cheaper and prime eligible, and what looks like a decent set of tips, but I'm not sure on the prices.
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Oct 31, 2012 01:24
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Hi, I was hoping someone more knowledgeable than myself could take a quick look at something I've been kicking around. My knowledge of electronics consists of what I learned in a high-school general science class, an electronics kit I had about 15 years ago, and a bit of soldering here and there. I'm planning to build a prop replica and I'm hoping to include some flickering LEDs to suggest arcing electricity. It would use a momentary push-to-make switch to activate while the button is held down. It has to fit within a pretty small space, and I want the battery to be rechargeable rather than replaceable. I was thinking one of these tiny-rear end lipos meant for micro remote controlled airplanes and helicopters: http://www.bsdmicrorc.com/index.php?categoryID=41&show_all=yes I'm hoping to drive 4-6 LEDs. I haven't done the math, but I had an RC helicopter with a battery of that type that had 2 steady LEDs, a flashing one, and two small high speed motors, so I can't imagine that's out of the question. I found these flickering LED: http://www.evilmadscientist.com/2011/does-this-led-sound-funny-to-you/ I'm planning to wire one each in series with another LED for a strong flickering effect and to save myself having to worry about an external flicker-circuit of some sort. Here's a quick diagram I whipped up:  Like I said, I haven't dealt with circuit diagrams in about a decade and a half, so please excuse any "minor" errors like reversed polarity. I imagine I'll probably have to throw in resistors once I do the math. Do I have any significant omissions/errors/etc with my general idea here? TerminalSaint fucked around with this message at 04:45 on Oct 31, 2012 |
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Oct 31, 2012 04:40
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TerminalSaint posted:Like I said, I haven't dealt with circuit diagrams in about a decade and a half, so please excuse any "minor" errors like reversed polarity. I imagine I'll probably have to throw in resistors once I do the math. That looks just fine, minus the resistors. Polarity is correct as well. The only issue is the LED forward voltage. For reference, red LEDs have a forward voltage of ~2V at nominal current. So, with 2 in series, you'd be dropping 4V across them, without even considering the drop across the resistor. I don't know what color you want to use, but the forward voltage might be higher. In order for this to work, you'll have to be running at well below the standard current, I'd imagine.
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Oct 31, 2012 04:58
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Presumably that's an issue I could handle by shoehorning in another cell or two in series?
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Oct 31, 2012 05:20
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TerminalSaint posted:Presumably that's an issue I could handle by shoehorning in another cell or two in series? I am not sure how the flickering diodes will interact with each other. Also they are not synced. You might end up with interference patterns in your flicker or even no noticeable flicker if the LEDs are close together.
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Oct 31, 2012 15:44
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I was a bit concerned about that, but I first found the LEDs in question here: http://www.evilmadscientist.com/2012/flicker-leds/ where they wire them in parallel with each other and series with other LEDs. As far as I can tell my project is essentially the same, just without the benefit of room for a battery box.
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Nov 1, 2012 00:31
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I have what I think is a basic op amp question. I tried building this circuit from the a TI application note (using a TL074CN): With R4 = R3 = 100k and R1 = R2 = 1k ohms. When I hook sig+ and sig- to ground I get 4.46V on the output and with both connected to +5V (VCC) I get 1.58V. Shouldn't I get 0V in both cases? Is the TL074CN not a suitable part for this application? The full circuit I was trying to amplify is a strain gauge but it wasn't working so I disconnected it and figured I'd try to get a baseline working and I'm having a hard time wrapping my head around these measurements. I've also tried with 1M and 100k for the pairs of resistors respectively.
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Nov 1, 2012 03:04
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Are you trying to operate with a single 5V supply?
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Nov 1, 2012 03:42
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CapnBry posted:I have what I think is a basic op amp question. I tried building this circuit from the a TI application note (using a TL074CN): If you're using a single-ended power supply (The V- on the TL074 connected to ground), that chip can't pull its output all the way to ground. You need a bipolar supply, like +5V and -5V). Generally op amps don't like to be near supply limits unless you get one specifically designed for it (and then you trade off other stuff), and for a TL074 5V overall isn't much supply voltage, so you won't have a lot of output range. An alternative to a split supply is a different reference, on R3, to a voltage between ground. The simplest option is to replace R3 with a voltage divider between your upper and lower supply. For example, if you set R3a = R3b = 2R4, where R3a and R3b are the upper and lower half of the divider, the divider will look like one resistance equal to R4 to 2.5V. Your output will be centered at this voltage. But you'd still want an op amp that's design for smaller supply voltages than a TL074. Are you using matched resistors? A differential amp is only as good as the matching of its inputs. Especially important if you've got high gain; yours is 100, so if you have a 10mV difference between + and - because of resistor mismatching, that'll be 1V at the output, and it would be easy to get a 10mV error with a large common mode input and resistors that are only matched to 1% tolerance. A better solution is to make all four resistors equal and use a matched resistor array for all four. Then if you want gain, add a gain stage after it. (If you do single supply with a reference divider, you need 7 equal resistors, using two in series for each part of the voltage divider.) An opamp with better DC performance and less offset would be better for this particular application, like an LT1013 (which still wants bipolar supplies). There are more modern opamps that work a lot better at lower supply voltages, including ones designed for sensors, but since I mostly do old school analog audio stuff I'm not that familiar with them.
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Nov 1, 2012 04:11
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movax posted:You can cut it down, the main thing that'll gently caress up your thermocouple is soldering it / otherwise affecting the junctions. Soldering the thermocouple shouldn't affect the thermocouple's performance, unless you're trying to measure temperatures higher than the melting point of solder (obviously). This is coming from Omega (pdf).
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Nov 1, 2012 04:16
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Base Emitter posted:If you're using a single-ended power supply (The V- on the TL074 connected to ground), that chip can't pull its output all the way to ground. You need a bipolar supply, like +5V and -5V). Generally op amps don't like to be near supply limits unless you get one specifically designed for it (and then you trade off other stuff), and for a TL074 5V overall isn't much supply voltage, so you won't have a lot of output range. I don't have matched resistors, just some 1% tolerance jobbers that I've got left over from another project. I figured I'd be able to account for any differences either in software or by placing other resistors in parallel to balance then out. I'm not sending a man to the moon, I'm just playing around with weighing things on my workbench. I'll keep your design notes in mind for when I decide to make a quality system. I'm trying to make do at this point with just parts I've got already without making a mouser order.
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Nov 1, 2012 14:31
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If you look in the datasheet for the TL074, it says on p8 that the output is rated to typically be able to go from -13.5 to +13.5V (the VOM parameter) when powered by +/-15V. It doesn't give any ratings for running off a single supply, but I wouldn't expect much, especially with only 5V. I googled "rail-to-rail 5v single supply opamp" and the OPA341 came up as the first PDF. If you look on p3, it claims to be able to swing to within 5mV of the rail (under certain conditions, may or may not hold true in other conditions). TLDR You need to give the TL074 more juice, man.
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Nov 1, 2012 15:03
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I've been using MCP6273 which is as cheap, easily available and is a rail-to-rail opamp, it should work for your purposes.
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Nov 1, 2012 19:28
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I need to know what the 12V signal lamps used in hifi amplifier are called, the one I need is a 12V 0.055A (.6 W) for example. How can i Google/eBay that?
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Nov 1, 2012 20:45
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longview posted:I need to know what the 12V signal lamps used in hifi amplifier are called, the one I need is a 12V 0.055A (.6 W) for example. How can i Google/eBay that? Are you talking about vacuum tubes like in a "tube amp"? I am not sure what you mean by signal lamp. Can you provide a picture maybe? Edit: I highly doubt you mean vacuum tubes given those specs, but I really don't know what you ask asking about.
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Nov 1, 2012 20:59
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Front panel indicator lamps, used to light up dials and indicators etc. from before LEDs were common.
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Nov 1, 2012 21:11
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longview posted:Front panel indicator lamps, used to light up dials and indicators etc. from before LEDs were common. Ahh, I see. Do you have a model number for the amp? That might help identify the lamp. Edit: Actually just "12v incandescent indicator lamp" turns up quite a few hits. Mostly panel mount stuff. There are a few images here. Are you talking about the "grain of wheat" style? armorer fucked around with this message at 21:28 on Nov 1, 2012 |
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Nov 1, 2012 21:20
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I didn't check the amplifier yet, only looked at it in the service manual which doesn't have pictures. The model number is XAMR74S10 which didn't give me any google results at all, only other info is 12V 0.055A. I may just put some orange LEDs instead...
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Nov 1, 2012 23:17
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longview posted:I didn't check the amplifier yet, only looked at it in the service manual which doesn't have pictures. Check XAMR74S17. Also, International Light/Gilway #7161. What you're looking for is a miniature axial lead lamp, possibly T1-1/4 size, with a 12V or greater rating.
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Nov 1, 2012 23:49
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Yeah, when you can't find a part, try chopping chunks off of the part number, and it will often give you a 'close' match that you can then figure out what your part is from. I searched for XAMR74 and it looks like you're looking for a "Technics/Panasonic 15v Panel Bulb". Sixide is right on the money.
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Nov 1, 2012 23:56
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I'm just going to throw this out there, but there aren't any sort of Electronics 101 or First Year Electronics theory courses that I can find on iTunes U or anything like that, are there? I've been going through a lot of resources, but in 100% honesty I learn best in a classroom environment. By which I mean listening to someone explain something and then connecting bits and pieces of information myself. Maybe it's just how my brain works, but hearing someone lecture is so much easier for me than reading the material in a book myself.
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Nov 2, 2012 00:04
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Maybe something like this? http://www.khanacademy.org/science/physics/electricity-and-magnetism/v/circuits--part-1
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Nov 2, 2012 00:10
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Martytoof posted:I'm just going to throw this out there, but there aren't any sort of Electronics 101 or First Year Electronics theory courses that I can find on iTunes U or anything like that, are there? Youtube has a wealth of lectures. I am actually partial to the ones from insert-Indian-University-circa-1990 professors for electronics. https://www.youtube.com/user/nptelhrd/videos?view=0 https://www.youtube.com/user/satishbojjawar78/videos?view=0 This content is a bit dated, but it's really quite good. Also, MIT https://www.youtube.com/user/MIT/videos?view=0
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Nov 2, 2012 00:22
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Yes, all of these are awesome, thank you!
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Nov 2, 2012 00:26
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CapnBry posted:I don't have matched resistors, just some 1% tolerance jobbers that I've got left over from another project. I figured I'd be able to account for any differences either in software or by placing other resistors in parallel to balance then out. I'm not sending a man to the moon, I'm just playing around with weighing things on my workbench. I'll keep your design notes in mind for when I decide to make a quality system. I'm trying to make do at this point with just parts I've got already without making a mouser order. You can use your unmatched 1% resistors and get 1% (or so) of error if you design your amplifier to have a gain of 1 (all the resistors equal). You mostly have an issue matching your resistors if you want high gain in the differential stage, because the error between the two input resists will be amplified by the gain. You can still have a gain of 100, just make the differential amp gain 1 and add a single ended, gain 100 amp after it. Sorry if I was unclear. You should be able to make this work with the bits you've got...
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Nov 2, 2012 02:27
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