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My first thought is just that 315MHz is an open band of the spectrum, used by all kinds of cheap consumer RF products like garage door openers, and the electrical ignition system for a bunch of explosives is really, really, really not the place you want to worry about signal interference. If I were doing it, I'd want to do some kind of message protocol with a checksum to trigger the ignition, or at least stick a microcontroller on the receiving end and program it to only respond if all four buttons are pushed in sequence within 5 seconds or something.
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Jul 2, 2014 22:02
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Mr. Bubbles posted:I'm a relatively inexperienced electronics hobbyist who has basic experience with putting together simple circuits (my credentials) What Sagebrush said about 315MHz being a horrible wasteland of all sorts of bullshit signals from all sorts of random equipment, and yes if you do that you're going to want to make really god drat sure that the signal you received was intentional and was from your transmitter. You might want to look into the Nordic-based RF boards, which you can get for cheap as hell on eBay, and they take care of most of the RF-related nonsense for you (although you'd still want some kind of checksumming or something). This, unfortunately, would require a microcontroller at each end. The "checksumming" doesn't have to be difficult or anything, like just require every command string to be prefaced with "joebobsawesomefireworkscontroller" or something equally unlikely to be accidentally received (yes I am aware this is not what checksumming is). In the interests of safety you're gonna want the physical lockout to be an actual keyed lock, while this may be sort of a pain in the rear end, you really don't want to gently caress around with this sorta thing (hell, if it was me, I wouldn't be using a radio link at all). Also, while I sorta doubt it applies to consumer-grade fireworks, you may want to check up on any relevant laws/regulations regarding building stuff like this (ie you may be required to have two physical safety mechanisms, etc). EDIT: This sorta thing, except I think I paid $20 for five similar boards on eBay. SoundMonkey fucked around with this message at 23:12 on Jul 2, 2014 |
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Jul 2, 2014 22:38
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SoundMonkey posted:What Sagebrush said about 315MHz being a horrible wasteland of all sorts of bullshit signals from all sorts of random equipment, and yes if you do that you're going to want to make really god drat sure that the signal you received was intentional and was from your transmitter. You might want to look into the Nordic-based RF boards, which you can get for cheap as hell on eBay, and they take care of most of the RF-related nonsense for you (although you'd still want some kind of checksumming or something). This, unfortunately, would require a microcontroller at each end. The "checksumming" doesn't have to be difficult or anything, like just require every command string to be prefaced with "joebobsawesomefireworkscontroller" or something equally unlikely to be accidentally received (yes I am aware this is not what checksumming is). Thank you. Yes, I do agree that may not be a good idea with the 315Mhz frequency--I didn't realize it was so ubiquitous. I did order an arduino, a couple of moteinos, and a variety of transceivers to play with for a couple projects I'm planning. I'll look into using that instead. And yes, the keyed lock is another nice idea. Thanks for your input. (also thank you Sagebrush)
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Jul 3, 2014 01:01
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One additional comment---you might want to consider trying model rocket igniters instead of bare nichrome. Instead of heating a large length of nichrome wire (requiring a lot of current, and taking time to heat up), they only heat up a few millimeters of wire...which is encased in a pyrotechnic material! Here's good diagram: http://www.hobbylinc.com/rockets/group/igniter.htm So, now you can run off a 9V battery (or preferably like 6x AA batteries), instead of something big. I can't say for certain if they'll ignite fireworks fuses (i did this test with cannon fuses a couple years back, but I can't remember how it turned out...), but they're cheap and you can get them from Amazon or a local hobby store.
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Jul 3, 2014 01:54
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I think that his plan was basically to cut little pieces of nichrome, wrap them around the fuses, and connect those to regular wires, not to make one giant loop of nichrome going to all the fireworks (which wouldn't work properly for several reasons). I did something similar in college with a sort of Rube Goldberg match-lighting machine, and found that an inch of 30ga nichrome will glow white-hot and then melt in half when you put 6v across it. Should work just fine as-is.
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Jul 3, 2014 02:03
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I'm not trying to be some dork who questions all the requirements, but does it have to be wireless? I've heard of really simple setups like this where you just send current down some reasonably thick copper to a bit of nichrome, and bam, igniter. If you want thin wire, then still do the relay thing, but you'd be able to skip pretty much the whole control circuit and just apply power directly to the relay.
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Jul 3, 2014 02:15
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Stabby McDamage posted:I'm not trying to be some dork who questions all the requirements, but does it have to be wireless? I've heard of really simple setups like this where you just send current down some reasonably thick copper to a bit of nichrome, and bam, igniter. If you want thin wire, then still do the relay thing, but you'd be able to skip pretty much the whole control circuit and just apply power directly to the relay. I guess it doesn't have to be wireless, but I wouldn't mind getting started with a wireless project for learning purposes. I do agree a wired solution would be much easier though 
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Jul 3, 2014 03:57
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Sagebrush posted:I think that his plan was basically to cut little pieces of nichrome, wrap them around the fuses, and connect those to regular wires, not to make one giant loop of nichrome going to all the fireworks (which wouldn't work properly for several reasons). ^exactly!
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Jul 3, 2014 03:58
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Mr. Bubbles posted:Thank you. Yes, I do agree that may not be a good idea with the 315Mhz frequency--I didn't realize it was so ubiquitous. I did order an arduino, a couple of moteinos, and a variety of transceivers to play with for a couple projects I'm planning. I'll look into using that instead. And yes, the keyed lock is another nice idea. Thanks for your input. (also thank you Sagebrush) The keyed lock is pretty much a critical piece if you're not going to be guarding the thing nonstop. A couple years back at the local Canada Day celebrations, I happened to know the pyro guy doing the fireworks (who is a complete idiot) and he took me out to the pier to check the stuff out. Walked up to the firing controller, like an actual professional one... it was powered on, and both keys were inserted and turned to the firing position. "Oh! Shouldn't be like that!"... then he continued his tour without removing either key. So yeah make it as safe as you can but the human factors are always the worst.
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Jul 3, 2014 09:09
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I want to drive a tiny piezo buzzer using an output pin from a PIC, and I'm wondering if I'm being a bit OTT with protection? The device will be subjected to vibration, and can get knocked about a bit, so I'm worried about voltage spikes being generated. I have two 5V zener diodes and a parallel resistor to suppress any spikes (this is straight from the buzzer datasheet), a series capacitor to remove any DC to prevent damage to the buzzer, and a series diode to stop any voltage getting back to the MCU pin. 
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Jul 3, 2014 12:52
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Sweevo posted:I want to drive a tiny piezo buzzer using an output pin from a PIC, and I'm wondering if I'm being a bit OTT with protection? The device will be subjected to vibration, and can get knocked about a bit, so I'm worried about voltage spikes being generated. At first glance, I think the diode + capacitor in series will prevent the circuit from working. Unless I'm missing something, the cap will charge up to Vio - Vforward and not pass any of the signal through.
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Jul 3, 2014 15:17
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I think you might have missed that the circuit is being fed with a square wave, not DC.
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Jul 3, 2014 15:39
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Sweevo posted:I want to drive a tiny piezo buzzer using an output pin from a PIC, and I'm wondering if I'm being a bit OTT with protection? The device will be subjected to vibration, and can get knocked about a bit, so I'm worried about voltage spikes being generated. D5 might not be strictly necessary, but it can't hurt. Looks good to me (assuming the PIC has a strong enough output to drive it)
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Jul 3, 2014 16:01
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Delta-Wye posted:At first glance, I think the diode + capacitor in series will prevent the circuit from working. Unless I'm missing something, the cap will charge up to Vio - Vforward and not pass any of the signal through. I'll be feeding in a square wave generated in software, so the cap was really just to catch any potential programming error that might lead to the output pin being driven high continuously. It can probably be omitted once the software is debugged. Slanderer posted:assuming the PIC has a strong enough output to drive it 25mA according to the PIC datasheet. The piezo datasheet doesn't state the current, so I assume it's derived from the other parameters. The only parameters given are peak-to-peak voltage (30V max, I'll be using 5V), resonant impedance (1Kohm max) and capacitance (8nF @ 1khz). The other alternative is driving it via a transistor (again, more or less straight from the buzzer datasheet), but that's a bit overkill if the buzzer is only going to draw a couple of mA. 
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Jul 3, 2014 18:27
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Sweevo posted:I want to drive a tiny piezo buzzer using an output pin from a PIC, and I'm wondering if I'm being a bit OTT with protection? The device will be subjected to vibration, and can get knocked about a bit, so I'm worried about voltage spikes being generated. Diodes pass DC. The AC coupling cap passes AC. The combination of the two of them is odd. If you're worried about voltage spikes then put another Zener on the micro output which directly addresses those concerns (and in both directions). That's better than the series diode which very well may cause problems (likely reduced volume). Personally, I like the transistor.
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Jul 4, 2014 10:19
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Sweevo posted:I want to drive a tiny piezo buzzer using an output pin from a PIC, and I'm wondering if I'm being a bit OTT with protection? The device will be subjected to vibration, and can get knocked about a bit, so I'm worried about voltage spikes being generated. D5 would definitely prevent the circuit from working (and would only prevent damage from positive spikes anyways). A more reasonable solution would be to put external clamp diodes to ground and the MCU supply rail. But I doubt a MCU pin could drive a piezo disk effectively anyways, so using an external driver is a better bet.
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Jul 4, 2014 14:21
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Sweevo posted:I'll be feeding in a square wave generated in software, so the cap was really just to catch any potential programming error that might lead to the output pin being driven high continuously. It can probably be omitted once the software is debugged. After thinking about this some more, I'd say go with this new arrangement. The antiparallel zeners should deal with both mechanically-induced voltages and potential back emf from driving it (I've heard of this a few times, but still not sure whether or not it makes sense). The transistor (and R3) will provide further protection. The cap isn't needed here (and I don't think before) because the parallel resistor should help to prevent a charge remaining in the piezo for any significant length of time (which i think is what causes the damage from DC).
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Jul 4, 2014 21:53
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Corla Plankun posted:I think you might have missed that the circuit is being fed with a square wave, not DC. How would the capacitor ever discharge though? When the pin is high D5 will allow the capacitor to charge, and when the pin is low D5 will prevent the capacitor from discharging like it normally would. It should rise until it hits the peak voltage of the pulses (minus the drop of the diode) and then stop passing anything. I also did a quick simulation, which also indicates that it'll rise to a steady voltage. I'd need to build it to go any further though, but it seems that the peak detector behavior would dominate.
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Jul 4, 2014 23:24
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Slanderer posted:After thinking about this some more, I'd say go with this new arrangement. The antiparallel zeners should deal with both mechanically-induced voltages and potential back emf from driving it (I've heard of this a few times, but still not sure whether or not it makes sense). The transistor (and R3) will provide further protection. The cap isn't needed here (and I don't think before) because the parallel resistor should help to prevent a charge remaining in the piezo for any significant length of time (which i think is what causes the damage from DC). Yeah I decided to go with the transistor option. I've got plenty of BC337s left over from another project.
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Jul 5, 2014 00:14
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Just to be clear before I do something dumb: the correct way to connect an optoisolator to an microcontroller as an input is to put the opto's emitter to ground, the collector to the uc's I/O pin, and use a pull-up resistor, right? Switching the low side of the circuit? Would there be any reason the internal ~25k pull-up in an AVR would not be acceptable?
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Jul 5, 2014 10:04
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Sagebrush posted:Just to be clear before I do something dumb: the correct way to connect an optoisolator to an microcontroller as an input is to put the opto's emitter to ground, the collector to the uc's I/O pin, and use a pull-up resistor, right? Switching the low side of the circuit? Would there be any reason the internal ~25k pull-up in an AVR would not be acceptable? Yes 25k pull up to what? Standard optos have no Vcc pin.
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Jul 5, 2014 11:50
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25k pull up on the collector-I/O lead to the microcontroller's Vcc, so that when the opto isn't conducting and sinking the pin to ground it doesn't wander. I have no real formal training in electronics beyond college physics, so I don't know if there are any strange effects I should be aware of, that's all.
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Jul 5, 2014 19:29
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The internal pull up is good enough.
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Jul 5, 2014 23:22
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Cool, good to know. On another topic, why are connectors so drat hard to source? Everybody has ten million poorly documented types that are almost, but not quite, what you want. I just want something like a Molex but with 6 pins in a block  e: aha finally found the part number. Thanks, random PC modding forum Sagebrush fucked around with this message at 02:50 on Jul 6, 2014 |
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Jul 6, 2014 02:07
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Yeah, I wish digikey had a layout like McMaster for organizing their overwhelming supply of connecters. Below is the 6 pin connecter I use. http://www.digikey.com/product-detail/en/76650-0076/WM8369-ND/2115933
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Jul 6, 2014 02:58
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Sagebrush posted:25k pull up on the collector-I/O lead to the microcontroller's Vcc, so that when the opto isn't conducting and sinking the pin to ground it doesn't wander. I have no real formal training in electronics beyond college physics, so I don't know if there are any strange effects I should be aware of, that's all. Oh, my bad, I thought the AVR was the opto for some reason. 25k is fine though if you're actually spinning a PCB I think it's good practice to put down an actual resistor.
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Jul 6, 2014 12:09
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We finally got the LED boards back in. I'm controlling them with a single PWM signal. It's easy to have 'constant' brightness, but they requested some effects. My naive solution was to just increase the PWM count on each cycle, but visually it looked like it saturated quickly and just hovered at near-max brightness for most of the time. This stackexchange question helped, but the formula in the 2nd answer is specific to 8bit. I have a 10-bit PWM, so I'm using the formula =1/(1+EXP(((A1/85)-6)*-1))*1023, the bolded part is what scales the S-curve to fit. I can't use the full range (100% duty cycle would blow the LED's) and there isn't enough Data memory to store the entire table. So I've got it down to 256 lookup values that go up to 50% duty cycle and it's looking pretty nice! No real question, just a followup to my earlier stumblings with LED brightness.
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Jul 7, 2014 19:14
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Stockholm makerspace had a member auction and I scored a sweet scope for about 60$  Kikusui 5650 apparently. I dont know much about that brand, buy its a 50mhz scope that works great so I am really happy! I only have a cheap Rigol digital scope so this is a nice addition.
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Jul 7, 2014 19:37
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I scored a Tektronix Type 422 last week because my boyfriend inherited it from an uncle and no one in the family knew what to do with it. It's not as swank as that thing but it's leagues better than the crappy USB-connected thing I'm borrowing from a friend. It lacks storage of any kind but I trust it a lot more than that thing's ADC.
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Jul 7, 2014 20:28
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Since we're pimpin scopes, here's mine (and my unusually clean workbench) Old LG. I don't remember the middle of hand but I'll edit it in when I get home. Edit: fixed the image. It's an LG OS-5020G 20 MHZ analog scope. Sitting above it is an Global Specialties 2001A 200khz function generator. Was given both since they were bound for the garbage. (Nothing wrong electrically with either. The beam focus nob had broken off inside the scope and some super glue fixed it, and the function generator doesn't output a TTL signal anymore) Not a bad score for free. Kasan fucked around with this message at 22:49 on Jul 7, 2014 |
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Jul 7, 2014 21:50
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Woooo my eBay adjustable buck regulator got here after... five loving weeks. Tune in tomorrow to see if I set my iPhone on fire! Also three ultrasonic rangefinders from DX. Can't remember ordering them, but hey, who doesn't wanna find some range?
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Jul 8, 2014 09:58
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Kasan posted:Since we're pimpin scopes, here's mine (and my unusually clean workbench) 
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Jul 9, 2014 00:43
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As a circuitry noob, I want an oscilloscope so bad and I'm not sure why. So... what exactly can they do?
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Jul 9, 2014 05:15
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kid sinister posted:As a circuitry noob, I want an oscilloscope so bad and I'm not sure why. So... what exactly can they do? The most basic thing they do is show an input voltage as a function of time which lets you analyze all sorts of things from the ripple in a power supply to making sure your microcontroller is transmitting the serial signal that you think it is. You can get a good old one fairly cheap (good new ones are very expensive) and you won't know how you lived without it once you learn how to use it.
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Jul 9, 2014 05:28
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Star War Sex Parrot posted:scopes huh drat, that's pretty sexy. 1ghz 4channel... I can't think of any use I'd have for those types of frequencies. How expensive was that thing? kid sinister posted:As a circuitry noob, I want an oscilloscope so bad and I'm not sure why. So... what exactly can they do? Scopes are used to measure changes in voltage. This means that you can (among other things) inspect waveforms in your circuitry. This can be used for all kinds of things. Verifying input/output levels when using opamps, Verifying that filters work as expected, Checking frequencies of clocks/other waves, Seeing how capacitators build up charge. All kinds of things basically. If you are going to build stuff with electricity, you will want one at some point.
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Jul 9, 2014 05:30
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kid sinister posted:As a circuitry noob, I want an oscilloscope so bad and I'm not sure why. So... what exactly can they do? They're like a multimeter, except instead of reporting a steady voltage, they plot it over a typically very short amount of time. This works best (or for analog scopes, only works) with a repeating signal. They're good for checking how stable a power supply is, measuring the frequency of AC stuff, that sort of thing. Digital scopes can also be used to check logic circuits or catch intermittent problems, because they can essentially "freeze time" when they see certain voltages or patterns. Beaten, really hard. Anyway, in my opinion it's worth getting a digital oscilloscope over an analog one when starting out because, even though they're more expensive, being able to freeze and look at non-repeating signals is super super useful. Arcsech fucked around with this message at 05:37 on Jul 9, 2014 |
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Jul 9, 2014 05:34
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I'm using my Tek 422 to measure some inductors. It doesn't have storage (I can't tell it to freeze frame so I can look at a one-time signal) so I can only use it for signals that continuously repeat, but that's okay since you can still use it for a ton of things. In this case I have the unknown inductor hooked up in series with a resistor with my function generator putting a sine wave through it. I have my scope measure the voltage across the entire circuit on one channel and just across the resistor on the other channel. The voltage scale across the resistor is set to half that of the voltage scale across the entire circuit. Then I adjust the frequency until they look the same (albeit phase shifted by 90 degrees) and toss that frequency into an equation to calculate the inductor value. This works because the impedance of the resistor is constant but the impedance of the inductor varies with the frequency so I adjust the frequency until the junction voltage is half the input voltage (that is, the impedance of both the resistor and inductor are equal) which is enough information to find out the value of the inductor. Edit: In my experience this is actually easier with a scope with X-Y mode (one that plots channel one against channel two) and you adjust the frequency until the X and Y intercepts are the same. Just makes it a bit easier to eyeball. My 422 can't do that though. BattleMaster fucked around with this message at 05:55 on Jul 9, 2014 |
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Jul 9, 2014 05:50
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LeCroy stuff is all foreign and exotic for me, everyplace I've worked has either been Tektronix or HP/Agilent. I will say the worst thing ever was when scopes went to running windows OSes. Ugh. Terrible. The funny thing is a 20 year old scope is now usually more useable than a 5 year old one, just because the windows is so old and busted on the 5 year old one (and no one has ever bothered to update the windows or even do a fresh install)
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Jul 9, 2014 06:03
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BattleMaster posted:and you won't know how you lived without it once you learn how to use it. Huh. It turns out that that's exactly what I thought they were for. The problem is: can anyone explain why I had that feeling? Or is that just the next logical step from working with a multimeter, wondering "yeah, if I can measure that accurately, that would be awesome"?
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Jul 9, 2014 06:05
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priznat posted:LeCroy stuff is all foreign and exotic for me, everyplace I've worked has either been Tektronix or HP/Agilent. I really like our expensive Lecroy scopes at work, which run Windows. I can pop in a USB drive and automatically export PDFs of my screen + custom defined measured values + annotations, along with my configuration file (making it real easy to recreate a particular setup), and possibly along with raw data too. If I have a lot to annotate, I can plug in a USB keyboard and save myself a bunch of time. I can plug the scope into the network and remote control it from a PC. I think I can also do all sorts of high-level scripting stuff. Half of this wouldn't be present without a real OS running on the scope, and the other half would exist (but would be janky as all hell).
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Jul 9, 2014 06:08
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