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If one was to build a circuit to measure density of smoke passing through a long, narrow chamber, what would be some approaches? My best idea right now is an LED + photoresistor combo. Obviously we're going to have to test and scale the values, but do you guys think this might work?
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Sep 25, 2012 22:01
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movax posted:There are two classes of device for that, if I recall correctly. Nephelometer will measure scattered light at a 90 degree angle in its basest form, with additional photodetectors needed to compensate for backscatter, etc. Absorptiometer is what you're thinking, in which you measure how much your light source got attenuated. Super helpful. We don't need standard units or anything, relative is fine.
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Sep 25, 2012 23:00
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Ball of aluminum foil or something. Copper braid?
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Sep 25, 2012 23:42
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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.
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Oct 29, 2012 00:04
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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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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 tuning a MOSFET driver circuit that I'm using to PWM a heating element at 31 Hz. I'm wondering if I have way too high a gate resistor. It's a 12V system, using an IRFZ48N MOSFET, and I'm driving it with a BC327 through a 1K resistor. Can't quite assemble all the math needed to calculate my gate resistor. Suspecting it should be much smaller. Our target current flow is ~8 amps through the MOSFET. (paging movax)
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Nov 5, 2012 16:17
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Honestly, this is my checklist for stripping electronics, and outside of this, I do not give a single poo poo: -Toroids -Electrolytics -Headers, connectors and jacks -Diodes *with long-ish leads* - I don't pull through-hole diodes unless they have a good 3/8" of leads on both sides -TO-220 voltage regulators and any worthy transistors - you can sometimes skeeze a couple of MOSFETS out of switching PSUs -Socketed ICs that will be useful - proprietary/unlabeled stuff I don't even look at twice. I don't desolder anything SMT for salvage, ever.
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Nov 12, 2012 22:33
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Martytoof posted:Oh yeah, I definitely didn't mean to sound emo over the math or anything. I'm having a great time figuring this stuff all out. I think I legitimately found something I am excited about learning, only I'm like 15 years too late to actually get into it and make it a career choice. But I guess it should say something that I'm actually as excited about learning this as I am about what I've considered my dream career field all this time. Don't sell yourself too short. For the past 50 years or so, it has become less and less popular to focus on hardware component electronics, due to Asian mass-production, automated assembly and the SE Asia engineer explosion. However, now there is virtually nobody around who can troubleshoot and fix things. Niche markets are holding strong, and it's easier than ever to get started blowing up transistors and hooking up the wrong resistors. Back when I was learning this poo poo in the early 90's, we had to work out of mail-order catalogs (operator, please stop calling me ma'am, i'm twelve, not a woman). Now you can either Amazon up some poo poo to tinker with the next day, or get literally any random gizmo or circuit board you want out of China with a couple weeks mail-delay. Get a good understanding of the laws (Ohm's, Kirchoff's, and the power law) and how common 3-pin semiconductors work, and you are basically ready to start building and fixing things. You don't have to know how many transistors are in that opamp (though learning the basics of opamps is strongly recommended). Jonny 290 fucked around with this message at 17:37 on Nov 16, 2012 |
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Nov 16, 2012 17:24
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Martytoof posted:I asked my dad, an EE, this exact question about 3.3 the other day. He shrugged and said "Iunno" When you put 5 volts through a 1:2 ratio resistor divider you get exactly 3.3. Suspecting that was the most convenient ratio to set it at, as 2.5V would have been a pretty low Vcc for the time in question.
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Nov 21, 2012 21:44
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I think the last time I got on a scope-shopping kick, I was looking at Tek 2213s on eBay? I don't want to drop more than a hundred until I can spend $1k or so on a quality one that will last me a long time. I wouldn't even rate one of those little mp3 player scopes for anything serious. Those little LCD displays are not known for their response time.
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Dec 9, 2012 20:27
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What value is that resistor? In theory, it should work, IF you have a significantly lower resistance through the water than you do through the resistor. Can you hook an ohmmeter up to your two wires going to the reservoir, and give us a ballpark resistance reading when it's full and then when it's empty (should be basically infinite on the latter)?
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Dec 10, 2012 19:15
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Minimize your variables first, get readings off the actual probe you're using, not the multimeter leads. You could also consider using a float switch. http://www.amazon.com/Liquid-Water-Horizontal-Switch-Aquarium/dp/B0056EWADA/ref=sr_1_1?ie=UTF8&qid=1355167348&sr=8-1&keywords=float+switch A local aquarium shop should have one for less than 10bux, and it'll be a simple, no-fiddling setup, open or closed.
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Dec 10, 2012 20:23
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LM386's are great little cheater chips. I ended up throwing one in a bass preamp and it sounded really good.
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Dec 12, 2012 05:59
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So, I've been an 'electronics guy' for decades, but admittedly cargo-culted some of it. As time moves on, I'm actually retracing my steps and relearning the fundamentals. This week's project was a wacky gift, and I homebrewed a miniature stoplight out of conduit fittings, LEDs and two 555 timers. I started off with a copied-and-pasted circuit, which didn't work. So, I got mad, and read the Wikipedia page for the 555. Then I read the datasheets. Then I studied the poo poo out of it some more until I understood how it _actually_ works. The next night, I sat down in front of my bench (NOT Multisim) and built a timer from scratch, using my own calculations and schematic. And it worked perfectly! I now 'get' the 555. Mini milestone.
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Dec 19, 2012 18:57
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longview posted:Charging an iPhone or similar device can take between 0.5A, 1A for an iPhone and something like 2A for an iPad and you need to provide resistors to the D lines to indicate how much current it is allowed to draw. The values and wiring is available many places online, test it on a breadboard with a current meter first. If you bumped the input voltage a bit (a non-problem pretty much as we're using those switcher converters) to 16-18V, you could use a common laptop power adapter for input. Might simplify. After Wozniak posted his insane octopus charger rig I seriously considered building something like this and mailing it to him, because that poo poo was shameful.
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Dec 28, 2012 20:47
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rotor posted:Hello Electronics Thread, Wait wait wait wait. This sounds vicious. Are you drat sure these are RS-232 serial ports? Toss us some pinouts or something to ponder. This should be a trivial part of the setup.
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Jan 3, 2013 00:52
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I'd go at least 18 gauge. One suggestion is to holler at a local HVAC place; they carry multi-conductor wire for thermostats and some of them should be heavy enough gauge that it should work. Not cheaper than waiting a day off Amazon, but instant gratification. The use of DB9 connectors for such an application angers me, as an aside.
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Jan 3, 2013 01:36
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Beat me to it. 2x3 Molex would be an even smaller footprint, have higher current carrying capacity, and if you spend the five dollars for the pin extractor Molexes are not hard to deal with at all.
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Jan 3, 2013 02:17
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peepsalot posted:Has anyone messed with winding their own transformers? I've had this idea for a while of making a sort of "binary" variac. Instead of a wiper, there would be multiple output windings(maybe multiple input as well) with turns in powers of two, and some relays or something could dynamically reconfigure to provide various outputs levels. The low turn windings could be done in extra heavy gauge, and higher turns could be lighter gauge to give optimal power output over all voltage ranges. Do things like this already exist, is there a name for them? Yeah, this is how substations adjust line voltage sag due to differing temperatures. They have fuckoff big transformers with several closely spaced taps at one end. If the voltage sags, say because warm weather heated up lines and their resistance increased, it'll change a tap to bump the output voltage up a little bit, at the cost of a bit more current on the input. Winding transformers is hoodoo, I have a couple hedgehog transformers that I've been building, but dudes that can hand-wind laminated core transformers deserve props.
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Jan 3, 2013 15:57
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I found that page a year ago and am still marveling at the work he did. We're planning our retirement/grey years to be on a mountaintop or somewhere with elevation change, and I was extremely impressed with his work. And yeah, the DIY 2,000 volt power line is ballsy. But he knows what he's doing.
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Jan 4, 2013 20:54
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Whenever I'm in a situation that appears to call for a Zener diode, I sit back and ponder for a moment, then figure out the correct answer to the problem. I've never liked using them as regulators. I would _maybe_ use one as the voltage ref for a BJT voltage follower, if I needed stable voltage at a few mA and the world's supply of TO92 regulators caught on fire. That's it, though.
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Jan 15, 2013 16:17
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RE: pinning to Arduinos, I found a good solution if you have a pile of old motherboards hanging around. If you yank off the 2-pin headers, rip out one row of pins and run your wires through the empty holes, you get really nice strain-relieved connectors. Hopefully pix make more sense. http://raspberryhigh.wikia.com/wiki/WiringAndBoards Also, you can see my 40-pin +5/GND extension bus on that page, which I'm proud of. 
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Jan 17, 2013 16:18
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If you do use tantalums, build the circuit and check your voltages on each side of the lines those caps go in, and make sure to orient the + side towards the more-positive DC voltage. They don't like to be hooked up with reverse polarity, at all.
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Jan 18, 2013 19:38
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Silver Alicorn posted:
Don't get hung up too much on the cap values being exactly that. Edit: I had some math in here but disregard, you may need a bigger one than I thought. I would say that 1 uF is fine but just start small and go up if you have issues. Jonny 290 fucked around with this message at 06:15 on Jan 19, 2013 |
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Jan 19, 2013 06:12
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How I cut my boards, with really good success rate: -Score on both sides with X-acto, lining up as close as I can -Place on edge of lovely MDF desk (you want that hard 90 deg edge) with cut lined up with edge -Use something like a book to hold down the part on the desk -karate CHOP! Don't ease it, snap on that thing. You've given it the weak point. Sometimes I go over it with a flat file afterwards to pretty it up (outside, of course) I can do anything from perfboard to double-sided glass epoxy board with this method.
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Jan 20, 2013 20:55
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Delta-Wye posted:I wish Sick of Beige had more options than just acrylic face/base plates. A few years back a buddy tossed me a trash bag full of unfinished, unstamped metal boxes shaped exactly like Altoids tins with a plain metal finish. One of the best hauls I've ever gotten; I'm still putting blinkenlights in those things years later and probably still have 30 left.
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Jan 21, 2013 23:01
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As much as I know about RF and tuned circuits and all that, I can't build an oscillator in Multisim or on a breadboard to save my effing life. I just don't get crystals yet. I mean, I do, but I don't. I really wish I could get a better hang of them to work on RF stuff more. Really need a scope or something. There's only so far a good DMM can take you.
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Feb 19, 2013 15:49
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I'm about to (probably) light $30 on fire here... http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=110925504614&ssPageName=ADME:X:RTQ:US:1123 I messaged the seller with the part number of a clean 15" 1680x1050 LCD out of a Latitude, and they say they can wire up a cable for it no problem. I've stripped a vintage-1998 lunchbox PC that was originally used as a Sprint network analyzer, and am shoving modern guts into it. This should work out for the display part nicely.
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Feb 25, 2013 20:13
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If you're adding USB connectivity to a device, do everything you can to avoid the mini connectors. The fullsize ones are fine. The micros are also fine. The mini connectors are _horrid pieces of shit_. I've made good money resoldering miniB's back on to 2.5" externals right before finals time.
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Apr 15, 2013 19:56
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Repair time! My Behringer (shut up) UB2442fx died last night. I'm getting typical pulsing starts from the PSU, about 5-8 hertz. I replaced a couple of suspect caps, but the ticking persists. I'm assuming something is shorted? I checked all four high speed diodes on the out rails (there are five - +/- 15V, +12v for lamp, +5 for logic and +48 for phantom), did not see any shorted or open. I have the schematic (part number is UB-SPSU2 for the PSU board), but am not too too swift with switchers. What else could be causing pulse starts? If worst comes to worst, I will build a linear bipolar for my 15v rails and hang a 7805 off the side for logic. I don't need the 12v for the light or the 48v for phantom power. Radio shack has that little 25.2 center tap that can do 2A, think this is enough to drive 15V regulators after rectification?
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May 6, 2013 18:16
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Here's a hilarious link that actually is to the schematic PDF for the power supply. http://www.electronica-pt.com/index.php/component/option,com_remository/Itemid,34/func,startdown/id,16037/ Looks like a TOP245Y is our controller IC. I have tested in-circuit: C13, C10, C6, C9, C2, D4, D5, D6. C9 read about 10 uF and I replaced with a 470/16. Measuring 1.1k on the dot between +12 and ground, unpowered of course - but that's a simple unregulated line so I don't think it'd be the cause. I'm just using my Amprobe, which farts out above 40 uF, but it's enough for go/no go. The effects board shat out a couple years ago, and coming back around, people are saying that bad caps can do that - suspecting via trashing the +5 rail. Common culprits seem to be D7/C13, IC3 and the little BD239/BD240 drivers. Jonny 290 fucked around with this message at 19:05 on May 6, 2013 |
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May 6, 2013 19:03
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Good calls. I don't have a scope unfortunately so it's DMM or nothing. Pretty sure C25 is just to drain RF noise from circuit ground to chassis, and it still malfunctions with the frame ground snipped. I don't know much about the TL431, and am trying to figure out how it's being used here. We clearly have some sort of divider which is feeding pin 3, and I know we can count R24 out as it's just limiting the opto current but after that I'm getting lost. Not to mention the secondary side of the +/- 15 rails.....pretty confused there as well.  E: Okay i've been reading and I think i got it. When +UR rises above ~16V, TL431 pin 3 rises above 2.5v. When this happens, pin 1 starts sinking current and turns the opto LED on, providing current to the C pin. Jonny 290 fucked around with this message at 20:42 on May 6, 2013 |
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May 6, 2013 20:06
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Archive.org put up the full run of Gernsback's Radio-Electronics magazine. '29 through 03. Get your project on! http://archive.org/details/radioelectronicsmagazine
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Jun 4, 2013 18:22
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Martytoof posted:Heyy, connectorchat! The term you're looking for is "bulkhead" connector, I think. I can't find any, yes I slaved through catalogs for you. I would take a male pin header, with the shroud. Find two small L-brackets. Epoxy them on to the ends of the shroud, mark your holes on the panel and drill. Here, Paint time! 
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Jun 4, 2013 20:16
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Linear PSU design time! Okay, we have 2x18VAC coming into the PSU i'm designing. I want +/- 15VDC at up to about an amp, maybe? I'm using LM7815 and LM7915 regulators. How much capacitance, before and after the regulators, should I be ballparking? What are decent ripple limits for bipolar power supplies feeding audio gear?
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Jun 24, 2013 19:09
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longview posted:Strictly speaking you only need enough capacitance to ensure the ripple dips won't fall below the dropout voltage for the regulator. Thanks, this is great. I'm building a replacement PSU for this lovely Behringer mixer I have that delivered juice via a $0.50 switching PSU board, so I assume it was putting out some pretty noisy shitpower, I think I will be able to improve on it. Second question: I need +5V in this thing as well just for a bit of logic, am I risking unbalancing the PSU rails by hanging a 7805 off the positive rail (after the filter cap, before the 7815)? I believe current draw is minimal, under 100 mA on the +5. Jonny 290 fucked around with this message at 18:17 on Jun 25, 2013 |
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Jun 25, 2013 18:15
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Alright, building the rectifier/regulator for my mixer PSU tonight. No more dilly-dallying. Remind me the brief points on how to do a bipolar linear. Transformer center tap goes to PCB ground, I float the diode ring and then run each of those through +/- filtering and regulation? Edit: Say I wanna use 7812/7912's for my regs. I need to run a voltage divider off the output to ground, putting the 7812's ground pin at the middle, right? I calculated that a 390/100 ohm divider will give me ~3.0 volts at the junction if it gets 15 volts from the regulator out. Jonny 290 fucked around with this message at 20:30 on Jul 22, 2013 |
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Jul 22, 2013 19:45
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I.....I found a 7915 in my junkbox last night. And of course I don't have a 7815. God hates me. (Yeah, I need +/- 15V, and a 5V low current logic rail).
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Jul 23, 2013 15:43
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| # ¿ May 21, 2024 23:47 |
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Beware that the low voltage wiring for thermostats has the _worst_ poo poo trash insulation you've ever seen. You even look at the outer jacket wrong, boom you just nicked three inner conductors. I mean, I'm an old beard at this poo poo, and I had to re-strip the first end four times. Jesus.
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Aug 2, 2013 16:02
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