/ohm/ - slightly early edition

>>1081026
>tp://pastebin.com/9UgLjyND
how long has it been like this and why did nobody fix it?

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working on getting a UPS working, got it for $30 at a recycler
these batteries are fucked right? I tried plugging it in but no lights would come on, nor would it power anything out the back

>>1081074

Most likely

you can try to charge them if you want

I want to play Shenzhen I/O in real life, what's a good microcontroller programmer to get? Should I use AVR?

>>1081118
AVR is a good start for assembly, but you'll find out that asm is tedious as fuck in real life

Is there a reason not to buy a UNO R3 CH340 rather than an "official" arduino.

In australia official ones are pretty expensive. https://www.dimearduino.com.au/collections/starter-kits/products/deluxe-uno-stater-kit
vs
https://littlebirdelectronics.com.au/collections/arduino/products/arduino-uno-r3-1

>>1081029
Nobody reads the op.
You still got people asking "where do I start?" Almost every thread.

>>1081074
They have a pretty short shelf life of a few years. The batteries are a huge mantinence cost when it comes to a UPS. Just installed a 1200 amp one and it's absurd how much the replacement batteries cost

will a Hantek 6022BE be fine for just doing beaglebone/arduino stuff. looking for a less than $150AUD oscilloscope

>>1081164
They're easy to blow up. I've destroyed two at this point.
Eventually got a DSO203. Does more, smaller, haven't destroyed it.

>>1081075
>12v batteries
>average is 2v
I don't know anything about batteries but that sounds beyond repair
>>1081156
>$170+shipping for fresh batteries
this is going to kill me

>>1081026
>>What software should I use to layout circuits?
KiCad : I've been using this stuff for almost 14 years and it's a gem.
EAGLE : if you just want to nigg some nigger shit.

>What circuit sim software do you use?
Workview office : old but gold
RFSIM99 : every time I need fürherious precision in RF

>Where do I get components and lab equipment from?
Junkyard and surplus are still the best place to get fine pieces of equipment for free or almost nothing.
Also try nearby HAM fags : look for a ridiculously huge antenna at some roof, get at the door, here comes the /diynosaur

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Hey lads. I have a fifteen something year old compressor, running 230V 50Hz, not sure on how much current it draws. Made by Thomas Industries, model 603-12. It's very similar to ones I see on ebay going for tens of dollars. The one pictured is from an ebay auction, 600-8.

Quite some time ago, a lamp switch has been wired up to the plug-end of the wire, and it seems rather shoddily done. The contacts for the switches seem fine, but I am worried about its possible dangers. The switch does spark up every time contact is made, and the spark does come out of the rocker's sides. The current switch is made of plastic, and it already has cracked from its age. The whole thing works, I would simply like to replace and rewire the switch. I have five or so feet of 10 AWG I am planning on using for the wire, but I am not sure on the kind of switch.The rest of the original wiring seems sound, a simple two pin configuration.

What kind of switch would you recommend for something of this nature? Clearly something rated for 230V, but I don't want to go overboard. I don't want to spend too much on it, just a quick touchup. Soldering would be fine, too.

>>1081201
Doesn't your compressor stops when it's full ?

If so, get rid of the lamp switch and the actual cord, and wire instead a brand new cord.

You don't need a lamp switch if that fucker auto-stops when full, neither to let it plugged when you are sleeping...

AND FOR GOD FUCKING SAKE, MAKE YOUR OWN THREAD INSTEAD OF FUCKING THIS ONE

>>1081143
IMO CH340 is the most painless usb-serial converter I encountered, so I can recommend it. Don't get FTDI shit, or that 2101 crap, the drivers for those suck harder than a black hole.

>>1081143
Official Arduino boards should not be bought. They only reason to buy them is to support the platform/community/company.

>In australia official ones are pretty expensive.
They are expensive everywhere.
Chinese clones from AliExpress perform just as well, but the quality control is less strict, so bear that in mind.

>>1081216
Not him, but I think he's fine posting here.
Would you rather a stupid question bump off a thread on diy or be contained here?

>>1081192
I would figure out how they are connected, its likely a series parallel configuration where four sets of two are connected in parallel. You might be able to find two fairly large batteries for cheaper than the 8 smaller ones in your picture. Depending on how it is wired up you might be able to get away with it.

>>1081259
I could get away with 4, it's a 48v 'pack'

lads, i don't feel like i've learned if i don't make things the hard way. am i being stupid? y/n

basically i want to make a power supply and i want voltage and current readout, but i feel lesser for not making my own voltage and current readout instead of a ready-made chinese one that i can simply plug in

>>1081232
i have like 10 different arduinos from aliexpress. they all work just fine.

>>1081273
I also keep hearing "I ordered X things and some of them were DOA!" so I felt inclined to add a little precaution note.

>>1081272
Are you going to wind your own transformer? What about caps?

Commercial PSUs often use off-the-shelf meters.

>>1081280
lol, not quite that level of crazy
yet

>>1081272

There's nothing wrong with using a pre-made readout meter, but there's nothing wrong with designing your own readout, either. It's pretty easy to do 3-digit digital voltage readout with an arduino and an opamp, and whilst current measurement is a little trickier (because you need to handle fairly high common-mode voltages for high-side current measurement).

Im trying to get started with the nRF51822 but cant seem to get queued writes working. Anyone here ever used it?

>>1081283
well i wasn't thinking arduino. i was thinking more op amps and schmitt triggers and flip flops and decade counters
I dont' know how i'm going to do current sensing yet though

>>1081283
>>1081316
It also got me thinking because I wanted to build a function generator too

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>>1081316
> i was thinking more op amps and schmitt triggers and flip flops and decade counters

Not that guy, but I think I love you. uC's are not without their place but you have no business calling yourself an electronics hobbyist if you do not know how to work with discreet logic. Stay the course you magnificent bastard.

>>1081321
>uC
Sorry to look stupid now, but what's that?
>I think I love you
I love you too anon
I'll try to stay the course lol. It occurred to me that i may try to build a discrete switching element (it'll probably be crude) with a diy square wave, diy voltage ramp? and other bits. I still have to read up on how exactly switching power works. I need a tracking preregulator though and my power supply project won't really reach the spec I want it to unless I can do it (trying to push a few amps on a linear supply with 35V input and 1V output is a thermal management nightmare)

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>>1081322
>but what's that?
a microcontroller. You know, like micro in SI.

>>1081328
yeah i figured the u was for micro. just didn't know what the C stood for. i get it now hah. derp.

but yeah i dunno. fuckin voltage readouts and current readouts with a differential amplifier (would probably have to use a 0.1ohm resistor to handle 10A load).. buncha hairy shit. and i still want/ need my switching tracking preregulator too

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What would you call this type of toggle switch that doesn't latch? You know, so you click it and it automatically returns back to position rather than stay where you put it.

>>1081341
Momentary toggle switch

>>1081342
Thanks m80

>>1081164
get yourself a used analog one off ebay. That's what I did. make sure it is described as working, or you're gonna have to fix it yourself. Or use it for a paper weight.
I bought a shitty one that works for ~130 USD. very basic features. CH1's volts/div was screwy. Took some MG chemicals 409B contact cleaner to the rotary selector contacts and works perfect now.

>>1081193
>KiCad
program sucks
extra complicated and gotta jump through 50 hoops to make it do what you need

>>1081381
That's true for every layout software I used.

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What search terms do I use when I want to find this type of wire? It's just two enameled wires from a pair of headphones, would be nice to not just have two loose cables but actually have them together in one wire.

>>1081438
>It's just two enameled wires

no it isnt. it's a kind of litz wire consisting of several insulated wires braided together (around a nylon core for strength) originally used for telephone handsets, coz it can be flexed for years without breaking.

>>1081467
Alright, good to know.
Any idea on how to find it?

>>1081471

google ''replacement headphone cable''

me, i'd just check my drawers, coz i probably have a dozen old heaphones with useable cables. especially old Sony headphones, like the MDR-64; they have cables that last forever.

>>1081474
No such luck, search term only yields aux cables. Thanks anyway.

>>1081474
Okay, I just found out they're also in earplug cables.

Soon to be Comp Engineering student (have a BA relised it's not what I want to do).
How do I begin IC/MCU programming? I think I need a serial programmer or something like that but really don't know what I need or anything like that.

>>1081478

serial programmers are only for very old school crap like PICs. nowadays any decent dev system will program thru USB. you just gotta choose whose gang you gonna join: RasPi, Odroid, Arduino, Udoo, Intel Quark D2000, etc. etc

>>1081026
I just ordered "how to diagnose and fix everything electronic". Want to rebuild an old console radio as a winter project, just because I like listening to radio and records and need something to do. Uh, wish me luck I guess.

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Looking for electrical advice, and this seems like the ideal thread.
I am trying to create a homemade sodium vapor lamp. The battery I currently have is a 12 volt 18 amp hour VRLA battery. The bulb I plan to use is a 120 volt, 35 watt high pressure sodium lamp.
I could hook up the battery to a 120 volt AC converter, and then to a ANSI 76 ballast, which connects to the bulb.
Would this work?
Also, what precautions should I take regarding the bulb housing?
Thanks.

>>1081316

There are a few 74-series DVM-on-a-chip type dealios you could use, otherwise you could hook an oscillator and a binary-to-7seg IC to a brain-dead parallel-output ADC.

For current, IIRC you can just put a low-value resistor in between the pass transistor and feedback point, then use a diff. opamp configuration to pull it to ground and amplify it to 1V per A. The only hard part is designing a diff. amp that's suitably close to linear at high common-mode voltages.

>>1081481
>PIC
>old school crap
u wot m8

>>1081481

None of these are uCs.

>>1081478

Get an mbed, there are lots of them and they're all better than Atmel shit. Shop around and buy one with a datasheet/TRM you like, don't rely on the built-in libraries being very good.

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Figured this was the best place on the innanet to ask. Are Gardner Bender tools any good? Shit tier, fair tier, good tier, great tier, or god tier?

>>1081492
>designing a diff. amp that's suitably close to linear at high common-mode voltages
I haven't read anything about that just yet. Can you explain anon?

>>1081490
That reminds me, i have always intended to make a michelson interferometer to use as a measuring tool of sorts. a sodium vapour lamp would be great to test it and see the spectrum it produces

>>1081509
I have handled them at the hardware store before.
Stuff is pretty poor, typical cheap imported stuff. Its price reflects its quality

Just another brand that used to be great in the 60s-70s that died and was sold to chinese importers

>>1081524
I hate when that happens.

>>1081524
>>1081526
maybe i don't get the draw, but i'm still using cheap ass pliers n shit...
why do these matter?
the most expensive tool i own other than soldering iron is the self adjusting wire stripper

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>>1081534
Cheap tools can work fine, some can be of very poor quality and work like shit. Ive had cheap diagonal cutters that wouldnt cut shit. Ive had cheap pliers where the jaws dont align correctly, and the cutters were shit. Ive had cheap wire strippers that got dull and wouldnt strip anymore.

I actually considered buying the GB brand crimpers, till I read the reviews. Look at the pictures. Pic related, the QC of these pieces of shit. Itd crimp, but it would be shitty.
https://www.amazon.com/Gardner-Bender-GS-388-Crimping-Electrical/dp/B00079LN1Y

I prefer to spend more money in the first place, and get tools that should last me a very long time.
Im not /ohm/, but im sure people in here have a similar ideology when it comes to electronic specialty or testing tools.

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just a quick reality check...
is this ok?

>>1081536
Ah fair enough. I know the value in a good well built tool, but at least for my amateur work i haven't really found a need nor desire for them yet. the self adjusting wire stripper is a god send though. As is the temp controlled soldier iron which heats up in like 30 sec instead of 3 mins.

I do agree that I would rather get something a bit nicer that will work better and last longer than something cheap that MIGHT last (but might not).
I've had pretty good luck with diagonal cutters though (the one pair I've owned. why are they called DIAGONAL cutteers anyhow?). luck with needle nose pliers wasn't so good (spring mechanisms were shit) but that's everything notable in my purchase history

>>1081557
I'd probably still put a resistor on the end of each row. not all LEDs drop the exact amount of voltage or consume the exact same amount of current, so you might get uneven lighting and loading

>>1081481
Arduino is actually programmed over serial with an adapter IC, and the others you listed aren't microcontrollers. Serial is much nicer than shit like JTAG and all those custom programming protocols used by various chips that often require high voltages and stupid expensive dongles that never work.
>>1081494
Are you trying to deny that PIC is garbage? The newer MIPS ones might be ok but the actual PIC isa is retarded.

>>1081557
You need a current limiter (resistor (or constant-current source) for each chain. Just limiting the current at the PSU won't work, as there's no reason for the current to divide equally between chains (chains with a lower total Vf will get more current).

>>1081496
>get an mbed

anything good for a newbie?

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>esp8266
>easyesp
>mosquitto
I managed to get it working but what about gui? All of those "home automation" servers looks like complete overkill. I just need temp display (web-based or android app), few digital IO, notification and timers.

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>>1081521

I can't find a good pic of the topology I'm thinking of, but basically you use a circuit like pic related and replace the battery with your power supply, but instead of taking the feedback voltage from the output of your PSU you take it from the input into the load. That way you can sense your current but don't have any voltage drop on the output from the current sense resistor.

>>1081570

MCUs are always a matter of personal preference, but I've had success using the FRDM-KL25Z (http://www.nxp.com/products/software-and-tools/hardware-development-tools/freedom-development-boards/freedom-development-platform-for-kinetis-kl14-kl15-kl24-kl25-mcus:FRDM-KL25Z).

>>1081570
Teensy 3.x?

>>1081844
If it's for power supply current sensing/limiting, there's usually nothing which forces you to use high side sensing. You could just put the sense resistor in series with the ground return, as long as you choose the place correctly.

>>1081883
You need to ensure that there aren't any alternate return paths (e.g. via signal grounds etc). Which typically means that the DC input has to be floating so that you can ground it after the resistor.

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I'm looking to design and build a VLF metal detector.

I have the general gist of how they work but is there anything wrong with my block diagram?

A lot of designs I've seen has the receiving coil much smaller than the searching coil, Where can I find some maths or something to develop the maths to this?

Also ( last question ) - Should I put an integrator and a VCO at the output stage to seperate the operating frequency to the hearing frequency or can i simplify it by using something like a strong 1kHz wave?

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I've finally got my first project into a prototype version.

>Set of RF-linked buzzers.
>Buzzer 1 lights up red/green to show if buzzer 2 is off/on, keeps doing this on a slow cycle.
>Pressing a button on Buzzer 1 will make buzzer 2 flash and buzz( via piezobuzzer) until a button on Buzzer 2 is pressed.
>Meanwhile, Buzzer 1 will flash a yellow LED in between the two buttons being pressed.

It shouldn't have taken so long (~5 days), but learning arduino code from scratch and styling the loops to achieve what I wanted was pretty tough.

Now onto a final, arduinoless version (with an atmega, timer crystal etc.)

>>1081201
Literally like every single switch is made for 230V 2X amps, 115V X amps. Switches are not something advanced or complicated, you'd end up spending more on a box or something if you did it /diy/.

http://www.ebay.com/itm/In-line-ON-OFF-Table-Lamp-Bed-Light-Cord-Controll-Switch-3-Core-Cable-250V-AC-6A-/401102740559?hash=item5d63961c4f:g:pF4AAOSwAvJXB1Mp

>>1081883
>>1081889
>If it's for power supply current sensing/limiting, there's usually nothing which forces you to use high side sensing. You could just put the sense resistor in series with the ground return, as long as you choose the place correctly.
high side is before the regulator and pass transistors, is that correct?
And what do you mean have the sense resistor in series with ground return? Why would that be any different than putting it on the high side?

>You need to ensure that there aren't any alternate return paths (e.g. via signal grounds etc). Which typically means that the DC input has to be floating so that you can ground it after the resistor.
Signal grounds? anon making the bench power supply here btw. Its supposed to be 12V from an old computer power supply (which I think means it isn't floating, since they're typically earth grounded), DC-DC boosted to ~34.5V, fed into a linear regulator and pass transistors. Still haven't decided if i'm going to go the hard way and make a nseparate voltage and current sensing board with logic ICs and op amps, generating voltage ramps n shit or what. And the bigger problem now is I've yet to figure out how to hack my drok boost converter so that i can make it be a tracking element instead of just spitting out 35V

>>1081901

5 days is actually good

my first projects took me months

now that I'm more experienced If I complete 1 thing per month I'm more than happy

>>1081220
What is wrong with FTDI, we often use their usb to serial or i2c converters without any problems?

>>1081940
"High-side" means sensing from the positive rail. It does not have to be before the pass transistor, but it should be before the point you take your regulator's feedback, so that the voltage drop in the sensing resistor won't ruin your regulation.
Putting the sense resistor in the ground return has the benefit that your current sense circuit does not need to handle the varying and relatively high output voltage in addition to the (small) current signal. The main drawback is that the ground of whatever is feeding your regulator is different than the "output ground" on your PSU's front panel.
This is not a problem when the input power source is floating (like transformer + bridge + caps), but it can be a problem if you use some ready-made switcher which has its output ground connected to the earth ground.

>>1082093
what do i need to know to understand this

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Is there an easy, non-destructive way of reducing the RPM of a 12v 2-wire DC fan? Basically, it runs at full power and is too loud, and the hardware it plugs into is unable to regulate current.

>>1082163
add a resistor to the line

>>1082163
You may need to use PWM.

Modern fans use a "brushless DC" motor, which is a multi-phase AC motor driven from an electronic speed controller.

The 12V supply is filtered to produce DC, and the PWM duty cycle measured and used as an input to the controller.

Thus, it emulates how a conventional brushed DC motor behaves when driven from PWM (which is how PCs have always controlled fan speed).

It won't necessarily emulate how a DC motor behaves in response to varying DC supply voltage, so varying the voltage with e.g. a resistor may or may not work.

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>>1082100
>what do i need to know to understand this

you need a somewhat deep understanding of general electronic design that you acquire from 1000's of hours of study and experimentation.

and you can ignore most of that post coz current limiting makes the most sense when it's on the positive rail. putting it on the negative wire is just asking for trouble.

as for how best to implement current limiting: just use a chip that does the job for you. for example, there are millions of LM723 designs around for you to implement. why re-invent the wheel?

>>1081891
bumpin' this.

>>1082228

VLF is old-school design: your grandmother's kind of metal detector. you dont want that. you wanna design (i.e. copy) a pulse induction machine. coz -- as your grandmother knows -- deeper is better.

>>1082235
kek'd

Hey /ohm/, third year EE student. Would "The Art of Electronics" be a good book to pick up for review/learning/design sorts of stuff? I've done a ton of analysis in my classes but little design or projects and I feel that my lack of practical knowledge is a huge deficiency.

>>1082310
Did you even bother reading OP?

>>1082320
ee students start reading & comprehension their senior year

>>1082235
they're both in use and they both have their benefits
I wanted to be able to discriminate

>>1081143
i bought a genuine pro mini because i needed hid support, which ch340 won't do.

Hope this is the right place to ask. I want to make an LED tail-light for my motorcycle to increase conspicuity. It currently has some chinkshit light on it with very little contrast between running light and brake light.

I've thrown some LEDs together for shitty school projects before but never made anything that really holds together well. I figure I can just solder some red LEDs into a board like pic related but I don't know about choosing the right LEDs and resistors and shit. Just looking through ebay I saw a pack of 140° LEDs with brightness of 12000mcd but I have no idea how bright that would actually look. Would a 3x3 array of those be at least as bright as your average car brake light?

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>>1082622
forgot pic

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>>1082622
The basic design of pic related is pretty solid, as long as it will be waterproofed, But wouldn't upgrading the chinkshit light be a better idea? If you hook up a current LED to a battery and measure the current and voltage across the LED, you'll be able to compare it to the current/voltage curves of LED datasheets and find one with a few times more brightness. And keeping the light's original housing would eliminate the need for waterproofing issues down the line.

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How would you go about remotely controlling a space heater like pic related?

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>>1082650

get one at home depot that's rated for the wattage (or amperage) of your gadget. other possibilities include X10, Insteon, etc: https://en.wikipedia.org/wiki/Home_automation

>>1082689
I wanted it to connect to some custom IoT shit (maybe esp8266/NodeMCU type stuff) so that I can control it from outside the house or have it turn on and off based on some preset parameter.

>>1082714
Well, then get a relay, some IoT shit, and connect them all together.

>>1082714

that doesnt preclude your use of RF or Powerline technologies to carry out the actual switching. just use you IoT stuff to activate the remote buttons using a transistor or tiny relay in parallel with it.

>>1082714
Solid state relay. But if you don't have experience with line voltage I'd probably get something more turnkey and UL approved.

>>1082622
140° is probably too wide for a tail light. The wider the angle, the less bright they will appear.

12 cd = 12 lm/sr.

A 140° (±70°) cone has a solid angle of 2π(1-cos(70°)) = ~4.13 sr
so the LED will have a total luminous flux of ~49.6 lm.

A typical 12V halogen bulb has a luminous efficacy of 24 lm/W, so each LED would be roughly equivalent to a 2W bulb.

But that's assuming that the 12 cd figure is an average over the cone, not the peak at its centre.

And assuming that it's an accurate reflection of normal operating conditions, not "the LED is capable of surviving for 10 milliseconds at that power level, provided that it is immersed in liquid nitrogen" (i.e. typical "lies, damn lies and data sheets" practice for measuring headline figures).

IOW: the only way to find out how bright they are is to test them.

Does anyone know anything about vintage radios and supplying capacitors for them? I have an amp from the early 60's, and I'm trying to find replacement caps for it. There are some that are voltage rated in DCWV, which I know stands for direct current working voltage, but others are rated in VCDW. Is it just referring to the same thing? Or is it a different rating of some sort?

>>1082969
> others are rated in VCDW.
You mean VDCW? That's just rephrasing: Volts DC (Working).

Nowadays, they'd just say "V".

I suspect that stating DC was just to emphasise that they shouldn't be used for AC applications (e.g. motor start/run capacitors).

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sup /ohm/

A while ago I got a couple of free broken screens from work that I though I could fix.

I think the t-cons are fucked and I don't have the money or the willpower to replace and/or fix them.

I'm adding an enclosure, removing the screens and using the backlight as a lightbox/drawing board.

Tell me.

Is pic related going to fuck my eyes up?

also sorry if the carpet triggers you.

>>1083350
maybe add some semi-transparent layer that will dim it a bit, it seems quite bright

>>1083353
A piece of sorted frosted glass was my first idea.

Don't have any at the moment, so I guess I'll wait a little before starting to use it.

Don't want to go more blind.

>>1081477
>also in earplug
>earplugs aren't headphones

Are muricans getting more retarded each and every month or what?

I bought this temperature controlled relay to control the fans in a project, but it only has 1 probe.

If I crudely wire 2 probes together will the controller just read the higher value from the two?

I want the relay to turn on when either the transformer or processor get over my threshold temperature.

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>>1083456
forgot pic

same one that bigclive reviewed recently

I've seen some hate against FTDI chips in this and other threads and I was wondering why? They may nog be the cheapest but we use them in various devices that we design and produce, mostly as usb to serial/I2C convetoes for easy communication with our hardware/software.

>>1083481
are they the same people that got so tired of knockoffs they made their drivers not work with the counterfeits?

is there a way to take an existing square wave and slowing it down by a certain factor - like a 555 circuit or something? turning a 200hz square wave into a 100hz?

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For same inductance/current rating, is there a reason to pick ferrite core inductor over non-ferrite one? Trying to figure out the difference between these two

>>1083486
look up frequency dividers. For simple cases you can just use binary counter

>>1083481
Yeah, it's weird.
Usually people bitch against the Chinese chips like the CH340 for their shitty Windows drivers and recommend getting FTDI chips instead.

I never cared because all these chips have decent drivers under Linux.

>>1083487
All I know from my classes is that ferrites are amazing materials for inductors and transformers because they are very soft magnets and pretty much nonconductive so they experience no magnetic losses through eddy currents. So if I had to pick one I'd pick the ferrite one. Dunno if it makes any practical difference for designing circuits though.

>>1083488
>frequency divider
thanks a bunch!

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>>1083487
There sure is, see "Comparison of Core Materials":
http://www.we-online.com/web/en/passive_components_custom_magnetics/blog_pbcm/blog_detail_electronics_in_action_72001.php

Basically for a ferrite core when you are operating 20MHz and up (some switching converters do this) your inductor becomes saturated (see image).

I want to cool a board with my own fan, but the device refuses to turn on without its stock fan plugged in which uses a proprietary connector. (I'm drawing power for my own fan from the power supply, not this header).
Can I just stick a resistor or something across the pins to trick it into thinking the fan is there?
How many ohms?

>>1083599
A lot of proprietary devices use a custom resistive network to keep others out. You'd need to probe the stock fan with an oscilloscope or possibly an I2C analyzer to be able to mimic it.

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>>1083350
>>1083353
>>1083354
Ok managed to source some glass
>£5 in the bargain basement of IKEA 20 miles down the road

I've decided that I'm making a light desk instead.

I have two of these and I'll put them side by side with a little switch for each.

Praying for:
>Somehow getting one if the salvaged power boards to work with both monitors
>Somehow getting one inverter to work similarly
>Being able to drill holes in the glass without it cracking

This should be fun. I don't often play with electronics and power electronics.

If anyone is interested. The output from the power board into the inverter is labeled 18v. No idea what sort of current draw, but I'm expecting it to be quite stable given that these things won't be on long and shouldn't heat up too much.

File: i'm a retard.png (8KB, 553x290px) Image search: [Google]

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Hi /ohm/,

Was wondering if I could get some help with this question, it's pretty simple but I can't get my head around it.

>>1081846
>Freedom boards
muh nigga. I worked with a FDRM-K64F last semester.
Though I wouldn't recommend >>1081570 starting with these. Too many registers to keep track of, somewhat buggy IDE (CodeWarrior, which I think it's based on Eclipse) and IMO little community and confusing documentation.

>>1083610
Here's my logic so far:

8V drop across the variable resistor when it's 10K. 1V drop across R2, 3V drop across R1

Current is 0.0008A -> R2 is 1250, R1 is 3750

File: IMG_20161113_190302.jpg (3MB, 4160x3120px) Image search: [Google]

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>>1083610

>>1083618
This is correct

I'm bored at work, so he's one way to do it via voltage divider equations

>>1083610
From a simple voltage divider you know that for the minimum resistance on the variable resistor will give
V0 = 12V * R2 / (R1 + R2 + 10k) = 1V (1)
Analogous to (1), the maximum resistance will give
V0 = 12V * (R2 + 10k) / (R1 + R2 + 10k) = 9V (2)

Now you just solve (1) and (2).

Answer is >>1083618

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>>1083626
>>1083629

Thanks for checking over my work anons, wasn't 100% convinced I was correct.

Looks like it's a long road ahead before I become a EE.

>>1083618

V0 = r2+pot / R1+R2+10k

solve for v0 = [1,9], pot = [0,10k]

>>1083630
Why don't you just check your results by applying the calculated current and resistances to see if you get the expected 1V and 9V?

>>1083599

if the fan has markings for voltage and current, just do ohm's law: R=E/I. otherwise, measure E and I first, then calculate. if it has more than 2 wires, then it may use some signal from those extra wires, so this may not work.

>>1083637
Even if it only has two wires, you can have a differential signaling protocol over a power connection.

Does anyone know of any resource that is a good introduction to vacuum tubes and stuff related to them?

>>1083594
To me it seems like ferrites would be always worse due their tendency to saturate. I guess their advantage is slightly lower cost?

>>1083774
Most switching power supplies don't run more than a few MHz, so ferrites are fine for most applications.

>>1083483
They didn't just make their driver "not work", they made it re-flash the USB vendor/product IDs.

>>1083774
First, it's not saturation. Second, the only inductors which /don't/ drop off at high frequencies are air-cored inductors (effectively, all inductors behave like air-cored inductors at sufficiently high frequencies, i.e. the core stops having any effect).

Third, I've never seen a switcher operate at 20 MHz. Even 1 MHz is fairly high (but not unheard of). Higher frequencies let you use smaller inductors/transformers: a given core has a given energy capacity (which tends to be proportional to size), and the maximum rate of power conversion is the core's energy capacity per cycle. So higher frequency means higher power for a given core size.

But then you have a dilemma: if you don't switch fast enough (which at high frequencies can require several amps of gate current), you lose efficiency due to time spent in the linear region. And if you do switch fast, you have more EMI to deal with: steep edges correspond to high-frequency harmonics, meaning that you have components at many times the switching frequency, and at relatively high power.

>>1083793
Ah:
core saturation = related to current
core losses = related to frequency

From my notes ferrite cores also come in many flavors, for my DC-DC converter I could not use an inductor which had a Carbonyl based core as it became too lossy >400kHz.
Do you know if there is a lookup table for different ferrite cores?

>>1083809
Yes, there are few (common) basic ferrite types and different manufacturers make their own variations of those. TDK/Epcos is one well-known maker. Their lineup: https://en.tdk.eu/tdk-en/529404/products/product-catalog/ferrites-and-accessories/epcos-ferrites-and-accessories/ferrite-materials
You can also check Fair-rite's and Ferroxcube's tables.

>>1083793
I saw an article about a 100MHz switcher couple of years ago. It was a research prototype and it certainly looked like it. But yeah, I think I haven't seen even 10MHz real world switchers.

>>1083774
Ferrite is a relatively expensive core material. It is used at higher frequencies due to lower losses.

File: DEKO-60W-220V-Temperature-Adjustable-Electric-Welding-Solder-Soldering-Iron-Handle-Heat-Pencil-Tool.jpg (59KB, 800x800px) Image search: [Google]

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Any anons tried these 6-10$ soldering irons from AliExpress?
They seem like a great deal for me, since I'll only probably need it for a short period of time, so its longevity isn't really important. I just want it to work well for a week.

>>1083791
Which is reasonable since FTDI is paying for those ID's and the knockoff chips steal those ID's. They could have taken the gentleman's road and just stopped communication between the drivers and a fake IC but I do understand that they wanted to fuck the copycats over, and from what I have seen it works because the knockoff arduinos use a different IC now.

Since we are talking about inductors, I ripped lots of toroids from switching powersupplies, can I repurpose those for my own switching powersupplies? Some cores have different colours such as blue, white, yellow etc.

>>1083958
The cost of IDs isn't a factor here. The issue is that Windows doesn't include generic USB-CDC drivers, so everyone selling USB-serial devices has to supply their own driver, even though they all do exactly the same thing. Given that there's a high chance that any given system will already have the FTDI driver installed, identifying as an FTDI device avoids the need to get your driver onto the system.

>>1083945
I remember that some anons on the chink shit threads on /g/ got them, and said that they were decent. The temperature control ones seem really gimmicky to me though.

how to i calculate how much voltage i need to overcome resistance? i want to make an electric furnace using nichrome/kanthal wire and a microwave transformer and need to know what ratio to rewind it so that i can give it maximum amperage while still having enough voltage to be able to pass through it.

>>1084108
V=IR?

>>1084108
Two pieces of advice:

Firstly, remember that the resistance of the wire will be significantly greater once warm, and you may not get the maximum current and therefore maximum power output once the furnace is up to temperature.

Secondly, using a microwave transformer is not necessarily a good idea. The transformer steps up from 230VAC to 2000VAC (at least in australasia) and incurs some losses as it does so. Assuming the transformer is lossless, if we say the voltage is stepped up 8x, then the maximum current is stepped down 8x. You will still only be able to pull the same power out of the socket regardless of the voltage, and the less lossy the better. By stepping the voltage up, you will need 8x more resistance wire because otherwise, through I=V/R, the current will be 8x greater through the same resistance wire than if you used it across mains voltage.

On the other hand, if you are using the high-current transformer mod, then you could get away with using significantly less resistance wire, making the furnace potentially simpler, though the losses from a high-current transformer are quite a bit higher.

You appear to have a misconception about resistance and voltage, so I'll clear that up for you. Ohm's law states that the current flowing through any conductor with resistance R will be equal to the voltage across the wire V divided by R, hence I=V/R, or more standardly, V=I*R. A current will always flow through a resistor regardless of the voltage or resistance because a resistor is still a conductor, but the current will be very low if the resistance is very high compared to the voltage. Inversely, if you put a high voltage across a relatively small resistor, then the current will be very high. If this high current is what you are aiming for, then be sure to make sure you don't reach the fusing current of the wire, which is the current at which point the wire will melt before it can dissipate the heat. A rule of thumb is to keep wall current <20 Amp.

>>1084141
Source: I own a couple of microwave transformers myself, one of which is a high-current mod.

>>1084142
not him, but do you use it to spot weld?

>>1084117
so v = 15 amps (current drawn by primary coil) * 20 ohms (resistance for a test piece of wire)? i would need 300 volts? that cant be right.

>>1084141
i thought heating wire dropped resistance as it heated up? either way i would be rewinding the transformer because i know 2000 vac and like 3/4 of an amp wouldnt do shit for heating it. so then with i=v/r it would be (see above for values) 15=v/20? or what?

Anyone bought electronic components from alibaba, dhgate, etc? Any advice one what to trust or not? Also any good AVR programmers on there for cheap? (or anywhere?)

>>1084162
Just search for what you need on AliExpress and sort by number of orders, you'll probably get a good thing for a good price.

>>1084141
He explicitly said:
> need to know what ratio to rewind it
I.e. he's not going to be using it to step voltage up.

MoT's are often used for welders because they have some leakage inductance which acts as a ballast and limits current. They're often used for DIY projects generally because they're readily available and have reasonably high power ratings.

>>1084155
> so v = 15 amps (current drawn by primary coil) * 20 ohms (resistance for a test piece of wire)? i would need 300 volts? that cant be right.
The power dissipated by the wire will be the secondary voltage times the secondary current, which will be approximately equal to the primary (mains) voltage times the primary current.

> i thought heating wire dropped resistance as it heated up
For conductors, resistance normally increases with temperature. But the effect is less pronounced for Nichrome than for most other metals.

>>1084108
First, the total power will be limited by the transformer core (and primary), and won't be affected by rewinding (although the new secondary will need to be able to handle the current).

Any given wire thickness will have a maximum current and a given resistance per metre. Power dissipation is W=I*V = I^2*R, so the properties of the wire tell you the maximum power dissipation per metre, which tells you how much wire you need.

Once the length is known, so is the resistance, and V=I*R gives you the secondary voltage. A transformer steps voltage up or down by a factor equal to the ratio of the number of turns. If the secondary has half as many turns as the primary, the secondary voltage will be half the primary voltage. So you'll need to know either the number of turns on the primary, or the number of turns on the secondary at a given voltage (note: this needs to be the RMS voltage, not the voltage of the rectified DC fed to the magnetron, which is roughly the peak voltage).

>>1084155
>>1084224
Any hand-wound coils will be lossy and not worth doing over simple mains power unless you have a shortage of resistance wire, unless there's a reason you want to use one?

There are some wire materials that decrease resistance as they heat up, such was the problem with the early carbon filaments in Edison's prototypal lightbulbs, but most, if not all conductors, will increase resistance with temperature.

>>1084148
I've never managed to get spot welding to work, but you need to fix a couple of thick copper (or silver I guess) electrodes to the end of the wires (2 gauge or so) so that there is very little resistance in the connection. Big eye connectors screwed to offset terminal lugs with short lengths of 6 gauge solid copper wire in them is probably a good method, and solder the joints if you're getting any heat in them. I chopped my transformer in half to salvage the secondary coil, but it means the casing rattles when turned on, so if you have any suggestions on how to fix this I'm all ears. I would recommend destroying the secondary coil with a hacksaw instead and poking it out with a screwdriver to save yourself the trouble. (The King of Random has a good video on this.)

>>1081331
>u

>>1084398
>2016
>people still don't have a Greek keyboard to type μ

File: Sharp P-951 C Series main board 1.jpg (3MB, 3664x2748px) Image search: [Google]

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So, I opened a portable vinyl disc player, and it has this main board. The other "board" isn't even a board, but 2 "rails" with 5 components attached.

I opened because it was not spinning correctly, it was as it had no sufficent power. I noticed the 1950s~1960s capacitors are not in very good state, so I will replace them.

But should I replace only them? Should I worry about the other components, like transistors, diodes, resistors, transformers, etc?

By the way, this board is the amplifier, right?

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>>1081074
I have the same ups at work. One day it started failing and we didnt do shit for months.
They looked pretty toasty when we opened the pack.

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>>1084702
It almost popped.

Reposting what I asked in the the sqt, since i got no answers:

Is there a cheap (<$20) AVR usb programmer that works? Would it be reasonable and cheaper to just make something like this:

http://www.instructables.com/id/AVR-ISP-programmer/?ALLSTEPS

and then use that to program a mcu to make a more advanced, usb compatible programmer?

>>1084764
Get an arduino or a teensy, you can upload a ISP programmer sketch and use it as a programmer.
I think a teensy is just below 20usd, an arduino might be slightly above 20usd.

>>1084767
>an arduino might be slightly above 20usd.
lul
AliExpress, Arduinos start at 2$. Teensy is the dumbest choice for a task like this.

>>1084768
You are right, i only checked the official site.

>>1084764
This works fine:
https://www.aliexpress.com/item/51AVR-SCM-Download-Cable-USB-ASP-ISP-Aluminum-Colorful-Shell-Download-Red-Blue-Indicator-Lamp-Support/32345564653.html

There are also a little cheaper ones that don't have a nice metal case.

Or if you have a Pi or similar, you can also make a (slow) programmer with it

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>>1083945 #
If you're going to buy chink irons at least don't buy the ones with a flimsy tip with shitty thermal mass. Those are painful to use since the tip cools down whenever it touches a big blob of solder, also I've had bad experiences with shitty tis that are eaten away and useless after a coupke of hours of soldering.
Don't expect the element to last too much.
I'm going to buy and use pic related until I have enough money to buy a Hakko.

>>1084791
Careful, some irons with those temperature knobs don't actually keep constant temperature.

For a cheap basic stationless iron, the Chinese 936D is a good option.

>>1084795
I already expected the temperature control to be just a power regulator without any kind of feedback.
Temperature isn't crucial in my case.

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What is a cheap way to generate 3 floating voltage supplies?
There's some cheap little transformer drivers from linear and maxim, but how to get 3 isolated outputs with a small footprint?

I found a wurth transformer with 1:1 ratios and 3 separate windings, do I just connect the driver side in parallel? Then the transformer AC output, can I rectify both wires and just have a single wire floating output or must the transformer be grounded?

Do I need separate winding or is there some way to split outputs using diodes?

>>1084834
If they all need to be isolated from each other (and from the primary), you need multiple windings. You only need one primary.

You need to use full-wave rectification on the secondary or the secondary current will have a DC component which will saturate the core.

Schottky diodes have a lower voltage drop than silicon.

The higher the switching frequency, the smaller the transformer core needs to be for a given power.

I have an end goal of being able to design and create my own prosthesis.

It needs to be able to take readings from EMG, convert it into values a small computer can understand like 1 for flexed 0 for relaxed, so if 1 then stall torque on dc motor if 0 then cut current.

Best book to go with, or books? Should I just go to beginner and head on from there?

>>1084879
Hue I asked the very same question a few months ago, if you want technical details it's best to have a look at the many masters/PhD online (can send you a few links once I get back from work). Datasheets for instrumentation amplifiers are also good like the TI INA826, instrumentation amplifiers is something you will end up using for EMG so might want to read up on that too (high input impedance is key for sensing EMG).
Also before you get your hopes up at best you can use EMG to sense very simple muscle movement, as in don't expect the row of contacts on your arm to be able to distinguish individual finger movement.

Still it's a super fun project to take on, lots of things you can learn about electronics.
The progress on my one has come to a halt (http://www.eevblog.com/forum/projects/emg-amplifier-circuit-decoupling-caps/msg995730/#msg995730), I found that INA827 had too low an input impedance and that my OP amps & full-wave rectifier did not behave well when supplied with a single rail, so plan to revisit it when I have time. Only advice I can give is start off with a circuit you know is going to work before you play around with variables.

>>1084616
I'm pretty sure that you are going to need to only replace the capacitors. The rest of the components don't really go bad. The only reason that the capacitors go bad is because there is a wet electrolyte in them that dries up over time.

There is a possibility that one of the other components has gone bad, but that is very unlikely, and your best bet is definitely the capacitors.

File: Sharp P-951 C Series main board 2.jpg (2MB, 3664x2748px) Image search: [Google]

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>>1085146
Thanks for the reply...

The sides with the tips are the positives, or the negatives?

>>1085147
To be honest, I'm not really sure. A lot of capacitors used in early electronics were not polarized, so that might be the case here. Many of these capacitors were used in audio equipment, and had one side that was marked with a band or something that would denote which side was closed off using a metal piece. In certain circuits, this notation was important because placement helped with sound. But like I said, I'm not really sure, and you'll definitely want to double check that.

Also, did you make sure that everything that moves is lubricated properly? I don't know how this turn table is set up, but proper lubrication might help

>>1085173
>A lot of capacitors used in early electronics were not polarized, so that might be the case here.
I think it depends on the technology of the capacitor. I think those are aluminium electrolytic ones, so they should be polarized.

>Many of these capacitors were used in audio equipment, and had one side that was marked with a band or something that would denote which side was closed off using a metal piece.
Nothing painted. The biggest capacitor of this device, located on the secondary "board", has a circular sinking on the rubber side. It is like what exist below the modern radial capacitors, but the purpose of this feature is only to make the rubber properly fixed, isn't?

>I'm not really sure, and you'll definitely want to double check that
I can't double-check, because I can't even single-check now. I don't know where the fsuck I could find this information.

>Also, did you make sure that everything that moves is lubricated properly? I don't know how this turn table is set up, but proper lubrication might help
Nope. But as you can see on >>1085149, the top-left capacitor on the image is completely corroded. You can see on the photos that electrolyte leaked all over the boards. This needs to be addressed first.

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Are there any non-shitty circuit simulators for linux?

Is my only option to use a virtual machine with PSpice installed on it?

>>1085183
Well, they sure look like normal polarized electrolytics. In that case the rubber side would be the positive electrode.

>>1085183
Tracing the circuit would give you some clues.

>>1085321
QUCS? LTSpice via Wine?

>>1085375
>In that case the rubber side would be the positive electrode.
How do you know that the rubber side is the + , and the side with the tip is the - ?

>>1084879

no need to re-invent the wheel. there was an openEMG project which seems to have morphed into this: http://openbci.com/

a few years ago i was sorta interested in the subject, so i tried to follow this project, however i found the design choices, and even the schematics so revoltingly bad that i bailed. maybe they've gotten better since then.

Anyone here familiar with the Latch-up effect?
I want to purposely make a 74HC32 Latch-up, then decap it and look at the die with an IR microscope.
My problem is that I so far only managed to fry a couple of in and outputs without actually triggering the effect.

How can I use a transistor or FET to switch an unamplified audio signal with a logic-level signal?

To expand on that, I want to run an audio signal of about .5V peak-center through either a FET or transistor, which will be switched by a 5V signal. I need to know which device is more suitable and what mode of operation I should look into.

>>1085584
As analogue switches, MOSFETs tend to be more suitable due to the lack of polarity (the drain-source channel will conduct in either direction, whereas BJTs only conduct one way).

Note that this doesn't apply to most power MOSFETs, as they have an inherent body (substrate) diode which means that they'll always conduct in the reverse direction (source-to-drain for n-channel).

File: FET-as-a-series-Switch-Circuit.jpg (39KB, 650x403px) Image search: [Google]

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>>1085382
Because that's how axial electrolytic capacitors are normally built - case is the negative electrode, meaning that the rubber plug side is the positive.

>>1085497
I've seen it happen couple of times with 4000 series logic. 74HC should be much more resistant towards it, so you might want to try with a different IC.

>>1085497
Before analog switch ICs (like 4066) became popular, JFETs were commonly used for that. Unfortunately you need negative control voltage for them.

>>1085584

probably a better idea would to use a purpose-made chip like the CD4016, CD4066, CD4051, and maybe others. this way you dont have to worry about finding a part with the just-right threshold voltage.

File: Brown components on Sharp P-951 C Series.jpg (2MB, 3664x2748px) Image search: [Google]

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Please, what are those components?
I can't recognize them. This is what is written on them:
>0.01M
>33V-

>>1085663

caps. probably .01uF at 33V. the voltage rating is what gives it away. caps are one of very few components with a printed voltage rating on them.

>>1085681
So, the M would mean MICROfarad?
That's strange, the Wikipedia article says that, prior to the 1960s, it was "MF"/"mf", not just "M".

Do you know which type of capacitor they are, too? Like, ceramic? By not being electrolytic, I should not worry about them?

>>1085687

looks like a poly-something cap. there are dozens of types just to confuse you, but it probably makes zero difference which one you use.
so could be polystyrene, polyester, polycarbonate, polyprolene, metal film, etc.

>>1085692
And I should not worry about them, because they tend to not fuck themselves like the electrolytic ones?

>>1085687
M tells the tolerance (20%). Most likely it's a polyester (mylar) capacitor. You could replace it with a ceramic capacitor if you wanted , but most likely it's not broken.

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My laptop charging port got fucked so i had to buy a replacement part. I'm a moron and got one a size too large and couldn't afford to buy another DC plug. Is there any way to nigger-rig this?

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>>1085703

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>>1085705

Suppose I want to convert an old 14.4v Nicad battery Drill to be corded.

How hard would it be to build a converter for it?

>>1085720
Not hard at all. You just need to find a 14.4V adapter and maybe do some soldering.

>>1081476
>>1081477
https://www.aliexpress.com/item/i/32680465637.html

>>1085723
Well ive soldered up some stuff before like following plans online to make guitar pedals, but I dont know anything about actually designing circuits.

Does it seem like an easy enough circuit to build and stuff into a dead battery?
Isnt it just a transformer and like 5 components?

>>1085723
>Not hard at all. You just need to find a 14.4V adapter

a drill can easily pull 10-20 amps when drilling into hard wood, so you'd need one big ass transformer that's gonna be heavy, expensive and hard to find. something like a computer power supply might work, using the 12V rail, but it's hardly elegant.

>>1082163
Depends on the fan. As anon said, some are designed to be controlled by PWM and may just stop completely if you put a resistor in. If you have a high-amperage fan, a resistor may be impractical. eg. 12v at, say, 0.8 amps is going to require a pretty fucking beefy resistor, maybe you could point the fan at the resistor to cool it... lol.

>>1085636
>I've seen it happen couple of times with 4000 series logic.
Any clues on the cause? Maybe I can get my hands at some 4000 series stuff.

What is the cheapest way to step up my 240V supply to about 400V? I need about 2.5kw of power.

>>1085882

AC or DC?

>>1085883
AC in, AC or DC out doesn't matter.

>>1085803
It was a long time ago, so take this with a grain of salt, but IIRC a charge pump using a 4011 was prone to that when its output was shorted to VCC or GND (I don't remember which one). When shorted, the charge from capacitors were dumped to the IC output, driving it above (or below) its supplies.

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>>1085884

there's this obscure thing called a transformer that does what you need. altho, at 2.5kW that fucker is gonna be heavy.

>>1085882
120/220 or 220/440 3kva transformer

>>1085900

you were 1 second too late, loser.

>>1085900
>>1085899
Thanks, can a transformer be overloaded or will it not supply more than what its made for?

>>1085903

if you overload it, it will start to smoke and boil. hopefully the thermal fuse, or regular fuse will blow before the wires melt. you need to look for CE or UL certification.

>>1085645
> you dont have to worry about finding a part with the just-right threshold voltage.
The signal is 0.5V, so that shouldn't be an issue here; A logic-level FET should be fine with 5V on the gate and 0.5V AC on the source.

>>1085882
240V AC is 240V RMS, 340V peak, 680V peak-to-peak. So you can get 340V or 680V with diodes and caps (but at 2.5 kW, those will be big caps). Or you could get a 3-phase supply (which will be 415V RMS between phases).

Otherwise you'll need a 2500 VA transformer, or a boost converter. The latter may be a viable option; a SMPS with active PFC starts by boosting the mains to ~400V DC.

It's debatable whether the transformer or the PSU will be cheaper. The PSU will certainly be lighter.

>>1085919
If your FET is advertised as "logic level" device, then it is guaranteed to have a body diode from source to drain. This diode will leak during the peaks of 0.5VAC signal.

File: Old ''5mf'' vs new ''5uF'' .jpg (2MB, 3664x2748px) Image search: [Google]

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>If i take a look at the size i would say its micro farad. Milli Farad caps are really really damn huge like you use them in amplifiers for car subwoofers.
OK. I bought the MICROfarad equivalents, and they look extremely smaller than the previous ones installed. Should I be worried by this difference?

I've got to drive some relays. I am going to use a uln2003 and a 5VDC supply. Relays are 5V coils. I want to have an led on indicator for the coil. Can I place an led and resistor across the could fromV+ to the pin and still have enough current to stay closed and drive the relay? Release voltage for the coil is 0.5V and it's resistance is 300 ohms.

>>1086036
ULN2003 can switch half an amp or so. Your relays need 5V/300R = 0.017A and your LEDs about the same. So yes, you can put them in parallel.
The idea to put the LED in series with the coil is unlikely to work, though.

>>1086024
>Code gayass

No you should not be worried about the size difference, that's technology improvement you are seeing. Do hope you got them from a reputable dealer though...

>>1086024
Yes, beside the capacitance another thing that determine size is chemistry and voltage. If i'm not mistaken some old electronics used an "M" for micro.

>>1086051
>>1086051
Thanks! It worked in simulation but I wanted to be sure before I ordered everything.

>>1086226
>If i'm not mistaken some old electronics used an "M" for micro.
So, I know, and thought that "mf" would be todays' "μF". Then I bought the "μF" equivalents of most approximated values. But the difference in size is enourmous. Does this means that I should have bought MILIfarads instead of MICROfarads?

>>1086201
>Do hope you got them from a reputable dealer though...
I got them from the Local Electronic Components Shop.

File: IMAG1127.jpg (815KB, 3264x1836px) Image search: [Google]

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>>1086282
No, Look at this picture. The small one is a 330uF. the larger one is 270uF.
in this application, the difference in size isn't due to their capacitance, but due to their rated voltage. The smaller one is just 25V, the larger one is 450V. It's generally a bad idea to replace a capacitor without it being of the same or greater voltage rating.
The two important values are the capacitance and the voltage.

>>1086282
>But the difference in size is enourmous.

no it isnt, it's moderate. enormous implies like 10x smaller.

>Does this means that I should have bought MILIfarads instead of MICROfarads?

no, caps get smaller with time thanks to better chemistry.

File: IMAG1132[1].jpg (887KB, 1836x3264px) Image search: [Google]

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>>1086282
and while >>1086294 is right, always make sure to check the voltage. Here's two identical electrolytic capacitors.
The older one is 1000μF (note how it's labeled "MF") rated to 15V. Hecho en Mexico, entre 1980-1985.
The new one is 1000μF rated to 16V.

File: IMAG1131[1].jpg (850KB, 1836x3264px) Image search: [Google]

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>>1086298
I had a small stroke. here's the right image.

File: Ehcap.jpg (71KB, 960x720px) Image search: [Google]

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>>1086299

Can we have a contest about old caps from countries that don't make a lot of Caps?

60s Canada

File: Slayer Exciter.gif (7KB, 525x285px) Image search: [Google]

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hey /ohm/

I'm fucking around with slayer exciters (poor man's weak tesla coil) i don't know why my transistors keep getting blown when i try to touch metal objects to the end wire of the secondary coil to try and get sparks. any help?

basically this schematic, but with a 10uF capacitor across the battery / power supply terminals as well.
I am using 2N3904s, have blown like 10 of them doing what i described. have also blown a TIP 41C

>>1086366
I should add, with a single 3904 it seems to be okay even when i touch metal objects to it trying to get the weakass sparks to show up. if i directly parallel two 3904s, then it'll blow if i try the exact same thing

>>1086369
You're using a 2N3904 when the schematic calls for a 2N2222. They're completely interchangeable most of the time, but this isn't one of them. 2N2222 can handle three times more current without exploding.

File: 70018-Free-shipping-10PCS-25A-1000V-diode-font-b-bridge-b-font-font-b-rectifier-b.jpg (205KB, 900x900px) Image search: [Google]

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i have a diode bridge ic 20a 600v similar to pic related. aside from caps to smooth the signal, how can i easily turn this into a 0-120vdc 20 amp max variable power supply? trying to stay away from transistors or secondary ics like lm317 if possible to avoid extra heatsinking and power loss. if not possible, what is the best way to do it?

>>1086392
>didn't read the post
i clearly said it's fine with ONE 3904 but not TWO

>>1086392
>>1086399
Also, I did say it even blew when using a single TIP 41C with heatsink. Loud crack and everything.

>>1086395
> how can i easily turn this into a 0-120vdc 20 amp max variable power supply?
You can't.

Switching supplies aren't "easy", a linear supply won't handle that combination of voltage swing and current (actually, you'll have a hard time handling either separately, let alone the combination).

>>1086409
God could you imagine a 120V switching supply? that thing would throw off so much EMI

File: 111.jpg (216KB, 990x707px) Image search: [Google]

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>>1086395
Easily? Variac, that bridge (ok, a bigger bridge) and a capacitor. Preferably preceded by an isolation transformer. It's going to be a rather shitty PSU, but might be sufficient for your purpose, whatever it is.

>>1086422
Depends on how it is made. Typical PC PSUs start with a 400V step-up switcher.

>>1086422
> God could you imagine a 120V switching supply?
Like the ones in every PC? Actually, the main switcher is running off either 170V/340V (rectifying and filtering AC givies you a DC voltage which is sqrt(2) times the RMS voltage), or 400V+ (the ones with active PFC start with a boost converter to get a neat sinusoidal current waveform, rather than the harmonic-heavy waveform you get from feeding rectified AC directly to a capacitor).

> that thing would throw off so much EMI
It's not the voltage that determines EMI, it's the current. 20A is less than most PC PSUs handle.

But switchers are complex. Particularly variable-voltage isolated topologies; most variable-voltage PSUs use a fixed-voltage isolated converter followed by a variable-voltage buck converter.

>>1086424
I suspect that he was planning on avoiding the expense of a 2400 VA transformer.

I mean, you can just rectify+filter mains then use a pot to vary the voltage, right?

>>1086424
>Step up to 400V
but why?

>>1086427
The ones in the PC don't switch 120+ V at 20A

>>1086438
> but why?
Because that's what boost converters do.

The reason for using a boost converter is that it's approximately a constant-current sink (the inductor is connected to the input; contrast with a buck converter, where the inductor is connected to the output and acts as a constant-current source).

This means that the PSU can shape the input current waveform however it wants. Active PFC shapes it to (almost) follow the voltage waveform, so that the PSU looks like a resistive load (1.0 power factor).

The main reason for active PFC is to eliminate the third harmonic, which results in neutral current in a 3-phase supply (a balanced 3-phase supply without harmonics should have zero neutral current; the neutral line is typically smaller or even absent as a result).

> The ones in the PC don't switch 120+ V at 20A
That would be 2.4 kW, which is a bit large; ATX PSUs go up to 1250W (although they're probably switching 3x the voltage at 1/3 the current).

Switcher EMI is determined by current; and the buck converter on the motherboard may be pushing 20A (that's 240W, which isn't that extreme for a high-end PC).

>>1086289
On the photo I posted, the old capacitor is:
>5mf
>6V DC
And the new is:
>4.7μF
>25V

So, the current is currently allright! The problem IS another one.

>>1086304
>Can we have a contest
My yellow ones on the photos were made on Brazil between 1950s~1960s.

I don't have more to post now, but you can post more of yours. I will look at them.

You forgot to inform the values of this 1960s Canadian one, though...

>>1086294
>But the difference in size is enourmous.
>no it isnt, it's moderate. enormous implies like 10x smaller.
The new 4.7μF 25V is at least 10x smaller, considering volume instead of only height, isn't it?

>>1086298
>>1086299
Great! Now I'm confident that the Farad values are right.

What would happen if they were wrong? Just to know... The capacitors wouldn't explode, because they have at least the same tension (Volts)! But with lower capacitance, they would charge and discharge more quickly. This would make the vinyl record player work more rapidly, fucking the sound and spinning at higher RPM, right? Nothing more? Like, no other components fucked?

>>1086593

electrolytic caps serve many different purposes, so we couldnt say for sure what would happen unless we looked at the diagram. the two most likely scenarios are

- filter caps: caps that are too small would introduce a little 50 or 100Hz hum into the audio, if they were too big, nothing would happen

- DC blocking caps: caps that are too small would create a filter that blocks very low frequencies, say below 200Hz, and if the caps are too big, it might allow 50 or 100Hz hum to get into the audio.

(50/100Hz hum is from the power lines in Yurop and lots of other places; in N. America and Japan, it would be 60/120Hz hum)

File: isolation transformer.png (34KB, 988x500px) Image search: [Google]

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I don't really get isolation transformers... like okay you aren't referenced to the mains but assuming you are grounded through your body's impedance if you touch either the live or neutral of the secondary of the transformer won't you still have +/-120Vrms across you referenced to ground and therefore get a shock?

>>1086684
The side you touch doesn't move in voltage, and the other side is forced to move instead. The secondary can "float".

>>1086684
The one you touch becomes referenced to ground through you, making it 0V. It "floats" to your absolute voltage, which is ground

The lead you don't touch becomes 120v to ground.
If someone else were to touch the other lead at the same time, you both could get shocked.

>>1086690
It's important to note that a RCD won't trip in this case

>>1086678
I don't care about mains hum. This can be fixed by replacing the capacitors. I just don't want components getting damaged.

Does anyone know of any explain-as-you-do style tutorials for Altium? The ones I've found are pretty shit and I'd ideally like to see someone step through the entire process of setting up a board in Altium.

>>1086760
Ask your sales rep

>>1086767
He told me "ask /ohm/"

>>1086684
Let's suppose you could actually get a shock, now imagine the path the current would need to take. What do you think?

>>1086771
My main issue is I'm not totally clear on why that voltage floats at the output. I know it is decoupled from earth ground but I figured touching it when grounded re-coupled it to earth ground and formed a ground loop. I am wrong about this as others have pointed out. The voltage will float and if I touch live neutral becomes 120V and if I touch neutral live becomes 120V and presumably if I touch nothing it's 120V between live and neutral. But why?

If I touch live why does that drop to 0V and neutral goes to 120V? Is it because when I touch it I load the circuit down so one rail drops in voltage and the other increases?

File: isolation.png (113KB, 988x500px) Image search: [Google]

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>>1086782
For simplicity, I'll use DC instead of AC
The earth is an ocean of electrons where the wire in the transformer is a shotglass.
The wire can drift to potentially thousands of volts relative to ground(think static) but it lacks the electrons to sustain any kind of current flow, and theres no complete path for the 120V to generate current flow.
When you first touch the wire, there could be a voltage there but it is quickly discharged as the ground potential flows into it.

Say the wire is floating at +100V. The atoms in that wire are missing electrons which gives it a positive charge. When you touch it, electrons flow through your body and equalize the charge(excess or lack of electrons) to that of earth. The number of electrons needed to do this is small, so it happens quickly and only a negligable amount power is dissipated by your body, so no shock or damage.

It's kinda like static electricity. It can be thousands of volts but no damage is done when you touch it and discharge it because it lacks the charge to sustain any current flow. The object you touched now has the same charge as your body and ground.

File: fluke-87-5-1000x1000.jpg (131KB, 1000x1000px) Image search: [Google]

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I need a new multimeter, my cheapo one finally gave up the ghost. I can get a Fluke 87 V for $275. Is there a better option out there for the price?

>>1086909
>Fluke 87 V
>$275
looks good anon. I think?
I am not familiar with flukes though. I bought an EEVblog 'edition' Brymen BM235 meter

>>1086782
If you connect the negative terminal of a 12V battery to ground, the negative terminal is at ground and the positive terminal is 12V above ground.

If you connect the positive terminal of a 12V battery to ground, the positive terminal is at ground and the negative terminal is 12V below ground.

Either way, so long as the other terminal isn't connected to anything, there's no circuit and no current flows.

File: v.jpg (50KB, 748x409px) Image search: [Google]

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>>1086782
No current implies no drop.

Any good ways to de- and reattach those glued-on clear foil flat cables with carbon tracks?
Already completely ripped one of those while trying to remove it.

File: RTExGdfUd.png (49KB, 455x258px) Image search: [Google]

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I'm trying to build an audio mixer as a small project and was wondering about volume control. In the picture, R2A is used for gain control of the amplifier, while R5A is a voltage divider to control volume. Is R5 necessary though? Isn't controlling the gain the same as controlling volume? or does R5 have another purpose?

File: lrfsim.png (150KB, 516x581px) Image search: [Google]

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What would you say is the closest you've come to programming your own waifubot?

I'd say SLAM robotics is coming pretty close for me. The robots became shockingly competent once I put a certain amount of time in. If I walk past them, they follow me like ducklings because my feet represent a discrepancy in their map. It's absolutely adorable.

So I'm about to buy a bass amp and I wanted to use an old PA cabinet I have in my house until I buy myself a proper cabinet. Thing is, that the cab doesn't say it's total impedance except for the main 15" speaker which is rated at 8 ohms. There are another 3 tweeters and a horn but there is no impedance marked anywhere. Is there a way to know each of the speakers impedance?

Is adafruit a decent source for parts? I was thinking of getting some breadboarding stuff from there because I only have one small one

I am getting some capacitors for some old audio stuff, and one of the things that I am trying to fix has some of those polyester film type capacitors, and I was wondering if those have to replaced as well. The thing that I am trying to fix is roughly 30 years old.

Why is learning electronics so hard?

>>1087004
gain and volume are different in that gain control can amplify the signal as well as attenuate it. If the gain is too high you can clip the signal by trying to drive beyond the power supply rails. It's not necessarily essential to have both, you can just have a gain knob, but they are different.

>>1087092
If you don't need things quickly, it's better to order from eBay or aliexpress, they tend to be much cheaper

>>1087109
Generally dry film caps don't go bad, just the wet film (electrolytics).

>>1087140
Okay, Thanks. I just wanted to make sure.

>>1085636
>case is the negative electrode, meaning that the rubber plug side is the positive
Thanks, confirmed.

so why isn't bigclive in the op

File: Replaced capacitors on SEMP P-951 C Series.jpg (2MB, 3664x2748px) Image search: [Google]

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>>1084616
>>1085146
>>1085149
>>1085183
>>1085375
>>1085382
>>1085636
>>1087171
>>1085378
>>1086024
>>1086201
>>1086282
>>1086289
>>1086529
>>1086294
>>1086298
>>1086299
>>1086304
>>1086585
>>1086588
>>1086226
>>1086282
>>1086593
>>1086678
>>1086699
THANKS FOR ALL THE HELP
I replaced all electrolytic capacitors.
Now, the vinyl record player can spin!!! It no more seems like a cassette player with weak batteries. Instead, it's spinning more quickly than it should, making the sounds appear some children toy with the voice of a insect (too sharp).

I can't put here a video of how it's working because this board probably doesn't accept video, or only accepts it without audio. So, impossible to show audio equipment, great.

Also, the brand isn't SHARP, it's SEMP.

Pic related!

>>1087176
There's probably a knob or screw somewhere to adjust the speed.

Also, do you have the thing set to 45 while playing a 33 1/3 record? Or it might be on 78 RPM if it's that old. I just want to make sure before I made you start changing settings that might not need to be changed in the first place.

File: Transparent component on SEMP P-951 C Series.jpg (2MB, 3664x2748px) Image search: [Google]

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>>1087189
It has this feature: 33rpm, 45rpm or 78rpm. None of these play the 45rpm record at the right speed. I think it might be the TONE adjustment, instead of the speed? There's a TONE knob too. On the back of it, there's this polystyrene film capacitor? Or I'm confusing the component types? If it's really a capacitor, could it be the cause of the problem?

It's written on it:
>MIAL
>500
>20%

>>1087192
That transparent component is most likely a diode, but I don't really know what it would be doing on a potentiometer like that. There might be a reason for it, but I am not aware of any.

I also think that the tone knob probably goes to the amplifier that powers that speaker, so it will probably have no effect on the play speed.

The knob that I was talking about would most likely be on the inside of the turntable, and would require a screwdriver to turn.

Also, do yourself a favor, and find a strobe disc to use. You turn on your turntable under a fluorescent light, and then adjust the turntable speed until the lines on the disc appear to be standing still. There are many available online to print for free. Just make sure to print the one that goes along with the power in your country.

File: Top of the portable vinyl record player SEMP P-951 C Series.jpg (2MB, 3664x2748px) Image search: [Google]

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>>1087202
>That transparent component is most likely a diode
It really seems like this capacitor here: https://commons.wikimedia.org/wiki/File:Folko-Axial-Bauform.png

>the tone knob probably goes to the amplifier that powers that speaker, so it will probably have no effect on the play speed
I can't really know if the speed is too hight or not. I deduced it could be the speed because a record spinning too fast generates a sharper voice. But wouldn't the TONE generate the same problem?

>The knob that I was talking about would most likely be on the inside of the turntable, and would require a screwdriver to turn
Oh, ok. I tought you were talking about this one outside (pic related, at the right side of the rubber circle).

>>1087208
Like I said earlier, I think that the tone thing has to do something with the amplifier in the thing instead of the actual play speed (think guitar amp). Since it is a portable player, they probably didn't want to waste too much space on many sound controls when they could use the space for something different.

>Oh, ok. I tought you were talking about this one outside (pic related, at the right side of the rubber circle).
There is that knob, and then there are often times ones on the inside of the turntable, or under the platter that are used to get the speeds down right (there should be one dedicated for each of the speeds of the turntable, if they do exist).

File: Screws under the portable vinyl record player platter SEMP-951 C Series.jpg (2MB, 3664x2748px) Image search: [Google]

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>>1087230
>There is that knob, and then there are often times ones on the inside of the turntable, or under the platter that are used to get the speeds down right (there should be one dedicated for each of the speeds of the turntable, if they do exist).
Hm, maybe those here? They are located under the platter, that I removed and put on the right side of the picture.

>>1087122
Keep at it anon

>>1087263
They might be. They are in the right location, the amount of screws matches the amount of settings, and they look like the proper type of screw.

The only way you can be sure is to try adjusting them by a certain amount that can be reversed if they don't do anything or if the result is bad.

File: calculator cable.jpg (182KB, 800x744px) Image search: [Google]

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>>1086998

if what you're talking about is these things, then, no, you cant reglue it. if you look hard enough, you might find a replacement, or if both ENDS of the cable have solder pads, you might replace it with individual wires, like this dude did: https://lowpowerlab.com/2012/12/29/ti-83-plus-screen-calculator-fix/

>>1087271

wat! those 3 screws arent any kind of adjustments, they just hold the motor in place. the rubber gaskets, 1 of which seems to have been squished, help keep motor vibration away from the rest of the unit.

Aside from the obvious non-contact amperage readings, are there any features that a clamp meter can do that a normal DMM can't? I'm looking to pick up a <$50 cheapo just to take some quick measurements on my woodworking tools, and so far I've only been looking for autoranging, min/max, and inrush as far as features go, but if there's something else they can do, I might as well see if I can get the extra features in my price range.

Whats the best option for cheap chink PCB fab ?
Its basic double sided, under 100mmx100mm and i only need two.
I've been looking at seedstudio, are there any cheaper options ?

File: Motor screw holes outisde view - SEMP P-951 C Series.jpg (2MB, 3664x2748px) Image search: [Google]

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>>1087271
>>1087399
Confirmed: these screws don't adjust anything...
And the rubber turned into brittle plastic.
1/3

File: Motor screw holes inside view - SEMP P-951 C Series.jpg (2MB, 3664x2748px) Image search: [Google]

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>>1087510
Here you can view that there's nothing relevant inside on these holes...
2/3

File: Rotor - SEMP P-951 C Series.jpg (3MB, 2748x3664px) Image search: [Google]

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>>1087512
There are CAPACITORS on the rotor. Should I pay any attention to them?
3/3

>>1087520
That's a self-governing motor or whatever it is in English. Faulty capacitor can make it run at wrong speed. Check/clean the contacts while you're at it.

>>1087520
Are you sure that is not a resister?

>>1087520
>>1087563

Yeah, it looks like a 390 ohm +-5% resistor

>>1087563
>>1087565
Under the resistor, there is a shiny metal can. It's a capacitor, isn't it? There are 3 of it.

>>1087544
>That's a self-governing motor or whatever it is in English.
You know the name in which language? I could not find the English name you said.

>>1087544
Universal motors? Usually when you have run caps going bad they mess up the current phase shift, affecting torque. But that's only when operating in AC, no?

I would bet the caps on the pic (>>1087520) are being used for noise suppression or something along these lines.

File: 2-PCS-Mabuchi-RK-384CA-24-V-DC-Motor-de-alta-velocidade-com-quadrupolo-Rotor-3.jpg (41KB, 646x458px) Image search: [Google]

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>>1087606
>I would bet the caps on the pic are being used for noise suppression or something along these lines.
Maybe?
This would be used to prevent noise getting in, or noise getting out?

>>1087616
getting out, caps on smaller electromotors are pretty common since their noise can fuck with the logic circuits in RC models and such

This might be a stupid question, but google didn't give any decent answers for it: why are industrial-type motors really massive and heavy when compared to motors in, for example, power tools with the same wattage? A 500W router weighs nothing compared to a 500W industrial motor

And a more practical question, is it bad to run 220/380V rated motors on 220V? Again I tried google and it was very inconclusive, some places say that if you hook up some capacitors it'll be fine, others say that it's bad for the motor and you should just get one specific for 220V

>>1087617
So, should I worry about these capacitors on the rotor?

>>1087624
>A 500W router
Internet router?

>>1087624
'industrial type' = induction motor (cap start/ cap run/ cap start & run ). high sustained power output, can take physical abuse

'power tool' = brushed motors, series or parallel wound. high power output for relatively short periods. also the manufacturers use funny methods to calculate power or just outright lie.

>>1087616
>>1087617
>out
Yeah, usually the noise (EMI) comes from brush arcing.

>>1087624
> is it bad to run 220/380V rated motors on 220V?
3-phase motor on a single-phase supply? It won't do the motor much good.

You can't synthesise 3-phase with passives (you can't phase-shift without attenuation). In theory it's possible with a transformer, but only if the load is constant (which it never is).

Realistically, you need either a motor-generator, a VFD, or a 3-phase supply.

so budget pcb manufacturers give minimum trace spacings and widths, but are there also granular distances between traces they can make? (eg 14 mil, 15 mil, 16 mil spacing but not 14.5mil)?

>>1087606
No, I mean one which has a built-in speed controller. In this case it resembles a classical steam engine governor - when the motor spins too fast, the contacts powering the motor open.

>>1087716
Yes and no. They use (very) high resolution printers to produce the films and different factories use different equipment. The resolution of the printers is higher than the etching precision.
You can choose the gerber file resolution (number of decimals and inch/mm) in some PCB editors, though.

>>1087624
>And a more practical question, is it bad to run 220/380V rated motors on 220V?
On a three phase-supply? Are you aware of what these ratings mean? You can operate the motor at 220V freely as long as it is wired in the proper configuration (Delta, in this case). That's how they designed it.
Now, if you are talking about running it in Wye(Y) by applying only 220V, then no, you're gonna stress it a lot depending on the load, because it will reduce the torque considerably, leaving the motor running at lower RPMs (-> more current).

>>1087746
>built-in speed controller.
>when the motor spins too fast, the contacts powering the motor open.
Oh, I see, never heard of those.
I know about induction motors that have something similar to the contacts you mentioned, but they are only relevant at the starting (auxiliary winding with a capacitor in series with a centrifugal switch, helps with torque at the starting).

>>1081026
anyone here use simulink to model circuits? i already have matlab for uni so i figure i might as well just use simulink, unless it's shit for some reason

>>1087785
never used it but as i understand it only offers generic components. that can be a big downside if you want to evaluate a circuit with parasitics in mind (eg to determine a mosfet's rise time), because adding those manually gets messy fast.

Just got a used Fluke T5-1000, but when I try to measure current I get no reading. Have tried google to no avail. Anybody know what I might try? Have heard they are prone to failure.

>tearing something down
>missed a screw
>use some force because I assume it's got some clips holding it in place
>circuit board snaps in half
every time

What's the difference between a 358 and a 741 op amp?

how do i get hold of big boxes of junk electronics to mess around with? I saw a Post Apocalyptic Inventor video where he says he got a massive box of random electronics junk off ebay, but doesnt specify beyond that

>>1087803
the only significant difference is the minimum supply voltage. there's no reason to prefer the 741.

>>1087805
i collected my box of trash by searching terms like "1000 resistor" or "100 nfet" on ebay and finding cheap results. you kind of need to know what you want when doing that, but there's a few obvious components to get in bulk like resistors, caps, inductors, p+n bjts, p+n fets (both power and signal), and the jellybean ics. you can get a good assortment for $20 and a great one for $50.

>>1087805

He probably bought a bunch of shit off of the "lowest price first" section of consumer electronics

The truth is that really isn't worth your time. If you want to get some actually useful or interesting shit you should buy broken things in the business/industrial category

new thread

>>1087810
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>>1087795

use a second multimeter to measure the resistance across the first ammeter. it will probably be infinite coz the internal fuse is blown.