/diy/ - Do It Yourself

>>1591036
AC is black magic.

I miss the old /ohm/ threads with the "problem ideas" section.

I have a lot of problem ideas and nowhere to go.

>>1591042
If these LEDs were made to hook up to 12V lead acid batteries on cars and such, they must have some current limiting deal (resistor?) built in, right? So could I swap that 12V lead acid out with a straight 3s pack or some 1s_p parallel pack with a boost converter?

>>1591045

I had to turn off my custom CSS to see if you were the BepMonster.

and you aren't. so I cannot help you

>>1591036
>no ohm in the title
lmao good luck finding this thread by searching

>>1591050
shit you're right I completely forgot

>>1591045
I've always wondered this, the COB LEDs seem to have no resistors on them but are usually just run off a car battery without any current limiting.

also what does "problem idea" mean

>>1591042
did you try /b/

>>1591051
you had one job
delet and start again

>>1591047
Has anybody tried the $1.49 nuggets at BK? Are they real meat?

I think I might stick an 18650 and USB board in this lantern.

>>1591057

I can sense bep shit even though my CSS hides your faggotry.

does anyone know any epic pranks I can pull with electronics?

might be a fun idea, I haven't seen anyone incorporate electronics into their pranks but there's all kinds of shit you could do

>>1591070
Who gives a shit, not like he's nearly as bad as he was last year. If I didn't introduce anti-samefagging measures (changing punctuation style) I could be as much of a pain in the arse as that guy.

>>1591055
>you had one job
>delet and start again

>>1591072
>>1591072
>>1591072

>>1591074
>not like he's nearly as bad as he was last year. I

>>1591045
>current limiting deal

>>1591045
I remember seeing you from another thread, lol

Hook it up to anything putting out 12v. As long as the source can push out enough current to keep the leds lit, you're good.

>>1591054
I don't know where the 'current limiting resistor' came from, but you can wire LEDs in series and as long as the source voltage is below the LEDs total voltage limit, no resistor needed. Its just like any other component with voltage and current limits. The resistors are only necessary if your source voltage is higher than the LEDs voltage limits.

>>1591041
take a course benis

>>1592154
put a 1V battery accross a green LED "forward voltage around 2V" and see what happens. it will burn.
LEDS and diodes have no built in voltage or current limit. When current moves across the junction they heat up the internal resistance drops causing more current to flow and heating up further into thermal runaway.

>>1592963
Have you ever actually done this? 1V is so far below the knee voltage it'll never get a chance to burn.
I put 2.5V from a power supply directly across the terminals of a regular 5mm ~2.7V LED and it's not thermally running away because practically no current is flowing.
So then I heated it up with a hot air gun to too-hot-to-touch celsius and the LED just barely glowed, probably 1-2mA, still no thermal runaway, and as it cooled it slowly stopped glowing.

>>1592979

I don't think you understand the term "thermal-runaway". It's a self-feeding mechanism, and once it is started, it's like a train going downhill that has lost it's breaks, thus the term "runaway".

>>1592986
I know exactly what thermal runaway is.
I tried to set up a scenario very similar to
>put a 1V battery accross a green LED "forward voltage around 2V" and see what happens. it will burn.
and the LED didn't burn.
Bottom line >>1592963 made a prediction, I tested it, prediction did not pan out.

>>1593004
Isn't that how those LED throwies work that were popular with hipsters? Just connecting a led straight to a coin cell?

>>1593008
Those hipster throwies are indeed just an LED connected straight to a coin cell, they are self-limiting because the lithium coin cell has a fairly high internal resistance.

>>1592979
>>1593004
Forgot about the I-V curves of diodes. You're right that 1V wont do it since its below the forward voltage but once you pass that threshold is when thermal runaway becomes more of an issue because of the exponential I-V curve. 1V on a 2Vf diode wont do anything but a 3-4V 18650 probably would.

What if someone (e.g. me) would make a telegram/discord/whatever bot that works like imageboards? If you say something to it, it will resend that to everyone else who also talked to him = you get anonymity.

It would assign short names for consistency it you keep chatting and reset it if you stop = no samefagging.

So you can shitpost /diy/ realtime. Would that work?

The problem I see, besides being a giant faggot like every other OP, is threading. You want to be subscribed to shit A but don't care about B. Maybe before starting to chat (e.g. you didn't chat for an hour) you have to pick a topic, for example /ohm/ or /qtdtot/, a simple tag. And only people interested in that topic will get those initial messages (OP), and they will see you as /ohm/new0f1a8g. Everyone else then could join the discussion by replying to that particular "OP" and the discussion then gets encapsulated. Meaning you still get messages from new OPs about shit you're into, but your messages will be forwarded into that particular topic only. You can abandon the thread by stopping chatting for some time, simply replying to another topic or by creating your own.

>nice blog, faggot

there's a better thread guys:
>>1591076

>>1591057
imo, they are trash. like inedible w/out sauce but you can't beat the price. they got some new seasoned ones might be better tho

Hey /ohm/, I have two questions that might belong in /sqt/

1) is it true that a 7805 can only output as much current as its input? As in, 12V@30mA -> 5V@30mA? Assuming it's fully heatsinked and everything

2) When a resistor is listed as "1/4W," does that mean it throttles at 1/4W? Meaning, a 14V input will always draw a constant 17mA, giving 0.238W: a 20V input will still only draw 17mA, and dissipate the rest as heat?

>>1595691
1 - no it will actually supply slightly less as there are operating losses
2 - holy shit no resistors don't work at all like that please read about Ohm's law and Joule's law before you fry whatever schmancy thing you want to power with those 5V

>>1595707
>before you fry whatever schmancy thing you want to power
Lmao it's literally a kit, I followed it to the T. Only difference is I replaced the L4931-5V with a 78L05, and now it's drawing way less current than it should be. I'm just trying to gauge whether I fucked up, and some quirk of the 7805 is doing it, or if the kit itself is broken

>>1595712
IIRC the 78L05 will only give you 100mA or so before it goes into current protection. Dunno what the original regulator is rated for, but that may be the reason.

>>1595718
That's the thing though. I tested it w/ a 100ohm dummy load, and it definitely gives at least 50mA. I only need 30 for the kit anyway, but when I tested it it was only pulling 10.4mA.

The reason I asked was, that 10.4mA is exactly 1/8W, when pushed through a 1Kohm resistor at 12V: as it just so happens, there is a 1/8W, 1kohm resistor in my circuit drawing from 12v, which also heats up noticeably. It seems like too much of a coincidence.

>>1595723
Well, that's odd. Have you tried measuring that resistor while it's hot? It's unlikely but it maybe has a large temperature coefficient. But again, it's unlikely. I'd check the power supply in case it trips some protection or something like that. Or there's also the fact that the 78L05 would be sinking something like 200mW under those conditions. Actually I think that last one is the most likely.

>>1591057
They're pretty good, and only $1 here.

>>1595723
Neither exactly not coincidence.
12V 1kΩ 12mA 144mW
1kΩ 10.4mA 10.4V 108.16mW
1/8W = 125mW

>>1595691
>2) When a resistor is listed as "1/4W," does that mean it throttles at 1/4W?
That is the ratting for how much energy it can dissipate (as heat). More and you risk burning it.