@Felthry okay rad, so literally just a battery, resistor, and a couple LEDs in series would be fine?

@kat again depends on the battery voltage! each LED you add in series will require another 2-4 volts depending on what color LED it is, so you'll need a higher voltage for more LEDs in series
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@kat you can put multiple LEDs in parallel without changing the voltage, but each LED will need its own resistor in this case, and you'll be pulling more current from the battery so if you want a lot of them you may need a beefy battery
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@Felthry okay that's clearing some stuff up, so if i want like 3 small white/orange LEDs, i'd want like

- in parallel, 1 resistor each, and a 2032 battery is fine

- in series, 1 resistor, and like... 2-3 stacked 2032 batteries i guess

@kat orange LEDs are going to be more towards the 2 V end of the spectrum and white ones closer to 4 V (for physics reasons, the voltage needed increases as you move through the rainbow from red to violet, and white LEDs are usually blue or violet LEDs with a color-altering phosphor added)

Note that 2032s can't provide all that much current for very long; expect the battery to last maybe a day or so if powering one LED at 10 mA (a reasonable current for an LED, depending on how bright you want it to be, though you can get high-efficiency ones that are reasonably bright even at 1 or 2 mA)

A pair of AAs or AAAs could get you longer runtime if you can fit them into the thing. Or you could use the 5V out of one of those USB power banks and have it be rechargeable (just cram the power bank in there, i don't recommend dismantling it)
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@Felthry so like if i want a little light capsule with a button on one end and a single bright LED on the other that i can insert into prints at the base, what battery is best for that

@kat It depends on how big you can let the capsule be--if it's big enough two or three AAs that's what I'd go with, but if it needs to be smaller.... How bright are we talking? If you just want it to be visible, a button battery or two might be adequate, but if you want it to be usable like a flashlight, you'd probably need to go to a lithium cell and that gets complicated due to the need for protection circuitry
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@Felthry i just want something i can put inside a transparent 3d print or something

i think it'll have to be smaller than a AA/AAA battery, i want to fit it into the base of a print

@kat we have zero knowledge of 3d printing stuff, is "the base of a print" some specific size or does it vary between things?
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@Felthry stuff like this

if i used AA/AAA batteries i'd have to make bases that are very wide/long, or have everything be like 2 inches off the table

@kat those're going to need a fair bit of illumination... have you considered having them not be battery-powered? Wouldn't be too hard to plug them in with a wall wart, and then you wouldn't have to worry about fitting a battery in there

I think you could probably fit some AAAs in there, though, without making it too high? Just have one of these https://www.digikey.com/en/products/detail/keystone-electronics/2480/ or something similar in the bottom of the enclosure, exposed so you can change the batteries

The link is to a three-cell holder, but you can get four-cell ones too
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@Felthry i kind of need something in the form factor of a tea light at most, four AAA batteries is a pretty giant square

iunno about hooking it up to a wall outlet, that seems a little overboard tbh

@kat @Felthry if I may offer a suggestion?

look into lithium-polymer batteries and USB-standard charging boards for them. sparkfun is a great place to start. LEDs draw so little power that you'll basically never overload one.

battery: https://www.sparkfun.com/products/13851
charger: https://www.sparkfun.com/products/10217

it should be easy enough to tap off of the board's battery connection points to power your LED circuit.

@LexYeen @kat didn't know they made those little charger boards, we've always made our own when needed
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@Felthry @kat they're apparently good for prototyping work, given the popularity and variety available.

@LexYeen @Felthry ah yeah i'm definitely not able to make my own charging circuitry but if there's a good cheap "buy this thing and wire it up like a regular battery and it makes it USB chargeable" that'd rule

@LexYeen @Felthry i guess alternately i could just like... somehow wire these up to be USB powered, get a USB battery, a cheap USB hub, and just some little microUSB cables and deal with having a black box behind/under them

@kat @Felthry USB is a 5v standard, with amp limits based on the spec IIRC.

@LexYeen @Felthry sooooo does that mean i can't power an LED with it or

@kat @LexYeen no that means there's more than enough power for an LED
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@Felthry @LexYeen also wait, so hooking the LEDs up in parallel means i can have as many as i want on a single power supply as long as its voltage is higher than one LED needs, right

@kat @LexYeen as long as the voltage is higher, and the total current isn't too much for the power source

every USB power supply should be able to handle 100 mA by the standard, and most can do at least 500 mA. one typical LED needs somewhere around 20 mA for max brightness, so you can theoretically power 25 of them off of a 500 mA supply
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@Felthry @LexYeen okay, so if i want i could just take a USB power bank i've got on my desk already, and like... just have a rechargeable battery

then i can just wire 3 LEDs in parallel, wire them to a USB plug, and plug a couple of those into the bank via a USB hub

and then when they stop lighting up i just recharge the bank

i'm assuming this wont work but i'm not sure where the problem is

@kat @LexYeen no that would work fine, as long as you put resistors in series with the LEDs

an LED without a resistor would just immediately fry
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@Felthry @LexYeen so like is it always just the same resistor before the LED if i'm hooking it up to a USB power line, or do they need different resistors if they're in series/parallel or if there's different numbers of them?

@kat @LexYeen same resistor regardless of number of LEDs, the resistor sets the current through the LED
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@Felthry @LexYeen okay rad, do i need a different resistor depending on the LED itself? or are they like... standard

@kat @LexYeen yeah it depends on the LED and the power supply voltage and the current you want to drive the LED at. The power supply voltage is fixed at 5 V if you're using a USB thingy, but the other two are your choices
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@Felthry @LexYeen so like... how wildly do LEDs vary? will i still need a bunch of different resistors even if they're all just drawing from USB

@kat @LexYeen if they're all different LEDs and not a bunch of the same part number, then yes, but if you only need like, five of the same type, they'd all use the same one

if you can give more info on what LEDs you want, i can give specific examples
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@Felthry @LexYeen i don't... really know what to shop for haha

is every individual type of LED just going to need a different resistor or is there any sort of standardization at all

@kat @LexYeen this isn't really something where standardization is even possible

the formula is ((power supply voltage) - (LED forward voltage)) / (desired current)

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@Felthry @LexYeen there's no standardization for LED voltage at all?? like not even a common one?

@kat @LexYeen the voltage isn't just something the person making the LED decides, it's constrained by physical limitations that depend on a number of interrelated things like the color of the LED, the exact semiconductor used, dopant concentrations, temperature of the LED (temperature is only significant in high-power illumination LEDs though)

so like i said, standardization isn't really *possible*
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@Felthry @LexYeen so you need a different resistor for every single LED? how do you even calculate it if it's impossible to know

how does anyone manufacture anything

@kat @LexYeen you read the LED datasheet, it tells you what the forward voltage is
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@Felthry @LexYeen so like... is it really just impossible to look up "2.5V LED" or something and find things that match

@kat @LexYeen no you can do that, but you'll probably only get red and orange ones, and maybe the old technology low-efficiency green, at that voltage
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