@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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@Felthry @LexYeen okay, so i can just look them up by voltage and i don't need every possible resistor between 2 and 5V, cool

that's what i was asking haha

@kat @LexYeen oh i didn't understand what you meant at all, sorry
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@Felthry @LexYeen so how do you actually... calculate which resistor you need to lower 5V to like 2.8V or whatever

i'm also assuming i'm missing like ten other factors i need to know to keep my house from catching on fire here

@kat @LexYeen it's just (5-2.8)/(desired current); the datasheet will also tell you what brightness you'll get at different currents and what the rated maximum current is
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@Felthry @LexYeen okay, so i picked out an example LED

3V would mean 2 over 20mA, the listed current

that gives me... 10 of something

@kat @LexYeen 2V/20mA = 100 Ω
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@Felthry @LexYeen okay, so you multiply it by 10 at the end??? and then what is 100 Ω

@kat @LexYeen no, remember that 20 mA is 0.02 A
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@kat @LexYeen 2/0.02 = 100
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@kat @LexYeen and 100 Ω is the resistance of the resistor you'll need
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@Felthry @LexYeen okay, so you convert mA to A, so it's a 2V difference divided by 0.02 A

so it's always voltage difference in volts over amperage in amps, and then the result is the Ω whatever of the resistor i need to order

@kat @LexYeen right

(Ω is the symbol for ohms, incidentally, if you needed the name)

also don't order resistors from ebay or something, get them from a proper supplier

not because you run the risk of getting bad ones or anything, you'll jus tbe massively overcharged. the average resistor costs about 1¢ if you buy in sufficient quantity, or maybe 10¢ if you just buy one, but if you get it on amazon you'll be paying something like $5 for five of them or something
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@Felthry @LexYeen i'm kind of scared to ask what voltage and current actually measure and how they relate to each other

@kat @LexYeen the usual analogy is to think of water flowing through a pipe; voltage is the water pressure, and current is how fast it's flowing
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