the Hearth @Felthry@awoo.space

@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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@kat @LexYeen and 100 Ω is the resistance of the resistor you'll need
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@kat @LexYeen 2/0.02 = 100
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@kat @LexYeen no, remember that 20 mA is 0.02 A
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@kat @LexYeen 2V/20mA = 100 Ω
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@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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@kat @LexYeen oh i didn't understand what you meant at all, sorry
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@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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@kat @LexYeen you read the LED datasheet, it tells you what the forward voltage is
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@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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@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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@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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@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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@kat @LexYeen same resistor regardless of number of LEDs, the resistor sets the current through the LED
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@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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@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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@kat @LexYeen no that means there's more than enough power for an LED
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@LexYeen @kat far more than enough current for a single LED even at the lowest current mode though

there are also higher voltage modes but uh. don't even start trying to get that working that's really complicated
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@LexYeen @kat one that protects against overdischarge? most of those just have a DW01 or something that protects against overcharging and overcurrent but not overdischarge
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@LexYeen @kat i can confirm that to be the case, yeah

you may run the risk of over-discharging the battery if you don't have a protection circuit as well, but that's not dangerous to anything other than the battery (it'll lose capacity faster and need replacing sooner, but no risk of fire or anything)
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