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Author Topic: People hate resistors for their LEDs  (Read 4133 times)
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When doing a quick test, I like to plug one leg of a standard led into the Arduino female. I have some 560 Ohm resistors soldered onto flex jumper wires at one end, and  croc-clips on the other. This is so I can clip the croc onto the other LED leg, and plug the loose end of the resistor into another female. The croc-wire-resistor makes it easier to move between components and arduino pins.

Come to think of it a croc-resistor-croc might also be useful.



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Craig Turner, blog: http://gampageek.blogspot.co.uk/ It helps with my learning if I write things down, esp. for others to follow (constructive comments welcomed to improve)

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I have similar - a couple of LEDs with a resistor soldered to one of the legs.
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I have similar - a couple of LEDs with a resistor soldered to one of the legs.

yea I have a small handful of those
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I got lazy and bought 50 "prewired for 6V red LEDs" from eBay.  Like these: http://www.ebay.com/itm/50-Pre-Wired-6v-3mm-Red-LEDs-PreWired-Red-6v-LED-/160596848997?pt=LH_DefaultDomain_0&hash=item2564517165

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I had a UV led on a pot and made the mistake of turning the pot too low. Weird smell.

Hardest part for me is trying to remember how to determine the resistor value, which I have to go search on to re-check even if I do think I remember just to be sure which I'm not. So I aim high as I don't like leds hurt-my-eyes bright anyway.
I run 340+ ohms at 5V with standard 5mm reds for indoor use. Maybe they'll live longer, certainly they use less power.

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I used 1k for nearly all my "indicator" LEDs.  With modern LEDs, that's plenty bright, and it's pretty-much always safe (<5mA)  1k resistors are useful for LOTS of things!
Now, when you get to illumination rather than indication, you can start worrying about "correct" LED resistors.
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I use this a lot.

http://www.hebeiltd.com.cn/?p=zz.led.resistor.calculator 
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I just remember the formula
(Vs - Vf)/.02 = resistor
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EVP; I bookmarked that page twice and Karma'd you once.

Crossroads, I never tried but can I get Vf using a meter on the led?

One way I can get at least close is get the led in bright light and see the V it generates.
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Use 5V and 270-330-470 ohm resistor, something in that range, measure Vf across the LED.
You cannot measure it without current flowing.
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Arduino for Teens available at Amazon.com.

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just do what i do, dont use resistors, i just keep using the leds till they pop and fizzle. they're so cheap just buy tons of em.  smiley-eek-blue
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Quote
i just keep using the leds till they pop and fizzle

Maybe fair enough on the bench but what about in production?

The BBT episode where Sheldon was on at Penny about her check engine light being on, and he wondered if there was a check the check engine light light. (As he does....)

Imagine the liability claims if peeps' engines blew up because the oil pressure lights had all popped and fizzled themselves to death?
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Quote
i just keep using the leds till they pop and fizzle

Maybe fair enough on the bench but what about in production?

The BBT episode where Sheldon was on at Penny about her check engine light being on, and he wondered if there was a check the check engine light light. (As he does....)

Imagine the liability claims if peeps' engines blew up because the oil pressure lights had all popped and fizzled themselves to death?

hmmm, maybe not using resistors is why i cant get the pin 13 blink sketch to work??  smiley-confuse and if you work with the engineers you spoke of in another post, the ones who ask everyone else for answers, you can easily lay the blame with them because they're clueless already!!  smiley-eek

lol but im only kidding bout not using resistors


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Pin 13 led has a resistor. I hope you're joking about not getting it to blink.

Feed a led low enough V and you don't need a resistor but at 5V the lifetime is amazingly short.
Back in the 90's I saw a 555 circuit that ran red leds on very short 9V pulses yet allowed a lifetime of minutes.... it said.... I never tried. The purpose of that one was to make very bright pulses for a fake laser.
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ya i was joking, that was a leftover from another post about ppl asking ppl on the forum to show them how to do blink 13 lol.
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