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Do i need resistors?

Discussion in 'General Electronics Discussion' started by mollekake, Jan 26, 2015.

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  1. mollekake

    mollekake

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    Jun 30, 2014
    Hello.
    I want to hook up my rgb led to an attiny85. The attiny runs on 3v, so, do i need resistors for my led?
     
  2. Gryd3

    Gryd3

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    875
    Jun 25, 2014
    Are you using a neoPixel?
    If not, it's always a good idea to use a resistor.
    Additionally, you may not be able to light the Blue led with only 3V, so you may actually need a transistor, a higher voltage supply and a couple resistors.
     
  3. Anon_LG

    Anon_LG

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    Jun 24, 2014
    No, the attiny85 only provides enough current to light the LED, not enough to blow the LED.
     
    Gryd3 likes this.
  4. mollekake

    mollekake

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    Jun 30, 2014
    Yeah ok that's what i thought. But a side note, i saw somewhere that you could hook up only the anode of the rgb led with a resistor to 5v, but everywhere else they hook up each color pin with a resistor. Which is correct? I don't think i fully understand how a common anode led works
     
  5. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    What LED are you using. It's just you might not have enough voltage to run the Green and Blue LEDs as Jerid mentioned. The Red will need a resistor not because it may be damaged but it will be a lot brighter than the others and may swamp the other colours.
    Adam
     
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  6. mollekake

    mollekake

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    Jun 30, 2014
    Using a common anode RGB Led from ebay.
     
  7. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    That narrows it down a bit :) Can you send me a link?
    Adam
     
    Bluejets likes this.
  8. BobK

    BobK

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    Jan 5, 2010
    You most likely need a higher supply (5V) and transistors and resistors.

    A 3V micro is not going to be able to supply 20mA to a green or blue LED.

    Bob
     
  9. mollekake

    mollekake

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    Jun 30, 2014
    Guess i'll have to boost it to a 5v :S Got any good suggestion on space saving but still getting 5v to the chip? 3 3v cell batteries through a regulator a good or bad idea?
     
  10. Gryd3

    Gryd3

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    Jun 25, 2014
    There are always multiple ways of doing things. That would work fine. Note that the regulator will waste some power and reduce overall battery life.
    What are you attempting to build?
    You could use a single 9V battery, or 4 x 1.5V batteries like AAAs or AAs.
     
  11. mollekake

    mollekake

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    Jun 30, 2014
    What other way would you suggest? I just want to make a small device that switches color at a push of a button (probably a interupt) driven by a attiny85
     
  12. Gryd3

    Gryd3

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    Jun 25, 2014
    Well.. because your LED is common Anode... the Attiny will be sinking current. (Active Low)
    This would keep the current draw down on the Attiny because it won't be 'powering' the LED.
    Perhaps there is a trick you can employ.

    My thought is using a zener diode as a voltage regulator.. because I am assuming current draw in the Attiny will remain incredibly small if you will be sinking current rather than sourcing it. I am also assuming that the state of the pins could not simply jump from a high to a low output.. you would need to set the pin to a high impedance mode to turn off the LED.
    I would feel a lot better if someone who has tried this gives some feedback.
     
  13. mollekake

    mollekake

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    0
    Jun 30, 2014
    yeah. Maybe i should order some cathode ones :p
     
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