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I have 3 LEDs powered by an Arduino; each LED has its own flash rate.

Now I want it to be powered by an external 12V power source and still have the flashing function of the Arduino?

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    You will need a transistor or a MOSFET to do that (one per LED). Just google that and you'll find many examples how to do it. On Arduino.SE, there have also been many questions about this topic. – jfpoilpret Dec 4 '16 at 8:36
  • Thank you very much! I tested it and it works perfectly! :D – Austin Grant Dec 4 '16 at 8:51
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Use a N-channel MOSFET, wire load to drain pin, source to (common) ground, and place a 1 kilo-ohm resistor in series with your arduino pins. Bear in mind that MOSFETs respond to voltage, not milliamps, on the gate - get one that responds well to 5V logic.

  • You do not need a series resistor with a MOSFET (although it does no harm). If using a bipolar transistor it is essential. – Milliways Dec 4 '16 at 22:38
  • @Milliways We discussed that before. Different strokes I suppose. – user400344 Dec 5 '16 at 0:12
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Or you could use a relay. Many small ones available for a couple of dollars.

  • Using a relay for such circuit would be just annoying because of "clicking" on relay. – Adam Rosiek Mar 5 '17 at 0:34
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    Hmmm, I didn't read that that was a criteria, not to mention that there are small, quit, solid state relays. – nkuck Mar 5 '17 at 0:38
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As has been mentioned, you could use an N Channel MOSFET, but preferably look for a Logic Level MOSFET. These are capable of being turned on by lower voltage levels such as on the pins of an Arduino.

Having said that, i have used two non logic level MOSFEt's in Arduino projects successfully. They are the IRF3205 and IRF 520 - both are readily availalable and will work OK with the Arduino output pins for your low-current-driving-an-LED requirement.

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