I got myself a bunch of superbright LEDs from Hobby King, e.g. http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=28507

Trouble is, HK doesn't give any data on the current or voltage drop of those LEDs. I'd like to build a small board that connects to a 4S LiPo, the APM's ARM LED output and then drives 1 red, 1 green and 2 white of those superbright LEDs. Unfortunately, without knowing the LED data I have no clue, how to dimension the resistors - which anyway would need to be BIG (3W...). I wonder if there's maybe some integrated driver circuit somewhere which I could use?

Could someone help me out here? :)


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  • "This is the main question - what do they mean with "input: 2.5 - 3 V"...?"

    That's the typical voltage drop across the LED junction, probably at rated power (3W). This might help you as well.


  • This may help you drive the LEDs

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  • The HK link for your LED would lead me to believe that this LED will have a voltage drop of 2.5 - 3.0 volts while dissipating 3W. Using ohm's law (P=VI) (3watts / 3volts = 1amp). We will be running 1 amp through this circuit. Now if you want to drive this from a 4S at, say, 16 volts, we can again use ohm's law (V=IR) to determine a resister value... (16 volts from LiPo - 3 volts dropped across LED) / 1amp =  13 ohms. Finally we can determine the power which the 13 ohm resistor will dissipate (P=VI)... (16 volts from LiPo - 3 volts dropped across LED) * 1amp = 13 watts. This circuit is going to run HOT and suck up a LOT of power! A more practical resistor value might be 18 ohms or higher. 

    Now if you want to control it from the APM, you will require some sort of buffer or switch. I would suggest a power FET should do the job nicely.

    Hope this helps. 

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