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Larson Scanner Kit with 27 LEDS

I want to hook up 3 LEDs in series to each output of the 9 LED board, having 27 LEDs total. Would I need to swap out the resistors? And what size power source would you recommend?


  • You probably can't really drive 3 LEDs in series directly from each output.   

    The absolute maximum voltage for the microcontroller is 5.5 V; do not exceed that value.    The actual voltage output may be up to 0.8 V below the input voltage, so you may get as low as 4.2 V output-- only 1.4 V/LED.  If this is the case, the LEDs may not light up at all, even without a resistor.  On the other hand, the voltage drop on the output may be lower, so it's possible that you'd get up to 1.83 V/LED, which may be enough to overdrive them.  So, you are trying to match the 3X the forward voltage of the LEDs-- a not very specific spec --to be less than or equal to the power supply, less the voltage drop of the microcontroller-- a not very specific spec.   

    You're welcome to try, of course, but I wouldn't guarantee that it would work.
  • Okay. Thank you very much!!
  • hey, if you're up for a little coding adventure, you could charlieplex 6 of the i/o lines on the scanner to drive up to 30 leds.  i did it once on a minipov with 64 leds, (sinking 8 leds on each of eight pins),  and didn't blow out any of the i/o.
  • Yep.  Potentially, the nine LED lines could be used to drive up to 9*8 = 72 LEDs through charlieplexing.
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