Rob ‘linear’ Arnold has put together a fantastic LED Series/Parallel Wizard.  Not only will it calculate the current limiting resistor you need, it will draw a circuit diagram, and give you full statistics on power usage.  If you are just getting started with Electronics, this is a great resource for learning about LEDs.  Experienced users will enjoy a quick check of their math.

The array above is designed for some Blue LEDs I have laying around.  I wanted them to run with 15mA which is well below their max, but still very bright.  In this case 1/4W resistors should be fine and each should be 120 ohms.  I should be safe hooking this array up to an Arduino since each LED will draw less than each I/O pin can handle AND total current draw is only 60mA.

Very Cool Stuff!


Fan of making things beep, blink and fly. Created AddOhms. Writer for News. Freelance electronics content creator for hire! KN6FGY and, of course, bald.


  1. Keith Powell Reply

    I’ve used Rob’s led calculator many times in the past, now it’s gone the “404” path. Any ideas on what happened ?????

    • Me to… since my first led burnout anno 2010 maby.. to my array of 200 rgb mix.. my guess.. He stoped paying for the hosting or grew tired of it. I tried a few times to rip the code from the page because of this but i cant recall if I at anytime succeded.

  2. Pierre Van Overmeire Reply

    calculator is no more work.
    Warning: main(/home/linear1/public_html/led/wp-includes/wp-db.php) [function.main]: failed to open stream: No such file or directory in /home/linear1/public_html/led/wp-settings.php on line 30

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