simulate this circuit – Schematic created using CircuitLab

I'm using Arduino Mega Pro 5V. Pins use a max of 40-50mA.

I'm connecting 3 RGB super bright 5mm LEDs. Currently wired in parallel each light with 100Ω resistor.

I'm hooking the lights up to fiber optic fabric and they just aren't lighting the Fiber optics up very well. I'm having them switch from Pink to Blue with PWM pins. I'm trying to figure out how to get the lights brighter. After thinking about it I'm confused to if I need the resistors or if I'm using to high since they are all connected to the same pin. I think this is dulling the light alot.

I need 10 lights total 2 groups of 3 lights and two groups of 2 lights so on the two lights I can see where I may need a small resistor but since the Aurdino already limits part of the current.

This is only my 2nd project, its for a costume Sewing I'm expert. I've only recently started adding electronics and I'm teaching myself so sometime need the help of other more experienced than me.

Here is the only information I have on the lights. And I'm Using the Arduino Mega Pro 5V from Sparkplug. Currently I'm using a lilypad max 40MA but I need more PWM pins so I'll be switching to sparkplug board (it shipped today) I tested my lilypad red pin with multimeter and it was drawing 30-40MA.

Condition: 100% Brand new and high quality Material: Plastic and metal Quantity: 100 pcs Mode: Common Cathode Forward Voltage: 1.8~3.4V Power: 0.06W Bulb Diameter: 5mm Total Length: 36mm Package include: 100pcs common cathode 4-Pins Led light

  • 9
    \$\begingroup\$ Does this arduino come with its own power sub-station to support the 50 MA of pin current? \$\endgroup\$ Apr 7, 2015 at 14:21
  • \$\begingroup\$ Datasheet of the LEDs would be nice... You have a beefy microcontroller that can output 50 mega amps of current. \$\endgroup\$
    – Golaž
    Apr 7, 2015 at 14:22
  • 9
    \$\begingroup\$ The Arduino doesn't limit the current. It has a limit on what you can safely draw. The two concepts are very very different. \$\endgroup\$
    – Majenko
    Apr 7, 2015 at 14:27
  • \$\begingroup\$ These links might help: electronics.stackexchange.com/questions/13613/… electronics.stackexchange.com/questions/154007/… \$\endgroup\$
    – akellyirl
    Apr 7, 2015 at 14:36
  • 1
    \$\begingroup\$ Attempting to draw 50mA from an Arduino pin will tank the voltage. \$\endgroup\$ Apr 7, 2015 at 16:09

2 Answers 2


The circuit you have is trying to draw far too much current from each pin, between 60 and 100mA per. Even if the pins could handle that much current, the MCU can't, which would result in the eventual destruction of the device. You should modify your circuit so that it uses low-side switching using transistors to draw current directly from the power supply instead of through the MCU.

  • \$\begingroup\$ Might be worth emphasis on the discrete transistors -- low-side switching directly using GPIO pins is popular for lower currents, and the GPIO push-pull driver can often sink more current than it can source... but still not as much as discussed here. As written, the discrete transistors are only apparent after following the link. \$\endgroup\$
    – Ben Voigt
    Apr 7, 2015 at 18:19
  • \$\begingroup\$ So I started searching switching and transistors and I'm not understanding what these are or how they work. I'm sorry I feel like by the comments that this is like well "Duh" lol but like I said I'm very new would anyone direct me to were and how to apply these? also I wanted to change to High Power RGB LED's ( i found 1W per color 3W total ones that I'd love to use because I think it would make my project really really bright) would these help? as well? Or is it something That I'll only still be able to use the Ultra bright LEDs with? \$\endgroup\$
    – Teresa
    Apr 7, 2015 at 20:21
  • \$\begingroup\$ @Teresa: Have you had a chance to read the linked question and answers? \$\endgroup\$ Apr 7, 2015 at 20:29
  • \$\begingroup\$ I did but several of them didn't seem to apply. I've already got separate resistors. I'm pretty sure that the transistor thing is my issue but I don't understand exactly what a transistor is how it works with PMW. \$\endgroup\$
    – Teresa
    Apr 7, 2015 at 20:42
  • \$\begingroup\$ Found a youtube video that explained it all how the arduino works with the transistor. Thanks Ben Voigt This is exactly what I needed! I completely understand! \$\endgroup\$
    – Teresa
    Apr 7, 2015 at 21:20

Now that a schematic has been added to the question, it looks like my guess was wrong - your schematic does have a separate resistor for each LED. My original answer is below.

It's hard to tell, but it sounds like you're doing this:


simulate this circuit – Schematic created using CircuitLab

This is a Bad Idea™. The voltage across the LEDs will only be as high as the smallest forward voltage, and you'll end up with 2 dim LEDs.

This related question gives some more in-depth explanations.

(If this isn't the circuit you're using, you'll have to post some schematics - we can't read minds!)

  • \$\begingroup\$ One pin from the Arduino goes each color pin on the light separate. So one pin to Three red pins on three separate lights. Each red pin has their own 100ohm resistor. Greens are on their own pin from the aurdino and each light green pin have having their own 100ohm resistor. I'm not exactly sure how to draw it out. hum... I'll see if I can Draw something lol it wont be as pretty as yours but I'll try to get the point across to how its working. \$\endgroup\$
    – Teresa
    Apr 7, 2015 at 16:03
  • \$\begingroup\$ You can edit your question and insert a schematic with the built in editor (that's how I made this one) \$\endgroup\$
    – Greg d'Eon
    Apr 7, 2015 at 16:04

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