I put a LED into 3.3V of the arduino and Ground, and it blew my LED violently, smoke was everyone, the whole half top of the led blew up across my room.

However, when i program the arduino with Pin13 HIGH per say, it will not blow up. Will be lit brightly. (Both using no resistors). However, if I plug mroe stuff in the board, for example, a lcd screen, rotary switches, and pushbuttons for my program, the LED dims to such a low brightness I cannot see.

Why is this? How Do I fix it?

Schematic: enter image description here

Note, that i am using a mega, and some of it is slightly changed, and LED is being powered from A0 (Or Pin 54 on Mega)

  • You have pin 13 tied to ground in that schematic. Are you really settling pin 13 to high output? It would be very useful to have the schematic for your actual circuit, not some other circuit which bears some loose resemblance to your circuit ☺️
    – Mark Smith
    Feb 11, 2017 at 23:06
  • yep this is the circuit i am using, just with addition to the led, and some pin changes. Yes I am plugging 13 to ground according to this schematic, found it suspicious but that is what it said on schematic. Feb 11, 2017 at 23:12
  • I'm surprised it's still working then. Don't tie high outputs straight to ground. Without seeing the code it's difficult to say what the right thing to do is, but probably just disconnect pin 13 and leave the switches connected to ground.
    – Mark Smith
    Feb 11, 2017 at 23:14
  • @MarkSmith does say at the bottom pin 13 stops flutter on the schematic Feb 12, 2017 at 1:18
  • It also says it's configured as input. Don't set it as output then.
    – Mark Smith
    Feb 12, 2017 at 7:51

2 Answers 2


You must use a resistor. See The care and feeding of LEDs

How Do I fix it?

Use a current-limiting resistor.

  • The question is, that i have more electronics attached to it, and without a resistor it is already dim to the point i can barely see it. Adding a resistor would make it worse, i wont be able to see it at all. Feb 11, 2017 at 17:11
  • No it won't. Try it.
    – Mark Smith
    Feb 11, 2017 at 17:29
  • For one thing, not using a resistor effectively channels almost all available current through your LED. That is taking power from other things that need it. Perhaps if you post a schematic?
    – Nick Gammon
    Feb 11, 2017 at 20:27
  • You are Right @MarkSmith, however, it dosent improve brightness at all. I can barely see it, just like before. Feb 11, 2017 at 23:00
  • What value resistor did you use, and what type of LED is it?
    – Mark Smith
    Feb 11, 2017 at 23:02

“I put a LED into 3.3V of the arduino and Ground, and it blew my LED violently ... the whole half top of the led blew up ...” –

Current through the LED was so high that a tiny interconnect wire blew up. In typical LEDs, an almost-invisible wire connects from the anode lead frame to the LED chip on the cathode lead frame (at left and right, respectively, on each of the three lead frames pictured below). That wire acted like a fuse and blew up. With such a fine wire, it doesn't take particularly much current to pop it.

The diagram below shows how current through an LED increases exponentially as voltage across it rises. The diagram is from "mikesflightdeck.com LED dimmer" webpage, a page which may be useful in helping you understand why LEDs need series resistors or some other form of current limiting, eg a constant-current circuit.

LED voltage vs current graphLED lead frame

When an LED is powered by an Arduino port output, the port's internal resistance is enough to limit LED current to non-lethal (to the LED) values. (However, the port itself may get burned out by delivering current beyond its 40 mA absolute max current rating.)

“However, if I plug more stuff in the board ... the LED dims to such a low brightness ...” –

The stuff being plugged in apparently is drawing enough current to drop the system voltage. This can happen if your Arduino is powered by a low-power source like a 9-volt transistor-radio battery, or a laptop USB port that can't deliver the 500 mA that a standard USB port is rated at.

If either of those causes is behind the problem, use an external power supply, plugged into the power jack or connected to Vin and Ground. You can buy suitable “wall-warts” online, or at an electronics store, or quite cheaply at second-hand or thrift shops.

But if neither of those causes is the problem, you may have a clone of an Arduino using substandard parts, and unable to deliver reasonable current through its regulators. In this case, find a well-regulated 5 V supply to connect between +5V and Ground or to the USB's power pins. Such supplies are available not only at the aforementioned venues, but also whereever USB phone-chargers are sold, since 5.0 V is what a USB phone-charger should deliver.

  • Good explanation, but the main point which is missed here is that you MUST use a current-limiting resistor in series with your LED. You are lucky not to have cooked the Arduino, and if you beef up the power supply attempting to stop the dimming, you WILL cook it. Different LEDs need different resistors, but 330R will probably get you started.
    – Mark Smith
    Feb 11, 2017 at 8:53
  • so what i dont get is why it is exactly doing this. To my understanding, dosent voltage affect whether or not my led blows? Feb 11, 2017 at 17:13
  • @MarkSmith, the answer mentions those points. Paragraph 3 says “LEDs need series resistors or some other form of current limiting” and paragraph 4, “the port itself may get burned out” Feb 11, 2017 at 17:25
  • @GeorgeJones, yes, voltage is involved. As shown in that graph of LED current vs voltage, LED forward current increases exponentially with voltage instead of a linear Ohm's Law increase Feb 11, 2017 at 17:31

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