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I'm trying to understand and adapt this tutorial:


to my own use. I am doing essentially the same thing, except I have this single color LED strip, and I don't fully understand how to power both the arduino and the led strip from the same power source.

I tried to wire it using the diagram above, and something started smoking (I think the IR transmitter). I don't know much about circuits, but I'm pretty sure that's not good.

In this diagram, the 9v represents DC power, the IR sensor on the left represents the transmitter, the IR on the right is the receiver, and the white LED is the LED strip, with two outputs (+ - )

In the fritzing diagram for that tutorial, they have the + from the LED strip going straight in to Vin on the uno, but they don't show how either the LED strip or the uno themselves are being powered.

Do I need two power sources?

Do I need a mosfet considering I'm only using a one color LED strip?

I've got the IR sensors working, so I don't need help with that, and I can connect one of these 12V switching power supplies to one of these DC power screw terminals to power the lights without any arduino control, so all I'm missing is how to turn the lights on and off with arduino, IE, how to go from the power supply to the arduino to the LED strip.

I don't need to PWM the LED strip - just shut it off and on.

If anyone can help me correct the fritzing diagram or explain what I'm doing wrong / what I should be doing instead, I'd greatly appreciate it.

2 Answers 2


enter image description hereNote that VIN pin and the 2.5mm DC Jack are connected. So in the tutorial one of these is getting power from a +12Vdc source and the other is supplying +12V to the +12v labeled pin on the LED string. Where the R G and B pins of the strip should be connected to Collectors of NPN's. Each of the NPN's bases are driven by Arduino Output pin and all the Emitters are connected to Ground.

So +12V supplies the DC Jack (aka Vin) the Arduino's local regulator converts that to Ground. The +12V via Vin supplies the LED's. And the Digital Outputs drive the base's of the NPN's. Which in turn act like a relay closing the perspective LED's to Ground, so they can illuminate. Where a Digital ONE or HIGH or TRUE on the BASE results in 5V above ground, which causes it to have low resistance.

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  • Sorry, I don't understand your diagram. Also, I think the details of my project are different. I am using a MOSFET (adafruit.com/datasheets/irlb8721pbf.pdf) so I'm dealing with G D S, and I'm using a single color LED strip - so + and - vs R G B + . Is it possible to explain your answer as it relates to the fritzing diagram? Sorry, I'm trying to understand but I'm not clear on a few things: is the 7805 the IC of the arduino? How does the power split both to the IC and the Vin? what is the R? What are the two resistors resisting? What about the breakbeams?
    – mheavers
    Feb 17, 2015 at 15:36
  • 1
    You can use a mosfet instead of the transistor in the circuit. If you use a mosfet you can keep out R1. Since you only have one color, you can ignore the 3x part. Only the dash-outlined circuit, you need to build. The rest is part of the arduino board. Including the Vin pin (which is connected on the board to the jack). R1 is to limit the base-current going into the transistor. Without it the transistor will burn out, and possibly the output-pin. R2 is a pull down, so the led doesn't light up during power-up I think the values for the two resitors are wrong. I'd use 1k for R1 and 10k for R2.
    – Gerben
    Feb 17, 2015 at 17:31

You asked: "Do I need a mosfet considering I'm only using a one color LED strip?"

Yes, absolutely. An Arduino logic line can only put out about 20 mA of power at 5V. That's not an unreasonable amount of power for a single low-power LED. An LED strip is likely to draw a lot more current than that, and it's pretty common for LED strips to use 12V, not 5V.

What LED strip are you using, and what input voltage and current requirements does it have?

You should be able to use a single power 12V power supply for your project. (assuming your LED strip needs 12V.) You'd feed it into the barrel jack of the Arduino. The Arduino's voltage regulator would use that to generate its 5V power. You'd also feed 12V into the power for your LED strip. You'd use a logic-level MOSFET to switch the power to the LED strip on and off. A logic level MOSFET is able to use a low current 5V signal from the Arduino to switch higher voltage, higher current loads like your LED strip with very little resistance, and thus with very little waste heat generated.

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