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Topic: Led Stripe 12V not glowing (Read 1 time) previous topic - next topic


Hey you all, probably is already written in the forum but I really dont understand..   Im an ignorant about all this but I desperatly need to know how to make it work.. help!
Im connecting a LED stripe (12V) to Arduino and is not working.
Concidering that Arduino cannot give 12V I thought that the light would have been just less intense but no, is not glowing at all.
I've read about a "Mosfet" or something like it?!

What shall I do to switch on the stripe?

Ran Talbott

Sep 14, 2009, 11:28 pm Last Edit: Sep 14, 2009, 11:29 pm by RanTalbott Reason: 1

LEDs are different from incandescent bulbs:  they won't light up until the voltage gets up to a threshold that's pretty close to their normal operating level.  Then the brightness goes up dramatically with very small changes in voltage.

Another difference is that they're not as tolerant of excessive voltages as bulbs:  15V will make a 12V bulb brighter and hotter,  and burn out somewhat faster than normal.  But it can be enough to make a 12V LED string into a "flashbulb" that only lights up for a fraction of a second.  So make sure your 12V supply really is 12V (a lot of cheap ones don't regulate their output voltage).

If you look on this page,  you'll find that a lot of the questions you'll be thinking up as you learn more have already been answered.

For this case,  you should just need a simple 10-cent NPN transistor to switch the "ground" side of the LEDs.  Check the examples in the Playground area for driving higher-powered LEDs,  and for driving small relays.



or if you are driving move than one output use a some thing like a ULN2803A.

I use than to power relays etc or power differant voltage loads.

Ryan B

I am new here myself, but after toasting some stuff, I found that an optocoupler works even better than a relay. You feed the logic level (5v) from the Arduino pin into one side and use it to switch the the 12V on the other side.

I used the 4N35 optocoupler. The optocoupler uses an LED and a phototransistor in a tiny IC package to connect the two halves. since the connection is made using only light, there is less risk of frying your precious Arduino. :)

What is nice about this setup is that you don't lose the ability to vary your output, like if you are using the Arduino's PWM output, although you may want to incorporate a small capacitor to smooth out the pulses into a more analog-like signal.


ok.... now I have the ULN2801A, a power supply 12v, arduino, a 12v led stripe. CAN SOMEONE TELL ME HOW CONNECT THESE THINGS? :-[

maybe is really simple (I hope) but i tried many times and i suppose that i fried my ULN2801A....



Sep 16, 2009, 01:56 am Last Edit: Sep 16, 2009, 02:00 am by peter224722 Reason: 1
I use the 3a which is better for TTL, but how it works is still the same.

Normally if you are lighting a LED etc are sourcing the current, eg volts is coming from the pin to Gnd.

With the ULN2801A/3A you are sinking the current, eg acting as a switch.

So the input side you need Gnd ( - ) and the pin .

The output side you need Gnd plus a ( + / Positive ) supply which is not necessarily the 5 volt driving the Ardunio , but any voltage up to 30 volts ?

eg the load goes from the output pin to the ( + ) supply

Don`t for get to connect both the Gnds together !! and Pin 10 is for a inductive load and should be taken to the ( + / Positive ) supply


You can just treat the LED as you would a motor (one direction only) in this tutorial :- http://www.thebox.myzen.co.uk/Workshop/Motors_1.html


DONE! now is blinking... i'm really happy!!!
the problem was the component... the first time i bought ULN2801A, but for arduino voltage is better ULN2803A (tnx to peter247)....

thank you all guys ;D


Hallo to everyone ..!
I've written on the blog some time ago, I thought I did solve the problem but I am again having the same trubles.. here is it;
To turn on and off my led stripes I've used this components: ULN2803AG, it worked for a couple of days.. after then it became really hot and suddenly it did not work anymore.
As suggested in the forum we used also ; ULN2803A but it never worked out.. (we thought it worked in the beginning, but actually it did not..)
We tryied to use new components but no good results, they would get extremely hot (we think that could be the problem ), we also changed Arduino but nothing happened.

Please someone can give a help ?..
we only need to turn on and off some led stripes using Arduino..



You most likely cannot run 1 amp total with that chip. I've not seen a specification for those LED arrays. If you allow the chip to be over driven it will fail.

That chip will easily drive 8 relays or you can use 8 resistors, transistors and diodes.



You most likely cannot run 1 amp total with that chip.

It is not most likely it is definite. You can only switch about 650mA total from these chips. For the explanation see:-


Jun 28, 2010, 09:20 pm Last Edit: Jun 28, 2010, 09:45 pm by HarvesteR Reason: 1
I set up the exact same circuit for a project, and had the very same problem of burning out a chip when the current was maxed out....
Nearly burned my finger on it, so hot it had become...

Thankfully I had a spare chip, a ULN2003AN that managed to withstand the current...


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