RGB LED strip

Hi everyone, i ordered a RGB LED strip but i simply can't turn it on... i searched for some days and i got no results.

my LED strip is powered by 12V since i'm working with arduino and it only has 5v output i understand that i have to use some NPN transistors. I'm using the TIP 121 since the shop didn't have the TIP 120... can that be the problem?

Post your schematic, let's see how you wired it up. TIP121 vs TIP120 should be fine. TIP121 rated to 80V, '120 only to 60V. At 12V, no difference. http://www.st.com/web/en/resource/technical/document/datasheet/CD00000911.pdf

so, the emitter is connected to the gnd , the collector to the LED strip and the base to arduino pins. is it right?

here's the schematic. http://postimg.org/image/xzp2sd35h/

I can't open stuff at postimg.org. Can you Reply and Attach the image?

Also, post the code you are running.

i just wanted to check how the strip works and build my own algorithm later, so i copied the code from adafruitto and tested it.
i noticed that if i move the strip slightly it turns some leds on but with very very low brightness.
i can’t see what i’m doing wrong but i guess it is pretty obvious…

#define REDPIN 10
#define GREENPIN 9
#define BLUEPIN 11
 
#define FADESPEED 5     // make this higher to slow down
 
void setup() {
  pinMode(REDPIN, OUTPUT);
  pinMode(GREENPIN, OUTPUT);
  pinMode(BLUEPIN, OUTPUT);
}
 
 
void loop() {
  int r, g, b;
 
  // fade from blue to violet
  for (r = 0; r < 256; r++) { 
    analogWrite(REDPIN, r);
    delay(FADESPEED);
  } 
  // fade from violet to red
  for (b = 255; b > 0; b--) { 
    analogWrite(BLUEPIN, b);
    delay(FADESPEED);
  } 
  // fade from red to yellow
  for (g = 0; g < 256; g++) { 
    analogWrite(GREENPIN, g);
    delay(FADESPEED);
  } 
  // fade from yellow to green
  for (r = 255; r > 0; r--) { 
    analogWrite(REDPIN, r);
    delay(FADESPEED);
  } 
  // fade from green to teal
  for (b = 0; b < 256; b++) { 
    analogWrite(BLUEPIN, b);
    delay(FADESPEED);
  } 
  // fade from teal to blue
  for (g = 255; g > 0; g--) { 
    analogWrite(GREENPIN, g);
    delay(FADESPEED);
  } 
}

Hi, you should have resistors between the Arduno pins and the transistor bases. A few KOhms should be ok. Otherwise you could damage the Arduino. Maybe you already did. Will those Arduino outputs still run 5mm leds ok (with 200~300R series resistors)?

thank you for the warning, i'll use 10k ohm resistors now. and yes, it still works fine with the usual LEDs.

10K is too high. 220 to 1K would be better.

djsarnaldo: i'll use 10k ohm resistors now.

A little too high. Try 1K~2K. Are you sure you have identified the base, collector and emitter legs correctly?

Also your diagram shows the 12V line from the strip connected to the 5V pin on the Arduino. Was that just a diagram error?

sorry, i know that must be the error now that you talk about it, i'm a noob with transistors. the thing is, arduino only gives +5v and i need +12v to power the strip and i thought the transistors would solve that problem. please explain me what i am doing wrong.. -.-

Your schematic is correct, IF you have the transistors wired correctly and the lack of base resistors didn’t damage the Arduoino. Does the chip feel warm or hot at all?
You also need +12V supply Gnd connected to the Arduino Gnd. It should be if the 12V is connected to the Arduino barrel jack connector.

no, i checked some times and they were cold.
i’ll check the wires and the connections. maybe it is just a bad connection between the breadboard and the wires

djsarnaldo: the thing is, arduino only gives +5v and i need +12v to power the strip and i thought the transistors would solve that problem.

Are you saying you do not have a 12V supply? And you thought the tre transistors would turn 5V into 12V? How are you powering your Arduino?

with a 12v supply connected to the arduino. which terminal should i use? there is no 12v pin

You need to make a splitter cable from your power supply so that the Arduino gets 12V at the barrel jack, and the +12V at the LED strip gets 12V. If the LED strip is not too long, 6 or maybe 9 RGB LEDs at the most, you could power it from the Vin header pin.

CrossRoads: I can't open stuff at postimg.org.

Hmm. Seems this link works better: |500x302

At least it works!

CrossRoads: Can you Reply and Attach the image?

Oh please don't!!

May work for some, but "Attachments and other options" is totally broken.

You can use forum attachments like this:

RGB_strip.png

Which involves attaching your pic and then posting, copying the link address, then modifying your post and attaching the copied link address. Yes, its is a minor pain!