# Supplying power to an 5V LED strip

I'm working on a project to create an infinity mirror based on an Instructables tutorial. Instead of the larger analogue LED strip that the author uses, I opted for a shorter addressable LED strip that runs on 5V.

I thought I would be able to run it off the 5V port on the Arduino, but that seems not to be the case. I understand that the strip can draw up to 3.3A and the Arduino can only supply ~0.5A, but I thought it would work fine if I only turned a few lights on (each one draws ~0.05A). However many lights I program the Arduino to turn on, I always see ~10 random lights with a bias towards red.

The fact that the lights are usually red and there are ~10 of them working at any one is evidence that it is a power issue (because red is lower power and 10×0.05A = 0.5A).

Does anyone have any ideas how I can either

1. turn on only a chosen subset of lights at one time, or
2. supply the appropriate power to the LEDs (preferably from a battery) ?

Here's the code I'm using below, on the chance I made some stupid mistake:

/* LedStripGradient: Example Arduino sketch that shows
* how to control an Addressable RGB LED Strip from Pololu.
*
* To use this, you will need to plug an Addressable RGB LED strip from Pololu
* into pin 12.  After uploading the sketch, you should see a pattern on the LED
* strip that fades from green to pink and also moves along the strip. */

#include <PololuLedStrip.h>

// Create an ledStrip object and specify the pin it will use.
PololuLedStrip<12> ledStrip;

// Create a buffer for holding the colors (4 bytes per color).
#define LED_COUNT 72
rgb_color colors[LED_COUNT];

void setup() {
}

void loop() {
// Update the colors.
byte time = millis() >> 2;
for(uint16_t i = 0; i < LED_COUNT; i++)
{
byte x = time - 8*i;
// colors[i] = (rgb_color){ x, 255 - x, x };
colors[i] = (rgb_color){ 0, 0, 0 };
}
colors[0] = (rgb_color){ 0, 0, 255 };
colors[1] = (rgb_color){ 0, 255, 0 };
colors[2] = (rgb_color){ 255, 0, 0 };

// Write the colors to the LED strip.
ledStrip.write(colors, LED_COUNT);

delay(100);
}


Thanks!

• Use a dedicated 5V/USB power supply, bypassing the linear regulator on the arduino. Also add a capacitor 1000uF or so at the beginning of the led strip, to help smooth any issues from inrush current. – Passerby Nov 25 '15 at 22:28
• The bias towards red, if it means the red is brighter, could suggest the voltage is dropping when the leds turn on. How are you powering your arduino. – Passerby Nov 25 '15 at 22:30
• @Passerby: I've tried USB, 9V battery, and both. It looks like most of the LEDs are completely red, and there are a few that are other colors. Should I use the Vin pin? – Zaz Nov 25 '15 at 22:34
• If you are using VIN or the dc jack, it turns off usb and goes through the regulator. A 9V battery will be especially bad. Use a USB or connect a Regulated 5V power supply to the 5V with 1Amp or better supply. – Passerby Nov 25 '15 at 22:36
• @passerby: he says the full LED strip wants 3.3 amps, so he'll need a 5 volt supply capable of 4 Amps or more to power both the Arduino and the LED strip. The LED strip's power should come directly from the power supply, not throught the Arduino. – Peter Bennett Nov 25 '15 at 22:59