RGB LED strip and power supply

Hey everyone - thanks in advance for your help! I want to use an RGB LED strip controlled by an Arduino. For now I powered the strip with an external power supply and the Arduino via the USB cable. Now I don't want to have to have a USB cable attached all the time, so I want to power the Arduino via the same external power supply. The LED strip needs 5V and can theoretically draw up to 3A of current with all LEDs on full brightness - with the application I have in mind, it should never go above about 1.5A (I measured the current during a test and it never went above 1A but could get a bit higher theoretically). I do have a 5V 2A power supply. Now I know I can't just plug it into the Arduino since I can't draw more than 1A of external power through the VIN pin for the LED strip since the diode on the Arduino is only rated for 1A. Can I just cut off the plug connector and solder 2 wires to the power line and connect the LED strip and the Arduino in parallel (sharing the GND), supplying the Arduino with power through the vin pin? Do I need to use a resistor in front of the Arduino to limit the current to 200mA or so or will it only draw as much as it needs?

Yes, you can connect them in parallel. No resistor needed, Arduino only draws what it needs. Connect to 5V to Arduino's USB connector, or to the 5V header pin with a diode from 5V (anode) to Vin (cathode) to avoid reverse driving the regulator. If you connect to Vin, there is not enough voltage for the regulator to work.

Thank you :) I just read the specifications again and it says it needs 7V-12V if supplied through the VIN pin (otherwise there's not enough voltage as you said). It also said that supplying it through the 5V pin is not recommended since it bypasses the regulator and can thus damage the board - could that be a problem or should it be safe since I will be using a 5V power supply? How would I wire the diode, attach the 5V power supply to the anode and then plug the anode into the 5V pin and cathode into the VIN pin? What about GND? How would I connect the 5V to the USB connector? Just solder a USB plug to the power source?

This is the wiring I am using right now by the way (with power to the Arduino coming through the USB connector): https://learn.adafruit.com/system/assets/assets/000/001/170/medium800/led_strips_lpdarduino.gif?1396769739

I've seen diodes soldered right to the 5V regulator. I've seen diodes soldered from the 5V header pin to the Vin header pin. Gnd is not involved in the connection. See page 11 http://www.ti.com/lit/ds/symlink/lm1117-n.pdf

You will be safe with the 5V supply - as long as you don't accidentally get the 5V & Gnd connections backwards.

If you cut the end off a USB cable and connect the +5/Gnd to the 5V power source that would be good too, then you could plug it into the USB socket on the board and it would be more secure than 2 pins stuck in the power header.