# Arduino External Power Supply

Hi,

I'm doing a Arduino UNO LED flashlight/light project for school. I'm using four 100 lumens LED that's rated for 3.4V forward voltage each. My instructor want me to use a arduino, but I know it only have a 5v output and that's not enough voltage. I can use a 9v battery to power the Arduino, but will need some sort of voltage booster or something. In additon, I will be programming the Arduino to do some sort of flashing to. Any suggestions or ideas will help. Thanks in advanced Boss...

Well, 5V is > 3.4V so why is that not enough?
How much current do they need? A current-controlled driver may be required to prevent them from overheating and burning out which the Arduino can control.

Rated:

3.4v x 4 = 13.6v

350mA each x 4=1400mA or 1.4mA

are you not connection you LED's in parallel? if so that means voltage is 3.4 yet amps = 1.4 amps.

Not sure what you circuit is, all 4 leds on at same time, one by one. etc.

Hard to guide you here.

KrisKasprzak: are you not connection you LED's in parallel? if so that means voltage is 3.4 yet amps = 1.4 amps.

Not sure what you circuit is, all 4 leds on at same time, one by one. etc.

Hard to guide you here.

Ah, Thanks. I forgot about hooking in parallel. So if I connect all 4 LED's in parallel individually from one another (4 strings), each led in each string should recieved same voltage as the power supply correct?

Example: Using 3.4v power supply and connecting 4 led's in parrallel with each other individually will equal 3.4v to each LED correct or am I wrong here?

Thanks Kris

Example: Using 3.4v power supply and connecting 4 ledâ€™s in parrallel with each other individually will equal 3.4v each LED correct or am I wrong here?

Yes, all in parallel.
If they need 350mA each, then a current controlled driver is needed for each, such as:

If you use a boost regulator to get >13.6V, you could use just 1 and wire the LEDs in series.
Check the regulators at www.pololu.com for one that will output say 15V and 350-400mA.
9V battery (the small rectangular type) only have a few hundred mAH capacity and are not intended to put out 350mA, use some AAs or Cs or Ds for current to the LEDs.