How do I add more current to an output?

total NOOB here.

trying to make a simple LED sign for my wife for mothers day. So it says:


Lighting each character separtely or whatever. So I don’t need to control each led separately, just each character separately. So what I don’t how to do is add current so that each letter can be made up of however many red LED’s it takes to make that letter in a perf board.
I have a mega, but was going to use a Duemilanove for this.

It will also be running a charlieplexed “open heart” if you know what that is. Which uses 6 pins I think.

Any advice, pointers, tips or tricks is greatly appreciated. I got 4 days to pull this off.



o what I don’t how to do is add current

You run each output through a transistor first. That will boost the current. Arduino Output to the base of the transistor through a 1K resistor. Emitter to ground, collector to resistor / LED, other end of this to the +5V.

We have some current-boost ideas here.

  • use BJT transistors
  • use MOSFETs
  • use a driver array like ULN2803

Thanks! I have a bunch of bc337, 2n4401, and 2n4403… will any of these work for my purposes?



2N4401 is ideally suited for LED DRIVER. It handles a few hundred milliamps. Around how many are the MAX LEDS are you stringing together off 1 pin?

Around 50 per pin