How do I add more current to an output?

Forum 2005-2010 (read only) General Frequently-Asked Questions
1

total NOOB here.

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

HAPPY MOTHERS DAY!

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.

Thanks,

Tony

2

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.

3

We have some current-boost ideas here.
Basically:

  • use BJT transistors
  • use MOSFETs
  • use a driver array like ULN2803
4

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

Thanks!

Tony

5

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?

6

Around 50 per pin