Powering Multiple LEDs with Mega Digital Output

Using Arduino LEDs and Multiplexing
#1

I would like your opinion on the best way to power multiple LEDs. I will be using 12 RGB LEDs with 20mA forward current powered with 5V as a panel indicator. The setup will be green for a positive result, red for negative result, and blue while running the experiment. The blue will be on the majority of the time (up to 10+ hours), and red or green once the result is obtained. I have 2 circuits in mind. The first is powering 12 LEDs directly from the Mega digital pins through a 250ohm resistor. The second is having a separate 5V power supply connected to a NPN transistor in series with a 250ohm resistor and LED, and using the digital pins just to apply the base voltage for the transistor (see attachment for schematic). The question I have is will I be drawing too much power from the Mega having 12 LEDs on continuously?

led driver.docx (170 KB)

#2

Use a transistor. Mega output pin is only good for 20-30mA of current.
12 LEDs in parallel each drawing 20mA is 240mA.
Your onboard regulator may get hot if the voltage at the barrel jack is high, like 9-12V.
You need a current limit resistor per LED and the NPN transistor “below” the LEDs sinking current to Gnd.

RGB LEDs.jpg
RGB LEDs.jpg960×720 37.9 KB

#3

Perfect. That is what I was thinking, but just wanted to clarify. Thanks.

#4