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Arduino maximum current draw?

What would the maximum current draw through an Arduino be? (ATMEGA328) - I'm planning on running 16 LEDs from it and I need to know if I should be powering them separately somehow.I have the appropriate resistors (100ohm and 180ohm LED dependent).

iceng3 years ago
For your understanding.
  1. A 2N3904 NPN transistor has a worst case saturated ON voltage drop of 0.3 Volts
  2. A single RED LED has a low forward voltage drop of 1.8 Volts
  3. Your power supply is 5 VDC
  4. Calculate voltage across the Resistor = 5 - 0.3 - 1.8 = 2.9 Volts
  5. You want to run 40 ma through the LED
  6. Ohms Law states R = V / I = 2.9 / .04 = 72.5 ohms
  7. You cannot buy that value so use a 75 ohm 5% resistor

Two RED LEDs in series case.
  1. Calculate voltage across the Resistor = 5 - 0.3 - 1.8- 1.8  = 1.1 Volts
  2. You want to run 40 ma through the LEDs
  3. Ohms Law states R = V / I = 1.1 / .04 = 27.5 ohms
  4. You cannot buy that value so use a 27.4 ohm 1% resistor

A
ResistorLED.JPG
The ABSOLUTE MAXIMUM package current of 200mA, and a ABSOLUTE MAXIMUM pin current of 40mA per pin is stated on the datasheet/

10mA per pin for 16 pins is the only safe point, unless you can guarantee that not all LEDs are ever driven at the same time

Powering them separately would require transistors
jonrb (author)  steveastrouk3 years ago
Cool, thanks!

I'm assuming there won't be any problem running them from the same power source as the Arduino (It can provide around 1.5A)?

If I'm running them off a separate power source, should I just run the pin's 'ground' combined with the LEDs' 'ground' (After going through the transistor) into the power source? (Like in this picture: http://bit.ly/15ep1ZB ) - I like to think that the arduino's GND just goes into the power supply's GND anyway, but I guess it's good to check.

Does it matter what kind (PNP and NPN) transistor I use, particularly? Will the models matter?

(Any switching will be done in millis)