Arduino uno digital output voltage

Other Hardware LEDs and Multiplexing
1

Hey guys, i am powering up an LED and have a question. If I power up the arduino via USB, the digital outputs are 5 volts right? But what if i power the arduino uno with 6 volts (4 batteries), would the LED receive 6 volts from the digital output, or the typical 5 volts. I'm asking this because i want to know if i should use a 200 ohm resistor or 300. Thanks

2

You could try using a voltmeter to test :slight_smile:

3

I'm sure you know the first part of the answer.

Powering it from 6 V - directly to Vcc - exceeds the Absolute Maximum rating of the chip, especially as with fresh batteries, it will be actually 6.4 V.

If however, you insist on living (your system's) life on the edge, then the chip will indeed attempt to approximate whatever Vcc you are providing, on its output pins.

And yes, the chip probably will not fail. Probably. But equally probably, when it does, it will be when you least expect it. There is a law that states this.

4

I'm asking this because i want to know if i should use a 200 ohm resistor or 300.

Quite honestly it does not matter, if you put your Arduino in danger like this what are a few more milli amps going to matter.

5

Sorry guys, i am a complete noob to this. How exactly am i putting my arduino in danger? I thought it can power up with 12 volts. What would 6 or 6.4 volts do

6

You can put 12V into the power jack but there is an on board regulator that drops that to 5V. Of course you can power the Arduino that way safely but your output voltage from the pins will only be 5V.

What you can not do is put a lower voltage than about 6.5V in that power jack pin as there is not enough excess voltage for the regulator to work. What you can't do is power the Arduino chip with more than about 5.5V which is what you seem to be suggesting. The pin output voltage is only ever the chip's supply voltage and so you can't change things.

7

Thanks mike. So i can power my arduino with 12 volts without damaging the LED's because the output is 5 volts, correct?

8

Yes :slight_smile:

For powering the Arduino you have two options

  1. Use the Vin/power jack. This voltage is regulated to 5V (so all outputs work with 5V etc) But the official range for this is from 7V to 12V. Like Mike pointed out, 6,5V is the bare minimum as the input voltage for the regulator to work correct.

  2. Use the 5V pin to directly supply the Arduino. As the pin name indicates it is designed for 5V but anything between 3,5V to 5,5V will work. But this voltage is not regulated and a to high voltage can damage the Arduino (and a to low voltage can make it unstable). In high state the Arduino will output this voltage.

9

With 5 volte and no resistors your LED will burn!!!!!