Arduino Voltage Sorcery

Other Hardware General Electronics
1

Dear friends,

Please help me find the answer to the following question :

An Arduino UNO is connected to the PC via a USB port, the Arduino will receive 5 V from the PC.
It can also be powered by a barrel plug +12V.

If I power lets say- 8 LED diodes, each LED from a different pin, with a 15mA current.
I will use 8*15mA = 120mA of current. That's fine.

Here comes the dark magic I cant comprehend.
One LED has a voltage drop of 2 V.

8*2 V = 16V

The drop is 16 V and we are powering the UNO with 5 or 12V. How come ? :o

Thanks for the reply :wink:

2

each LED from a different pin,

You answered your own question.

3

You DO have current limiting resistors in series with each LED ( 150 ~ 470Ω)? Don't you?

4

The LEDs are on separate circuits so the
voltage drops do not add up.

5

TheMemberFormerlyKnownAsAWOL:
You answered your own question.

Did I ? :open_mouth: Hmmm......

in the previous example 5v goes in the Arduino, 16V goes out of the Arduino. That is a -11V balance.

I know that each Arduino analog and digital pin can supply 5V, but I'm confused how the Arduino receives 5v

input, and can deliver like 15 I/O pins * 5V output.

The voltage drop is confusing me.

If you power 2 LED from a 5V battery, the 2 LEDs will drop 2*2 volts, and 1V will be used by the resistor.

But if you power an Arduino with a 5V battery, you will be able to power what, like 15 LEDs from 15 different I/O pins ?

If you have 5v in, how can you drop more than 5V.

Is this dark magic, or am I missing something? :smiley:

6

Hi,
Draw and post a picture of your circuit and we will explain it to you?

Tom... :slight_smile:

7

You are confusing a series circuit, in which the voltages add up the way you suggest, with a parallel circuit, in which the voltages are all the same but the currents add up. I note you have correctly added the currents.

8

PerryBebbington:
You are confusing a series circuit, in which the voltages add up the way you suggest, with a parallel circuit, in which the voltages are all the same but the currents add up. I note you have correctly added the currents.

Boom ! Exactly :slight_smile: Drinks on me Perry !

The I/O pins are having a parallel connection with the Arduino's 5V ?

9

The I/O pins are having a parallel connection with the Arduino's 5V ?

Yes, exactly.

Drinks on me Perry !

Works for me! :slight_smile: