# 2 LED's in serial ?

Hi Guys,

Just wondering if this will be ok to do ?

I've got some RGB 5v led's that I want to us as eyes that change colour. Am I ok in thinking I can wire these in series directly to the arduino pins rather than using a resistor ?

these were the ones I got.

http://www.ebay.co.uk/itm/120738434604

thanks

Steve

I've got some RGB 5v led's

How do you know they're 5 volt?

Sorry, I just presumed they were on looking at the ebay link I think they are around 3v now

Do you think I will be safe for serial ? I am to a use analogWrite to alter the pulse to them.

thanks

Do you think I will be safe for serial ?

No. See here for why:- http://www.thebox.myzen.co.uk/Tutorial/LEDs.html

You can't wire these LEDs in series anyway.

You require a resistor with an LED, regardless of the voltages used.

Put simply, an LED is a semiconductor junction device. A semiconductor junction device always has a voltage drop, but doesn't have any internal resistance.

In other words, it will drop a specific amount of voltage in a circuit, but it will not affect the current flow.

Using Ohm's law, we know that I=V/R - the current is the voltage divided by the resistance. We have a known voltage - the supply voltage, 5V. Semiconductor junction devices have no resistance, so the resistance is 0.

Simple maths: I=V/R = 5/0.

What is 5 divided by 0? It's a bang, that's what.

Anything divided by 0 is infinity. That's infinity amps being drawn out of the Arduino IO pin - the pin that can only supply up to 40mA. Poor pin.

So you have to add some resistance to make up for the lack of resistance in the LED.

So remember kids - an LED with no resistor is like a short circuit.