Multiple LEDs on one pin

Hey guys,

I'm a freshmen EE major and I, quite unfortunately, don't know much about electronics yet (I actually just changed my major from business to EE.) I was thinking about creating a project that has red, blue, and green LED connected together and sequencing through them. My question as of right now is can I connect, lets say, 10 LEDs together (by just soldering the cathode of one to the anode of the other) and connect the remaining anode to a pin and the remaining cathode to a ground will damage my Arduino?

From what I've read, a pin supplying 5V of current will supply more if the connected components "demand" it (aka the huge difference of electron density) and I'm guessing this will damage the chip.

Is this correct? Also, if I have future questions such as this, where can I reference to?

Thanks!

No, you can't do that. The pin will only ever supply 5V to your LEDs, and each LED in series needs about 3V, so once you get more than 2 (3 would need about 9V.)

and yes, if you draw more current than a pin can source (about 40ma MAX) you will cook the chip

Mmm toasty. My favorite kind of ATmega. ;D

If you're not worried by brightness you could wire 10 leds in parallel, each with a 1 k resistor and get away with running them on one digital pin. Say 2.2 forward voltage = 2.8 mA per LED X 10 = 28 mA - easy.....

Ah, I see. What would I have to do in order to power 300 LED at 3mA each? This is just theoretical, so I guess my real question is: how do power a device that require more than 12 pins (I think?) x 5V = 60V?

External power sources, transistors, possibly relays, and shift registers :P.

300 LED at 3mA each

You won't get anything bright with 3mA but see what your total current is:- 300 * 0.003 = 0.9A

So that means you need an external supply.

How fast do you need to refresh the pattern? for a shift register you need 300 / 8 = 38 shift registers

Do you need to control the brightness, if so forget shift registers and look at putting them in a series of 8X8 matrices controlled by it's own chip.

It seems what I’m trying to do is a bit beyond my level right now.

Thanks everyone! :slight_smile: