LED Cube 4x4x4

Step 6 Choosing resistor values

There are two things to keep in mind when choosing a resistor value for your leds.
1) The LEDs
2) The AVR

The AVR has a maximum combined current rating of 200 mA.
This gives us 12mA to work with per LED.

You also don't want to exceed the maximum current your leds are rated to.

I used 220 ohm resistors on my cube. This gave me about 12mA per led.

Comments

[brujita038]

Do you use 220k ohms or 220ohms ? because these blue resistors looks like 220k, not 220

[Ryan McDougall]

Could I use 200 ohm resistors instead of 220 ohms for the LEDs

[FFNN]

could u explain a bit more on choosing the resistor values?

In my understanding the resistor value should be obtained using this equation
( Source Voltage - LED Voltage Drop ) / Amps.

So for a blue LED with forward current 30mA and forward voltage:3.6V
The resistor shoud therefore be (5v-3.3v)/30mA = 56ohm?

[FFNN]

Just saw this below

"Yeah, but if you light up all 16 LEDs in a layer at 25mA, you'd be pulling double the AVR's max rated curren"

isn't that avr is coded to light up the led one by one very quickly?
So that it seems to be lighted up at the same time?

[Tadmen]

I have green leds with the following specs:
Forward Voltage: 2, Reverse Current <=30mA, Forward Current: 30mA. Will they work and could you help with the resistor value here.
Thanks

[DanielIt]

Well i calculated that for a 4.5V supply(counting the 0.5V drop inside the Atmega16), for a 2V led @ 25mA you get an 100 Ohm resistor @ 1/8mW. I am using the same Led's on my project and they look cool, just that i used a 47Ohm resistor to get them to light a little more,as in the daylight you cant see the effect.

[piersg]

 Yeah, but if you light up all 16 LEDs in a layer at 25mA, you'd be pulling double the AVR's max rated current. 

[Tadmen]

Thanks for your help. I'll try to build it soon.

[LetsExplodeSomething]

i would like to build one but it all looks too complicated for me.

[forte1994]

what is the other port for?