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### Topic: Groups of LEDs per pin (Read 840 times)previous topic - next topic

#### Emoo

##### Apr 18, 2012, 11:35 pm
Hey all,

I am painfully new to Arduino (my very first project was just a few weeks ago for my studio class  ), so do forgive me if I struggle with stupid things or if this is the wrong forum.

Anyway, for my final project in my interactive viz studio, I'm making a small starscape with different modes (all off, twinkly, all on, etc) and roughly 80-100 LEDs and an IR sensor to notice when someone is touching it. Here's the general concept:

I don't actually want to control each LED individually; instead, I want to put them in groups of 8 to 10 to make managing the light patterns easier. My first assumption would be that I ought to put the LEDs in each group in parallel. If that's right, then my next question: What's the simplest/best way to power that many LEDs (current count on my illustrator file is 80, could still grow)? At some point, every light in the panel would need to be on simultaneously.

Any advice here, or if you know of a nice/straightforward? tutorial, that would be great.

#### winner10920

#1
##### Apr 19, 2012, 03:00 am
Transistors or logic level mosfets, whicever you prefer will allow you to control larger currents
or for that amount you may want to look into shift registers, or even the max7219 or similar device which can do 64 individual controlled leds

#### Emoo

#2
##### Apr 19, 2012, 05:50 am
Well transistor was the only thing I understood in your reply, so I'm think I'll look into that...XD

#### winner10920

#3
##### Apr 19, 2012, 01:02 pm
You'll probably need(8x20ma=240ma per group) and atleast a hfe of (240/20=12) so a pn2222 will work with ic max @600ma, and hfe at 150ma is 100min( so even 5ma should turn the transistor on)
all the led negatives will go to the collector, the emmiter to the ground, and the base thru a resistor(220ohm-1k) to the arduino ouput
ofcourse all the leds will need resistors don't forget

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