# Help with circuit - Alot of leds

Hi all

Im really new to arduino and electronics, so i am hoping that someone can point me in the right direction on this one..

Im doing a project in school, which basically is about dimming 9 sets of 75 leds each. I want to use the pwm output to dimm the sets of leds (depending on sensor input) but my problem is how to get enough power to light up so many leds and still be able to control the dimming?

Can i provide power to all the leds with one power supply or would it be better to provide power for each set of leds individually?

I have made a quick sketch that maybe explains the problem more clearly.

If its not clear what i want to do, please let me know. Hope that someone can help me out with the electronics - the coding should not be a problem :)

The sketch:

You don't say what the rating of the LEDs is - they could be SM LEDs, taking 5mA or less each, or they could be LumiLEDs, taking hundreds of milliamps each.

Arh sorry, this is the info from the supplier:

Forward Voltage (V) : 3.1~3.6
Forward Current (mA):20

OK, so 20mA * 75 = 1.5A per block.

That is way more than an Arduino can supply, so you'll need a MOSFET per block of LEDs. This needs to be a logic level MOSFET - if you do some searching around here, you'll find loads of design ideas and tips.

In total, you'll need 9 * 1.5 = 13.5A at around 3.5V - about 50W

However, I don't think you want to use a 12V supply, because you'll end up wasting too much power.

I will try to look into how to create a MOSFET circuit.

I think i will go for an individual power supply for each set of leds. I think it will be the most logic + i will be able to extend the whole thing with more sets of leds.

So if i get my hands on some 5v 2amp power supplys that should do the job?