Ambitious first project

Hey all, firstly - i'm new to the forum (and arduino) so be gentle with me :)

My plan is this:

I've got a Raspberry Pi, Arduino, PiNoIr Camera Module, an LGH-5036 Infra-red Illumination Board with 36 Infra-red LED's, 2 servos and plenty of time on my hands.

I have dismantled a 450w ATX PSU to use to supply power, as they have a 3.3v, 5v, 12v power rail and i need 12v to supply to the IR board.

From my reading on the web (,288817) it appears that the minimum load requirements for a 450w ATX PSU are

3.3v - 0.1a 5.0v - 0.2a 12v - 0.1a

so, am i right in assuming that to get step 1 working (safely power the IR ring), i simply need to attach an LED to the 3.3v power rail with a 220 ohm resistor, the IR ring to the 12v?

also, what the heck do i put as a bare minimum over the 5v rail?

I've been playing for a couple of days so am beginning to understand the arduino a bit more.

i will no doubt be asking more about this project as time goes on - so i apologise in advance.


How much current does the IR ring take? How much does the Arduino and RasPi take?

thanks for the reply. The uno uses 46.5mA on the 5v rail whereas the raspberry pi uses 1.2A at on the 5v rail. i have several different 5v rails, so for safety i was going to run them on separate rails.

You need to ensure the minimum load currents are flowing or you cannot trust the PSU not to over-voltage on its outputs. You haven't said what current the IR unit takes and the Arduino is not enough load on the 3.3V rail.

You can probably safely power your RasPi from the 5V rail of the PSU. But you will need to suck some current from the 12V and 3.3v as well. If your RasPi fries, it's your fault! :P

A more useful title might be "How to power Arduino with ATX PSU ?"


thanks for all the replies. very useful info. point taken about the title. and as for cooked raspberry pi - sounds tasty :stuck_out_tongue:

i’m planning on playing more with the electronics tomorrow. as for current for the IR ring - i have no idea! that’s why i want to meet the minimums before i put anything on them.

Usually a 5 to 10 watt power resistor is used to load the 5v rail.

Well, for the 5V rail you will need a 25 ohm, 2 watt resistor (which only really needs to be 1 watt). Be warned, these are somewhat back-of-the-envelope calculations and might be erroneous.