Raspberry Pi RGB PWM Controller - Help!

[XL5]

A bit of backstory: I have a 19" cabinet that has a strip of RGB LED's in the top, at the moment they are just soldered directly to a power supply that means they are always red. The ups supports SNMP, as do a number of other devices, and I think it would be cool to change the colour of the lights according to the status of things. They could go red if a server is down, or white if there's a power cut, so that I can see better.


The controller needs to be networkable, and be capable of controlling 3 channels of PWM independently. At the moment I'm planning to use a raspberry Pi. Obviously the Pi doesn't have enough juice to run a 12V LED strip like this, so some sort of transistor based device will have to do that work.

I'm thinking of designing a board that will plug onto the GPIO pins and have all the necessary components on it. It would take a 12V power in and using transistors it could power the LED's based on output from the GPIO.

If I'm putting a board on the Pi that will take 12V it makes sense to also use that 12V power supply to power the Pi, so I think I should put on some sort of regulator down to 5V and include a USB port to plug the pi into.

Anyway, this is as far as I have got, and I need some guidance...

[filip_cro]

Doing it with FETs/MOSFETs may be easier. Use transistor to connect LEDs to GND. (open collector or open drain)
Is Ri Pi 5V output? Maybe you will need to use drivers.
For 12V to 5V use switching mode power supply. Linear regulators wont be able to do 3.5 W (0.5A x 7V) without heat sink.

[XL5]

Doing it with FETs/MOSFETs may be easier. Use transistor to connect LEDs to GND. (open collector or open drain)
Is Ri Pi 5V output? Maybe you will need to use drivers.
For 12V to 5V use switching mode power supply. Linear regulators wont be able to do 3.5 W (0.5A x 7V) without heat sink.

Thank you for your response. Though, I think you'll have to dumb it down a bit for me. Sorry!

Where would I put MOSFETs? I didn't understand what you said about transistors..

Could I use multiple regulators to spread the load and generate less heat on one component? Otherwise, what would a switching power supply involve?

[filip_cro]

NPN (N-MOSFET)
E (S) to GND
B (G) to Ri Pi
C (D) to LED cathode
+12V to led anode

[XL5]

Ah, that makes sense, very similar to the transistor.