RGB LED strip for PC HDD activity LED

Advice needed. Maybe a stupid question

but I would like to illuminate my PC case with a RGB strip and sync it with the PC HDD activity LED. I would like to power the Arduino board, RGB strip and the RGB module with 12v from the PC power supply and use analogue read with the positive output of the HDD activity LED pin on the motherboard.

As far as I know the 3.3v, 5, and 12v on the power supply all share the same earth.

Would I be right in saying that the ground from the HDD activity LED output doesn't need connecting because the Arduino board is powered by the same earth?

Would I be right in saying that the ground from the HDD activity LED output doesn't need connecting because the Arduino board is powered by the same earth?

Right.

...and use analogue read with the positive output of the HDD activity LED pin on the motherboard.

That's a digital output. You should be able to read it as digital unless the voltage is too low, and in that case you can read it as analog.

You certainly don't need an Arduino for this. It would be completely wasted. All that would be required for a single colour led strip is a transistor. What model of transistor depends on how many LEDs in your strip. How and why do you want to use an RGB strip?

Thanks DVDdoug.

PaulRB what type of transistor would I need for a single colour strip up to 0.5A?

RGB would just give me more choice of colour with Arduino.

For 0.5A, you could probably use bc337. Or many other npn transistors with similar specs.

If you can't find a single colour strip you like, then using an RGB strip would require an "Arduino" to mix the preferred colour using pwm. You could use an Arduino to prototype the design, but then once the code is debugged, upload it to an ATtiny. The Arduino could then be kept for future projects. You would still need two or three transistors, because the outputs of an Arduino or ATtiny can't deal with 0.5A or anything over 5V.

Thanks PaulRB I will do a bit more research on transistors.