Is it posible? i think i read somewere if i use wire 39 on the ide cable and make it act as a switch? will this work? can someone explain in detail if so please Thanks fellow nerds
Two things that might dampen your enthusiasm: 1. Cold cathodes have a warmup time, just like all fluorescent tubes. It might not be readily apparent when you power on your system, but if it's getting turned on and off repeatedly, it'll be a lot more visible. 2. You'll need to build a circuit to drive the CCFL tube. Pin 39 is the activity signal, but it's designed to drive LEDs. A CCFL inverter will draw around .5A, while an LED is capped at 20mA (that's 25x less). At the very least, you'll need a transistor that can cope with a .5A load (2n2222A is a good choice, .8A max), with pin 39 connected to the base and resistor in series between the two to properly drive the inverter. For increased safety, I'd use an optoisolator (search that term on the forums, explained it way too many times to do so again) between the transistor and pin 39 so nothing bad can possibly happen to HD (assuming it's wired correctly of course).
Well, you'd need a relay, that's for sure. What a relay does is take a lower power signal and use that to drive a higher powered signal. So, if you complete the lower-powered circuit, the relay can switch to "on" and allow the higher-current/voltage to flow. You'd want a "NO" or "Normally Open" relay, so that when the activity light should turn on, the relay will. You don't have to use pin 39, unless you want activity lights for more than one drive. Here's two problems with this: 1. Sourcing the right relay You'll need a relay that can be operated by very low voltages. I think the power from the HDD activity header is 3.3v, but don't quote me on that. I'm sure the signal from pin 39 is less. You'll want to make sure, as it depends on the motherboard. The other end of the relay would have to handle 12v, as you'll want it connected between your PSU and inverter, but that shouldn't be a big problem. 2. "Flicker" When I had a CCFL, it would take a little bit to turn on, kind of like how an overhead fluorescent light "flickers" for a little bit before it comes up to full brightness. I'm not sure if it's fast enough so that you'll actually see the light come on during small access. This you'll have to try for yourself. If this is flawed, please, step in and say something, as I'm still learning most of this stuff as I go. As always, use the search, I remember seeing people ask about this before. Edit: Ooops, I'm too slow.
relays tend to wear out if they are swiched rapidly, but then again so do CCFLs. The transistor would be a better way, alough with a realy you would get a cool clickety clickety sound (but u would need a transistor to drive the relay anyway!).
Don't ever try to run a mechanical relay directly from the HDD activity header, the coil takes far too much current. And without a safety diode you could do mucho harm.
On the HDD, pin 39 sinks current rather than providing it. So you can have it switch about 20mA of whatever voltage you feed it, up to around 5v, maybe more depending if the IC on the drive can handle more than Vcc(its positive supply). A 2n2222A may work but you would have to use a pull-up resistor since it is NPN and the signal is active low. Also you need a transistor with a gain (hFE) of at least 25 (20mAx25=.5A), the 2n2222 should be around 100 since it is a GP transistor, I would check the datasheet though. EDIT: forget all of that last paragraph you need a PNP transistor with a gain >25 and thats it. Or an opto-isolator would work. No pull up-resistors needed I was a bit messed up when I posted that (amazing what sleep depravity will do to you)
The IDE specs say it will be open-collector and fitted with a 10k pull-up to 5V, so it can only provide 0.5mA if you link direct to the cable, socket or drive with an NPN switch. You could probably safely add a second parallel pull-up to increase that. But it would be on with no drive activity, not on with activity. The activity header has reversed diodes in the paths from the 2 cable sockets so can't provide nothing, only sink around 25mA as CoD says. If you're going direct to pin#39, 2 ways are a PNP transistor switch (limiting base current to under 25mA) on 5V, driving an NPN to level-switch to 12V, or an optoisolator with NPN current booster both on 12V.
