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question about hard drives and LED lights? Answered

Hi guys,
I'm trying to do this --> http://www.scribd.com/doc/3216005/Make-an-analogue-hard-drive-meter for a little jukebox/media centre I'm building.

I have a basic VU meter all ready, and also a potentiometer.

I've just pulled apart an external hard drive and I'm hoping to tap into the 'activity light' on the front to drive a simple VU meter.  It's a basic Western Digital external 1TB, but it has two little LEDs that flicker blue (alternately, but sometimes together!  Not sure what drives each light?!) and I'm just wondering what my next step is.  There's the basic hard drive, and a little SATA->USB controller board attached that features the two LEDs.

I've attached a pic, sorry it's not great.  The Two LEDs are shining out from underneath the card, and you can see a little row of soldered connections on the topside of the board that run the LEDs, at the closest corner to us (the viewer).

My question is: there appear to be 4 soldered connections on the two LEDs poking up.  What do I want to solder the VU meter to, and what are the risks to avoid?  Any comments/thoughts are welcome.  Thanks  :-)


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8 years ago

Get the disk drive model number off the hard drive itself and look up the specs on wdc.com, they should have documentation for the pinouts for all the jumpers on there and that may give you some clues and tell you which is anode and which is cathode. Typically, one LED shows "activity" generally reads and writes to the disk, but it doesn't seem very precise. WD MyBook sometimes has a Cylon Scanner type effect with a string of white LEDs along the edge of the MyBook, it has no real function other than to look cool as far as I can tell. Just a wild guess, but maybe one LED is for reads and the other is for writes. It's probably 5 VDC, you want to get the positive and negative from the LED to match up with the VU meter. I'd probably take some alligator clips and just try hooking it up temporarily and see what happens, it's low voltage and polarized, either it will work or it won't but I don't think anything will blow up. As long as you aren't sending voltage into the jumpers from an external source or trying to use it drive something that draws a lot of current, it should not damage the drive, I would not try to use it to drive an electric motor or an incandescent bulb for example, but a VU meter or LED should be fine. You'll want the potentiometer in series so that you can lower the voltage so the meter doesn't just max out all the time. Good luck!


Reply 8 years ago

Great answer. Thanks very much cdslashetc!