I recently built a new PC and noticed after I was done that the hard disk light was almost impossible to see. I tried different LED's that were more efficient and even thought about modifying the motherboard. But, I decided to avoid that risk and make things interesting by designing this circuit instead.
Since I didn't know how the LED was being driven on the motherboard, I decided to use an optoisolator (ISO1) to act as an interface. This provides electrical isolation as well as an equivalent load. Since the current going to LED was already pretty weak, I chose a device with a photo-darlington transistor amplifier. This provides a minimum current amplification of 15 or a Current Transfer Ratio of 1500%.
I had some Disk Drive power Y-connectors and I cut one of those up to use as the power jack, J1. The +12 signal will be a yellow wire and ground will be one of the black wires.
R1 was chosen to provide about 20mA of current through either a blue or white LED. I used a Panasonic LNG992CFBW blue LED and it looks pretty cool.
To connect the circuit, turn off your PC and remove the cover. Locate and remove the HD LED connector from your motherboard (MOBO) and connect it to the two pin header, JP1. Plug J3 onto MOBO in place of the original LED connector. Locate an unused HD power plug and connect it to J1. If one is not available, you may have to purchase and install a Y-adapter.
Remove the original LED from the socket on the front of your computer and replace it with your new, exotic LED. Apply power to the PC and observe the HD LED. If it does not flash with HD activity, you may have to rotate J9 or D1 to get the polarity correct.
Once operation has been verified, button your computer back up and invite your friends over to see your new exotic machine. Trust me, once this modification has been completed you will know when your hard disk is being utilized.