bit-tech.net :: HDD Power LED

HDD POWER LED

Thanks to CliVE for giving me the idea for this simple mod. Basically it is an led array which normally glows blue and changes to red during hard drive activity. The idea is to replace the standard case HDD led with this circuit and position the led array behind intake grills or around the inside of the PC case if you have a window.

The circuit uses an opto-isolator to prevent damage to the motherboard. The opto-isolator switches IC1, which is an inverting octal buffer, used to drive the leds. When the HD is idle the blue leds are lit and pin 14, via the diode "pulls" the input to the red leds low, turning them off. During HD activity the blue led outputs go "high", extinguishing the blue leds. With pin 14 now "high" the diode stops conducting, allowing the 10K resistor to "pull" the red led inputs high, causing the red leds to light. The circuit can be built on to a small piece of strip board. The red and blue led pairs and associated resistors can be swapped over to reverse the effect. The circuit is powered from the computers 12V supply with a Molex connector and connected to the motherboard header using the lead and connector from the original HDD led. I strongly recommend fitting the circuit board in a small plastic box to prevent it shorting out on the PC case.

Parts List with Maplin stock code.

4N25 Opto-isolator – AY44

ULN2803 - QY79

1N4148 Diode - QL80

2x10K Resistor – M10K

4x430R Resistor – M430R

4x220R Resistor – M220R

8x Red led - UK51

8x Blue led - NR84

Strip board – JP47

Molex plug – JW64

The Circuit Diagram

Here are a few pictures to help with the construction.

Board layout. The red wires go to the leds. Note. Pins 3 and 6 on the opto-isolator are not used and have been bent up out of the way.

Underside of the board. Note the breaks in the copper strips. The breaks can be made with a spot cutter, hand drill or in this case, a Dremel!

Finished unit in its box

Lid on, ready for fixing in the PC and plugging in. Experiment with the position of the leds for the best effect.

Circuit board photographs supplied courtesy of CliVE who suggested this project.

Here are some pics of the circuit in action. Obviously the flashing effect doesn't show up on a still picture but I'm sure you get the idea. Because the leds are on wires they can be positioned for the best effect. Just experiment.

Here the leds are behind the grill. No HDD activity.

With HDD activity.

Here the leds have been placed behind the window. HDD off.

HDD on.

Happy Moddin’.

Any questions? Ask them here.

HDD Power LED

by Macroman on 13th December 2001

Basically this is a high power led array which normally glows blue and changes to red during hard drive activity.

HDD Power LED / page 1