HDD Eyez - Geek on a Leash

Intro

Time to do some modding again. Like in most of my mods, the idea is to keep the costs down and not to make the mod too complex to put together. What I have heard from our reader feedback, this is the way to get new people to get interested about the modding scene. Sure we all love to see all those full scale modding projects that can take hundreds of hours but in many cases it all comes down to adding this kind of small details together. Learning to make these will get you started with that mega project in no time. :)

The Idea

The target

I don't usually show the end result as the first picture but in this case it might help you to understand what we are about to make here. The idea is quite simple actually. On/Off blinking Hard-Drive led can get quite annoying sometimes or it doesn't seem to fit the overall theme of the case or a project. Why not make it smoothly fade in and out when there is some HDD activity? These following steps will show you how to do just that easily and with only small amount of money.

This is also a good time to give credit to our ModGallery and Forum member; Acd. He posted some images from his modding project to the gallery and that was the time when I got interested about the way he made the skull eyes glow. His circuit was quite different from what you are about to see but the end result is more or less the same. So, thank you Acd for the idea and basic circuit.

The Circuit

The Circuit

In short: We receive pulses from motherboard's hdd led header. We get the pulses by removing the wire that goes to the original hdd led and replace it with our own wire that leads to our circuit. Optoisolator will charge the capacitor that is connected to the base of the in-built transistor. When the hdd activity gets faster, the 'ACT'-led will start to shine more brightly because the charge inside the capacitor is getting higher. After this, when the activity dissapears, the capacitor will start to discharge via the base "leg" of the transistor and keep the led lit. When the charge of the capacitor goes slowly down, the led will get dimmer and dimmer and finally stop shining completely.

Was that short enough? :) To get more out from the schematic I'll explain it bit further. The two pins on the left of the image are the two wires that will get connected to the motherboard's hdd led pin header. The polarity will matter because there is a led inside the optoisolator. There will be no harm on getting the polarity wrong the first time, just flip the connector over and the circuit will work correctly. 4N35 next to them is the optoisolator that will receive the pulses and charge the electrolytic capacitor that is connected between the ground and pin 6. of the chip. Be sure to check the polarity of the cap when connecting it. 'ACT'-led and properly calculated current limiting resistor R1 gets connected in series between the positive supply voltage pin (in this case +5 pin from Molex connector) and the pin 5. on the 4N35 optoisolator. Pin 4. will then get connected to the ground to complete the path for the current.

That was the basic circtuit. As extra, I have added a 'POWER'-led and R2 current limiting resistor parallel to all this. This will act only as a power indicator and the led will be lit when the computer setup is powered on. You can leave these two components off if you wish. On the far right are the actual connector pins for the +5 and ground from Molex connector. You don't have to worry about them, as they are drawn only for PCB (printed circuit board) manufacturing purposes.

List of the stuff you need:

OK1	4N25, 4N35 or similar optoisolator. Datasheet
C1	Electrolytic capacitor. Anything from 22 microfarads and up. Higher value will give you longer delay to get the led lit but it will also make the led glow longer after the hdd activity have ended. I used 33 microfarad cap for this article.
ACT-led	Led or leds that have the color that you want.
R1	Current limiting resistor for the 'ACT'-led. Value will depends on the needs of the 'ACT'-led.
POWER-led	Any led or leds that have the color that you want.
R2	Current limiting resistor for the 'POWER'-led. Value will depends on the needs of the 'POWER'-led.
Misc	Pin connector for the hdd pin header on the motherboard and molex connector to take the power from. These can be easily "loaned" from some old case

Ready

Ready for retail markets?

While I decided to make a PCB for the circuit, it doesn't mean that you have to. Use breadboard or just solder those components together without any board and it should still be fairly easy. PCB just makes the whole thing look more "professional"... Do we really want that? Anyway, takes a lot of developement time away from the manufacturers when they decide to copy the circuit so... ;)