Installing LEDs

[SinCrisis]

I saw that from your google link, it looks super complicated... My knowledge of electrical things is nearly nonexistent, I'm not even comfortable with circuits. I was hoping for some straightforward solution like wire mobo to something and then wire something to LEDS, and then LEDS back to mobo...

[Konrad]

Hmmm. I remember these things used to be sold as modding accessories, but I just can't find any online. I think that desktop HDD indicators are dying off, especially in this age of SATA and decent software monitoring; a terrible shame (I would prefer each and every drive has it's own LED, lol).

A not-too-difficult option would be to buy some kind of sound-activated light module (like this); you could wire your mobo LED headers into the device (replacing the audio sensor), you could replace the LEDs with whatever bunch you prefer (within limits), the LED bank doesn't have to be mounted on/in the unit itself.

Here's a variation of the circuit described in my above post.

[Edit: link here for detailed circuit description and schematics, construction notes, and worklog.]
[Edit 2: Ç'est un joli projet en Français, sorry. There's always google translate ... it's somewhat English-readable anyhow (lol, except in French: LEDs are called DELs, IC is CI, and vert/jaune/rouge are green/yellow/red).]

And here is a link to yet another variation, again with details and schematic.

You really can't reduce the electronics complexity much beyond this to get the effect I think you're trying to get, whether you want your LEDs to light up as a single unit or as a bar graph. Notice that the important parts (LM3914 and associated components) are always the same. This is about as easy as it's going to be without just buying a premade accessory. Maybe the other guys here can explain their relay idea.

A more complex variation (scanning "Knight Rider" style) here. And of course a programmable controller can do just about anything you like, though it would require detailed electronics knowledge.

[SinCrisis]

I want the entire small bar to light up. I want to put this behind plexi so when the HDD is active the light will flash and the silhouette i have on the plexi will become visible with a kind of strobe lightish style. The reason i need the LED bar is because the original LEDs with the case are very old and dim so its not bright enough.

[Konrad]

Okay, this is probably your best approach.

The 6-pin part on the left is a 4N27 optoisolator ... it is basically a matched photodiode and phototransistor in a single package. Because of the optoisolator there is no chance of damaging your mobo, even if you reverse any of the connectors or parts. Still, be careful to ensure that you connect the 4N27 correctly: pin-1 (or the closest corner) is always somehow marked differently from all the others on an IC; in this diagram pin-1 = pin-A and is marked by the semicircular divot at the top of the IC - there are many different 4N27 parts and they might have different pin designations, always use datasheet pinout for the exact part you obtain. The 4N27 itself consumes virtually no power (aside from miniscule capacitive losses).

There are many 6-pin (DC) optocoupler/optoisolator devices. Some listed here. Pretty much any of them could be used in this sort of low-power application, more robust parts (which cost a little more) can handle 1A or more.

In this circuit, everything to the left (ie, the mobo) is electrically isolated from everything on the right (3 LEDs being driven by a separate 5V source), the transistor in the 4N27 is used as the "switch" - the presence of a (5V) signal between the A- and K-pins opens the circuit between C- (collector) and E- (emitter) pins. Assuming the 5V comes from a molex connector (red wire), all the grounds on the right side of the circuit (including the unused B-pin) should be connected into the molex black wire. Or both black wires, to ensure extra fault tolerance. The last pin (on the left) is unused in this circuit, do not connect it to anything. Your PSU should be able to drive many many LEDs (unless it's already very sick, lol); as long as you properly ground the circuit (with the black wires) there's really no chance of the PSU being damaged, although you can blow your LEDs with too much voltage (they never flame, mostly they just "pop" inside their plastics) and you can cook the 4N27 if you force it to conduct too much power (30V/100mA=3W input or output, 5300V isolation). You can even use these same parts in a 12V circuit (though then you'd need some extra resistors and maybe some cooling on the 4N27) or you can adapt these parts to all sorts of "activity" triggered circuits, such as adding a 5V fan to cool your HDD when it's active, etc.

Use a separate molex (any standard 4-pin, even floppy connector) for this. Do not attempt to splice into the mobo 20-pin/24-pin ATX power connectors (or even use an unconnected 4-pin 12V mobo connector) unless you really know what you're doing; doing so will no longer isolate this circuit from the mobo. You could use separate battery power if you like, or even a separate PSU (with proper grounding).

Switching time is ~2.5µs, meaning it might not turn the LEDs on/off fast enough to indicate brief flickers of activity, although this would be undetectable by the human eye. The 4N27 isn't rated for high-frequency (>1kHz) operation, so this sort of circuit isn't suitable for monitoring SATA drive activity.

The value of R is important; higher R values allow less voltage (LEDs will be dimmer), lower R will allow more voltage (LEDs will be brighter), too high (too bright) will shorten the life of the LEDs or burn them out entirely. In this circuit, LEDs are shown wired in parallel; you can calculate the value of R using an LED Resistor Calculator. You'll need to know the forward voltage drop (Vf) for your LEDs (different for each type/colour); if you don't have a part spec/datasheet then you can use a chart like this or use a meter to measure the voltage drop in a powered circuit. It's not critical to get precise values and you can experiment a bit to "tune" a fixed brightness level you prefer, just be conservative so you don't burn the LEDs with overvoltage. If they start getting warm/hot then you're approaching (or exceeding) their "safe" limits. LEDs are basically very tiny semiconductors built into big plastic "lens" enclosures; when they get hot they don't have enough surface area to cool down and so they "pop" and cease conducting forever. Note that resistors are also rated for wattage; they basically waste power (as heat) and get warm/hot, you need to ensure your chosen resistor can handle the expected wattage (1/2 Watt should be fine, higher is always better).

You can use as many LEDs as you like (within limits) as long as you change the value of R. If you use some sort of bank/module which contains a number of LEDs then you'll have to know the Vf and current (mA) ratings of the entire unit. Most generic LEDs are 5mm ("tombstone") rounded cylinders; typical values for Red are 1.8-2.0V @ 20-30mA, Green/Yellow/Amber/Orange 2.0-2.2V @ 20-30mA, Blue/White 3.3-4.5V @ 30mA. I doubt you'll be using IREDs or UVEDs. Low-voltage and superbright LEDs are also available, as are low-power (10mA and 20mA) versions. SMT versions are very tiny and difficult to work with and the extremely high brightness specs (mcd or flux) they advertise cannot be directly compared to "normal" LEDs (brightness ratings are calculated based on emitter surface area, which is scaled very differently for SMT parts).

Cost for a single circuit shouldn't be an issue. You'll need a molex connector, mobo headers (connectors), some wires, and of course all your LEDs - you can cannibalize or salvage these easily. If you pay $0.40 for your 4N27 and $0.10 for your resistor then you've been robbed.

Hope this helps.

[SinCrisis]

Thanks Konrad, for this component, will I be able to just pick one up at a home depot? The online sources i found seem to want me to purchase in bulk...

[Drum Thumper]

I'd personally would give Radio Shack a go.

[Konrad]

Electronics stores have these sorts of parts. I don't mean consumer electronics (stores that sell TVs, stereos, CDs, DVDs, etc). I mean nerd electronics.

I don't know where you live, but for me some of the local stores are places like RP Electronics, Active Tech, Main Electronics Supplies, SMI Electronics. Like you, I prefer shopping locally whenever possible (and your part list is not at all exotic) ... your local yellow pages and a few phone calls will probably be more useful than searching online, search under electronics "suppliers", "distributors", "industrial", etc. Or ask an electronics nerd where he buys his stuff; Radio Shack is not the first/best destination, just one that's convenient.

[Drum Thumper]

Radio Shack is not the first/best destination, just one that's convenient.

Agreed. But if you lived where I do, you would realize that if you want to shop locally, it is your only choice.

[billygoat333]

Agreed. But if you lived where I do, you would realize that if you want to shop locally, it is your only choice.

this.

[SinCrisis]

unfortunately, it seems that radio shack is my closest option and thats at least a 20 minute drive away. People in my area don't DIY... the only hardware store nearby that i knew of was a sears that closed a couple years ago so... i will check radioshack. Why are they a bad option? Will they be over priced?