# Thread: HDD LEDs - How to make some

1. ## HDD LEDs - How to make some

I have a Promise SATA card hooked up to 3 SATA drives to be my fileserver. The card has LED pin headers for drive activity. However, my case doesn´t have four additional LED lights for HDD - or any spare ones I can use.

I have tried a google but can´t find any guide - so does any one know how to hook up LEDś to this pins? Or point me to any guides to making HDD actvitiy LED´s?

2. get a voltmeter and measure the voltage across the pin outs of the card, ur looking for a spike that shows when constant activity is goin on.

then u head to maplin and buy some leds that are rated for the voltage that u measured and solder em on

3. Thanks for the help - not got a voltage meter unfortunately - may have to borrow one.

However I would have thought that the output from the card would be a standard voltage (like say a motherboard pin header) as it is designed to have those two pin standard led headers for standard case lights to be plugged in. I just want to know how those lights are hooked up on a case (if its simply a led on some leads, or maybe a resistor in the middle or a circuit board).

Cheers......

4. Just the LED with a bit of cable and a header, that's all you need - almost certain they'll be 5V LEDs.
http://electronics.howstuffworks.com/led.htm
http://www.knightlight.co.uk/pr-led_assemblies.asp

5. An inline resistor to limit the current is strongly advisable. Yes, you may find that many 'manufacturers' skimp on them (or they rely on possible inbuilt resistors)...

'5V' LEDs heh. These are pretty much LEDs with a known forward voltage with an inline resistor calculated to limit optimal current (~20mA) drawn.

From Ohm's Law, V= IR

R = (Vsupply - Vforward)/current; in this case 20mA, or 20x10^-3, or 0.02. When driving superbrights I tend to push them to around 25mA and sometimes even 30mA. Usually red has a Vf~2V, blue~3.3-3.8V.

6. bsodmike - Not quite following your formula (not quite electronic minded). If I was to say pop into maplins and buy 4 blue LED's - what resistor should I buy?

I imagined they would be 5v LED's but read somewhere (can't find where and it may be an old article) that motherboards pushed out only 2v from those pin headers, hence early pc's using most green or red LED's

7. Now here is what I would do. Every single penny counts in PC making, so any LED they use will be cheap. I would just connect up a cheap LED. Bung it on, and if it doesn't work try it the other way around.

Just measuring the voltage on the open pin won't work. You would need to measure it with an LED already attached to measure the voltage drop across the LED.

The reason for this is that there is bound to be a resistor on that pin, and with just a voltmeter across the pins no current will be flowing through the resistor and so it is as if it isn't there. You would need to measure open circuit and then with a known load resistance to calculate the series resistance they have included. A google for "effective series resistance" or "thevenin equivalent" will boggle you with maths.

There are two reasons why I say there is bound to be a resistor on that pin.
1/ If the pins get shorted out, the resistance saves anything blowing and the card company don't get a warrenty return.
2/ A resistor on the circuit board is cheap, but fancy high voltage LEDs are not.

8. You should be able to connect an LED straight to the header - cases don't have built in resistors on their LEDs so the header will have a current limiting resistor. Using a cheap LED as a test case is a good idea though.

9. Thanks all - may just pop into maplins and test the theory out on a very old machine I have lying around witha bare led. Anyone know where I can buy those small two pin header plugs to hook up to the pins?

10. They should be 0.1 inch pitch, very standard. If the LED outputs on the card are in a standard header strip, you might even be able to saw the end off an old floppy cable to ditch the unused strands of ribbon and plug the LEDs into the other end.

A quick look on Maplins website, they seem to do headers:

Note that you need a 2 pin shell, and a pack of pins to solder onto your wires.

11. why dont u just rob ur mates of their LED's?

12. DanceswithUnix - thanks for the Maplins link.....

13. danceswith unix is correct the card will already put out the correct voltage for red/green etc no resistor needed - in fact resistors are only needed with leds when supply voltage exceeds rated voltage.

if you are in uk i'll send ya down some leds plus any parts needed if i can find them (leds def - other parts unsure till i look ) save ya being robbed by Maplins . did see some superbright pinks the otherday