PC indicator leds

[Bad Influence]

I know Craig's done this... I want to put a blue/purple/white (haven't decided) LED as a HDD indicator light for my PC. I don't know what the voltage is on those leads. I'm assuming that every mainboard uses the same output to the indicator LEDs so that the case manufacturer knows how to setup the LEDs on the faceplate.

My question... What, if any resistor would I need to use inline for doing this?

 

[star882]

Disconnect any LED already on the wires, and measure the voltage.
If less than the LED's forward voltage, you will need to build a circuit to boost the voltage.

 

[Albany Tom]

Originally posted by star882:
Disconnect any LED already on the wires, and measure the voltage.
If less than the LED's forward voltage, you will need to build a circuit to boost the voltage.

<font size="2" face="Verdana, Arial">LED's on computers are normally just driven with a resistor from the 5V supply. (If you disconnect the LED, and use a good meter, you're going to read 5V.) Because the resistor is probably designed for less than 20mA current, and a red or green LED, you'll get less current from your blue or white LED, but it should still work fine. The option is to replace the surface mount resistor with a smaller value one.

NOTE: The led's on the case I'm not sure of. Look into the case and see if the resistor is there, or on the motherboard. If it's in the case, then it might not be surface mount, and may be easier to change.

 

[The_LED_Museum]

Some motherboards only feed 2.9 to 3.3 volts to their LEDs, and GaN models simply won't work. In these cases, the power is tapped off the CPU B+ and a lot of the newer chips require less than 5 volts now.
So you'll need to either meter it with the LED removed (open-circuit) or test-plug the desired LED into the connector before committing to sticking it in the case.

 

[Albany Tom]

Some of the servers we use have those. I know what you mean, in a bright room they're almost impossible to see. (We often take the front panel off, on the Dell servers, the lights are on a circuit board behind the panel. Probably not like that on a PC.) Red high brightness should be brightest, without changing any of the resistors.

You could also try a piece of wax paper in front, to see if your roughing the surface idea will help any.

 

[Lucien]

Originally posted by star882:
Disconnect any LED already on the wires, and measure the voltage.
If less than the LED's forward voltage, you will need to build a circuit to boost the voltage.

<font size="2" face="Verdana, Arial">Actually I've tried doing something like this for a friend, he had SCSI and IDE disks on his system and wasted them both to use the same indicator LED on the casing.

I tried using a simple AND gate logic chip, the triggering voltages that I measured (roughly) should have been enough to be picked up as a "1" by the chip, but it didn't work.

The problem seemed to be that the the two wires that connect to the LED are not a signal and ground wire, instead one wire is kept at a "high" voltage (3-5V) and the other wire matches that voltage when the LED is supposed to be off, and drops to ground when the LED is supposed to come on.

There is an IC, the ULN2803, which is a driver chip that behaves the same way. Input is either on or off, and when off, the output voltage matches whatever the voltage is on the device being driven (current flow is zero). When on, the output goes to ground, allowing current through the device to be sunk through the chip. This chip probably won't help you any, but if you need a setup to test whatever circuit you build, I guess this chip could be used.

And unfortunately I haven't built one for my friend yet, so I can't help you there...

 

[Bad Influence]

hmmm... sounds like fun. I'm afraid to do anything too invasive as my MB is irreplaceable at this point. (1st gen ATHLON board w/ "Irongate" chipset

) and I already sent the "spare" computer into blow'd up mode

with a temporary lapse of sanity & logic. (there's a reason those power cables have a ground on them

).

For S&G's I might try wiring a blue LED up just to see if it'll illuminate. The main reason for this is because the "factory" LEDs are 3mm thru a "lightpipe" and the case sits on the floor, so I can't even see the HDD light come on from this angle

. I'd like to drill out the lightpipes and glue the 5mm LED into place.

Next question: if the LED leads off the MB aren't supplying enough voltage to drive a GaN LED, would a red or yellow be feasible? I'm far from an expert on LEDs... but I know rat-shack has yellows & reds..not suitable for flashlight usage, but maybe good enough for indicators?

I suppose if all elsee fails, there's always the option of sanding the ends of the light-pipes to diffuse the light coming out... at least it would be visible from this angle.

Help, as usual is always appreciated. Thanks for the quick responses guys.

 

[PlayboyJoeShmoe]

This all mkes me ask a silly question. Here at 'work' (home office at Dads house - we are SMALL business!!!)the Gateway box here beside me has no HDD light! It rather bothers me sometime.

I'm not ready to dive into the case, but thought I'd toss it out for discussion???

 

[PsycoBob[Q2]]

Most motherboards have all the important connectors for the case LED's (power, HDD) but you'll need to do a custom job if you want the network card too (I've done it). On all the systems I've found, the case LED's are direct-drive from the motherboard's pins. If it doesn't work, turn the connector around, and try again.

MOST boards will gleefully drive any normal LED, even blue and white ones. Just don't expect to be able to direct-drive your LS without burning something. My P4 board (Asus P4B266, for those interested) will drive any LED I've hooked up. I even used a DC-DC solid-state relay to control a green LS as (depending on the day) my network or HDD light.

Older systems are a blessing- many 486-era cases will use a normal LED and a cable that has connectors on either end for the mobo and LED. Great for experimenting, far better than anything else I've found. Old Tower-style server cases had REALLY long LED cables.