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Questions abut harddrive Activity LEDs.

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New Member
Feb 21, 2002
Hi there!
I've got an idea that I would like to do. On the front of the computer you often have a LED that shows when the harddrive (here on abbreviated as "HD") is doing stuff.

I have 14 HDs in one of my cases and thought that it would be cool to have one LED for each HD, so I could se when stuff is happening. Along time ago I remember seeing on the drives that they had small LEDs soldered on them. Is this still in practise?? I havn't seen any blinking in my case so i guess not :)
Yes, on some IDE-card you have a connector for this, but that is just to see if any of the HDs connected to that controller is doing anything. I would like to have more info, I would like to see which of the HDs is working.

I also have three LAN-cards and I thought of having those LEDs rewired to the front also.

One thing that is that I know absolutly nothing about LEDs and that sort of stuff.. I've been looking at IBM.com for some info about how I could do this, but I'm not sure really what info I'm after. I've read everything they have about some of the drives in the computer, but I couldn't find anything that says "This is the info you need".. :D

So what's my questions? Well here they come:

1. How do I get the info when every single HD is working? (Is this even possible)
2. What kind of LED should I use to show this?
3. How do I find out what kind of LED is used on my LAN-cards?
4. Can I just put the new ones in parallell or do I take the old away and run a cable to the front? (I think I saw that someone had done this, but I cant find the link again)

I know that there is ALOT of knowledge on this board so I was just thinking that it can't hurt to ask...

[email protected]

New Member
Mar 14, 2002
The signal:
Pin 39 in the IDE-cable is the ACTIVE used to the HD-LED. I haven't tested this theory yet but if you connect a led to pin 39 (LED) and pin 40 (GND) you should be able to get the led to work. But I also think that the signal from other HD's is going to be indicated...

In theory, if you could block the signal from the IDE-cable and just care about the signal that the HD gives on pin 39... Maybe you could skip to connect pin 39 to the IDE cable and just use it for the external LED you want. That should work.

Which LED:
When connecting LEDs voltage is important. Measure thevoltage to be sure.

Regards Jens

Captain Slug

Helpful Senior Member
May 23, 2001
Asteroid B-612
I would assume that pin39 and 40 are using either 2 volts or the native 5 volts of the drive. But if not could someone PLEASE correct me on the correct voltage so I can try this?


New Member
Feb 21, 2002
According to a whitepaper at IBM:
(link to that paper: http://www-3.ibm.com/storage/hdd/te...0A87C487256AFF00595B6B/$file/D120GXP_sp30.pdf)
PIN	Signal	I/O	Type
40	GND

I/O= "I/O" designates a input/output common
OC = "OC" designates open-collector or open-drain output

pin 39:
This is a time-multiplexed signal which indicates that a drive is active, or that device 1 is present. This signal is driven by Open-Drain driver and internally pulled up to 5 volts through a 10kohm resistor
During Power-On initialization or after RESET- is negated DASP- shall be asserted by Device 1 withing 400ms to indicate that device 1 is present. Device 0 shall allow up to 450ms for devide1 to assert DASP-. If evice 1 is not present, device 0 may assert DASP- to drive a LED indicator
DASP- shall be negated following acceptance of the first valid command by device 1. At anythime after negation of DASP-. eithe drive may assert DASP- to indicate that a drive is active.

Lowerdown i read:
The interface logic signal has the following electrical specifications:
Input High Voltage: 2.0 V min
Input Low Voltage: 0.8 V max
Output High Voltage: 2.4V min
Output Low Voltage: 0.5 V max

What all this does say.. I don't have a clue. It seems that it should be a 5V diod between pin 39 and 40. But also that I by this should se both drives on that cable...

Anyone have any ideas??

Iron Hawk

Jan 19, 2002
Groton, CT
DASP (Drive Active/Slave Present):
A connection signal used by Hard Drives on pin 39 which helps report to the Master drive the presence of the slave drive.

The computer determines if there is a second (slave) drive attached through the use of Pin 39 on the connector. Pin 39 carries a special signal, called Drive Active/Slave Present (DASP), that checks to see if a slave drive is present.