[TriLUG] Hardware Question: 2.5" IDE Drive Connection

[Aaron S. Joyner]

Scott Chilcote wrote:
> Hi Folks,
> 
> I have a piece of equipment that has an internal 2.5" IDE drive
> (notebook size).  It would be very useful to have an LED that shows
> drive activity, and there is a place on the cabinet for one.
> 
> Has anyone seen a wiring diagram or a cable sold anywhere that would let
> me attach an activity LED to a drive this size?
> 
> Thanks,
> 
> Scott C.

So I don't know what your application is, if it's a PC or what.  You say
"notebook size", which leads me to believe it's not a notebook...

Typically there is a pair of pins on the motherboard that provide
something that might be called an "IDE Activity" light, which you can
hook up a standard 0.100" centered jumper pin to, with an LED on it.
These could be scavenged from most any old PC case, or also assembled
from parts via Mouser or Digikey.  It'd be better to just ask around
before the next meeting, surely someone on this list can cannibalize an
old case and give you an appropriate LED and cable.

If on the other hand, you don't have a motherboard involved, and want an
answer to your actual question...

General consensus from some Googling around seems to indicate that on a
standard 40-pin IDE connection, it's pin 39.  The extra 4 pins on a 2.5"
hard drive are for power and I think a master/slave setting, so they
shouldn't matter for purposes of this discussion.  If you're comfortable
with a soldering iron inside the case in question, tapping into the pin
shouldn't be too hard.  This diagram will probably get you started:

http://www.pjrc.com/tech/8051/ide/ide-sch.gif

It's part of this article about using an IDE hard drive with an 8051 chip;
http://www.pjrc.com/tech/8051/ide/

Note the 470 Ohm resistor in series with the LED.  Note: according to
the diagram the pin sinks current, as opposed to sourcing it, as I would
have sort of expected.

Best of luck, let us know how it turns out!
Aaron S. Joyner