Re: HARD DRIVE ACTIVITY LED
- From: nospam@xxxxxxxxxx (Paul)
- Date: Sun, 04 Jun 2006 10:41:10 GMT
In article <1149382935.276151.281950@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
"Bobby" <bwickes@xxxxxxxxx> wrote:
Hello, All!
Could someone tell me which pins on the IDE interface provide hard
drive activity? Also, what specific LED would you recommend?
Thanks!
Bobby
There is some info here.
http://www.pjrc.com/tech/8051/ide/wesley.html
What I cannot tell you, is if there is any unintended
consequences of picking off the signal as the
author of that web site has done. Caveat emptor.
The author of the above web page, used a 330 ohm resistor
and a LED. The current flow would be (5V - 2.0V) / 330 =
about 9mA of current. The 2.0V is a rough value for a red LED,
and other color LEDs use a bit more more voltage than that.
9mA should be plenty for a high efficiency LED. Remember
that a logic chip on the disk drive has to sink that 9mA
current, so don't force it to sink more than that. In
other words, try a 330 ohm resistor or one with higher
resistance, like 470 ohm, 680 ohm and so on.
Radio Shack sells LEDs and resistors. That should be a
good enough source for the job. There are specialized LEDs
available from obscure sources, but that would be more
trouble than it is worth. If you change the color of
the LED, recompute the above equation, taking the new
value for the forward voltage drop into consideration.
(That is the 2.0V in the example above.) That is where
a LED product that you can get a datasheet for, comes in
handy.
Note that the forward voltage drop for the LED, is actually
a function of the current. My picking the value of 2V
is just an "engineering guess" intended to arrive at a
rough value for the resistor quickly. You may refine
your calculation by using the curve in the datasheet, if
you want. (Fig.2 here shows about 1.9V at 9mA)
http://www.liteon.com.tw/OPTO/SPEC/DATABOOK.NSF/PASN/DS20-2002-243/$file/LTL81HKEKNN.pdf
DASP- is pin 39 in the T13 document (while the above web
page referred to it as /ACT). 12mA drive is available
on DASP, of which some current would be used by the motherboard
pullup, if provided.
http://www.t13.org/docs2002/d1532v2r1a-ATA-ATAPI-7.pdf
Try your first experiments, with some old drive you don't
use anymore. Just in case :-)
Also, realize that overloading the drive capability of
DASP- may take time to show an effect. I remember a guy
I worked with many years ago, overloaded a driver like the
one inside the disk drive, with 3X the normal current. It
only took about two days of running, before the chip was
killed :-) And that is why we don't want to make the LED
too bright - potential overload.
Paul
.
- References:
- HARD DRIVE ACTIVITY LED
- From: Bobby
- HARD DRIVE ACTIVITY LED
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