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Question About Hdd Activity Led


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#1 petegas

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Posted 07 May 2004 - 06:26 PM

I read the tutuorial at

http://www.xbox-scen...les/hdd-led.php

and am confused about his choice of resistor (220 ohm). seems too high, especially given the LED (picture says it Vf is 6V) - unless he is using a 12V source (12-6)/220 = 27mA, reasonable - in which case all of his references to source voltage of 5V are wrong.

Am i missing something here, or do regular ohms law formulas need to be adjusted in some way when doing this mod? What are the voltages on the IDE line when the HD is active/not active?

#2 petegas

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Posted 07 May 2004 - 07:21 PM

In other tutorials about LEDs too it seems the resistors are always higher than what I am getting using standard ohms law formulas.

For example LEDs on the low end of things (red ones) require 2V (most blue ones want 3.3v)

so using a 2V LED with 5V source at 20ma,
(5-2)/.02 = 150ohms

and for blue LEDs at 3.3v and 20mA R would be 85ohms

I don't see why you'd ever want a resistor higher than 150 ohms for a single LED.

Comments?

#3 spicymeatball911

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Posted 07 May 2004 - 10:52 PM

I did it it with 5v source and just 100 ohm resistor, worked beautifully

#4 blindbug

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Posted 08 May 2004 - 12:33 AM

its not necessarily for just the LED... it is also for any return signals that might be interpretted by your hard drive as, for example, format or something of that nature... so dont think of it as saving a .75 cent LED and it being lit up slightly less than it could... think of it as protection of your whole xbox tongue.gif

this is all theoretical on the chance that something weird like that would happen...

#5 spicymeatball911

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Posted 08 May 2004 - 01:34 AM

Yeah just adding to what blind bug said, I was accidently using the 12v source by accident with a color mismath on my cathode, anyways, the extra voltage dropping into the 39th wire would case the xbox to freeze up whenever alot of loading time happened, or at start up...

#6 petegas

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Posted 08 May 2004 - 04:44 PM

QUOTE (blindbug @ May 8 2004, 02:33 AM)
its not necessarily for just the LED... it is also for any return signals that might be interpretted by your hard drive as, for example, format or something of that nature... so dont think of it as saving a .75 cent LED and it being lit up slightly less than it could... think of it as protection of your whole xbox tongue.gif

this is all theoretical on the chance that something weird like that would happen...

I don't think any control signals are sent on pin 39 . . . that is why it is used for HDD activity, and I think a slave check on bootup but that is it. I was a bit concerned about driving the value high as well via the 5v supply - I don't know enough about the ATA standard to be certain which is why I'm wondering.

Seems strange that the pin is asserted low with activity? I thought it asserted high when there was activity. Unless the LED goes off with activity - which way does it work?




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