PC Hard drive activity led

Thread Starter

Sharpen047

Joined Apr 19, 2012
51
I have been looking for a way to hook up a different led to my hard drive activity indicator.
I would like to hook up a high power led for inside of the case, shining into the end of an acrylic rod.
Could i do this with a mosfet or something similar?
Thanks in advance!
Note: I have a white 5mm led in there now running at about 3.5v.
 

R!f@@

Joined Apr 2, 2009
9,647
Yup ! just find a logic level MOSFET that can handle the LED current first. Then come back
 

Thread Starter

Sharpen047

Joined Apr 19, 2012
51
This will be my second circuit but probably my 5th perf board project. I've been able to replace LEDs on my external hard drive to my digital dash in my car to my 90mm fan LEDs that are insider motor.
My first circuit was a 555 led dimmer.
I think I am pretty good, not great but if it's hard it's just a new challenge.
If I can't do it I'll probably be back for another option haha.
 

R!f@@

Joined Apr 2, 2009
9,647
I guess this is not new.

U need to tap of the HDD activity LED. I believe the LED is driven in common ground mode. I am not sure on this.

Does ur mobo has a direct grounded HDD led and the anode is switched. Check this and come back
 

BMorse

Joined Sep 26, 2009
2,675
Most HDD activity LEDs are usually switched by the ground lead, the +5 is always on.... and also make sure the current you draw for the new LED can be handled by the HDD Led driver circuit, or else, you will be buying a new HDD and possible a MB.
 

Thread Starter

Sharpen047

Joined Apr 19, 2012
51
Ok if i put the power led positive on the power led + and the negative on the hd activity - it acts as the hd indicator meaning common anode.
either way if - is on the case both light up continuously.
 

Thread Starter

Sharpen047

Joined Apr 19, 2012
51
Most HDD activity LEDs are usually switched by the ground lead, the +5 is always on.... and also make sure the current you draw for the new LED can be handled by the HDD Led driver circuit, or else, you will be buying a new HDD and possible a MB.
I would like to use a mosfet or something similar to use less than or equal to what it currently uses. hopefully.
 

R!f@@

Joined Apr 2, 2009
9,647
Do u know how to figure out the polarity of the activity led ?
In lamen terms. do u know how to find the switching side of the activity led ?
 

wayneh

Joined Sep 9, 2010
16,102
I would like to use a mosfet or something similar to use less than or equal to what it currently uses. hopefully.
Right, and you can absolutely do this once you know whether you need to switch on with a high voltage (use an n-channel, logic level MOSFET) or a low voltage (use a p-channel, logic level MOSFET) at the existing LED. You need to know how the existing LED is switched; by applying a voltage or by completing a path to ground.

There are ways to reverse the logic, for instance if you already have the "wrong" kind of MOSFET and want to use it, but you might as well do this the easy way.
 

Thread Starter

Sharpen047

Joined Apr 19, 2012
51
it completes the ground to light the led up. positive is constant, ground is the variable.
That what it means?
 

R!f@@

Joined Apr 2, 2009
9,647
It means the LED is driven by the collector of a transistor.

So now u need to make a little circuit.
 

Thread Starter

Sharpen047

Joined Apr 19, 2012
51
That would mean an NPN type right?
I don't know how to calculate a resistor value for the base of the transistor.
Is that all the circuit would need? A resistor and transistor?
 

R!f@@

Joined Apr 2, 2009
9,647
See the pdf.

I was thinking on making the circuit as simple as possible.
I used MOSFET's . Mostly N channel. Never made a circuit using a P Ch Mos.
Since the HDD led signal collector out, I thought of going for P channel MOSFET.

Since MOSFET are voltage driven, we won't need a transistor to buffer the drive. Just connect the HDD activity pin (not the 5V one) via 10Ω 0.25W resistor to LSP2.
Vcc goes to 5V. Or u can connect this to the HDD LED Vcc.

U have to find a P channel Logic level MOSFET that can handle ur LED current.

The Power LED cathode goes to LSP3.

I did not draw the LED cause I dunno what type of LED u had.
I believe u know how to calculate resistor values used in series with the LED. The LED positive depends on the power LED voltage u have. It can be 5V or 12V.

The unmarked resistor in the diagram can be any value from 4.7K to 15K

Remember to use a series resistor with the LED.
 

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Thread Starter

Sharpen047

Joined Apr 19, 2012
51
so the vcc goes to 5v then the lsp2 will go to the negative of the hdd led?
just want to be sure.
 

BMorse

Joined Sep 26, 2009
2,675
also keep in mind that if you have multiple hard drives installed the motherboard multiplexes these all together.... and also, why stick with the boring single LED mod? Go for an activity metering type of display where you can actually "see" how hard the drive is working, just like I did here >>
http://youtu.be/ux6TC0doJrk
http://youtu.be/4ALTbuU9FZY
adds a much better visual effect... :)
 

BMorse

Joined Sep 26, 2009
2,675
I'm doing fine R!f@@, how have you been? Been real busy with "real world" projects have not had much time lately to get on here but I still pop in once in a while..... I will see if I can dig it up, I had built that circuit a while ago, it based on the LM3916 Audio VU meter IC and a couple of Op-Amps....

Edit:
I forgot I had this up on my site already, here is a link to it.... http://www.morse-code.com/id201.htm
 
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