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  Will a resistor on a USB port 5V line leave the port usable? 
 
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Jan 22, 2009, 05:29pm EST Reply - Quote - Report Abuse
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Edited: Jan 23, 2009, 05:15pm EST

Replies: 15 - Views: 5062
So, long story short ... I'm modding my laptop. ^_^ ... and I need <5V.

Since there's no molex connectors, I'm just going to solder directly to a USB connection internally. Now, I'm no electrical engineer, so I'm wondering if by doing this with a resistor, will anything I plug into the port get the original 5V or the 3V or so which will be going to the fan (on the other side of the resistor).

Here's as**tball'd diagram of what I want:
http://img522.imageshack.us/img522/1364/usban7.png

So, will that USB port still work? If not, no biggie. I wouldn't plug anything that draws too much out of it, probably my wireless mouse dongle.


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Shawn Langley Jan 22, 2009, 06:13pm EST Reply - Quote - Report Abuse
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Edited: Jan 22, 2009, 06:14pm EST

 
>> Re: Will a resistor on a USB ports 5V line render it unusable?
I regularly siphon power from USB in the exact way you are (whole desk and under desk is lighted up this way has quite a neat glow effect as LEDs are hidden behind objects and stuck to topside under desk), it shouldn't be a problem in practice but I would be careful on how much load/current you draw remember 500mA!

Also your'l find (at least in my experience) USB ports are insanely sensitive to shorts usually a single one will kill it(yes many I have destroyed.... I usually will test something on a cheap powered USB hub first before plugging it into a mobo port) , so make sure no bare wires if your testing things.

PS. more specific to your point as I went off on a tangent yes you should just be able to get a small/slow fan to run and a USB wireless dongle i would recon without doing any working out.

Having voices in your head is normal. Listening to them, common. Arguing, acceptable. However, when you lose the argument, you're in trouble.
Jan 22, 2009, 06:24pm EST Reply - Quote - Report Abuse
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>> Re: Will a resistor on a USB port 5V line leave the port usable?
Well, shucks. I might just do this then. :P I'm off to RadioShack this afternoon to get the resistors, hopefully I don't melt/blow up/destroy anything. ('_')

Post some pics of this lighted setup!

Jan 22, 2009, 09:24pm EST Reply - Quote - Report Abuse
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>> Re: Will a resistor on a USB port 5V line leave the port usable?
Well I picked up some 10, 15, 22, and 33ohm resistors tonight. That way I can play around with getting the right fan speed. I can always use some extra resistors for later projects anyway. ^_^

I'll post back when I get it working. Thanks for the tips, Shawn. :_)

Jan 22, 2009, 11:44pm EST Reply - Quote - Report Abuse
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>> Re: Will a resistor on a USB port 5V line leave the port usable?
F**k I forgot to buy heatshrink. :(

Reason   Jan 22, 2009, 11:56pm EST Reply - Quote - Report Abuse
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>> Re: Will a resistor on a USB port 5V line leave the port usable?
Just saw this thread, don't forget to buy heatshrink, mcfly!

What's the fan for?

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Jan 23, 2009, 12:58am EST Reply - Quote - Report Abuse
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Edited: Jan 23, 2009, 01:03am EST

 
>> Re: Will a resistor on a USB port 5V line leave the port usable?
It's the CPU/chipset cooling fan.

The fan now is temp-controlled by the BIOS. When the CPU temp is >=55C, it's on low. If the temp is <55C, it's totally off. With no fan, the temp slowly creeps up to 55, then the fan comes on, cools it to 54 and shuts off.

So it ends up going on/off/on/off/on/off, about 3-4 seconds each time. The result is insanely annoying.

There are absolutely no temp settings in the BIOS, and Acer hard-coded the fan controls, meaning no software fan control is possible. I've already applied Arctic Silver 5 and undervolted the CPU in my efforts to keep it cooler, but it only ends up delaying the inevitable rise to 55C by a couple of minutes.

The actual fan is 3-pin (voltate, ground, tachometer), so I tested the result of running the computer without the fan connected at all, and it will alert me that the fan is not responding. So I plan on leaving the tachometer line connected to the motherboard, and connecting the voltage and ground lines to the 5V USB line for a constant RPM fan. :_) That way if something does go wrong, the tach sensor will still pick it up.

My normal CPU voltage is 1.25V, using RMClock I set it to it's top P-state at a lower 1.025V, and it ran 18 hours on Orthos without a crash, never needing to get past the lowest RPM setting of the fan. So I figure if I undervolt all the time and use a big enough resistor to keep the fan at about the same RPM as that lowest setting (maybe a little faster) ... I'm good to go! :)

This will certainly void my warranty ... but ah. Almost everything I own that came with a warranty I voided at some point. :P

Shawn Langley Jan 23, 2009, 04:38am EST Reply - Quote - Report Abuse
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>> Re: Will a resistor on a USB port 5V line leave the port usable?
Just a thought you probably already have done it but rather than having the cable leave the laptop and plug into some sort of USB pass-through connector, you could solder it to the traces of the connector inside the laptop to make things neater,

Also depending on how technically minded you are and even if you wanted to, if USB doesn't provide enough power or its interfering with something that's connected to USB, look up the schematics of the motherboard if you can find them, and you can draw the 5v from somewhere else, IE a ground point and a +5 point maybe from a mosfet ect

Having voices in your head is normal. Listening to them, common. Arguing, acceptable. However, when you lose the argument, you're in trouble.
Jan 23, 2009, 11:35am EST Reply - Quote - Report Abuse
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>> Re: Will a resistor on a USB port 5V line leave the port usable?
Just a thought you probably already have done it but rather than having the cable leave the laptop and plug into some sort of USB pass-through connector, you could solder it to the traces of the connector inside the laptop to make things neater,

That was my plan from the start. :) I don't want to have random cables sticking out the side. :P

The fan is a 5V, 400mA fan. My wireless mouse dongle, according to the Device Manager, is using 100mA. After the resistor, the fan should be drawing about 200-300mA, so it should be good to go with the mouse. :)

Although as an aside, are there any USB port "plugs" that I could buy? In case I decide not to reserve that port for the fan, something I could put in there to prevent me or anybody else from inserting a device?

Reason   Jan 23, 2009, 08:06pm EST Reply - Quote - Report Abuse
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>> Re: Will a resistor on a USB port 5V line leave the port usable?
MkFly said:
Although as an aside, are there any USB port "plugs" that I could buy? In case I decide not to reserve that port for the fan, something I could put in there to prevent me or anybody else from inserting a device?

Get an old 128 or 256 flash drive, cut off the USB connector and glue it in there. Or any broken/unwanted USB device, for that matter. Maybe stick something over the contacts to make sure there's no stray voltage.

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Jan 23, 2009, 10:31pm EST Reply - Quote - Report Abuse
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>> Re: Will a resistor on a USB port 5V line leave the port usable?
Well that would work, but I was hoping there was some kind of manufactured plastic plug I could use. :~

Shawn Langley Jan 24, 2009, 04:14am EST Reply - Quote - Report Abuse
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Edited: Jan 24, 2009, 04:17am EST

 
>> Re: Will a resistor on a USB port 5V line leave the port usable?
Piece of neoprene foam carefully cut with a scalpel? Carefully cut your'l do a better job than any manufacture!

Also if your really insistent on using plastic for some reason and cant find what your looking for, eBay for "Polymorph" is solid plastic till about 80oc then it becomes like blue-tack can mold it in any shape you want and then let it cool it'll go solid again (heat it up in a cup of boiling water)

Having voices in your head is normal. Listening to them, common. Arguing, acceptable. However, when you lose the argument, you're in trouble.
Dr. Peaceful Jan 25, 2009, 12:02am EST Reply - Quote - Report Abuse
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>> Re: Will a resistor on a USB port 5V line leave the port usable?
You just can't get your hands off your hardware, can't you, McFly? LOL ;)


Jan 25, 2009, 12:21am EST Reply - Quote - Report Abuse
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>> Re: Will a resistor on a USB port 5V line leave the port usable?
kekekekekeke ^_^

So I think what I'm going to do for that port is put a mini Bluetooth dongle in like this one:
http://www.newegg.com/Product/Product.aspx?Item=N82E16833242001

The one I have now is 100mA, so I'm betting that one is similar.

Jan 30, 2009, 10:28pm EST Reply - Quote - Report Abuse
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>> Re: Will a resistor on a USB port 5V line leave the port usable?
Alrighty! So, yesterday I ordered that Bluetooth adapter above, and I picked up some heatshrink from the Shack. :_) Probably will work on this tomorrow.

I bought a Bluetooth mouse to replace my standard wireless one (I'm just using it with my bigger BT dongle), and I'm surprised by how great it works.

Shawn Langley Jan 31, 2009, 04:14am EST Reply - Quote - Report Abuse
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>> Re: Will a resistor on a USB port 5V line leave the port usable?
So when are you planning to mod in a window and some case painting now your a pro?

Having voices in your head is normal. Listening to them, common. Arguing, acceptable. However, when you lose the argument, you're in trouble.

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