Variating voltage for a bulb

[curtis1552]

I want to install a low voltage iridecent bulb in the front of my case which gets more power depending on how much current my computer is pulling. (more peripherials/cpu/etc usage and the bulb gets brighter)
I looked into Hall effect switches attached to different power cords but I don't think that it would work (or be cost effective).
Does anyone know if i could run the HDD light lead and several others into a parrallel circuit to power the bulb?

+ HDD lead ----------------------------\
+ Power lead -----------------------------Bulb---->negative
+ return line from 24 pin connecto t'd ---/

(this will be for a HAL9000 style mod)

[EmAn]

im not sure how to do it that way but you could open your psu and make some kind of wattage meter either going from the terminals where the 120 / 240v line comes in or have it meter the rails and have it put out a small charge from that to power the light

[Mpegger]

A wattmeter would have to be plugged in between the wall outlet and the line to your psu. That is the only way to measure the wattage something is using (just in case EmAn's explanation wasnt clear enough).

[tricknasty]

wow that sounds like a cool mod on paper. but i would be careful.
As components are being used i dont think theres a large fluctuation in power, so the measuring device will have to be sensative, or measuring ampacity like Mpegger said.

[redwraith94]

You may be better off using a Pulse Width Modulation device.

To vary the brightness of a light bulb you have two options,

1. Vary the voltage that the bulb receives, this is probably more difficult for this project.

2. Switch the power to the light bulb on and off many times per second. Normal light dimmers do this, and so do most fan controllers. You would probably be best off modding a fan controller. (This is Pulse Width Modulation)

I don't mean to be a douche, but I think you mean incandescent, iridescent is used when something is shimmering, the other type being flourescent.

You could probably find a 12v light bulb for automobile interior, and wire that up to a fan controller. This still leaves a problem of making a watt meter interface with the fan controller.

Normally fan controllers increase the amount of time the power is on (The Pulse Width) by turning a nob. It would be a fairly complicated circuit to interface those two.

The other route would be to have a few settings for wattage, and build a switching circuit that does the same thing, that would be worse though, from a building standpoint.

It is kind of problematic because usually the pc will be drawing say 200 watts (depending on your rig), and it may spike to 300 occasionally. The three biggest spikes will be:

Processor use (say gaming, Prime95, F@H etc.)
Video card use (gaming)
Hard disk use ---This will be the least for modern rigs, unless you have a raid array.

If the numbers above are correct you would want the light bulb off at say 200w, and full bright at 300. I am assuming? It really depends, in order to do this you will need the least amount of power that your computer is using when it is sitting at idle.

http://www.thinkgeek.com/gadgets/travelpower/7657/

Something like that will tell you. If you are comfortable hacking wires apart, then it is also possible to put a Volt Ohm Meter between the psu, and Motherboard hdd, graphics card etc. But we would really need more info about your rig, and you could possibly kill it this way.

They may make something like this already, but I don't know of it.

[aja]

interesting thread!

I would seriously consider using a light like THIS (http://www.instructables.com/id/EECBH5S42FEP2870OC/) - it would look amazing!

[curtis1552]

OK, I have absolutely no problem hacking wires.
Yes, I did make a typo - incandecent not iridecent.
I'm going to test it on an old Gigabyte 7ixe mobo with a 733 Amd slot A, but the final product will be using a ASUS a8v-e se with athlon 4400. Nvidia 6600 with water cooling.
A fan controller won't work for what I want becuase I want the light to vary automatically.
After looking at lightbulbs more I have realized that I need to use a lower current for the bulb: the bulb I found thatfits my "style" requirement is an automotive brake light.
http://autoparts.pricegrabber.com/bulbs/eurolite/m/38596223/(the max wattage on the bulb is 30)
Now I need to determine what wires to hack. I'm thinking that I will only be able to use one or to to power the bulb because of the low wattage requirement. So it would probably be wires 10,11, or 14 because they are the +12 volt and -12 volt wires.
Or should I hack the ground wires, and which ground wires?

[geoffchad]

I'll reccomend using LED's for this one and avoid automotive bulbs. They are too big, too bright, and too hot for what you want.

Or you could do something like a graphic equalizer (the bar displays are available pretty cheap too).
http://www.blackcabin.com/IMAGES/equalizer.gif
Usually they are like 7 segments vertically oriented. That wont be terribly bright though, but it will probably be bright enough when you're looking at it.

The problem isnt the bulb/LED and dimming it - the problem is meausurement of the power used. As your voltage is staying theoreticlaly the same, you need to measure the current flowing out of the power supply - which will be extremely difficult to get a good value - espicially as most common ammeters dont go over 10A. You dont want something in series with ANY of the main power rails to the mobo/cpu. If that component fails, you're going to risk damage to your hardware, and whats more - you dont want any voltage drop to lower the voltage your components get.

Do you want to get total power use, or just the cpu? I'd reccomend using temperature probes, as those are going to be the easiest and most consistent way to measure power, as power use is directly releated to the heat put out from an IC, its the most logical choice while staying simple.

Personally, I'd reccomend you pop open the power supply and get a temperature probe onto one of the regulator transistor heat sinks, as close to the actual IC as possible. While its not very accurate, neither is dimming a bulb. Then check the value it puts out under bench testing and cold at idle. Use that data to PWM the bulb/led to dim it accordingly. That'll be the easiest and cheapest method, though not the most accurate -- But it'll void the warranty on your power supply.

[djrussell]

could you do something with a fan connection? my motherboard has two that it can vary fan speeds with. i assume if you hook a bulb up to them it would vary the light output just as it does the fan speed. it would be according to system temp or cpu temp (unless you can hook up your own sensor) but i think that's about what you're aiming for.

i dunno. shot in the dark here.

[curtis1552]

I think i'm goning to try the fan connection, I'll be water cooling, so i'll use the cpu fan plug.