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Need help with wiring on/off switches for fans...

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Mar 6, 2002
Monroe, Georgia
I would like to have 4 switches.

Switch 1: 1 Large Case Fan
Switch 2: 3 Small Antec Fans (used as case fans)
Switch 3: for an added Antec fan mounted on the MB Heatsink.
Switch 4: for an added Antec fan mounted on the video card Heatsink.

This is what I bought at Radio Shack...

4 Each:
Toggle Switch
SPST Submini
Contacts rated 3A at 125VAC/1A at 250VAC

4 Each:
Green Subminiature LED Indicator Lamps
Absolute Maximum Ratings (25 C)
Power Dissipation: 100mW
Forward Current: 30mA
Optoelectrical Characteristics
Forward Voltage:
2.1V @ 20mA
Luminous Intensity:
2.5 mcd @ 10mA
Peak Wavelength: 565nm
Long lead is anode (+) connection

As you probably guessed, I would like to wire these LEDs into the circuit but I have minimal wiring experiece, so I willl need your help. I am not even sure the switches/LEDs combo will work.

I am good with a soldering iron, but will need your help on how to wire the on/off switches and LEDs.

All replys/suggestions welcome.

this should work: you will need to find a resistor to reduce the 12v to 2.1v

im going to go look up the resistance that you will need for those resistors.

just repeat this diagram 4 times and connect them to the same molex.


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No prob. i figured that a pic would most clearly show what needs to be done. just be sure to put that resistor in, or your led will burn out.

ohms law states that V=IR therefore R=I/R

R=(12volts -LED voltage required)/(current in milliamps)*1000

R=(12volts -2.1)/(20)*1000

R=495 ohms

you will need a 495ohm resistor (look for 500ohm)
All I could find at Radio Shack were these:

1/2 watt 5% tolerance

What do you think?
that may work. Just keep in mind that the more resistance the less power so your led will be a bit more dim.



so you will be puting only .8 volts through your LED. that may not be enough.

you could put 2 resistor in series (one after another) to get a total of 500

ie 250+250=500 or 100+400=500...

putting resistors in parallel is a bit more complicated however.

list me the resistors you have and i will try to help you find a good combination.
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You know, I could go back and do the cobo thing. They had a 510-Ohm that was sold in a pack of resistors, about $11. The cobo idea might be the best way to do it.

So for the cobo, would you just solder them in line, one behind the other?
I hate to bring this up, but since you're using toggle switches you'll already know when the fans are on.
"Combo" meaning, putting a few resistors in line to total 500Ohms.

Iron Hawk is right. It looks cool.:D
I will have to post a picture of what I have completed so far. I mounted the switches and LEDs into the bay. Looks good, now all I have to do is the wiring. I might tackle this tonight.
This is what I picked up:

Pkg. of 5
1/2 watt - 5% tolerance

Pkg. of 5
1/2 watt - 5% tolerance

I can combine one 470-Ohm with two 15-Ohms.

470+15+15 = 500-Ohms.

I also picked up a $1.99 PCB; I can soilder the 12 resistors to this small board to keep things from getting out of hand.

I don't know about you, but I am having fun.:p

Do I really need these switches, nope! :rolleyes:

But since when did that ever stop me.
yeah, pcb boards are great. the 470 might not bring the voltage down enough so it would be a good idea to put 1 or 2 of the 15s in.

let us know how it goes. if you too much voltage goes through the LED the led may get warm and its life will go down. the worst that could happen is that the LED will burn out. you could probably get away with putting 2.5volts or more through it, but its never a good idea to run things out of spec.
Last night I got one complete circuit working and installed.

When I first threw the switch, NOTHING!:( Then I realized I did not plug in the power :rolleyes:

NOW it works! :D

Tonight, I will work on the other 3 circuits and take some pics. I will try and post them tonight.