CM Scout - tapping into LED on/off switch

J

jjsparx

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Sep 7, 2011
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Hi,

I have searched high and low for an answer to this question and cannot find anyone with the same situation. I came very close to it in this thread but it stopped before I had all the answers.

Basically I have purchased some after market LED fans that include an on/off switch on the body of the fan, these I thought would be an excellent replacement for the existing fans and still keep the LED on/off switch function on the front panel.

My only problem is that I cannot work out which wires to cut into to maintain the on/off switch - I presume that I can simply snip the switch off the after market fan and wire it into the existing wiring for the CM stock fans.

To make matters slightly more complicated I am planning to run these fans with PWM control on the motherboard, but power them from the PSU. I have purchased this product:

http://www.overclockers.co.uk/showproduct.php?prodid=CB-031-AK&utm_source=froogle

This appears to give me power to the fans from the PSU (not stressing the motherboard's power) and the ability to run the fans at different speeds depending on load via connection to the motherboard 4 pin PWM header.

The above bit I can work out on my own, it's just the replacing of the stock fans and the wiring to the LEDs that I can't figure out. Any help with this is greatly appreciated.

Many thanks in advance,

Jamie
 
Can you post a picture of the fans, so we can see what you're dealing with?
 
Hi thanks for the response. I have taken these pics from another website, hope this is OK.

Picture of switch:

08.jpg


Picture of 4 pin PWM connection:

09.jpg
 
Well, rats. In order to give a worthwhile response, I'd need to know 1) how the switch in your pic is hooked up to the LEDs, and 2) how the switch on the case is wired. Is the switch wired to 5V? 12V? Or is it just a dumb switch that completes the circuit for the LEDs?
 
Having had a better look at the connections, I can see that there is a red and black wire running from the rear LED fan and the front LED fan that merge into a set of green+white and red+black wires, these then go directly to the switch with a couple of resistors on the green+white cable. The switch is a 5V switch.

I will try to take some pictures, but as the wiring is running through the case it will be hard to work out what goes where.

It looks like I can just snip the black and red wires from the existing fans and connect them to my switch wires coming from the new fans. Is this correct?

Also if I wanted to add a 3rd LED fan with the same control from the front panel can I just add to the existing wires and daisy chain without any issues? The only reason I mention this is because of the resistors in place for just two of the LED fans, if I add a third fan to the mix will the resistors cope?

Many thanks,

Jamie
 
Please excuse the very crude picture, but hopefully this will explain how all the fans are wired in. Which wires do I need to cut into and wire in the switch for my leds? I don't think 12v power is a concern as this will be handled by the motherboard and PSU combination cable I previously mentioned.

2el42nl.jpg
 
That picture, crude though it may be, is worth a thousand words. And it makes me wonder a few things. It looks like the front fan's LED gets 5V from the button (through a resistor), and the rear fan's LED gets 5V directly, with the negative lead switched. That seems odd to me, as such a design requires a double-pole switch (which is more expensive). In any case, we can work with it.

If you're just replacing two fans, it should be straightforward: cut the new fan's wires, cut all four wires on the switch, and then hook one fan's LED's wires to the green/black wires (doesn't matter which way) and the other fan's LED's wires to the red/gray wires ( again, polarity doesn't matter).

If you are adding more than two fans, it gets a bit trickier, and we'll need to know how the LED is wired to the switch--is the switch on the high side (12V) or the low side (GND), and is it between the LED and the LED's resistor?
 
Mohonri thanks for the info, that is very helpful. I was thinking of cutting the wires earlier on in the circuit to save me buying new wiring etc. Will the image below work with regards to the LEDs switching only? I am not sure about the power to the fans yet until I get the cable I mentioned in my first post and see how it connects up.

21azl3r.jpg
 
If you're just replacing two fans, then it's simple--hook up the wires from the fan's switch to the black/green and red/grey wires, and leave the molex connector unplugged. That way the switch will simply provide continuity, rather than power. The new fans don't need power from the switch (and in fact, if you wire it wrong, you'll short out your PSU. Which sounds bad, but is no big deal with modern power supplies--they just shutdown on overload).

If you're looking to power the old fans' LEDs plus new ones, or if you're looking to power more than two fans, I'll need to know how the LEDs themselves are wired up with the switch on the fan. One of the wires from the switch will be tied to either the GND or 12V rail. If you can figure out which rail the switch is tied to, I'll be able to give you a final answer.
 
Mohonri said:
If you're just replacing two fans, then it's simple--hook up the wires from the fan's switch to the black/green and red/grey wires, and leave the molex connector unplugged.
Click to expand...

Excellent, thanks for that info. I presume that the power for the LEDs (and fans) will come from the motherboard/psu combination cable I now have? It's basically a molex plug that connects to the PSU that feeds the fans power and a motherboard 4 pin plug that feeds the fans the PWM signal via a 3 pin socket.

I will try to get a picture of the circuit board for the fans as the blades pop out and reveal what's underneath. I had a quick look, but to my untrained eye I couldn't really tell.

The only thing I may want to do at some stage is add another LED fan and keep the on/off LED switching that the other two fans will have. Can I just "piggy back" off either the red/grey or black/green wires or will that be too much for the resistor to handle?

Will hopefully post a picture this evening for you.

Cheers,

Jamie
 
The LEDs on the new fans are powered by the 12V that goes into the fans, and have their own resistor. Which means that I made a mistake in my earlier post. You'll want to bypass the existing resistors attached to the case's button. You can do this by either attaching your wires between the resistor and the button, or you can put a wire across the resistor to short it out (all the current will go through the bypassing wire, rather than the resistor).

If your new fans are identical (and I assume they are), then you should be fine attaching the wires for the LEDs of both fans to the same pair of wires coming from the case switch. When you do so, however, make sure that you're attaching identical wires from the LEDs to the same wire on the button. In other words, make sure that the wires which are attached to the middle of the fans' switches are tied to one wire (let's choose red), and make sure the wires which were attached to the switches' outside pins are attached to the second (in this case, gray). If you get them switched, it won't cause any damage, but the switch won't work. If that happens, switch two of the wires.

That way, you'll get two fans working off one side of the case switch. Then later, you can use the other side of the case switch for a different fan.

Remember, though--DON'T PLUG THE MOLEX IN! Doing so shouldn't cause any damage, but it'll make your PSU freak out and shut down.
 
Mohonri said:
The LEDs on the new fans are powered by the 12V that goes into the fans, and have their own resistor. Which means that I made a mistake in my earlier post. You'll want to bypass the existing resistors attached to the case's button. You can do this by either attaching your wires between the resistor and the button, or you can put a wire across the resistor to short it out (all the current will go through the bypassing wire, rather than the resistor).
Click to expand...

I think I get it now, I will have a play at the weekend and see what happens. I managed to take these pictures of the inside of the new fans. Not sure if this makes any difference though.

I will hopefully get time this weekend to give this a go and post back with my results.

Inside fan left side:

wjcr2g.jpg


Inside fan right side:

29fee5d.jpg


Many thanks again,

Jamie
 
I can't really make out how the switch is hooked up from the pictures--the picture is too dark and out of focus.
 
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