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Electronics Wire LEDs to PWM + molex

Discussion in 'Modding' started by DarkSable, 10 Mar 2014.

  1. DarkSable

    DarkSable What's a Dremel?

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    Hey guys!

    So here's the deal. I made a purchase recently from Newegg Flash, and got a huge roll of RGB light strip for $30. Trouble is... mine has problems.

    [​IMG]

    The lights themselves are the same as every other kit, but the controller and such are, erm... cheap quality. I was playing around with the remote and about half the buttons aren't even soldered correctly. However, that's fine for what I want them for.

    In my mod, my radbox is going to have three molex connections running to it - one of which will only be used to power two fans. It will also have two PWM connections, so here's what I'm thinking. I want to take these lights and make them automatic. They would take power from the molex connection, and do one of two things:

    1) Either (the easier option, I think), I would take the PWM signal and piggy back it to the power on the lights - basically they would just be shining white, but the intensity of the light would vary depending on how intense the fans are being run at.

    2) I would get a temperature sensor and hook up the RGB lines so that the color goes from blue to red as the temperature increases. The trouble is that I'm pretty sure this option would require an actual PCB in order to control the gradation, wouldn't it? Unless there's a temperature sensor that runs variable amounts of voltage through it.

    Anyways, I could use some help with trying to figure out how to wire this up - if you guys have ideas, throw them out there! At some point here I'll be dismantling my current computer in its entirety. (which I'm loathe to do because even though I can't game on it, I'm still writing my updates with it, and would have to switch to using the netbook that only exists for taking notes at school.) When I do that, however, I'm going to play around with how to power this dang thing... but any pointers in the right direction would be absolutely valuable.


    Just as a side note, my ideal would be to have these things go from blue to purple to red as the temperature increases, but I haven't the slightest idea how to do that. Any thoughts? (I was thinking if I played around with resisters and put the temperature sensor on the R line... but I'm still bloody confused on how to do the wiring.)
     
    Last edited: 12 Mar 2014
  2. Tealc

    Tealc What's a Dremel?

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    1) You'd need a transistor to make the switch from 5v PWM to 12V to power your LEDs and it would have to be able to sink enough current for the LEDs. I used an IRL510 when I did this, which is a logic level Mosfet it is good for switching at around 3v. There are probably much better Mosfets out there I could have used but my limited knowledge of Mosfets led me to get that one, plus it was only £1 so that was a bonus. I went for low side switching I seem to recall. The veroboard PCB I made was around 2cm square and has a fan header for the incoming PWM.

    2) You could use a couple of thermistors and two 555 PWM circuits to switch the LEDs as required to the blend you require. Alternatively and probably easier, although less fun you could use an Arduino, a thermistor or even better a LM335 sensor, a bit of code and a few passives to do an even better job of blending. Arduino can be run off the USB 5v and can be built on veroboard for a few (insert your local currency here) once you get it up an running on a devevopment board. I picked up an Arduino copy board for less than £10 off ebay.

    I'm not sure if the PWM controller that came with the LEDs could be utilised.
     
  3. DarkSable

    DarkSable What's a Dremel?

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    Hey, thank you for the reply!

    The Arduino is definitely an option, but the problem is this: There's no option for it to have USB power or an actual PWM connection. I have three molex connections and two PWM cables that it can piggyback off of, but that's it.

    I'm thinking that a temperature sensor is going to be by far my best bet. Would it be possible to use the 12v from the molex and run it to the LEDs, have the blue be full on, and have the red be connected to the PWM signal with a transistor to boost the power?

    Sorry if the above is an incredibly foolish question - I know my way around computers, but not electronics.
     
    Last edited: 12 Mar 2014
  4. Tealc

    Tealc What's a Dremel?

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    Ok if you can't use a USB lead for power you could use the 12v from any PC Molex peripheral connector but the onboard voltage regulator will have to dissipate some energy as heat. It shouldn't be a problem. You could also hack a USB connector and a Molex and route 5v straight in of course and that would be even better.

    If you want the colour change to occur based on CPU temperature you will need to split off the 4th pin from the CPU_FAN header and use it as an input on your Arduino. You could use a PWM splitter cable for this purpose, or make your own wiring. With the Arduino you would be able to determine the duty cycle of the PWM and control your output LEDs accordingly, and as PWM duty cycle is a factor of the CPU temperature any corresponding increase or decrease would directly affecting your lighting.

    If you wanted to go with ambient case temperature you would just use a temperature sensor as mentioned before and work off that.

    Yes but that would be easy enough do to but you'd only get a mix of red and blue in that case, and you'd not be able to tweak for a desired colour blend. You'd only see full colour mix at 100% duty cycle on the PWM and if your system is like mine it never happens under normal conditions. It might work out ok though and for the sake of a bit of wire, a logic level mosfet and a few donor connectors it might be worth a shot.
     

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