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Thread: Gizmo making help wanted

  1. #1
    Hexus.net daveham's Avatar
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    Gizmo making help wanted

    I want to make an item that will help me with overclocking....

    ....basically I want to be able to reset my CMOS without opening the case.

    I have (like most motherboards) a 3 pin header for CMOS reset where putting a jumper on 1-2 is normal and 2-3 in reset (or vice versa).

    I want to modify a cdrom audio cable by cutting the 4 pin socket down to 3 and moving the wires to run straight through. I will then connect this to the 3 pin cmos reset header.

    I will cut the other end's socket off, and via a drilled/cut pci blanking plate, fit a switch that is accessed from the rear outside of the PC. This will be a dipole switch that will switch betwen 1-2 and 2-3.

    Can anybody help me with a few questions....

    1) what would happen if this switch was accidently activated whilst the PC was on?

    2) can anybody recommend a cheap type of switch that is hard to accidently activate, but still accesible.

    3) can you foresee any other problems?

    4) if this works and I make a few would anybody be interested in one at cost?


    Cheers, Dave

  2. #2
    Senior Member SilentDeath's Avatar
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    1) mobo = dead.
    2) one of these with one of these ?
    3) only as the result of user error... testing this for example
    4) I wouldnt, unless it would provide more functionality than the reset switch i stole fomr an old case, which Ive been using for this purpose for a few months... lots of other people might though.

    A way to add functionality (to make me buy one ) and to aviod 1 and to get round 2, and also to allow you to use a less crap switch, you could have a simple circuit using the 5v_sb to prevent it being accedently switched, the people over at bit-tech.net forums should be able to help with that - though I will *attempt* to now...

    If you used a NOR logic gate, it can be quite simple -
    This part "74 HC 02 N" from maplins (search code UB01B)
    Pin 2 goes to 5v_sb, pin 3 goes to ground, and pin 1 is the output. If either pin2 or 3 is logic 1 (high) then pin 1 stays at 0v. If neither are 1 then the output goes high.
    You then connect the output to the base of a transistor - not sure what type you would need. When the base is high, the collector allows current to pass through the emmiter, compleating your circuit, reseting your bios - assuming the switch was pushed. This would also protect if you accidently left the switch closed then turned the pc back on - easy to do I think if you cant see the switch as its round the back of the case

    I *know* Ive missed lots out, so doing this and not knowing anything but what ive typed, will probably result in a dead pc.... When im more awake tomorrrow Ill think about it more...

    To get the 5v_sb (which is probably the best way to know if the pc is in any way on) you would have to either take it from the ATX connector or somewhere on the mobo - not the most practical way of doing this if you wanted to sell it....
    However to do this the NOR would need to be powered, and theres little point in using a molex with +5v or +12v, as it still wouldnt provide 100% safety for the mobo...

    really this level of safety *SHOULD* be intergrated into mobos in the first place...

  3. #3
    Kirstie Allsopp Theo's Avatar
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    You could, of course, use a keyswitch instead of a toggle switch. Should the switch be mounted externally, and you knock it, you won't risk buggering up your motherboard. The key is required to activate the switch, so as long as you.... bloody hell I'm drunk.

  4. #4
    Senior Member SilentDeath's Avatar
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    bleh! I spent ages thinking of that... keyswitch probably best though..

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    If you dont want to have a key you could always use two switches mounted far enough apart so is unlikely they would ever be switched by accident. You could mount one of the two switches (springy plunger thingy like a fridge door or car door switch) on the base of the PC so when it is on your desk or on the floor the circuit is broken as a fail safe. To reset arm the circuit with the primary switch then tilt your PC off the desk or floor to close the fail safe switch. Sounds daft but hey it should work.

  6. #6
    Senior Member Kezzer's Avatar
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    hmmm. Ok, a 3 pin header for the three pins so you have the two positions. Make some sort of electrical switch hooked up to a case switch which inserted a pin and retracted the other when it was pressed.

    Sounds like a challenge. Make sure you've got a good few old boards lying around

  7. #7
    Hexus.net daveham's Avatar
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    I am thinking keyswitch here.....this would leave plenty of room on the backplate. Can anybody think of anything useful to wire up to to for external access?

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