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Momentary Switch to Toggle Fan.

Discussion in 'Electronic Design' started by [email protected], Feb 12, 2007.

  1. Guest

    I'm having a bit of trouble here. I am a sophomore Computer
    Engineering student at Psu. I recently bought a new computer case,
    and the front has an 80cm fan with LED's and what-not. The problem is
    that it is very loud. To make matters worse, it runs on a four-pin
    molex, and the speed isn't variable. Additionally, I share the room
    with a roomate, and the lights are kinda bright, esp. when its dark.
    The case is acrylic, and the side panels are screw-on, so I can't
    even unplug it.

    Now my Idea is to use the 'reset' button, which is useless with a
    'power' button above it, to change the speed, as well as turn it off.

    My plan is to us a binary-output counter (SN74LS163), and tie the
    one's and two's places into a 2 to four DMUX (Say an SN74LS139A).
    I'll then use the momentary switch(reset button) as the clock for the
    counter. This will let me cycle between four different circuits:
    Unmodified, 80%, 40%, and off.

    Now implementing the logic is no problem. The issue I have is using
    the 5v logic outputs to actually control the 12v fan. I looked into
    Tri-State buffers, but even if I was able to find one that took 5 and
    12 volt inputs, none have the necessary 150 mA capacity. Now I talked
    to an EE buddy of mine and he suggested that I could use a few
    transistors to switch it. Alas, transistors aren't one of my strong
    points, and I dont know how to use them, or even what type to get. I
    pretty much need to use a 5v, 20 mA max low/high signal to start/stop
    a 12v current that may go up to 250mA, without frying any ICs, and can
    last for at least two years of continuous use.

    I tried searching the internet for a few hours, but couldn't find the
    info I needed. I eventually found this group, and I'm hoping somebody
    here can help.

    Cheers.
     
  2. Gibbo

    Gibbo Guest

    Several hundred people here can show you, very simply, exactly what you
    need to do with the output of yout TTL IC to feed your fan so it goes on
    and off as you dictate.

    But ask yourself one question..........

    Why do you think the fan is there in the first place? Just to annoy your
    roommate?
     
  3. kell

    kell Guest

    Get a quieter fan, maybe. allelectronics.com has an 80 mm fan, part
    number cf-257 for $3.50. Says it's 21.0 dBA...
     
  4. There's rumored to be a CMOS COOKBOOK with the circuits you need in it.


    --
    Many thanks,

    Don Lancaster voice phone: (928)428-4073
    Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
    rss: http://www.tinaja.com/whtnu.xml email:

    Please visit my GURU's LAIR web site at http://www.tinaja.com
     
  5. You obviously have never met his roommate.

    --
    Many thanks,

    Don Lancaster voice phone: (928)428-4073
    Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
    rss: http://www.tinaja.com/whtnu.xml email:

    Please visit my GURU's LAIR web site at http://www.tinaja.com
     
  6. Buy a quiet fan.
     
  7. Guest

    Several hundred people here can show you, very simply, exactly what you
    Several hundred perhaps, but can you?
    I live with Mike Tyson. He'll bite my face off.


    This is one of those little pet-projects that I want to do regardless
    of the neccessity. There are two other molex fans in the case,
    withought lights, and I've aready ordered three-pin replacents, as
    well as a green cold cathode strip light. But the front fan is
    special. I want to be able to build a little board with a female
    molex and some pins soldered on, and I can just plug everything in an
    have it work. The only hurdle left is what transistors to use, and how
    to connect them. Additionally, is there a better way to implement the
    switching besides a counter+dmux? This design is simpler, and has
    less wiring than a J-K solution, so I'm thinking its the best choice,
    esp. as I have all of the neccessary parts.
     
  8. Guest

    Found an excellent resource:

    http://www.winpicprog.co.uk/pic_tutorial_extras.htm

    This page seems to clear up a lot of the uncertainty about the
    outputs. I'm going to draft up a schematic and run it past another EE
    buddy.

    Keep in mind that other people with the same situation may come
    through here on a google search, and it would be good to have clear,
    concise, solutions. I may post up a schematic, and let ya'll know how
    it goes.
     
  9. amdx

    amdx Guest

    Don, your humor has been showing lately.
    I liked your answer to the guy that wanted to melt ice off the driveway.
    "The obvious solution is to move the driveway to where there is no
    ice."

    From sunny Florida,
    Mike
    P.S. I don't miss winter in Michigan
     

  10. Then you need to chose your boyfriends with more care. he would
    probably bite the computer, too.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     

  11. He just copied some guys TTL COOKBOOK. ;-)


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  12. me

    me Guest

    wrote in @j27g2000cwj.googlegroups.com:
    You could also look here http://www.cpemma.co.uk/index.html
     
  13. John Fields

    John Fields Guest

    ---
    Yes.

    I've emailed you a schematic since you can't access
    alt.binaries.schematics.electronic from Google groups and posted it
    there as well for anyone else who might be interested.
     
  14. Guest

    I got your email, however it was all garbled. I saw the words
    'Fanspeed.pdf' So I assume you meant to send it as an attatchment,
    not as ascii text. I'm interested in seeing what your version looks
    like, and how it compares to my own.

    I don't have access to a scanner right now, but the general layout is
    a four-bit counter with the 1's and 2's places fed into a 2-to-4
    Dmux. The first three Dmux outputs each go to a PNP transistor, which
    mediate the current to the fan, while the fourth goes to ground,
    disabling (or rather, not enabling) the fan. As each output is
    selected, the output goes from high to low, allowing the 12v current
    to pass through the Transistor(s).

    Total # of parts: Two ICs, Seven resistors, three PNP transistors, a
    capacitor (used to stabilize clock), and various wires and
    connectors. Done properly, it'll take up less space than a saltine
    cracker, and depending on the quality of the ICs, last for years.
    Total cost: less than 5 bucks, esp. since I can get most of the parts
    for free.
     
  15. John Fields

    John Fields Guest

    ---
    OK. I think I know what happened. I sent the post to abse as an
    attachment and to you in the same post, but I think Agent defaults
    email attachments to inline text, so that's what it sounds like from
    your description. I'll send it to you again as an attachment and
    we'll see what happens.
    ---
    ---
    No need to scan it, I know exactly how it works, and I think you're
    going to have a problem because the TTL part won't be able to pull
    the transistor bases up to 12V to turn them off, since its Vcc is
    +5V.
    ---
    ---
    Mine has one chip (an HC4017) three 2N4401 NPN transistors, five
    1/4watt resistors, three power resistors to slow the fan, and a
    diode and a capacitor to debounce the switch. Take a look at a 4017
    data sheet:

    http://focus.ti.com/lit/ds/symlink/cd74hc4017.pdf

    and you'll see that it has the decoded outputs coming out,
    eliminating the need for the demux. Plus, its out outs are positive
    true so you can drive NPNs and get away from the PNP level shifting
    problems.
     
  16. Guest

    Mine has one chip (an HC4017) three 2N4401 NPN transistors, five

    Awesome. Data sheets=good! I don't know if I'll be able to get one of
    those chips or not, but do you have a schematic for this design?
     
  17. kell

    kell Guest

    There's just one thing I don't get. After you turn the fan down,
    what's going to keep your computer from overheating?
     
  18. John Fields

    John Fields Guest

     
  19. Guest

    Still nothing, john.

    I managed to scan the schematic that I designed, and touched it up a
    little. Does it look electrically sound to everyone? I'm pretty sure
    about the logic, its the transistors I'm worried about. Will a five
    volt High signal block the current? And if it goes low, will current
    be allowed to pass? What model of transistor should I get? I
    calcultae that it will need to provide at least 150 mA at 12v to power
    the fan, so a >=2W tran. is required. A link to the image that (I
    hope) works is here:

    http://allyoucanupload.webshots.com/v/2002723092834367425
     
  20. John Fields

    John Fields Guest

    ---
    Current will pass through all the transistors all the time.
    ---
    ---
    No. With the transistor fully saturated the voltage drop across the
    collector-to emitter junction will be about 100mV, so since:


    P = IE, P = 0.125A * 0.1V = 0.0125 watt


    Even if there was a volt across the transistor the power it would be
    dissipating would only be 1/8 watt.


    ---
    That won't work, for the reason stated earlier.

    what you can do to fix it is this: (View in courier)

    +12
    |
    +-------+
    | |K
    [MOTOR] [DIODE]
    | |
    +-------+-->TO OTHER DRIVERS
    +5V |
    | [R]
    [1K] |
    +5V | C
    | +-----B 2N4401
    [10K] | E
    | C |
    FROM DEMUX>---+----B 2N3904 GND
    E
    |
    GND


    Just duplicate the circuit for each demux output.
     
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