Simple transistor problem

Discussion in 'General Electronics Chat' started by davidGG, May 11, 2013.

  1. davidGG

    Thread Starter Member

    Dec 22, 2012
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    Hello everybody. I'm working on a project to reset my router using an RF module controlled by a microcontroller.

    PNP TRANSISTOR (disregard the position of the 'c', I put it to close the the base)

    I have a transistor connected to my router/microcontoller like so...
    [​IMG]

    now when I finalize the circuit (connect battery to power rail which is connected to the microcontroller) the router remains off and I am able to hear a very faint (high frequency) screeching noise. Why is this not working?

    I am able using the transistor/microcontroller to successfully switch on and off LEDs, but not my router.

    Here is a verbal description of how my transistor is set up just incase I made an error there.
    Connected to my base is a low coming from my microcontroller
    Connected to my emitter is my source voltage coming from wall outlet and pin connected to high from battery
    Connected to collector is my router.

    All help is appreciated
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    Why do you want to reset your router?
     
  3. davidGG

    Thread Starter Member

    Dec 22, 2012
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    0
    every so often the router speed goes really low until you manually reset it. The router is in an upstairs bedroom and it becomes very tedious to go upstairs to reset it every hour. Yes I know I can just buy a new one, but I'd like to learn a thing or two from this project.
     
  4. MrChips

    Moderator

    Oct 2, 2009
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    How much voltage and current does the router require?
     
  5. davidGG

    Thread Starter Member

    Dec 22, 2012
    51
    0
    12VDC
    1A

    As far as I know, BJTs don't have a voltage drop, right?
     
  6. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    The power supply ground, the μC ground, and the router ground all have to be common. Are they?
    Are you sure the router needs a high level for reset?
    Is the power supply voltage providing the proper voltage level to the router? If it's too high, it can damage your router.
     
  7. MrChips

    Moderator

    Oct 2, 2009
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    I think he is trying to switch the power supply with a PNP transistor.
     
  8. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    That makes more sense than what I was thinking.
    So just the μC and the router grounds have to be common.
    I would use a p-channel MOSFET for the switch.
    PNP or PMOS, he will still need a level-shifter of some sort to switch 12V from a μC.
     
  9. davidGG

    Thread Starter Member

    Dec 22, 2012
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    Ohhhhh, can you please explain why the router and μC ground have to be on the same rail?
    I didn't have it set up like that, didn't think it made a difference.
    Will test tomorrow morning when the internet is not being used.
    Thank you :).

    and isn't my power supply ground the same as my router ground? or am I missing something here.
    I am using two sources for EMF. A battery and a Netgear wall-wart.
     
  10. Pencil

    Active Member

    Dec 8, 2009
    271
    38
    Oh yes they do. Find datasheet for your transistor and look
    at Vce (Voltage Collector to Emmiter).

    You will possibly be better of using a transistor to switch
    a relay, which in turn will switch your power supply ON/OFF.

    Look HERE for some basic transistor used as a switch schemes.
    Note: on that page, Hfe for the transistor is used in the calculation
    for base current. I believe the general consensus is to use Ib=Ic/10
    when using a transistor as a switch.

    If you intend to use a MOSFET instead of a transistor, which would
    possibly be a better idea with a micro controller, and need help just
    ask.
     
  11. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    If I understand what you are trying to do, you need to use one of the options in the attachment. Note that the MOSFET version is much more efficient (draws less current) and has less voltage drop.
     
  12. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    If your router is just slowing down, can't you just address it through your browser and command a reset? That's what I do when mine gets too slow.
     
  13. davidGG

    Thread Starter Member

    Dec 22, 2012
    51
    0
    Hello again,
    I found the source of my problem which was the resistor connected in between the microcontroller and the base of the transistor. When I remove the resistor, the router turns on.
    However, after about 10 seconds, the microcontroller gets very hot.
    I was using a 1k resistor, will using smaller resistance solve this problem?
    Why is this happening?

    Thank you.
     
  14. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    Did you use one of the circuits I posted? If not, then that's what's wrong.
    Post your schematic. Please make it a little cleaner than the first one.:D Include all parts and connections.
     
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