Transistor switching ne555 circuit

Discussion in 'The Projects Forum' started by ardudriver, Dec 27, 2012.

  1. ardudriver

    Thread Starter New Member

    Dec 27, 2012
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    Hi all, I realized a toggle button using ne555, so everything is ok.
    Now, I'd like to add the possibility to simulate pressing over digital signal from mcu.
    I thought to use a transistor (which should act as a switch) but it does not work, the circuit is correctly closed, but not 'clicks' as if it were closed by pressing the button.
    The problem is probably due to the logic of charging and discharging of the capacitor, here the two schematic before end after changes:
    http://www.flickr.com/photos/91531577@N08/8313927732/
    I noted that every time I press the button, the polarity of the two ends of the button are reversed and so I added a diode to avoid that the current flow over the transistor, this system would be fine only when the polarity of the terminals A and B (indicated in the schematic) were respectively + and -, and not the opposite. I would avoid for this solution to use a relay.
    I think that it is technically more interesting solve the problem by using a handful of components if possible, what do you think?

    New Happy Year to all.

    driver
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    You have the NPN transistor connected incorrectly.
    Connect the collector to pins 2 and 6.
    Connect the emitter to GND. You may eliminate R12.
     
  3. ardudriver

    Thread Starter New Member

    Dec 27, 2012
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    Hi MrChips, i tried to do what you told me but unfortunately not good. I'm afraid that is insoluble, I'm sorry ...
     
  4. MrChips

    Moderator

    Oct 2, 2009
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    There is a solution.

    But first you have to say what you are trying to do.
    What is supposed to happen when you press the pushbutton.
    What is supposed to happen when you stop pressing the push button.
     
  5. ardudriver

    Thread Starter New Member

    Dec 27, 2012
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    Thanks for your interest, until now no one has been able to give solutions.
    This is a toggle button, a button that keeps the ne555 PIN3 output high or low, and so it's okay. I would, however, do the same with an MCU controlling, replacing the button with a transistor that receives a signal from MCU on the base. It seems that the current flows, but there is something wrong, because the output of the ne555 remains on high. I do not know, maybe it depends on the capacitor is discharged and recharge probably. A reliable solution would be to use a relay, but I'd be sure that I can do no other solution. I do not know other ways to make a toggle button and I don’t want to use mcu code. You know another way to make a toggle button? to try an other way. Thank you.
    </SPAN>
     
  6. MrChips

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    Oct 2, 2009
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    What is a "toggle button"?
    You have not explained it very well.
    My concept of a "toggle button" is, push once, output goes high. Push again, output goes low.
    Keep on doing this and the output alternates between high and low.

    If this is what you want then a 555 is not the right solution.
     
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  7. ardudriver

    Thread Starter New Member

    Dec 27, 2012
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    Yes! is what you said, press once to have a high output, and one other time to go low. If you have an alternative way avoiding the ne555 I would be able, I'm not an expert, I now know only this way.
     
  8. MrChips

    Moderator

    Oct 2, 2009
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    Then what you need is called a "toggle flip-flop" and can be made using a D-type, T-type or J-K flip-flop, such as CD4013, CD4027, SN74LS74, SN74LS76.
     
  9. ardudriver

    Thread Starter New Member

    Dec 27, 2012
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    Interesting, you may politely tell a circuit on the web that do this thing? I wanted to solve with a handful of transistors, but if you can not do anything, as long as the swith are independent of MCU, but at the same time can be used by MCU.
     
  10. MrChips

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    Oct 2, 2009
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  11. ardudriver

    Thread Starter New Member

    Dec 27, 2012
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    Well I saw the circuit and is probably what I need, i can control the circuit using the mcu over trigger. Excuse my ignorance though, but if I want to use at the same time a button, where should I put?
     
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