Need help with a couple of 555 monostable circuits, trigger and reset

Discussion in 'The Projects Forum' started by CproAAC, Mar 12, 2014.

  1. CproAAC

    Thread Starter New Member

    Mar 8, 2014
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    0
    I'm just learning how to use the 555 timer and I can't figure this out. I'm looking for a couple of 555 monostable circuits

    First one is the trigger longer than the output. I've searched but couldn't find any circuits that I could understand. I was able to find this youtube video watch?v=GnjbtXQG1ic that shows exactly what I want to do.

    Second is the trigger and reset using the same push button switch. I want to use a button to activate the monostable timer. Let's say 30 seconds. Within that 30 seconds, if I want to end the output, I push the trigger button again to reset the timer.

    Thanks in advance.
     
  2. #12

    Expert

    Nov 30, 2010
    16,347
    6,835
    Back up. Think about what you need, and it isn't, "how to use the trigger pin as a stop command". The trigger pin will not re-start the time count and it will not stop the time count while a monostable configuration is running. You need to back up to what you need as a function, not, "how to make pins do what they weren't designed for".
     
  3. CproAAC

    Thread Starter New Member

    Mar 8, 2014
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    0
    I'm not asking how to make pins do what they're not designed to do. I'm asking for a circuit that can trigger (pin 2) and reset (pin 4) using the same switch.
     
  4. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,504
    380
    hi,
    Would a latching push switch be acceptable for your project.?

    The type that push once latch ON and remain ON until pushed again for OFF and remain OFF.??

    E

    EDIT:
    If yes, this circuit I did some time ago would work, adjust R1 C2 for 30 seconds
    http://www.ebay.co.uk/sch/i.html?_n...=84&ff14=25&ff17=latching+pushbutton+switches
     
    Last edited: Mar 13, 2014
    CproAAC likes this.
  5. DerStrom8

    Well-Known Member

    Feb 20, 2011
    2,428
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    I would use a j-k flip-flop between the switch and the 555, with Q1 connected to a transistor between pin 2 of the 555 and ground, and Q0 connected to a transistor between pin 4 and V+. The switch would be on the clock input of the flip-flop (connecting to +5v), and j and k would be connected to +5v. I think that would work, but I have to admit my brain hasn't been working very well lately. I'm sure someone would correct me if I'm wrong.

    Good luck,
    Matt
     
    Last edited: Mar 13, 2014
  6. CproAAC

    Thread Starter New Member

    Mar 8, 2014
    3
    0
    I figured out the first problem. I've given up on the second problem. Now, I need help with another. How can I trigger and reset using positive voltage?
     
  7. DerStrom8

    Well-Known Member

    Feb 20, 2011
    2,428
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    I generally use a NPN transistor with the collector connected to pin 2 and the emitter connected to ground. Apply a positive current to the base and it will switch on, connecting pin 2 to ground, thus triggering (or depending on how you connect it, resetting) the 555.
     
  8. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,813
    1,105
    If you're still interested in doing this, here's one way. A short press of the button (<0.7 sec for the R2,C1 values shown) just resets the 555 monostable. A longer press first resets then (re)triggers the 555.
     
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