Time on/off delay

Discussion in 'The Projects Forum' started by inwo, Feb 5, 2014.

  1. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
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    Came up with what I think is a minimum component dual timer.
    Integrated trigger and time delay off.
    It's a solution for/from another thread.

    As I just woke up and drew it out before I forgot, I'm wondering if someone would check for errors?

    Low pulses trigger after reaching duty cycle set by R3-C3.
    Minimum time on set by R2-C2.
    Input low = always on.

    D1 keeps C2 low and ready for full delay off cycle.

    I don't know if this is unique or I've reinvented the wheel, but it seems to do what I need.
     
  2. #12

    Expert

    Nov 30, 2010
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    Just adding some labels.
    A bit scatter-brained right now. Can't seem to cerebrate.
     
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  3. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
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    Thanks for looking.
    Wish I could do that!:)

    The schematic sw I use didn't even have a 555. I had to build it.

    I see one problem already. The 1MEG will need to be a little larger to let pin 2 get down to 1/3 of supply and trigger reliably. (your helpful label reminded me)

    This is for a tank level indicator.
    http://forum.allaboutcircuits.com/showthread.php?t=94220
    I can't believe on/off timers are so hard to find.

    edit:
    Don't bother with the math.
    Times are immaterial.
    Just basic function is fine,
     
    Last edited: Feb 6, 2014
  4. #12

    Expert

    Nov 30, 2010
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    What? Add labels or cerebrate? :D
     
  5. #12

    Expert

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    When power is applied, C3 immediately raises trigger above 1/3 Vcc and that sets the output low (no LED).
    When power is applied, pin 6 is low and waiting while R2 starts charging C2 towards 2/3 Vcc, therefore output is high.

    Illegal condition. Results undefined, and I haven't even gotten to the switch. We need somebody to simulate this to see if I'm wrong.
     
  6. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
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    Yeah, I'm hoping for simulation.

    I believe there are 555 gurus on here. If it works, I'd like to no if it's unique. (in a good way)

    If it doesn't work, someone can point me to a minimum timer, that does delay on AND delay off, from a low side switch.

    This is the only way I can build circuits. Waking up with an inspiration. I never learned how to learn from others.:(

    I may get time to build it tomorrow.
    Haven't worked with 555s for years, but still have parts. Maybe even a board that I can solder up.

    Thanks again.:)
     
  7. #12

    Expert

    Nov 30, 2010
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    Slow on and slow off seems like it can be done with a cmos Comparator or op-amp and an RC, which, after all, is what a TL555 is, but containing a bunch of decision makers.
    12V, resistor, SPDT switch, capacitor, Schmitt trigger, viola. Am I missing something?
     
  8. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
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    As you say, that's what a 555 timer is.

    If someone comes up with a <8 component dual delay with other components, I'll check it out. (not counting switch or indicator)

    I started with discrete components. Then thought, why? By the time you get trigger levels, latch, and hysteresis.
     
  9. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    The circuit works after a fashion.

    Close S1 and hold it closed. After 4 seconds pin 3 goes high. Open S1 and after 4 seconds, pin 3 goes low.

    Simply closing S1 and releasing it before pin 3 goes high does nothing. Likewise, holding S1 closed keeps pin 3 high for the duration of the time S1 is closed plus 4 seconds.

    I suppose there is a use for the circuit, but it seems more likely to require a toggle switch for S1 than a momentary push button.
     
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  10. #12

    Expert

    Nov 30, 2010
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    I'm just too busy to really pay attention lately. Go to Off Topic and see my Lucky Day thread. I hope you have something to add to that thread.:)
     
  11. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    Cerebrate, cerebrate. Dance to the music.
     
  12. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
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    Hope to get it built later.
    The push button will be a level sensor that is either on, off, or bouncing.
    From what you say it will work just as wanted.

    It will ignore some bounces-on and some bounces off.:)
     
  13. tracecom

    AAC Fanatic!

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    Don't tell #12, but I can do it with a 50 cent micro-controller and a .1uF cap (not including the switch and indicator.)
     
  14. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
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    Put it together last night and it works as I had hoped.:)
     
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