555 Timer - Single pulse,

Discussion in 'Digital Circuit Design' started by Lubos Setvak, Feb 3, 2019.

  1. Lubos Setvak

    Thread Starter New Member

    Feb 3, 2019
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    I am trying to design a 555 timer circuit that produces a delayed output single pulse so there is no switch as circuit gets power it will switch in 10sec. for apprx.1 sec long negative pulse,,, it will act as a switch but ,output after pulse will not remain any power neither earth ,i want to use in my car to disable start stop switch it is annoying press start stop button every time ,when i turn on ignition will power up circuit than i start engine and start elapsing 10 sec and than automatically turn off start stop button
    any help how the circuit should look like?thanks
     
  2. Reloadron

    Distinguished Member

    Jan 15, 2015
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    What you want is a two stage timer similar to the below drawing, a circuit by Forrest M. Mims III featured in an old Radio Shack Engineer's Notebook. The idea being the first stage is triggered and when it times out the second stage is triggered generating a One Shot pulse. Personally I would not modify the existing start system as it was designed the way it was for a reason but it's your system.

    Two Stage Timer.gif

    Again, I advise against modifying the start system and be happy we advanced from getting out and using a crank. Anyway you would want a modification of the above to get your triggering and output pulse the polarity you want or mentioned.

    Ron
     
  3. sghioto

    Well-Known Member

    Dec 31, 2017
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    Different layout using the NE556. When power from the ignition is applied the output pin #5 stays low for about 10 seconds. Then the output from pin #9 activates the transistor for 1 second providing the negative pulse.
    SG
    EEE NE556 dual timer.PNG
     
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  4. Lubos Setvak

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    Feb 3, 2019
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    It is possible to use 2 x 555 in this layout
     
  5. crutschow

    Expert

    Mar 14, 2008
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    Yes.

    If the timing is not critical, below is the LTspice simulation of a simple circuit using one CD4093 quad Schmitt-trigger NAND IC, that should generate the signal you want.
    You can tweak the times by changing the values of R1 (delay) and/or R2 (pulse).

    It wasn't clear to me exactly how you want to inhibit the Start-Stop switch, so you will likely need to add a transistor, and possibly a relay to this circuit's OUTput, as the CD4093 can only drive a few mA load.

    upload_2019-2-4_13-37-1.png
     
  6. MisterBill2

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    Jan 23, 2018
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    Why bypass the start-stop system? That makes no sense at all. Driving a car demands full attention.
     
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  7. Reloadron

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    That was my thinking.

    Ron
     
  8. MisterBill2

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    IN ADDITION, the electrical system in a car is far more complex, and the physical reality of adding such a circuit could certainly lead to a disaster.
     
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  9. Reloadron

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    Yeah, i sort of allured to that when I mentioned in post #2:
    Would I do it? Nope but I try real hard, super hard, not to do what I figure to be unwise. Not saying that has always worked out for me as sometimes I ignore the voices in my head. :)

    Ron
     
  10. Lubos Setvak

    Thread Starter New Member

    Feb 3, 2019
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    Why bypass? Because it is anoying pressing button start/stop after every start engine, it is very discutable function if is usefull i am living in town more likely are queu and start stop is undesire in this case
     
  11. Lubos Setvak

    Thread Starter New Member

    Feb 3, 2019
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    O
    signal from crank can by very unstable even more advanced would be get signal from runnig engine but that i am afraid i was thinking only if i could brake canbus signal, i was looking at your circuit resistors R3 and R4 are potentiometers? Could specify exact sizes all capaxitors
     
  12. MisterBill2

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    Jan 23, 2018
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    I was able to double my car's MPG through manual on/off engine switching. The huge flaw with the automatic system is that it is not nearly smart enough. The best arrangement would be 100% manual but with automatic shift to neutral with every switch off, and re-engage after every start. It would take a focused driver so that excludes half the population, but it would work very well at saving lots of fuel.
     
  13. Reloadron

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    R3 is a fixed 1/4 watt 24K resistor and R4 is a 1.0 Meg Ohm potentiometer. The idea is a 556 timer chip is actually two 555 timer chips in a single chip. R1 and C1 form the time for the first stage, that's why C1 is labeled 1-100 uF. R4 and C6 are the timing network for the second stage.

    Actually what I see as a better and much simpler circuit is Crutschow's circuit in post #5. Much less complicated than a two stage timer using a pair of 555 chips or a 556 chip.

    Ron
     
  14. Lubos Setvak

    Thread Starter New Member

    Feb 3, 2019
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    Thanks for answer i draw with lay out start stop switch i would say transistor would be fine because is informatiom wire not power one i would say 100mA max 200mA i would appriciate if you could draw circuit exact values rezistors capacitors tranzistors as i apologize i am still amater in this fields. As i mentioned 10sec it does not have to be exact can be 8 sec or 12sec elapsing time and one shot negative pulse approx. 1sec as i am thinking will take press switch. Thanks
     
  15. crutschow

    Expert

    Mar 14, 2008
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    Here's the circuit with an added MOSFET to connect to the ECU connection on the START/STOP switch.

    Edit: Modified Schematic
    upload_2019-2-6_14-5-43.png
     
    Last edited: Feb 6, 2019
  16. Lubos Setvak

    Thread Starter New Member

    Feb 3, 2019
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    I suggest the pins on gates are as i draw it on sheet. Question, what is for the additional circuit with resistor n.o 3 and capacirors n.o 3
     
  17. KennethZiegler

    New Member

    Feb 7, 2019
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    This is a right solution.
     
  18. crutschow

    Expert

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    If you mear R3 and C3, that's to filter out any spikes on the vehicle electrical system.
     
  19. Lubos Setvak

    Thread Starter New Member

    Feb 3, 2019
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    Ok resistor R3 what is the value? 100 ? Ohms, kiloohms?
     
  20. Lubos Setvak

    Thread Starter New Member

    Feb 3, 2019
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    On first layout you have resistor R3 10? and second layout R3 100
     
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