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Synchronization of pulses

Discussion in 'General Electronics Discussion' started by Sravanthi, Jun 29, 2015.

  1. Sravanthi

    Sravanthi

    72
    1
    Feb 4, 2015
    Hi...

    I am having multiple 555 timer as a astable multivibrator with the same charging and discharging circuit.

    How can I synchronize the output pulses.

    Please help in this issue.
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Use one 555 as master timer, use the others as monostable multivibrators triggered by the first one.
     
  3. Laplace

    Laplace

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    Apr 4, 2010
    If you need synchronized pulses from identical timers, why are you using more than one timer?
     
  4. AnalogKid

    AnalogKid

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    Jun 10, 2015
    Please post your schematic. Without it, you will not get a meaningful answer, only guesses.

    ak
     
  5. Sravanthi

    Sravanthi

    72
    1
    Feb 4, 2015
    HI...

    Here I am attaching the circuit.

    Here input (Either 0V/5V) coming from before stage is connected to Vcc of different astable multivibrators. Same charging and discharging circuit is shared by all multivibrators.(Frequeny is 3kHz)
    So pulses coming from this astable multivibrators I want to synchronize.

    So can you suggest a method to do this.
     

    Attached Files:

  6. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Not possible. Each multivibrator has to have its own timing components. You may use the same values for different multivibrators but then they will not all operate at the same frequency due to tolerances.

    But: As all timers shall output the same pulses, why not use a single timer and distribute the output signal to the different loads as suggested by Laplace in post #3? Are we missing something or are you not giving us the full information?
     
  7. Sravanthi

    Sravanthi

    72
    1
    Feb 4, 2015
    Thank you for reply.
    Here I am not distributing the pulse to the load . Based on the incoming signal from before stage to Vcc of multivibrators some only will give the pulses. These pulses I want to synchronize.
     
  8. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    I'm sorry, but I don't seem to understand. If a bunch of monostable multivibrators is triggered by the same input signal, the outputs are scnchronized (with respect to the input signal). If the multivibrators have different timings, then the outputs will be active at different times as defined by the respective timings. If the outputs shall have the same timing, a single multivibrator suffices.

    Can you draw a timing diagram showing inputs and ouputs to explain in more detail what you want to achieve?
     
  9. Sravanthi

    Sravanthi

    72
    1
    Feb 4, 2015

    I want to generate pulse based on the input status (means if input fed to the Vcc of multivibrator is zero then there wont be any pulse at the corresponding multivibrator, if 5V is fed then it will generate a pulse). This input status will be keep on changing.

    In this manner a number of multiple multivibrators are connected with different inputs fed to Vcc of multivibrators.

    Any time among all these multivibrators few will only give the pulses.

    I want to feed these pulses to combinational logic. So before feeding to next stage I want to synchronize these pulses.
     
  10. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Let's see if I understand correctly:
    • Feed the output of each multivibrator to the D-input of a flipflop.
    • Feed a high speed clock to the clk-input of the flipflops.
    • Use the outputs of the flipflops for the now synchronized pulses.
    When you need precise timing, 555s are not the best choice. You could use digital clock generators (dividers) controlled by a central clock and thus inherently synchronous. You can use the input signal to start/stop the digital clock generators.
     
  11. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    @Harald Kapp has already told you that it is impossible to synchronize the pulses from independent astable multivibrators even if all have the same RC timing components. Moreover, your "triggering" inputs appear to be asynchronous, so why would you expect the output pulses to be synchronized with anything? And why are you applying your external "triggering" signals to the Vcc input of each astable multivibrator? Why not use the INHIBIT/RESET input of the 555 timer and leave Vcc applied at all times?

    Many years ago, while working with Texas Instruments SN74xxx series TTL integrated circuits, I had the problem of synchronizing an asynchronous external event (a switch closure IIRC) with the clock signal used by the logic. It was important that this external event not result in a truncated output pulse because of asynchronous timing between the real world event and the independent clock transitions. Just in the nick of time, I discovered that Texas Instruments had solved my problem with a dual pulse synchronizer integrated circuit, the SN74120. Unfortunately this part is now obsolete, although you may still be able to find a few. Or, you can build a discrete logic version using the schematic provided on the data sheet. With this part, you use just one clock generator, replacing all your "astable multivibrators" with one pulse synchronizer for each input.
     

    Attached Files:

  12. Sravanthi

    Sravanthi

    72
    1
    Feb 4, 2015

    Thank you for reply...

    In the given idea what is the advantage gained in synchronization of pulses by feeding the external input to the reset pin of the 555 timer.
     
  13. HellasTechn

    HellasTechn

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    One other point you may want to keep in mind is that the 555 timer is an IC that can not be used when precice sync pulses are required. Also its output can be affected by ambient temprature. This IC is generally used in simpler circuits that dont require sync of high accuracy.
     
  14. Sravanthi

    Sravanthi

    72
    1
    Feb 4, 2015

    Hi...

    Thank you for reply...

    Is there any particular IC that can be used in synchronization of pulse application.
     
  15. AnalogKid

    AnalogKid

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    Jun 10, 2015
    The way I read this, the requirement is for one clock source, multiple input (enable) signals, any one of which can start the clock, and multiple gated outputs. Let's assume four input signals. A 555 with a 4-input OR gate driving the Reset pin, and the output goes one input of each section of a quad AND. Each input signal goes to 1 OR input and 1 AND input. The Clock is off until at least one input goes high. The only downstream circuits that receive a clock are those that "request" one with their input signal.

    ak
     
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