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    This is a pulse generator with adjustable duty cycle made with the 555 timer IC. The circuit is an astable multivibrator with a 50% pulse duty cycle. The difference from the standard design of a 555 timer is the resistance between pins 6 and 7 of the IC composed of P1, P2, R2, D1 and D2.

    The diodes D1 and D2 set a definite charging time for C1 which produces a 50% duty cycle in a normal case. The duty cycle (n) is dependent on P1 and P2 in the following manner:

    n = 1 + P2/P1

    If P2 = 0 (n = 100%) then the frequency can be approximately calculated with the following formula:

    f = 0.69/((2*P1 + P2 + 4.7kΩ)*C1)

    Pulse generator circuit diagram

    pulse generator

    Oscilloscope Captures

    As you can see in the captures the duty cycle is not between 0% and 100% but it is within reasonable range. I’ve used a 20K for P1, 100K for P2 and 10nF for C1.

    Printed circuit layout of the pulse generator

    pulse generator pcb

    Components List

    C2 = 10µF
    C3 = 0.1µF
    R1 = R2 = 4.7K
    D1 = D2 = 1N4148
    IC = 555
    C1, P1 and P2 must be calculated

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    26 Responses to "555 Pulse Generator Circuit"

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    1. I luv PWM’s!! been building different ones for about two years now, Thats how I came to electronics intrest @51,,now 54. I like the simplisity of this circuit and the use the infamous 555, but where is the parts list? I could experiment,, but I do that anyway just doing what I am instructed. Thanks Ed

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    2. nice circuit and usefull any time..

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    3. I like it because it has a 50% duty cycle and the PCB layout is also provided.
      Thank You,
      GuruSantiago

      Want to learn more about electronics?

      The GuruSantiago can help. Checkout his videos here:

      http://www.youtube.com/user/ElectronicsIsFun
      And follow him on twitter @ElectronicsFun

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    4. or you can put the pcb with components?

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    5. Hi, can you write the value of C1, P1 and P2 because i don’t know how to calculate it. Thanks.

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    6. Heloooo,!! JIM KEITH NE555timer chip which has been configured as a astable multivibrator(oscillator), or square wave generatos just teach me how to enter in the duty cycle and the frequency and the calculator will compute reasonable value for the resistors and capacitors …tanx

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    7. Hi,

      Can the duty cycle be adjusted from 0% to 100% without drifting the frequency?

      Thanks.

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      • Jim Keith Jim Keith says: on October 18, 2012 at 11:31 pm
          member

        Independent duty cycle control is not possible using the standard 555 circuit. There may be some improved 555 circuits, but I am unaware of any that do this.

        However, I am working on a novel voltage controlled oscillator (VCO) that may do this well. Stay tuned.

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      • Jim Keith Jim Keith says: on October 19, 2012 at 4:00 pm
          member

        OK, I now have concocted a 555 circuit that does just that. Variation of the duty cycle from 2% to 98% affects frequency less than ±1%.

        Will publish soon.

        it is a dangerous thing to say “never,” because you may have to eat your words sometimes.

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      • Nice to hear the good news!

        Please let me know when you publish it.

        Thank in advance.

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      • Jim Keith Jim Keith says: on October 20, 2012 at 7:34 pm
          member

        Now published. It may be found on home page.

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      • any luck on the 555 function generator with null frequency drift with duty cycle adjustment?

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    8. taufeqabdullah says: on July 15, 2013 at 6:30 am
        member

      Hi,

      How many pulses does this circuit generate?

      Thanks

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    9. awesome I am using multisim now to build custom version. thanks for your efforts great job. cant find the your home page. though.

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    10. dilip desai says: on September 14, 2013 at 10:42 am

      good one,i make small type harmonium usin 555 timer ic, is the best for all.

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    11. Hi
      Can you to publish then component layer on PCB? Thank….

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    12. hi! i have completed a project to make a pulse generator with less than 50% duty cycle using a 555 timer and 2 potentiometers. but later on, my professor wants me to compute for the time on and time off.
      so here’s the problem, the only formula i’ve got is this,
      Ton=.7(Ra+Rb)C and
      Toff=.7RbC,
      i’ve used this formula before for astable multivibrators. But unfortunately the answers i’ve got don’t match the output from my actual pcb circuit.
      My other professor told me that i have to use different formula. And again, unfortunalely, i don’t know any. So for those who knew, please answer. and thanks in advance! :)

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    13. I would like to make this pulse generator. When I shop for the 555 timer I see an endless number of different part numbers. Are all these 555 timers the same?

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      • There are subtle differences to keep in mind:
        1. Package style DIP or SMD
        2. Bipolar or CMOS –projects generally use bipolar unless CMOS is indicated
        3. Manufacturer –generally does not matter
        4. Temperature range –generally does not matter

        In most applications, either bipolar or CMOS devices work equally well.

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    14. R1 and R2 can be 1 kolomh or 550 omh. P1 and P2 can be 200-50 kiloomhs, then work must be best.

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    15. Hi, I built this pulse generator with the components listed. I used 10µF capacitor for C1. So far I only get around 1 pulse per second and barely any change when turning pot. The duty cycle seems to have better resolution throughout pot range. I swapped 100k and 20k pot with each other and got pulses up to 3 per second. What I need is a frequency range of around 5 to 200 pulses per second. The duty cycle is not that important for my project. I redid this eight times and never got the frequency to go any faster… Is this timer capable of a faster pulse rate? What am I missing here? Thanks..

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    16. I allso try, not liked me, so I leave it. Better use TL494.

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