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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

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

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"

1. Ed says:

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

Like or Dislike: 0  0

• ElectroSchematics.com says:

Hi Ed, I published the components list, I hope is ok now.

Like or Dislike: 0  0

• Fatma says:

svp qui peut m’aider à faire une conception d’un générateur carré avec fréquence variable de 50Hz à 10KHz et rapport cycliquen=50%

Like or Dislike: 1  1

• Steve says:

I just bought one of these, I don’t have it yet though.
http://www.ebay.com/itm/181096913621

Like or Dislike: 0  0

2. nice circuit and usefull any time..

Like or Dislike: 0  0

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

The GuruSantiago can help. Checkout his videos here:

Like or Dislike: 0  0

4. ZERO says:

or you can put the pcb with components?

Like or Dislike: 0  0

5. Zacker says:

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

Like or Dislike: 0  0

• Yunneck says:

Like or Dislike: 0  0

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

Like or Dislike: 0  0

7. joomunm says:

Hi,

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

Thanks.

Like or Dislike: 0  0

• Jim Keith says:

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.

Like or Dislike: 0  0

• Jim Keith says:

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.

Like or Dislike: 0  0

• joomunm says:

Nice to hear the good news!

Please let me know when you publish it.

Like or Dislike: 0  0

• Jim Keith says:

Like or Dislike: 0  0

• warren says:

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

Like or Dislike: 0  0

8. taufeqabdullah says:

Hi,

How many pulses does this circuit generate?

Thanks

Like or Dislike: 0  0

9. warren says:

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

Like or Dislike: 1  0

10. dilip desai says:

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

Like or Dislike: 0  0

11. ISMA says:

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

Like or Dislike: 0  0

12. kim says:

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!

Like or Dislike: 0  0

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.

Like or Dislike: 0  1

14. Al says:

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

Like or Dislike: 0  0

15. steve says:

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..

Like or Dislike: 0  0

16. Al says:

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

Like or Dislike: 0  0