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DIY Hobby projects, diagram, schematic

Electronic Circuits

DIY Hobby projects, diagram, schematic

555 Variable Frequency Square Wave Generator

electronicecircuits, June 9, 2010August 17, 2023
555 Variable Frequency Square Wave Generator

555 Variable Frequency Square Wave Generator

This simple 555 Variable Frequency Square Wave Generator produces a variable frequency output of 2800Hz to 120KHz with this values.

555 Variable Frequency Square Wave Generator oscillator circuit

PARTS LIST
R12.2kΩ
R24.7kΩ
VR1250kΩ
C10.001µF (102)  mylar capacitor
C20.01µF (103)  mylar capacitor
IC1NE555

The 555 is connected for astable operation. Here the timing resistor is now split two sections, R1 and R2+VR1, with the discharge pin 7 connected to the junction of R1 and R2+VR1. When the power supply connected, the timing capacitor C1 charge towards 2/3 Vcc through R1 and R2+VR1. When the capacitor voltage reaches 2/3 Vcc, the upper comparator triggers the flip-flop and the capacitor start to discharge towards ground R2+VR1. When the discharge reaches 1/3 Vcc, the lower comparator is triggered and a new cycle is started.

The capacitor is then periodically charged and discharged between 2/3 Vcc and 1/3 Vcc respectively. The output state is High during the charging cycle for a time period t1, so that

t1=0.693(R1+R2+VR1)C1

The output state is low during the discharge cycle for a time period t2, given by

t2=0.693(R2+VR1)C1

Thus, the total period charge and discharge is

T=t1+t2

=0.693[R1+2(R2+VR1)]C1 (seconds)

so that the output frequency is given as

f=1/T

=1.443/{[R1+2(R2+VR1)]C1} (You can get frequency in KHz, when R1, R2, VR1 in KΩ and C in µF)

Example:

R1=2.2KΩ

R2+VR1=100KΩ

C1=0.001µF

F=1.443/{[2.2+2(100)]×0.001}

=7.136 KHz

Frequency is adjusted with potentiometer VR1.

To get accurate frequency, you can use regulated power supply.

555 Variable Frequency Square Wave Generator
555 Square Wave Generator

Please send your ideas, which are very important for our success…

Electronic Circuits Oscillator Circuits

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Comments (12)

  1. Occupational Therapy says:
    August 1, 2010 at 8:26 am

    well written blog. Im glad that I could find more info on this. thanks

    Reply
  2. XxHEATxX says:
    February 23, 2011 at 7:17 am

    Very nice post, this is just the information I needed. TYVM

    Reply
  3. PEP says:
    October 4, 2011 at 4:10 am

    I am gonna make this nice little circuit…

    Reply
  4. ali says:
    December 18, 2011 at 2:29 am

    very very good site

    Reply
  5. MELCHIOR says:
    March 17, 2013 at 6:05 am

    Ótimo.
    Muito bom mesmo.
    Poderia colocar mais outros modelos para hobistas.

    Reply
  6. pu says:
    August 6, 2013 at 8:01 am

    I need to generate a frequency from 10HZ to 200HZ using 555.Please help me in selecting the values R1,R2 and C1.

    Reply
  7. HackerCow says:
    October 25, 2013 at 5:08 am

    Hey!
    First of all, great post, thanks for that.
    I am currently waiting for the parts for this circuit to arrive and in the meanwhile I have simulated it with NI Multisim. My problem is that i get a very unstable (if that’s what that is called?) frequency.
    Kinda like this: http://img132.imageshack.us/img132/9382/7kr5.png
    I hope anyone can help me out.

    Reply
    1. HackerCow says:
      October 25, 2013 at 5:12 am

      Okay I already solved the problem, silly me chose the wrong power supply.
      Thanks for the post though

      Reply
      1. HackerCow says:
        November 9, 2013 at 5:11 pm

        Now I built the circuit and attached a small speaker to it and all that happens is that the voltage goes up once. I have attached a 9V battery to test it and double-checked all the items used. Could you help me out here?

        Reply
  8. Varun says:
    February 7, 2014 at 8:42 pm

    Hi thanks a lot for the post. I’m looking to make a similar circuit but with output varying from t=0.25s to t=0.05s. Please help me know the required resistor and capacitor values for this.

    Thank You

    Reply
  9. Kandace says:
    September 27, 2014 at 4:18 pm

    Do you have any video of that? I’d care to find out some additional information.

    Reply
  10. Abody says:
    December 15, 2014 at 1:58 am

    Hiii
    This is nice post ..Thank you for this information

    Reply

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