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    NE555 astable frquency

    Hi,
    How do I calculate the frequency of this circuit?
    Click image for larger version. 

Name:	NE555 frequency.png 
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    Thanks.

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    Re: NE555 astable frquency

    For a rough estimation, assume RV1 in center position, ignore diode voltage drop, use formula for astable operation in data sheet (R1=1k, R2=5k).



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    Re: NE555 astable frquency

    Quote Originally Posted by FvM View Post
    For a rough estimation, assume RV1 in center position, ignore diode voltage drop, use formula for astable operation in data sheet (R1=1k, R2=5k).
    Why is R2=5k?



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    Re: NE555 astable frquency

    RV1 center position, 10k/2 is effective R2 value (ignoring the diode voltage drop).



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    Re: NE555 astable frquency

    Quote Originally Posted by FvM View Post
    RV1 center position, 10k/2 is effective R2 value (ignoring the diode voltage drop).
    Thank you for your answer!
    So the frequency is : f = 1.44 / ((R1 + 2*R2)*c) = 13KHz ?



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    Re: NE555 astable frquency

    frequency of your circuit is:

    1/((R2+k*Rv1)+(1-k)*Rv1)

    where 'k' as per figure is 0.41

    - - - Updated - - -

    Quote Originally Posted by srizbf View Post
    frequency of your circuit is:

    1/((R2+k*Rv1)+(1-k)*Rv1)

    where 'k' as per figure is 0.41

    add 1.44 in numerator.



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    Re: NE555 astable frquency

    Quote Originally Posted by srizbf View Post
    frequency of your circuit is:

    1/((R2+k*Rv1)+(1-k)*Rv1)

    where 'k' as per figure is 0.41
    But by using your equation the frequency will be : 9 * 10^(-5) Hz !!



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    Re: NE555 astable frquency

    Quote Originally Posted by Blue10 View Post
    But by using your equation the frequency will be : 9 * 10^(-5) Hz !!
    again a typo.

    the term 'c' is left out in denominator.

    so the freq is of the form:

    1.44/((R2+kRv1)+(1-k)Rv1)C2



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    Re: NE555 astable frquency

    Since the frequency of the 555 doesn't vary much with the setting of the duty-cycle pot, the value you get using 1/2 the pot resistance should be good enough for a reasonable estimate of the frequency.
    Zapper
    Curmudgeon Elektroniker



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    Re: NE555 astable frquency

    @Blue10
    where did you find that circuit?



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    Re: NE555 astable frquency

    That circuit is all over the internet.
    Hey Google: 555 oscillator circuit with duty-cycle adjustment



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