# NE555 astable frquency

1. ## NE555 astable frquency  Reply With Quote

2. ## 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).  Reply With Quote

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3. ## Re: NE555 astable frquency Originally Posted by FvM 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?  Reply With Quote

4. ## Re: NE555 astable frquency

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

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5. ## Re: NE555 astable frquency Originally Posted by FvM 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 ?  Reply With Quote

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6. ## 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 - - - Originally Posted by srizbf 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.  Reply With Quote

7. ## Re: NE555 astable frquency Originally Posted by srizbf 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 !!  Reply With Quote

8. ## Re: NE555 astable frquency Originally Posted by Blue10 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  Reply With Quote

9. ## 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.  Reply With Quote

10. ## Re: NE555 astable frquency

@Blue10
where did you find that circuit?  Reply With Quote

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11. ## Re: NE555 astable frquency

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

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