555 timer

  • Thread starter Winzer
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  • #1
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I need to build a timer(using a 555) with a frequency of about 1KHz and a duty cycle of about 25% to provide my clock signal. So the 555 is obliviously in astable mode. From my engineering data sheet:
[tex]D=\frac{R_B}{R_A+2R_B}[/tex]
[tex]f=\frac{1.44}{\left(R_A+2R_B\right)C}[/tex]
where C is my capacitance value and the two R's my resistance values. This should be a strait forward calculation right?
then from the above equations
[tex]R_B=\frac{D 1.44}{C f}[/tex]
and[tex]R_A=\frac{D 1.44}{C f}\left[\frac{1}{D}-2\right][/tex]
right?
I get [tex]R_B=36k\Omega[/tex] and [tex]R_A=72k\Omega[/tex]
This is a capacitance value of [tex]0.01\mu F[/tex]
Does this look correct?
Thanks
 

Answers and Replies

  • #2
Redbelly98
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Looks good.

72 kΩ isn't a standard resistor value, but you could just use two 36k's in series.
 
  • #3
dlgoff
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Or a potentiometer. You would be able to adjust out the tolerances from the other resistor and capacitor.
 

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