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555 Timer Duty Cycle

Hi,

I'm trying to use a 555 timer to produce a PWM waveform however can't find any reference as to how the value of the resistor* can be used to calcuate the duty cycle. Is there a formula that says something like when you use Xohms it gives 2X% duty cycle?

Cheers,

Michael

*
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Reply to
Michael
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"Michael" wrote in message news:UY2Bh.331518$ snipped-for-privacy@fe3.news.blueyonder.co.uk...

Bill has a calculator.

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Reply to
Tom Biasi

Hi,

Thanks, I've put the formula into Excel and everytime I change of the values (R1,R2,C1) it changes both the frequency and duty cycle. Is there a way to change only the duty cycle once you have the frequency you want?

Cheers,

Michael

Reply to
Michael

when

Look to alt.binaries,schematics.electronic for an attached file...

values

Reply to
Lord Garth

"Michael"

** Not possible by varying only one resistor.

A pot will do it:

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......... Phil

Reply to
Phil Allison

Thanks guys,

Michael

Reply to
Michael

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