How can you alter the duty cycle on a 555 timer while keeping the frequency the same?

Question

Im trying to alter the duty cycle on a 555 while keeping the frequency output the same.  Is there a way to do it simply or do I need to program a pic to do it?

pinned_911 · Accepted Answer

its all about adjusting your RC constants. heres a website that allows you to fiddle with em and it calculates the on/off or duty cycles for you

http://ourworld.compuserve.com/homepages/Bill_Bowden/555.htm

if you want to keep the frequency the same, just make sure your T1 and T2 total to the same amount of time

allbright · Answer

you could have neglected the optimal values for the resistances, which relies upon upon the voltage Vcc. i think of you will see the optimal Ra+Rb resistance could be below 3.4 Megohms with Vcc of 5 volts. i'm no longer great comfortable with the R1=0 approach. If i prefer 50% duty cycle, i'd evaluate working the timer at two times the needed frequency, and then using a divider (divide by using 2) to generate the fairly precise 50% duty cycle. this would be a CMOS or TTL "turn flop" divider.

Anonymous · Answer

I cant think of a way.  If the duty cycle is faster than the output, you would lose data when the cycle repeats twice between outputs.  If it was slower, you would get repeat outputs.

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How can you alter the duty cycle on a 555 timer while keeping the frequency the same?

3 Answers