555 Timer Calculator (Backwards)

[German_EE]

There are plenty of 555 calculators on the Internet but for what I want they are all operating the wrong way around! All of them let you input the two astable resistor values and the capacitor then they show you the resulting frequency, mark/space ratio and pulse width.

I want it the other way, start with mark/space ratio and frequency then give me the component values. Does anyone know of a web site that can calculate this?

[soldar]

So you know time on and time off. And you have the formulas. And you know algebra. What's the problem?

[patrick1]

depending on what your doing with the output, i recommend using a 1uF cap. and pin 8-7 100k pot, and pin 7-6 2ohm resistor

i have not had any problems with burnt pots. and it will give you 45hz too about 2.1khz,  convenient range for what i do...

however it comes with the proviso of the pin 3 output pulses are on average 95% duty on,  good for driving a 4017,

and the pin 2 out is perfect for driving opamps because its a very straight up sawtooth.