555 calculation in astable mode

[eplanet]

Hello dear friend
could you help me for designing a LED blinker with  two properties:
5 seconds LED on and 2 seconds LED off and repeat.
how can i calculate space time and mark time for these R1 , R2, C1 for making 5 and 2 seconds?

View attachment 41834

 

[audioguru2]

Didn't you look at the datasheet?
It shows how to simply calculate the charge resistors, the discharge resistor and the capacitor.

 

[eplanet]

yes absolutely but i have only time for on/off and haven't any parameters like resistors and capacitor for using formulas.
i think i should revers working. because when you have resistors and capacitor you can use 555 calculator for result.
and result are space and mark time

 

[Hero999]

The LED should be wired from pin 3 to 0V in order to have a duty cycle of greater than 50%.