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# What resistor and capacitor values to use to switch circuit for 2 sec with 555 timer?

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#### tash_h1

##### Newbie level 3
Hey, im using an astable oscillator circuit, with a 555 timer, and i want to switch the circuit on for about 2secs, and off for about 4secs. Can anyone help me with what resistor values and capacitor values to use?

Thanks.

Re: 555 Timers

For T_high, you calculate it by making use of caps. (at pins 2 and 6) discharge equations,

And vise versa in case of T_low, where you calculate it from the charging equations of caps at pins 2,6..

I assume that you know how to write such charging and discharging equations,
then, knowing T_high and T_low, you can find easily the time constant of the circuit (time constant = RxC), by proper value of C you then can get R, and this will give square wave output with the required duration (duty cycle = 50%)...

If you need further information, then let me know,
Best Regards,

Re: 555 Timers

you can do it yourself with this 555 calculator **broken link removed**

Have fun
phil

Re: 555 Timers

Hi
Take a loock also on this wee site **broken link removed**).

Re: 555 Timers

try using the datasheet of 555 u will get the formula for the same

Re: Sotfware 555 Timers

U can find a good software for 555's calcules

the name is 555 designer,

I remember i have that soft in my PC...

Re: 555 Timers

Thanks to everyone who replied and who helped a great deal!!

Cheers!!

Re: 555 Timers

No problem, I'm glad to help u...

Re: Sotfware 555 Timers

fuevarde said:
U can find a good software for 555's calcules

the name is 555 designer,

I remember i have that soft in my PC...

Great program !! How did you do it?

Please if you have further similar programs that are used to design anyother applications with other ICs, so upload them here

thanks

Re: Sotfware 555 Timers

fuevarde said:
U can find a good software for 555's calcules

the name is 555 designer,

I remember i have that soft in my PC...

Great program !! How did you do it?

Please if you have further similar programs that are used to design anyother applications with other ICs, so upload them here

thanks

I have another one for LM555 calculations, but is not free,

and i cant find a keygen or crack in the internet

but u can use a trial version!!!

I hope u enjoy it!!!

Re: 555 Timers

IT EXPLAINS THE 555 THEN IT GIVE YOU SOME FORMULA FOR WHAT YOU WANT WITH DRAWING

I TRIED TO USE THOSE FORMULA PRACTICALLY AND IT WAS FULLY SUCCEEDED

ALSO TO HAVE ACCURATE RESULTS YOU HAVE TO CONNECT THE 555 TO +5V NOT MORE OR LESS................TO MAKE 5 VOLT POWER SUPPLY TRY THE FOLOWING LINK:

NOTE: THE (LM7805) IN BUILDING THE 5VOLT IN THE PREVIOUS PAGE MUST BE PUT ON HEAT SINKER FOR HIGHT CURRENT
NOTE: YOU CAN HAVE HIGHTER OUTPUT CURRENT BY PUTTING ANOTHER (LM7805) IN PARELLEL

THE DATASHEET OF LM7805:

https://www.ortodoxism.ro/datasheets/fairchild/LM7805.pdf

555 Timers

i think tash_h1 has not understand the circuit of 555 as astable multivibrator. Read this then u will understand better

Bibin John
www.bibinjohn.tk

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