• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Astable 555 Circuit with Ton < Toff

Not open for further replies.


New Member
Hello dear friends.

I need your valuable help for a little circuit I'm designing.

It is a small circuit whose output I want to keep ON for one second and then stay OFF for 8 seconds. I've tried with a 555 in astable mode, but in all settings I've read the Ton> Toff. I have been testing with two LEDs connected to the 555 output (one connected to VCC and one to GND).

For simulation purposes, I am using two resistors of 47k and 10k with a capacitor of 220uf which turns on the red led for about 8 seconds and the green led for 1 second. But the behavior I want is the red led 1 second ON and then the green 8 seconds ON.


I know you will recommend me to use a PIC or AVR. I have similar circuits that work perfectly, programmed in PIC 12F675 or ATTiny85, but I prefer to leave the uC for more complex projects.

Any suggestions on how I can use a 555 for this?

Thank you very much in advance.


Active Member
You can connect a diode across R5 to achieve duty cycles beyond 50%.
by doing this TH~= 0.693*R4*C
and TL= 0.693*R5*C


Well-Known Member
Most Helpful Member
Not open for further replies.

Latest threads

EE World Online Articles