# understanding of NE555 Astable mode

#### ali111

Joined Nov 13, 2016
3
Hi
I just understood how NE555 works and when we can set and reset its flip-flop. In the below we can see the simplest circuit we can make with it .

I made a LED flasher with it. I want to know how this circuit works. (I mean whole circuit; I knew how NE555 work as well.)
Lets porpuse Vcc = 9v and the flip-flop is SET; to reset that we need more that 6 volts(2/3Vcc) to connect with pin 6; (in the circuit we delete reset pin by connecting it to VCC)
Now lets porpuse the flip-flop is RESET, we need less than 1/3VCC or ground connect to pin 2 to SET the flip-flop.
My questions
1. why the flip-flop RESET while we don't have more than 2/3VCC connect to pin 6?
2. why the flip-flop is reset or set in a period of time?
3. What is C1 doing in the circuit?
Please answer the questions with details; I'm working on this circuit more than 3 days but I can't undrestand the whole circuit. I'm a web programmer and I need details to undrestand things.
Thanks a lot

Last edited:

#### ali111

Joined Nov 13, 2016
3
Thanks bertus,
I read the posts but I still have no undrestanding of the circuit!

#### ali111

Joined Nov 13, 2016
3

#### hp1729

Joined Nov 23, 2015
2,304
Hi
I just understood how NE555 works and when we can set and reset its flip-flop. In the below we can see the simplest circuit we can make with it .

I made a LED flasher with it. I want to know how this circuit works. (I mean whole circuit; I knew how NE555 work as well.)
Lets porpuse Vcc = 9v and the flip-flop is SET; to reset that we need more that 6 volts(2/3Vcc) to connect with pin 6; (in the circuit we delete reset pin by connecting it to VCC)
Now lets porpuse the flip-flop is RESET, we need less than 1/3VCC or ground connect to pin 2 to SET the flip-flop.
My questions
1. why the flip-flop RESET while we don't have more than 2/3VCC connect to pin 6?
2. why the flip-flop is reset or set in a period of time?
3. What is C1 doing in the circuit?
Please answer the questions with details; I'm working on this circuit more than 3 days but I can't undrestand the whole circuit. I'm a web programmer and I need details to undrestand things.
Thanks a lot
Reset is an active low signal. Your drawing does not indicate this. Trigger is low and Discharge is low also.