I need someone to explain how this circuit works

Thread Starter


Joined Jun 11, 2016
i have a physics assignment and it is to do with constructing a circuit and explaining how it works, constructing it was easy but i dont know how to explain to my teacher how the circuit works.



Joined Mar 31, 2012
So... what is your question? Are you wanting someone to write up an explanation that you can turn in?

Can you look at the data sheet for a 555 (and whatever other reference material you have available) and explain what, say, the left hand 555 is doing and how?


Joined Mar 30, 2015
Welcome to AAC!

Since you're new, you should understand that members don't do homework for you. You need to post your best effort and members will try to guide you to a solution.
constructing it was easy but i dont know how to explain to my teacher how the circuit works.
Since you've constructed the circuit, what does the first timer do to the second?


Joined Nov 29, 2014
I'm assuming you have some understanding what 555 times does.
On IC1, what does pin 3 do?
What does that to to transistor that is is connected to ?
What does the transistor do to pin 4 on IC2 and what is pin4 on IC2?

Is you answer these questions, you will know what the circuit does.


Joined May 4, 2016
Explain this circuit by describing what happens in the circuit on a component by component basis. Start off on the left side of the circuit and work your way to the right side of the circuit. Explain how the circuitry triggers the first timer and how the circuitry between the first timer and the second timer works. Then explain how that circuitry affects the second timer. If you have an oscilloscope, viewing the waveforms at various points in the circuit would help you explain what happens.

If you are totally lost, it might help to read descriptions of the operations of other circuits.

Thread Starter


Joined Jun 11, 2016
Sorry, i am new, what I was trying to say is, I know how the 555 works but I'm not sure what happens when there is two. I cannot ask my physics teacher because he is completely useless. The circuit was given to me by my physics teacher and i've been toying around with the resistors and even added a led light so that i can count the ticks visually, i am just not sure how the two 555's work together. Is it the same as one? does it create a delay? is it even essential to have two?


Joined Aug 21, 2008
Answer these three simple questions (simple with an NE555 datasheet in hand) and you will know how it works.

What the 2nd '555 (the one on the right) configured to do if that transistor isn't there?

What happens to pin 4 of the second '555 if the transistor turns on?

One the second '555, what is the function of pin 4?