The Learning Circuit 70: 555 Timers - How Bistable Mode Works

Thank you.

Yay! You are very welcome.

Thank you Karen.

I could not understand why the output pin stays on when the first button is released. It stays on as long as the threshold pin’s potential is below two thirds of Vcc. So, for example,  it will stay on as long as the threshold pin is connected to ground.

To be honest, I was scared by the details of the 555 timer. But now, thanks to you, this chip looks much less scary to me. You are doing a great job. Thanks again.

Hi Dave,

You are right. I must have tried to edit out of the mail box window. When I bring up the full thread the edit option is there.

John

"...I can't edit the original post..."

If you were still inside your 'Inbox' when you tried to edit, then it doesn't usually give you the option to do so.

Instead if you click on the main document title, or your comment timestamp (e.g. '2 Months')

https://www.element14.com/community/docs/DOC-94845#comment-256064

to open the document outside of your Inbox, then it should then give you an Actions option, under which there is the Edit option.

However you may have found another anomaly...

Hi Frank,

I couldn't find my schematic of the two different circuits until just now. Here is what they look like.

John

Yeah, since I've made so many videos about 555 timers, I was trying to not repeat myself too much. Looking back there are a few times I should have kept in details such as this. Those editing choices get difficult when trying to keep the videos under 10 minutes.

Thanks for the feedback!

Really great video. It would have been complete if you can talk about the RS flip-flop inside the 555 timer.

I fear that people may get confused why the output state is preserved even if you release the button. If it's just comparator then as soon as you release the button it should flip the state back.

Regards,

Aswin

Thanks John,

I wasn't aware there were two methods and just wanted to make sure I am not missing something else :-).  They do show how neat your work is, even on a breadboard.

Hi Frank,

I don't know if they never got properly inserted or what. I can't edit the original post so I will insert the pictures here.

The pictures add a little color but are probably irrelevant as they don't really show much.

John