Help with 555 as a delayed shutdown switch.

Thread Starter

ocean750

Joined Jul 15, 2020
16
Hello.
Could you please help me out ?
I am trying to build a circuit that would use two push button in order to turn ON and OFF a system.
When pressing the ON button, it will be latched using a relay.
I would like that when the OFF button is pressed, a timer from a 555 will count back some time, and when it is done, the system will shut down.
I would like to add a relay where the arrow is showing, and for that relay to be activated from the 555.
I tried a few times but could not get it to work.
How should I build the circuit ?

Thank you
 

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Thread Starter

ocean750

Joined Jul 15, 2020
16
Thank you for looking in to my question.
I did manage to activate a 555 circuit .
And now I understand that I did not explain my question well.
The ON button activates the entire system, including the 555 circuit.
And some other things after the Vo (I don't think it is relevant so I did not draw the rest).
I would like that when the OFF button is pressed the shutdown to be delayed.
I could not figure out how to power the relay after the ON was pressed and to be able to shut it down when delayed.
I did not build the circuit with the cutoff relay because I could not get it to "work" on paper.
 

crutschow

Joined Mar 14, 2008
25,256
It could be done with two 555's.
The first acts as a bistable latch and the second as a one-shot.
LTspice simulation below:
The R5C1 values shown give an off delay of about 5 seconds.
Those can be changed to give whatever delay you want.

The circuit comes up in the OFF state when power is applied.

The Out output can drive a relay with an added N-MOSFET driver (add suppression diode across coil).

1594840986823.png
 

Alec_t

Joined Sep 17, 2013
11,513
Here's a suggestion:-
LatchedDelayedOff.png
With the relay de-energised, the current consumption of the whole circuit is a fraction of 1uA, so no switch-off of the whole circuit is needed. The pot allows adjustment of the delayed shut-off. The 4 Schmitt inverters are all in the one IC. D3/D4/V2/V3 are for simulation only.
 

eetech00

Joined Jun 8, 2013
1,969
Here's a suggestion:-
View attachment 212256
With the relay de-energised, the current consumption of the whole circuit is a fraction of 1uA, so no switch-off of the whole circuit is needed. The pot allows adjustment of the delayed shut-off. The 4 Schmitt inverters are all in the one IC. D3/D4/V2/V3 are for simulation only.
I like and was about propose the same. But don't you have to set the initial state of the flip flop? (the output may bounce on power-up which is not desirable).
 

Thread Starter

ocean750

Joined Jul 15, 2020
16
It could be done with two 555's.
The first acts as a bistable latch and the second as a one-shot.
LTspice simulation below:
The R5C1 values shown give an off delay of about 5 seconds.
Those can be changed to give whatever delay you want.

The circuit comes up in the OFF state when power is applied.

The Out output can drive a relay with an added N-MOSFET driver (add suppression diode across coil).

View attachment 212255
what happens if the user press on the ON button twice (by mistake) won't the bistable change state ?
it is important that the system will only shutdown with the delayed OFF button.
 

crutschow

Joined Mar 14, 2008
25,256
But don't you have to set the initial state of the flip flop?
A capacitor going from the OFF switch go ground should insure the output is OFF at power-on.
(Add a small resistor in series with the switch to avoid any contact pitting from the capacitor discharge.)
what happens if the user press on the ON button twice (by mistake) won't the bistable change state ?
No, it's a bistable latch, not a toggle flip-flop, so it only changes state once, no matter how many times a button is pushed.
You need to press the opposite push-button to change the state back.
 
Last edited:

Thread Starter

ocean750

Joined Jul 15, 2020
16
what happens if the user press on the ON button twice (by mistake) won't the bistable change state ?
it is important that the system will only shutdown with the delayed OFF button.
Thank you for the explanation.
What is the function of diode D1 ?
 

Thread Starter

ocean750

Joined Jul 15, 2020
16
It could be done with two 555's.
The first acts as a bistable latch and the second as a one-shot.
LTspice simulation below:
The R5C1 values shown give an off delay of about 5 seconds.
Those can be changed to give whatever delay you want.

The circuit comes up in the OFF state when power is applied.

The Out output can drive a relay with an added N-MOSFET driver (add suppression diode across coil).

View attachment 212255
Hi, sorry for the long delay.
I have just finished building it, and it works beautifully :)
thank you
 

soyez

Joined Aug 17, 2020
26
Hello.
Could you please help me out ?
I am trying to build a circuit that would use two push button in order to turn ON and OFF a system.
When pressing the ON button, it will be latched using a relay.
I would like that when the OFF button is pressed, a timer from a 555 will count back some time, and when it is done, the system will shut down.
I would like to add a relay where the arrow is showing, and for that relay to be activated from the 555.
I tried a few times but could not get it to work.
How should I build the circuit ?

Thank you
To associate capacity to the 555 clock chip, we interface around 5-15V to VCC, pin 8, and we interface pin 1 to ground. We associate a 47KΩ resistor to the positive voltage gracefully and afterward to stick 2. We interface pin 6 to stick 2 and afterward associate a 100μF capacitor to ground.
 

Thread Starter

ocean750

Joined Jul 15, 2020
16
To associate capacity to the 555 clock chip, we interface around 5-15V to VCC, pin 8, and we interface pin 1 to ground. We associate a 47KΩ resistor to the positive voltage gracefully and afterward to stick 2. We interface pin 6 to stick 2 and afterward associate a 100μF capacitor to ground.

after pressing the OFF switch, OUT and OUT1 work just fine.
is there a way that once OUT drooped back to LOW, OUT1 will also drop to LOW ?
currently it strays at HIGH until I press on the ON once more.
 
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