Understanding 555 module with delay off.

Thread Starter

Confalone

Joined May 15, 2022
1
As a novice maker, I'm looking for a module to have a safety feature in my project. I don't think I fully understand the functionality of a 555 module. Or which one is the best for my project.

Power source: 9 volt battery.
Action: Press and hold a momentary switch to complete a task (close the circuit). If momentary switch is released, the task ends (open circuit). If the momentary switch remains on, the 555 module times out and ends the task (opens the circuit) at the end of a specific time (10 seconds).

Any direction or mentorship is greatly appreciated.

C
 

MrChips

Joined Oct 2, 2009
26,088
I don't fully understand what you are asking.

A 555-timer is just an electronic integrated circuit. How it behaves depends on how it is configured.
I am going to guess that by 555 module you are referring to an off-the-shelf circuit purchased from any one of the online merchants.

Ignore the module for the time being and let us try to understand the functionality you seek.
At this point this is only one design suggestion of which there are not many options available.

1) Press and release the button within 3 secs, the machine operates for the duration the button is pressed.
2) Press and release the button after 3 seconds, the machine operates for 10 seconds.

Edit:
Having reread your post, this is the operation I infer from your description.
1) Press and release the button within 10 secs, the machine operates for the duration the button is pressed.
2) Press the button longer than 10 seconds, the machine operates for 10 seconds.
 

Hymie

Joined Mar 30, 2018
1,081
As a general rule, semiconductors should not be used in a safety function unless there is redundancy in the circuit, such that a single component failure will not result in the safety action of the circuit being compromised.
 

AnalogKid

Joined Aug 1, 2013
10,054
Several different kinds of circuits and modules will do what you want. Do you want to build a circuit, or buy a module?

For either option, we need more information. What is the output of the circuit/module driving? Is it the control pin of another device, a one horsepower furnace motor, or something else? Depending on what you are doing, this could be as simple as 1 transistor plus a few passive components.

ak
 

crutschow

Joined Mar 14, 2008
29,779
Will the current of the 555 continually connected be a problem?
A standard 9V rectangular battery wouldn't last long if the 555 is always powered.
Edit: If the 555 were powered from the PB, then that wouldn't be a problem.

There are also ways to do what you want, other than a 555 module, that draw no significant quiescent current.
Below is an example using one CD4093 IC package.
If the PB is held on, the output will go back low in about 10s, otherwise the output will go low when the PB is released.

1652650083338.png
 
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k1ng 1337

Joined Sep 11, 2020
531
I don't fully understand what you are asking.

A 555-timer is just an electronic integrated circuit. How it behaves depends on how it is configured.
I am going to guess that by 555 module you are referring to an off-the-shelf circuit purchased from any one of the online merchants.

Ignore the module for the time being and let us try to understand the functionality you seek.
At this point this is only one design suggestion of which there are not many options available.

1) Press and release the button within 3 secs, the machine operates for the duration the button is pressed.
2) Press and release the button after 3 seconds, the machine operates for 10 seconds.

Edit:
Having reread your post, this is the operation I infer from your description.
1) Press and release the button within 10 secs, the machine operates for the duration the button is pressed.
2) Press the button longer than 10 seconds, the machine operates for 10 seconds.
I read it as a monostable one shot timer that completes the cycle as long as the switch is held closed and is interrupted if the switch is opened.
 

Tonyr1084

Joined Sep 24, 2015
6,884
Press and hold a momentary switch to complete a task (close the circuit). If momentary switch is released, the task ends (open circuit).
If the momentary switch remains on, the 555 module times out and ends the task (opens the circuit) at the end of a specific time (10 seconds).
What I'm picking up is this:
1) Press and hold the button for (lets say) two seconds. When the button is released the function abruptly ends.
2) Press and hold the for longer than 10 seconds the function ends at 10 seconds regardless of how long the button is held.

What comes to mind for function #2 is a "One Shot". A One Shot is activated by the press of a button for ANY duration. The One Shot continues to provide power for ONLY a specific amount of time. In other words wither you press it for one second or 100 seconds, the process will go on for ONLY 10 seconds (if that's what has been designed for.

However, for function #1, you may need additional components such as a 2 input A N D gate. Both the 555 timer AND the switch must be held to complete the function. If the operator releases the button after 2 seconds (less than 10 seconds) then the process stops. IF the operator holds the button longer than 10 seconds the One Shot ends the function because the AND gate requires two high inputs to produce a high output.

Now, I'm old school electronics and not very versed at that. These days there's probably something far better than my approach. If so - someone more versed will likely have advice above and beyond my advice. I'm not proud. I'm not the smartest guy here. I'm not as sharp as a fuzzy tennis ball but I'm not so dumb either.

Good luck. That's about all I can add to this thread.
 

eetech00

Joined Jun 8, 2013
3,149
Use a 555 monstable with a NC momentary button.
The button closed holds the timer reset pin low, so the output is initially low. When the button is pressed, the timer is triggered, the output goes high, and the timer runs. If the button is still held when the time expires, the output wil go low. If the button is released before time expires, the timer is reset, and the output returns low. See below.

Button pressed and held longer than timeout.
1652679753427.png

Button pressed, then released before timeout.
1652679860186.png
 
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crutschow

Joined Mar 14, 2008
29,779
Below is the LTspice simulation of a 555 circuit that, I believe, does what you want:
It's powered from the switch, so draws no power when not active.

1652678075032.png
 
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