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    Delay on-instant off with 555 timer

    Good day folks. I'm trying to build a little circuit for a project of mine which requires pressing a button to toggle an output in the following fashion: if the button is held for around 5s, the output goes high. When the button is released, the output goes low instantly. If the button is released before the output actually goes high, the next press of the button should require 5s again before the output goes high again. This last bit is important, because what I was able to find was THIS circuit which uses the 555 timer to create a delayed-on circuit.

    There's a couple of caveats I'm facing though: obviously you can see there's no button there - the countdown essentially starts when power is first applied to the whole circuit, so I'm not quire sure where I should drop the button. I guess I could cut VCC to the whole circuit using a SPDT. Even after the fact, I simulated this circuit and although it works, there's still the problem I mentioned earlier: if the button is released too soon, before the output actually swings high, the next press turns it on instantly, since the capacitor is still charged and pin 2, TR, is pulled to GND immediately. I cannot figure out how to overcome this...I tried coming up with various ways to "discharge" that cap so it'd be ready for a new cycle, but couldn't find one that works.

    Most circuits I've seen work in the completely opposite way: the turn-on is instant and they SLOOWLY discharge the cap to get a delayed-OFF...

    Any ideas on how to achieve such result ? Thanks.

    EDIT: here's another idea I came up with and simulated and seems to work. I ditched the 555 entirely and used a MOSFET instead. I got the idea after watching THIS here video which coincidentally or not also talks about a delayed on>instant off scenario towards the end.
    Attached Files
    Last edited by Dannyx; 08-11-2019, 12:25 PM.
    Wattevah...

    #2
    Re: Delay on-instant off with 555 timer

    How about this, using SPDT switch?
    Attached Files
    Last edited by budm; 08-11-2019, 02:01 PM.
    Never stop learning
    Basic LCD TV and Monitor troubleshooting guides.
    http://www.badcaps.net/forum/showthr...956#post305956

    Voltage Regulator (LDO) testing:
    http://www.badcaps.net/forum/showthr...999#post300999

    Inverter testing using old CFL:
    http://www.badcaps.net/forum/showthr...er+testing+cfl

    Tear down pictures : Hit the ">" Show Albums and stories" on the left side
    http://s807.photobucket.com/user/budm/library/

    TV Factory reset codes listing:
    http://www.badcaps.net/forum/showthread.php?t=24809

    Comment


      #3
      Re: Delay on-instant off with 555 timer

      Thanks. So use the switch as a means to "reset" the FET ?

      BTW, the simulator is HERE if you wish to mess around
      Wattevah...

      Comment


        #4
        Re: Delay on-instant off with 555 timer

        When SW is in N.C. (released), the cap is discharged through 100 Ohms so the relay will be off almost instantly.
        Last edited by budm; 08-11-2019, 02:10 PM.
        Never stop learning
        Basic LCD TV and Monitor troubleshooting guides.
        http://www.badcaps.net/forum/showthr...956#post305956

        Voltage Regulator (LDO) testing:
        http://www.badcaps.net/forum/showthr...999#post300999

        Inverter testing using old CFL:
        http://www.badcaps.net/forum/showthr...er+testing+cfl

        Tear down pictures : Hit the ">" Show Albums and stories" on the left side
        http://s807.photobucket.com/user/budm/library/

        TV Factory reset codes listing:
        http://www.badcaps.net/forum/showthread.php?t=24809

        Comment


          #5
          Re: Delay on-instant off with 555 timer

          What if I drop the resistor instantly and just short the cap out ? Arcing at the contacts ? I'm not going to do that, but I'm just curious.
          Wattevah...

          Comment


            #6
            Re: Delay on-instant off with 555 timer

            You can do that but it is not good practice. If you have good meter that can capture the discharge current then you can see what it is with and without resistor.
            Never stop learning
            Basic LCD TV and Monitor troubleshooting guides.
            http://www.badcaps.net/forum/showthr...956#post305956

            Voltage Regulator (LDO) testing:
            http://www.badcaps.net/forum/showthr...999#post300999

            Inverter testing using old CFL:
            http://www.badcaps.net/forum/showthr...er+testing+cfl

            Tear down pictures : Hit the ">" Show Albums and stories" on the left side
            http://s807.photobucket.com/user/budm/library/

            TV Factory reset codes listing:
            http://www.badcaps.net/forum/showthread.php?t=24809

            Comment


              #7
              Re: Delay on-instant off with 555 timer

              will a diode work i wonder ?

              Comment


                #8
                Re: Delay on-instant off with 555 timer

                I was thinking the same thing.
                Wattevah...

                Comment


                  #9
                  Re: Delay on-instant off with 555 timer

                  Think about it, all we want is to discharge the caps down to basically 0V, so using diode the cap will not discharge to 0V because when the Voltage is <Vf of the diode it will no longer conduct, so basically the Voltage on the cap will go down to about 0.6V. So why do want to use diode, and what is the reason? The 50K is still in circuit so it will still keep on discharging the cap but it will take a long time to fully discharge charge the cap.
                  Last edited by budm; 08-11-2019, 11:11 PM.
                  Never stop learning
                  Basic LCD TV and Monitor troubleshooting guides.
                  http://www.badcaps.net/forum/showthr...956#post305956

                  Voltage Regulator (LDO) testing:
                  http://www.badcaps.net/forum/showthr...999#post300999

                  Inverter testing using old CFL:
                  http://www.badcaps.net/forum/showthr...er+testing+cfl

                  Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                  http://s807.photobucket.com/user/budm/library/

                  TV Factory reset codes listing:
                  http://www.badcaps.net/forum/showthread.php?t=24809

                  Comment


                    #10
                    Re: Delay on-instant off with 555 timer

                    Just realized a time-delay relay would work just as well. Sure it's a bit bulky, but more fool-proof.
                    Wattevah...

                    Comment


                      #11
                      Re: Delay on-instant off with 555 timer

                      Originally posted by Dannyx View Post
                      Just realized a time-delay relay would work just as well. Sure it's a bit bulky, but more fool-proof.
                      If thats the case maybe there is a solid state time delay relay that would work and be less bulky

                      Comment


                        #12
                        Re: Delay on-instant off with 555 timer

                        Originally posted by R_J View Post
                        If thats the case maybe there is a solid state time delay relay that would work and be less bulky
                        Or, a 25c microcontroller that lets you change your mind, later, as to how the circuit should operate in a variety of circumstances (e.g., is there a dead time that should be enforced after the cycle completes but before it can be triggered, again?)

                        Comment


                          #13
                          Re: Delay on-instant off with 555 timer

                          Correct. That would work too for the "overkill" version, but would require a dedicated supply to run. The relay method COULD work straight off 230v. True, I haven't offered a description of the purpose of the build, that's why you guys are free to suggest any possible implementation of this idea, from simple to "scientific".
                          Wattevah...

                          Comment


                            #14
                            Re: Delay on-instant off with 555 timer

                            Untested, I should just stick it in the simulator but too lazy.
                            Attached Files

                            Comment


                              #15
                              Re: Delay on-instant off with 555 timer

                              2 switches or rather one . and 2 relays .plus your timer circuit . will let you wire it up .

                              Comment


                                #16
                                Re: Delay on-instant off with 555 timer

                                Oh...btw, if you had a NC momentary switch, there is a trivial solution
                                I guess the assumption is that we had a NO switch.

                                Comment


                                  #17
                                  Re: Delay on-instant off with 555 timer

                                  Yep, SPST N.C. will work too, N.C. will short out the timing cap until the sw goes open when pushed.
                                  Never stop learning
                                  Basic LCD TV and Monitor troubleshooting guides.
                                  http://www.badcaps.net/forum/showthr...956#post305956

                                  Voltage Regulator (LDO) testing:
                                  http://www.badcaps.net/forum/showthr...999#post300999

                                  Inverter testing using old CFL:
                                  http://www.badcaps.net/forum/showthr...er+testing+cfl

                                  Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                                  http://s807.photobucket.com/user/budm/library/

                                  TV Factory reset codes listing:
                                  http://www.badcaps.net/forum/showthread.php?t=24809

                                  Comment


                                    #18
                                    Re: Delay on-instant off with 555 timer

                                    Originally posted by Dannyx View Post
                                    Correct. That would work too for the "overkill" version, but would require a dedicated supply to run.
                                    Your "dedicated power supply" could be an LED and a 1/4W resistor. If an HE device, it might even light up to indicate "power supply ON". And, you can EXACTLY time those 5 seconds -- or 327 seconds (instead of relying on temperature compensated RC's to do the timing).

                                    Comment


                                      #19
                                      Re: Delay on-instant off with 555 timer

                                      Originally posted by eccerr0r View Post
                                      Untested, I should just stick it in the simulator but too lazy.
                                      What simulator do you use for this ? Just curious.
                                      Wattevah...

                                      Comment


                                        #20
                                        Re: Delay on-instant off with 555 timer

                                        Originally posted by Dannyx View Post
                                        What simulator do you use for this ? Just curious.
                                        For me, "Headspice"¹. You use whatever you want to simulate it.





                                        ¹ - simulated in my head.

                                        Comment

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