Capacitor for momentary switch?

Discussion in 'Electronic Design' started by MrQuan, Feb 21, 2007.

  1. MrQuan

    MrQuan Guest

    Dear all,


    I'm a complete novice at electronics and need help selecting a
    capacitor (I guess this is what I need).

    I have a momentary switch that is wired to a controller board. The
    controller has a resolution of one second, in that it scans it's
    inputs once a second only. Sometimes when I push the button too fast,
    the controller misses it and doesn't register the input.

    I'm hoping there is a way to connect a capacitor into the switch
    circuit so that it's held closed for longer than a second no matter
    how fast I push the button, and therefore registering the input on the
    controller without fail. I've measure 5VDC across the switching
    connection, incase that information helps.

    Can anyone share a solution for this problem I'm having? ...and
    perhaps even suggest the right capacitor to use, if in fact a
    capacitor will solve this?


    Many thanks,
    MrQuan
    MrQuan, Feb 21, 2007
    #1
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  2. MrQuan

    John Barrett Guest

    "MrQuan" <> wrote in message
    news:...
    > Dear all,
    >
    >
    > I'm a complete novice at electronics and need help selecting a
    > capacitor (I guess this is what I need).
    >
    > I have a momentary switch that is wired to a controller board. The
    > controller has a resolution of one second, in that it scans it's
    > inputs once a second only. Sometimes when I push the button too fast,
    > the controller misses it and doesn't register the input.
    >
    > I'm hoping there is a way to connect a capacitor into the switch
    > circuit so that it's held closed for longer than a second no matter
    > how fast I push the button, and therefore registering the input on the
    > controller without fail. I've measure 5VDC across the switching
    > connection, incase that information helps.
    >
    > Can anyone share a solution for this problem I'm having? ...and
    > perhaps even suggest the right capacitor to use, if in fact a
    > capacitor will solve this?
    >
    >
    > Many thanks,
    > MrQuan
    >


    Capacitor wont do it -- you need a pulse stretcher, which may be more
    trouble than its worth.. you can make one with a 555 timer easy enough..
    look for "one-shot" circuits where, when triggered, the circuit turns on for
    a specific period of time, then resets and waits for the next trigger.
    John Barrett, Feb 21, 2007
    #2
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  3. MrQuan

    EdV Guest

    On Feb 20, 11:33 pm, "MrQuan" <> wrote:
    > Dear all,
    >
    > I'm a complete novice at electronics and need help selecting a
    > capacitor (I guess this is what I need).
    >
    > I have a momentary switch that is wired to a controller board. The
    > controller has a resolution of one second, in that it scans it's
    > inputs once a second only. Sometimes when I push the button too fast,
    > the controller misses it and doesn't register the input.
    >
    > I'm hoping there is a way to connect a capacitor into the switch
    > circuit so that it's held closed for longer than a second no matter
    > how fast I push the button, and therefore registering the input on the
    > controller without fail. I've measure 5VDC across the switching
    > connection, incase that information helps.
    >
    > Can anyone share a solution for this problem I'm having? ...and
    > perhaps even suggest the right capacitor to use, if in fact a
    > capacitor will solve this?
    >
    > Many thanks,
    > MrQuan


    Using a toggle switch might work. Of course this may make operation a
    little goofy but it is better than it not working at all.
    EdV, Feb 21, 2007
    #3
  4. MrQuan

    John Fields Guest

    On 20 Feb 2007 21:33:35 -0800, "MrQuan" <>
    wrote:

    >Dear all,
    >
    >
    >I'm a complete novice at electronics and need help selecting a
    >capacitor (I guess this is what I need).
    >
    >I have a momentary switch that is wired to a controller board. The
    >controller has a resolution of one second, in that it scans it's
    >inputs once a second only. Sometimes when I push the button too fast,
    >the controller misses it and doesn't register the input.
    >
    >I'm hoping there is a way to connect a capacitor into the switch
    >circuit so that it's held closed for longer than a second no matter
    >how fast I push the button, and therefore registering the input on the
    >controller without fail. I've measure 5VDC across the switching
    >connection, incase that information helps.
    >
    >Can anyone share a solution for this problem I'm having? ...and
    >perhaps even suggest the right capacitor to use, if in fact a
    >capacitor will solve this?


    ---
    Since you know the controller's limitations, why not just hold the
    switch down for longer than one second?


    --
    JF
    John Fields, Feb 21, 2007
    #4
  5. MrQuan

    MrQuan Guest

    On Feb 22, 12:01 am, John Fields <>
    wrote:
    > On 20 Feb 2007 21:33:35 -0800, "MrQuan" <>
    > wrote:
    >
    >
    >
    > >Dear all,

    >
    > >I'm a complete novice at electronics and need help selecting a
    > >capacitor (I guess this is what I need).

    >
    > >I have a momentary switch that is wired to a controller board. The
    > >controller has a resolution of one second, in that it scans it's
    > >inputs once a second only. Sometimes when I push the button too fast,
    > >the controller misses it and doesn't register the input.

    >
    > >I'm hoping there is a way to connect a capacitor into the switch
    > >circuit so that it's held closed for longer than a second no matter
    > >how fast I push the button, and therefore registering the input on the
    > >controller without fail. I've measure 5VDC across the switching
    > >connection, incase that information helps.

    >
    > >Can anyone share a solution for this problem I'm having? ...and
    > >perhaps even suggest the right capacitor to use, if in fact a
    > >capacitor will solve this?

    >
    > ---
    > Since you know the controller's limitations, why not just hold the
    > switch down for longer than one second?
    >
    > --
    > JF


    Well, that's fine for me in the workshop, but this solution was really
    aimed more at the people whos offices and buildings these are
    installed in. The controller is used for HVAC and access control. I
    have seen some of my colleagues label push buttons with "push and hold
    for one second", I was just hoping for a more elegant approach!
    MrQuan, Feb 21, 2007
    #5
  6. MrQuan

    MrQuan Guest

    On Feb 21, 11:42 pm, "EdV" <> wrote:
    > On Feb 20, 11:33 pm, "MrQuan" <> wrote:
    >
    >
    >
    > > Dear all,

    >
    > > I'm a complete novice at electronics and need help selecting a
    > > capacitor (I guess this is what I need).

    >
    > > I have a momentary switch that is wired to a controller board. The
    > > controller has a resolution of one second, in that it scans it's
    > > inputs once a second only. Sometimes when I push the button too fast,
    > > the controller misses it and doesn't register the input.

    >
    > > I'm hoping there is a way to connect a capacitor into the switch
    > > circuit so that it's held closed for longer than a second no matter
    > > how fast I push the button, and therefore registering the input on the
    > > controller without fail. I've measure 5VDC across the switching
    > > connection, incase that information helps.

    >
    > > Can anyone share a solution for this problem I'm having? ...and
    > > perhaps even suggest the right capacitor to use, if in fact a
    > > capacitor will solve this?

    >
    > > Many thanks,
    > > MrQuan

    >
    > Using a toggle switch might work. Of course this may make operation a
    > little goofy but it is better than it not working at all.


    I was actually looking at different switch alternatives, but I think
    for aesthetic reasons a push button style is my only option as it will
    be mounted to a small panel on a wall.
    MrQuan, Feb 21, 2007
    #6
  7. MrQuan

    MrQuan Guest

    On Feb 21, 4:55 pm, "John Barrett" <> wrote:
    > "MrQuan" <> wrote in message
    >
    > news:...
    >
    >
    >
    > > Dear all,

    >
    > > I'm a complete novice at electronics and need help selecting a
    > > capacitor (I guess this is what I need).

    >
    > > I have a momentary switch that is wired to a controller board. The
    > > controller has a resolution of one second, in that it scans it's
    > > inputs once a second only. Sometimes when I push the button too fast,
    > > the controller misses it and doesn't register the input.

    >
    > > I'm hoping there is a way to connect a capacitor into the switch
    > > circuit so that it's held closed for longer than a second no matter
    > > how fast I push the button, and therefore registering the input on the
    > > controller without fail. I've measure 5VDC across the switching
    > > connection, incase that information helps.

    >
    > > Can anyone share a solution for this problem I'm having? ...and
    > > perhaps even suggest the right capacitor to use, if in fact a
    > > capacitor will solve this?

    >
    > > Many thanks,
    > > MrQuan

    >
    > Capacitor wont do it -- you need a pulse stretcher, which may be more
    > trouble than its worth.. you can make one with a 555 timer easy enough..
    > look for "one-shot" circuits where, when triggered, the circuit turns on for
    > a specific period of time, then resets and waits for the next trigger.


    I see how this solution would work, however as you say it looks like
    more trouble than it's worth... I'll have to look at alternative
    solutions I guess. I have been mounting neon indicators next to the
    push buttons, so the user gets feed back whether they have actually
    switched anything - and this seems to be working. I was just hoping,
    if it were easy enough, to make it totally robust. Thanks
    MrQuan, Feb 21, 2007
    #7
  8. MrQuan

    John Barrett Guest

    "MrQuan" <> wrote in message
    news:...
    > On Feb 22, 12:01 am, John Fields <>
    > wrote:
    >> On 20 Feb 2007 21:33:35 -0800, "MrQuan" <>
    >> wrote:
    >>
    >>
    >>
    >> >Dear all,

    >>
    >> >I'm a complete novice at electronics and need help selecting a
    >> >capacitor (I guess this is what I need).

    >>
    >> >I have a momentary switch that is wired to a controller board. The
    >> >controller has a resolution of one second, in that it scans it's
    >> >inputs once a second only. Sometimes when I push the button too fast,
    >> >the controller misses it and doesn't register the input.

    >>
    >> >I'm hoping there is a way to connect a capacitor into the switch
    >> >circuit so that it's held closed for longer than a second no matter
    >> >how fast I push the button, and therefore registering the input on the
    >> >controller without fail. I've measure 5VDC across the switching
    >> >connection, incase that information helps.

    >>
    >> >Can anyone share a solution for this problem I'm having? ...and
    >> >perhaps even suggest the right capacitor to use, if in fact a
    >> >capacitor will solve this?

    >>
    >> ---
    >> Since you know the controller's limitations, why not just hold the
    >> switch down for longer than one second?
    >>
    >> --
    >> JF

    >
    > Well, that's fine for me in the workshop, but this solution was really
    > aimed more at the people whos offices and buildings these are
    > installed in. The controller is used for HVAC and access control. I
    > have seen some of my colleagues label push buttons with "push and hold
    > for one second", I was just hoping for a more elegant approach!
    >


    OK -- solution number 2 -- get a dual flip-flop chip (74LS74)... button
    hooks up to the Set line, which will "remember" the button press until the
    processor reads the data and deliberatly resets the flip-flop by pulsing the
    Reset line.. each chip will handle 2 buttons and no messy R/C timing needed.
    John Barrett, Feb 21, 2007
    #8
  9. MrQuan

    Rich Grise Guest

    On Wed, 21 Feb 2007 06:38:53 -0800, MrQuan wrote:
    > On Feb 22, 12:01 am, John Fields <>
    >> ---
    >> Since you know the controller's limitations, why not just hold the
    >> switch down for longer than one second?

    >
    > Well, that's fine for me in the workshop, but this solution was really
    > aimed more at the people whos offices and buildings these are
    > installed in. The controller is used for HVAC and access control. I
    > have seen some of my colleagues label push buttons with "push and hold
    > for one second", I was just hoping for a more elegant approach!


    Then that is definitely the way you want to leave it - it protects the
    system from being turned on/off accidentally when somebody just bumps
    the button.

    Cheers!
    Rich
    Rich Grise, Feb 21, 2007
    #9
  10. MrQuan wrote:
    > Dear all,
    >
    >
    > I'm a complete novice at electronics and need help selecting a
    > capacitor (I guess this is what I need).
    >
    > I have a momentary switch that is wired to a controller board. The
    > controller has a resolution of one second, in that it scans it's
    > inputs once a second only. Sometimes when I push the button too fast,
    > the controller misses it and doesn't register the input.
    >
    > I'm hoping there is a way to connect a capacitor into the switch
    > circuit so that it's held closed for longer than a second no matter
    > how fast I push the button, and therefore registering the input on the
    > controller without fail. I've measure 5VDC across the switching
    > connection, incase that information helps.
    >
    > Can anyone share a solution for this problem I'm having? ...and
    > perhaps even suggest the right capacitor to use, if in fact a
    > capacitor will solve this?
    >
    >
    > Many thanks,
    > MrQuan
    >

    Have the pushbutton set a flip flop and the sampler reset it.


    --
    Many thanks,

    Don Lancaster voice phone: (928)428-4073
    Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
    rss: http://www.tinaja.com/whtnu.xml email:

    Please visit my GURU's LAIR web site at http://www.tinaja.com
    Don Lancaster, Feb 21, 2007
    #10
  11. MrQuan

    amdx Guest

    "MrQuan" <> wrote in message
    news:...
    > Dear all,
    >
    >
    > I'm a complete novice at electronics and need help selecting a
    > capacitor (I guess this is what I need).
    >
    > I have a momentary switch that is wired to a controller board. The
    > controller has a resolution of one second, in that it scans it's
    > inputs once a second only. Sometimes when I push the button too fast,
    > the controller misses it and doesn't register the input.
    >
    > I'm hoping there is a way to connect a capacitor into the switch
    > circuit so that it's held closed for longer than a second no matter
    > how fast I push the button, and therefore registering the input on the
    > controller without fail. I've measure 5VDC across the switching
    > connection, incase that information helps.
    >
    > Can anyone share a solution for this problem I'm having? ...and
    > perhaps even suggest the right capacitor to use, if in fact a
    > capacitor will solve this?
    >
    >
    > Many thanks,
    > MrQuan
    >

    There are ways to use an SCR to stretch your pulse.
    Might take 1-cap 2-resistors and an SCR. Off the top of my head.
    Mike
    amdx, Feb 21, 2007
    #11
  12. MrQuan

    amdx Guest

    "MrQuan" <> wrote in message
    news:...
    > Dear all,
    >
    >
    > I'm a complete novice at electronics and need help selecting a
    > capacitor (I guess this is what I need).
    >
    > I have a momentary switch that is wired to a controller board. The
    > controller has a resolution of one second, in that it scans it's
    > inputs once a second only. Sometimes when I push the button too fast,
    > the controller misses it and doesn't register the input.
    >
    > I'm hoping there is a way to connect a capacitor into the switch
    > circuit so that it's held closed for longer than a second no matter
    > how fast I push the button, and therefore registering the input on the
    > controller without fail. I've measure 5VDC across the switching
    > connection, incase that information helps.
    >
    > Can anyone share a solution for this problem I'm having? ...and
    > perhaps even suggest the right capacitor to use, if in fact a
    > capacitor will solve this?
    >
    >
    > Many thanks,
    > MrQuan
    >

    I posted a schematic on alt.binaries.schematics.electronic
    of a circuit I used to debounce a switch, but I think you can
    modify it to stretch your pulse.
    Mike
    amdx, Feb 21, 2007
    #12
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