Slow, Automatic Light Dimmer

Discussion in 'Electronic Design' started by Aaron407, Jul 17, 2006.

  1. Aaron407

    Aaron407 Guest

    I'm hoping someone will have some insight into a simple design for a
    type of light dimmer. I'm looking to build a light dimmer that, after
    given power by an external timer, will slowly rise from a low dim on
    the ac light output (ie. low rms voltage level) to the full voltage
    over a course of about 15 minutes. I'm looking for 120Vac input, and
    hoping to not require a microcontroller to control anything (not too
    into programming). My biggest issue is how to control the voltage
    variation that slowly without a manual control or microcontroller.
    Overall, I'm just looking for a starting point to base my design on.
    I'm an electrical engineering graduate so I do have some background, so
    please throw some ideas at me, I'm all ears.

    -407
     
    Aaron407, Jul 17, 2006
    #1
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  2. Aaron407

    PN2222A Guest

    "Aaron407" <> wrote in message
    news:...
    > I'm hoping someone will have some insight into a simple design for a
    > type of light dimmer. I'm looking to build a light dimmer that, after
    > given power by an external timer, will slowly rise from a low dim on
    > the ac light output (ie. low rms voltage level) to the full voltage
    > over a course of about 15 minutes. I'm looking for 120Vac input, and
    > hoping to not require a microcontroller to control anything (not too
    > into programming). My biggest issue is how to control the voltage
    > variation that slowly without a manual control or microcontroller.


    OK 407.
    So. D'yer know how a dimmer works? Go find that bit out.
    Then you'll discover you need a ramp on the control voltage what triggers
    the SCR (you _do_ know about the SCR?)
    That ramp is gonna be real, real ... slow.
    So you need to figure about high value resistors and low leakage capacitors.

    Am I going too fast?

    PN2222A
    fsubt 250MHz.
     
    PN2222A, Jul 17, 2006
    #2
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  3. Aaron407

    Aaron407 Guest

    Um, yeah, I do know about the conduction angle for firing an SCR to
    control the rms voltage you jackass, you don't have to patronize me.
    FYI, I focus on large power systems for my degree but I was hoping to
    start exploring electronics a little more, thanks for all the help.


    PN2222A wrote:
    > "Aaron407" <> wrote in message
    > news:...
    > > I'm hoping someone will have some insight into a simple design for a
    > > type of light dimmer. I'm looking to build a light dimmer that, after
    > > given power by an external timer, will slowly rise from a low dim on
    > > the ac light output (ie. low rms voltage level) to the full voltage
    > > over a course of about 15 minutes. I'm looking for 120Vac input, and
    > > hoping to not require a microcontroller to control anything (not too
    > > into programming). My biggest issue is how to control the voltage
    > > variation that slowly without a manual control or microcontroller.

    >
    > OK 407.
    > So. D'yer know how a dimmer works? Go find that bit out.
    > Then you'll discover you need a ramp on the control voltage what triggers
    > the SCR (you _do_ know about the SCR?)
    > That ramp is gonna be real, real ... slow.
    > So you need to figure about high value resistors and low leakage capacitors.
    >
    > Am I going too fast?
    >
    > PN2222A
    > fsubt 250MHz.
     
    Aaron407, Jul 17, 2006
    #3
  4. On 16 Jul 2006 20:58:27 -0700, in sci.electronics.design "Aaron407"
    <> wrote:

    >I'm hoping someone will have some insight into a simple design for a
    >type of light dimmer. I'm looking to build a light dimmer that, after
    >given power by an external timer, will slowly rise from a low dim on
    >the ac light output (ie. low rms voltage level) to the full voltage
    >over a course of about 15 minutes. I'm looking for 120Vac input, and
    >hoping to not require a microcontroller to control anything (not too
    >into programming). My biggest issue is how to control the voltage
    >variation that slowly without a manual control or microcontroller.
    >Overall, I'm just looking for a starting point to base my design on.
    >I'm an electrical engineering graduate so I do have some background, so
    >please throw some ideas at me, I'm all ears.
    >
    >-407

    How about a binary counter with a R2R network on the output, and use
    the FF state of the counter to inhibit the clock input.

    It will be better than a RC type time constant. The clock could be
    mains derived. One of the problems is that the normal incandescent
    lamp does not have a linear relatioship between volts applied and
    light output


    martin
     
    martin griffith, Jul 17, 2006
    #4
  5. Aaron407

    Aaron407 Guest

    Thanks Martin, I'll look into it. I really appreciate sincere help.


    martin griffith wrote:
    > On 16 Jul 2006 20:58:27 -0700, in sci.electronics.design "Aaron407"
    > <> wrote:
    >
    > >I'm hoping someone will have some insight into a simple design for a
    > >type of light dimmer. I'm looking to build a light dimmer that, after
    > >given power by an external timer, will slowly rise from a low dim on
    > >the ac light output (ie. low rms voltage level) to the full voltage
    > >over a course of about 15 minutes. I'm looking for 120Vac input, and
    > >hoping to not require a microcontroller to control anything (not too
    > >into programming). My biggest issue is how to control the voltage
    > >variation that slowly without a manual control or microcontroller.
    > >Overall, I'm just looking for a starting point to base my design on.
    > >I'm an electrical engineering graduate so I do have some background, so
    > >please throw some ideas at me, I'm all ears.
    > >
    > >-407

    > How about a binary counter with a R2R network on the output, and use
    > the FF state of the counter to inhibit the clock input.
    >
    > It will be better than a RC type time constant. The clock could be
    > mains derived. One of the problems is that the normal incandescent
    > lamp does not have a linear relatioship between volts applied and
    > light output
    >
    >
    > martin
     
    Aaron407, Jul 17, 2006
    #5
  6. Aaron407

    Fred Bloggs Guest


    > I'm hoping someone will have some insight into a simple design for a
    > type of light dimmer. I'm looking to build a light dimmer that, after
    > given power by an external timer, will slowly rise from a low dim on
    > the ac light output (ie. low rms voltage level) to the full voltage
    > over a course of about 15 minutes. I'm looking for 120Vac input, and
    > hoping to not require a microcontroller to control anything (not too
    > into programming). My biggest issue is how to control the voltage
    > variation that slowly without a manual control or microcontroller.
    > Overall, I'm just looking for a starting point to base my design on.
    > I'm an electrical engineering graduate so I do have some background, so
    > please throw some ideas at me, I'm all ears.


    It depends on what kind of effect you are trying to achieve, the timing
    is not so much an issue as setting the triggering angle. If you want the
    brightening ramp to be barely perceptible ("slowly") then there is
    something called the Weber-Fechner Law which relates actual light output
    intensity to changes to human perception. This roughly means that if the
    bulb drive is increased in discrete increments, then the increase
    between increments should be no more than 10% of the intensity
    corresponding to the preceding drive. Since the circuit most likely will
    use binary counters, this adds other constraints. If say you decide to
    use 64 drive levels, as derived from a simple resistor ladder off 6-bits
    of counter, and the increment is set to 8% , then this gives you
    (1.08)^64~ 120 to 150 range of intensity for the ramp. The 64 drive
    levels also implies 15 x 60 /64 = approximately 14 seconds of dwell at
    each level, and this is 15 x 60 x 60/64= 844 line cycles, the most
    readily available time base. So your basic circuit will be to initialize
    for an RMS output of Vmax/150, count cycles, increment the DAC counter,
    servo the bulb drive to Vmax/150*1.08, and so forth until the drive
    produces Vmax. I'll leave it to Jim Thompson to work out the best
    configuration of parts for you- he has plenty of time on his hands and
    claims to relish a challenge.
     
    Fred Bloggs, Jul 17, 2006
    #6
  7. On 17 Jul 2006 07:25:46 -0700, in sci.electronics.design "Aaron407"
    <> wrote:

    >Thanks Martin, I'll look into it. I really appreciate sincere help.
    >
    >
    >martin griffith wrote:
    >> On 16 Jul 2006 20:58:27 -0700, in sci.electronics.design "Aaron407"
    >> <> wrote:
    >>
    >> >I'm hoping someone will have some insight into a simple design for a
    >> >type of light dimmer. I'm looking to build a light dimmer that, after
    >> >given power by an external timer, will slowly rise from a low dim on
    >> >the ac light output (ie. low rms voltage level) to the full voltage
    >> >over a course of about 15 minutes. I'm looking for 120Vac input, and
    >> >hoping to not require a microcontroller to control anything (not too
    >> >into programming). My biggest issue is how to control the voltage
    >> >variation that slowly without a manual control or microcontroller.
    >> >Overall, I'm just looking for a starting point to base my design on.
    >> >I'm an electrical engineering graduate so I do have some background, so
    >> >please throw some ideas at me, I'm all ears.
    >> >
    >> >-407

    >> How about a binary counter with a R2R network on the output, and use
    >> the FF state of the counter to inhibit the clock input.
    >>
    >> It will be better than a RC type time constant. The clock could be
    >> mains derived. One of the problems is that the normal incandescent
    >> lamp does not have a linear relatioship between volts applied and
    >> light output
    >>
    >>
    >> martin

    WRT Fred's good info, you could use a photocell to monitor the light
    output, and effectively put lamp in a feedback loop, this might give
    you a linear response, or it might just be a bit OTT for a simple
    device


    martin
     
    martin griffith, Jul 17, 2006
    #7
  8. "Fred Bloggs" <> wrote in message
    news:...
    >
    >> I'm hoping someone will have some insight into a simple design for a
    >> type of light dimmer. I'm looking to build a light dimmer that, after
    >> given power by an external timer, will slowly rise from a low dim on
    >> the ac light output (ie. low rms voltage level) to the full voltage
    >> over a course of about 15 minutes. I'm looking for 120Vac input, and
    >> hoping to not require a microcontroller to control anything (not too
    >> into programming). My biggest issue is how to control the voltage
    >> variation that slowly without a manual control or microcontroller.
    >> Overall, I'm just looking for a starting point to base my design on.
    >> I'm an electrical engineering graduate so I do have some background, so
    >> please throw some ideas at me, I'm all ears.

    >
    > It depends on what kind of effect you are trying to achieve, the timing
    > is not so much an issue as setting the triggering angle. If you want the
    > brightening ramp to be barely perceptible ("slowly") then there is
    > something called the Weber-Fechner Law which relates actual light output
    > intensity to changes to human perception. This roughly means that if the
    > bulb drive is increased in discrete increments, then the increase between
    > increments should be no more than 10% of the intensity corresponding to
    > the preceding drive. Since the circuit most likely will use binary
    > counters, this adds other constraints. If say you decide to use 64 drive
    > levels, as derived from a simple resistor ladder off 6-bits of counter,
    > and the increment is set to 8% , then this gives you (1.08)^64~ 120 to
    > 150 range of intensity for the ramp. The 64 drive levels also implies 15
    > x 60 /64 = approximately 14 seconds of dwell at each level, and this is
    > 15 x 60 x 60/64= 844 line cycles, the most readily available time base.
    > So your basic circuit will be to initialize for an RMS output of
    > Vmax/150, count cycles, increment the DAC counter, servo the bulb drive
    > to Vmax/150*1.08, and so forth until the drive produces Vmax. I'll leave
    > it to Jim Thompson to work out the best configuration of parts for you-
    > he has plenty of time on his hands and claims to relish a challenge.
    >


    This really is a perfect application for a small PIC or other
    microcontroller. It would be difficult to make an analog ramp for phase
    angle to produce a visually linear change in intensity over a long period.
    A PIC could use a lookup table that could be adjusted for the desired
    effect. This would compensate for the problem that voltage is not linearly
    related to phase angle, and also lamp brightness is not linear with
    voltage.

    Since so many things are now being done with PICs, it is important to have
    a good working knowledge of their capabilities. They are also often much
    cheaper and smaller than the equivalent set of conventional logic ICs or
    linear components, and have the advantage of simple reprogramming to make
    changes, rather than twiddling pots or changing components.

    I have the phase modulation PIC code already working for my SCR board, and
    it could be readily adapted to this project. I'm willing to email the code
    and help with some of the specific programming and circuitry. You can get a
    complete development kit (PicKit I) for about $30 from www.microchip.com.
    Good luck.

    Paul
     
    Paul E. Schoen, Jul 17, 2006
    #8
  9. Aaron407

    PN2222A Guest

    407, man, you cut me to the quick! J***A***? This is usenet,dude. We do
    have our standards.

    What I'd be looking to do for this problem is this:

    Zero-crossing circuit starts a timer when the line voltage is zero.
    Prolly the timer's a 555 or so. At the beginning of time (your 15-minute
    interval)
    the timer waits 8.32msec and sends out a quick pulse.
    That pulse fires the triac, turning the lamp on for a bit, until the next
    zero-crossing.

    As the time runs out of the hourglass, the delay drops from 8.32msec to
    zero, or nearly so.

    So I want a circuit that drops the trigger voltage steadily (more or less)
    from some initial voltage down to zero. Typically an R-C network. Maybe
    with a current source to make the ramp linear, and some low-input current
    buffers.
    Depends on how accurate, and how complex.

    At this point, somebody will insist that it's easier to do with a PIC.
    They'll be right.

    PN2222A
    pinout ebc, looking at the package.
     
    PN2222A, Jul 17, 2006
    #9
  10. Aaron407

    Aaron407 Guest

    Ok, I realize I may have been a little harsh, but when a person is
    patronized without a request for any clarification, I believe that this
    is lowering oneself to a sub-par professional standard and comes off as
    mere ignorance to me.

    Anyway, as for your solution, that was actually the direction I was
    originally headed in to begin with as I have some experience with 555
    timers and RC circuits. I just stated the problem broadly as to not
    limit myself to any particular foundation for design. However, as you
    stated, there will likely be many people that will claim that a PIC
    solution is much simpler, and I will probably succomb to the peer
    pressure and follow suit, but I'd like to keep my options open at this
    point.

    407


    PN2222A wrote:
    > 407, man, you cut me to the quick! J***A***? This is usenet,dude. We do
    > have our standards.
    >
    > What I'd be looking to do for this problem is this:
    >
    > Zero-crossing circuit starts a timer when the line voltage is zero.
    > Prolly the timer's a 555 or so. At the beginning of time (your 15-minute
    > interval)
    > the timer waits 8.32msec and sends out a quick pulse.
    > That pulse fires the triac, turning the lamp on for a bit, until the next
    > zero-crossing.
    >
    > As the time runs out of the hourglass, the delay drops from 8.32msec to
    > zero, or nearly so.
    >
    > So I want a circuit that drops the trigger voltage steadily (more or less)
    > from some initial voltage down to zero. Typically an R-C network. Maybe
    > with a current source to make the ramp linear, and some low-input current
    > buffers.
    > Depends on how accurate, and how complex.
    >
    > At this point, somebody will insist that it's easier to do with a PIC.
    > They'll be right.
    >
    > PN2222A
    > pinout ebc, looking at the package.
     
    Aaron407, Jul 17, 2006
    #10
  11. Aaron407

    Dennis Guest

    PN2222A wrote:

    >
    > At this point, somebody will insist that it's easier to do with a PIC.
    > They'll be right.
    >
    > PN2222A
    > pinout ebc, looking at the package.
    >
    >


    Something like ww1.microchip.com/downloads/en/AppNotes/40171a.pdf
     
    Dennis, Jul 18, 2006
    #11
  12. Aaron407 wrote:
    > I'm hoping someone will have some insight into a simple design for a
    > type of light dimmer. I'm looking to build a light dimmer that, after
    > given power by an external timer, will slowly rise from a low dim on
    > the ac light output (ie. low rms voltage level) to the full voltage
    > over a course of about 15 minutes. I'm looking for 120Vac input, and
    > hoping to not require a microcontroller to control anything (not too
    > into programming). My biggest issue is how to control the voltage
    > variation that slowly without a manual control or microcontroller.
    > Overall, I'm just looking for a starting point to base my design on.
    > I'm an electrical engineering graduate so I do have some background, so
    > please throw some ideas at me, I'm all ears.
    >
    > -407
    >

    Use a PIC or a BASIC STAMP of course.

    Not using a microcontroller for this ap is fundamentally insane.



    --
    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, Jul 18, 2006
    #12
  13. Aaron407

    -berlin.de Guest

    martin griffith <> wrote in sci.electronics.design:
    > On 17 Jul 2006 07:25:46 -0700, in sci.electronics.design "Aaron407"
    > <> wrote:
    > >Thanks Martin, I'll look into it. I really appreciate sincere help.
    > >martin griffith wrote:
    > >> On 16 Jul 2006 20:58:27 -0700, in sci.electronics.design "Aaron407"
    > >> <> wrote:


    [...]

    > >> How about a binary counter with a R2R network on the output, and use
    > >> the FF state of the counter to inhibit the clock input.
    > >>
    > >> It will be better than a RC type time constant. The clock could be
    > >> mains derived.


    15 min at 60 Hz gives a count of 54000. A 16 bit counter would fit
    nicely.

    Anno
     
    -berlin.de, Jul 20, 2006
    #13
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