terrarium lighting fade up and down

Discussion in 'The Projects Forum' started by piranha3380, May 16, 2014.

  1. piranha3380

    Thread Starter Member

    May 28, 2013
    30
    3
    heya guys here is a fun one

    i have this bigass terrarium thats gona get my diy thunderstorm module but i also whant to fade the light at dusk and back up in the morning,

    ime using moeler plc's so i got the outputs,
    i was thinking of a 12 volt systeem whit a mosfet and a capacitor,

    my idea was that if the plc switches the power on (12v) a capacitor starts slowly charging taking the mosfet whit it and slowly turning the lights on and in the eavning turn 12 volt of and the cap wil slowly drain taking the mosfet down and the bulb on life power,

    the idea is fun but i need advice from someone that maby done this or knows how to,
    the problem is keeping live (230v) and plc 12 volt seperated while stil managing output, dont need any live going into my plc array

    if someone could guide me or draw something even if its on a napkin or som ile be happy,

    whit kind regards
    piranha
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,546
    1,252
    Not nearly enough information.
    Are the lights AC or DC?
    What voltage?
    What power or current?
    Florescent, incandescent, halogen, LED?
    How long is the fade time?
    Fade to completely off or just a lower light level?

    ak
     
  3. piranha3380

    Thread Starter Member

    May 28, 2013
    30
    3
    they are 230v 50 watt incandescent ac mains lamps witch i like to controll,
    i whould like the duration to off and on be set by a potentiometer,
    from compleetly off to compleetly on in a few minutes and revers in the eavning only by applying 12 volt on/of to it
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,153
    3,059
    The trouble with this plan is in using a MOSFET in linear mode. This requires that it dissipate much more heat than when it is fully on or fully off. Depending on the answers to AK's questions, this heat could be a problem.

    A MOSFET's linear action is also a fairly narrow range of voltage, and the fading capacitor may not give the dimming profile that you like.

    This all leads up to recommending PWM control instead, especially since you already have a PIC. Using PWM will give you complete control to achieve any dimming effect you want. And the demands on the MOSFET are easier to predict.

    [edit] Oops, didn't see #3 when I responded. Didn't expect an AC load. Was thinking LEDs.
     
  5. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,546
    1,252
    The easiest approach might be to start with a traditional triac-based lamp dimmer to handle the power functions, then figure out how to control it the way you want. Since those dimmers are pretty simple and have a pot, you might be able to parallel the pot with an optocoupler that is driven by a looong ramp or a simple counter-plus-D/A ramp. This gets you power line isolation, critical for this project.

    ak
     
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