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Thread: dome light dimmer (with delay)

  1. #21
    lez
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    Yeah I think you will find a small construction error, I have not built this but it looks like a working stable design to me.

    (only reason I didnt build was my car has one of these in OEM)
    Lez, more widely known as flez1966

  2. #22
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    Kronos(or anyone else) what exactly is a 1k2 resistor? by process of elimination I see two 2.2K resistors, with 3 red bands, that are not mentioned on the diagram. Is that what you mean, 2.2K?

  3. #23
    Vik
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    I am on Drugs......

    Sweet Marihuana or hasjes, hmmmmmmmmm


    But never again say something bad about ms paint. it's the best.....


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    It's not MSPaint I have a problem with. It's spending so much time creating drawings with it. Of course, it could be said that spending a couple dozen hours per year fiddling with MSPaint would be better than spending a couple grand for Photoshop....
    I'd rather pay the cash for PShop and spend the extra time hanging out with ViK...
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  5. #25
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    Red face GREAT design

    I was thinking - can't this just be accomplished by just a capacitor? The rest seems kinda unnecissary - but then again, I'm not an EE and only know enough about this stuff to get me in to some real trouble.

    I'm sure that I'm probably way wrong, but if any light can be shed on why I'm worng, it would be appriciated because I do love to learn.

    MANY thanks! I'll be building one of these hopefully this weekend when I put my new alarm system in.

    Ciao!

  6. #26
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    Dome light dimmer problem

    I constructed the entire circuit as per your supplied schematic, and matched it with the photo of the end product. when i tested it, it worked perfectly well, giving negative 12 volts dc in the bulb output terminal which stayed on before dimming off. problem is that it does not have enough current to light the bulb. although voltage across the output is 12 v, the current is only about 200 mA. why is this happening. the resistances i am usign are 470ohm, 100 ohm and 1.2k ohm. are they ok?

  7. #27
    Newbie gr_diver's Avatar
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    Problems!

    Hello friends of the forum! I am sorry to bring back an old topic.

    I tried making the dimmer, from the schematic kronos kindly posted a while ago.

    To begin with, I must say I have no idea about electronics. I am quite keen on electrics though, and assembling small circuits is not a problem. I assembled the dome dimmer, but I cannot get it to work.

    One suspicion I have is that the parts shop did not have the LM258P, but gave me a LM358P as a substitution. Are these two interchangeable? I downloaded their datasheet, it is the same for both, but I couldn't understand if I can swap them...

    Furthermore, I tried measuring the voltages at pins 2/3 of the IC. Pin 3 indeed has approximately half the voltage of the source. The voltage on pin 2 slowly increases and exceeds that of pin 3. In fact I am using a 9V battery for bench testing, and the voltage on pin 3 reaches 8V . Pin 1 has no voltage, and this is why, I think, the LED does not get lit. If with the IC removed I momentarily short pins 1&2 on the soldered socket, the LED will flash.

    Any help would be greatly appreciated. I am building this to install in my '78 car.

    Thank you in advance!

  8. #28
    Newbie gr_diver's Avatar
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    Small update!

    Stupid as it might seem, I had not connected pins 4 & 8 of the LM358 to + and - respectively. I said I am a complete amateur. Not on the schematic, not done! But from the pictures i figured them out...

    Now the circuit works, the LED lights when power is applied, then fades. Re-enganges if I ground the "door" lead and immediately fades if I connect the ACC lead to +.

    BUT, it seems like it can't handle the current of a 10w bulb. I replaced the bulb with a led (with a resistor to feed it from +12V) and with it the circuit works nicely! But it can't work with the car's bulb... Seems like I have the same issue as Khurram.
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  9. #29
    Newbie gr_diver's Avatar
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    Ok, I think I figured it out, after reading this article:

    http://www.satcure-focus.com/tutor/page4.htm

    I realized that the base did not receive enough current, to make the collector-emitter path "open" as needed, and allow sufficient current flow through. So I replaced R6 (39kΩ) with a 0-10kΩ potentiometer, and set just enough for the bulb to get fully lit during the delay stage. The potentiometer could go further than the point where the bulb reaches full brightness, but because of my ignorance on such operational things I decided to set it just enough.

    I also used a small heatsink on MJE3055, because after fiddling with the circuit for about 10mins to set the delays to my liking, it had gotten hot. Now it gets just warm...

    Thank you for your time!
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  10. #30
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    help me

    can you tell what is acc

    where should i cannect it

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