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I would like to build a circuit that will fade my dome light when I close my door on my truck.
this circuit will need a + input and a + output so i can connect it inline with a couple of amps because i have ground lights on here they are just two clearence lights I would say maybe no more than 3 amps
Just close the door and the light fade out
All the circuits that i have is neg switching<p>Thanks
Myp71

will something like this circuit work for me.<p>I have a relay inside the truck to turn on dome lights if I put this circuit inline with the relay power+ out and light power + in this will work right?<p>Thanks<p>http://electronic-circuits-diagrams.com ... ages/3.gif

If you plug in a large cap, then when the door closes the cap feeds the light for the amount of capacitance value equal to a time discharge VS "R" value of the bulb. <p>A large value will be needed, and some of the newer types can handle it, and still be small.

I think Chris touched on the heart of the circuit filing a capacitor but concider a few dimmers.
http://www.discovercircuits.com/L/lite-dimmer.htm<p>The idea is to isolate that part of the circuit that will employ this particular function.<p>It does'nt always come down to the least parts
sometimes it's whats available in quantities from surplus at a reasonable price or ideally an inexpensive ready made board that just needs a few mods.

Check out this thread on another forum. I posted a schematic there which I simulated, but have not built and tested.

Wow wee, that last link was quite a heated posts I was wanting to know what happened I got lost.<p>
Thanks for the prev info
Myp71

The simplest way is a hi-current diode (3A) in series with the lamp, and a large cap in parallel with the lamp, after the diode. The diode provides isolation (precaution) , and the cap stores the voltage. Large (10,000uF ?!?) cap's are avail. for auto amp power supplies. Haines has them. 631-348-1750. order a catalog.
4 ohms (lamps) and 10,000uF, what's the constant?
T=RC

You're going to need a lot more than 10,000uF to keep that lamp on for any significant amount of time.<p>Most dome lights have a switch on their base to bypass the door switch and turn the light on. You might want to look at picking off the door switch signal, and using power from the switch "Always On" side to do PWM for lamp control. That's what gives the "Cadillac" look of dome light smoothly fading out after you close the door that you're looking for.<p>Bulb resistance goes down as it cools, which will tend to mess up your effect if you're using a cap. A PWM circuit will take up less space and cost less than that mongo cap, too.<p>Can't give more advice without a wiring diagram.<p>Good luck.
Chris

They have million farad caps these days, and huge ones [300,000 uF] the size of a flash light battery and smaller. <p>The only draw back on these super caps is “the feed in” must be slowed down a little bit, as they don’t like huge current slams inwards. <p>Long before the bulb "cools", it will be out.

here is a wiring digram of the dome light circuit in my truck
I have an photoelectric eye circuit that controls the dome light via a relay so what I was guessing that this circuit for dome light fade out when doors are closed would be connected in between the relay power+ out and dome light power+ in, so when there is no power coming from the realy(door closes)this circuit will take over and fade out the dome light almost instantly.<p>I would like to have it when the door closes instead of just going off have it so it fades out<p>Thank you very much
The photo cell circuit can be seen under topic 'pot help'
Myp71
Ryan

anyone happen to have anymore help on this thread, I would like to get this thread going again and this project.<p>also the pwm circuit sounds good how do I build and what is a pwm

my p71,
I know you asked for a fade out circuit, but do you really need it to fade? Because instead of that, you could use a large cap (I think only about 5,000 to 10,000, a pushbutton switch and a relay. When the door opens, the pushbutton activiates, charging the cap, and the relay pulls down, turning on the light. When the door closes, the cap drains through the relay, and it will turn off in about 5 - 10 seconds.

O.k, using Mike's Idea With the relay and cap.just tweaking it a little bit ( you know we all have to come up with are own ideas to make us look good )By using a relay to change the polarity over to negitive from plus then using a cap but then just add on a power fet.only thing is this the only way to change polarity? I have three relay's on just the dome light circuit but what's another one Right? <p>Thanks Mike for your help if this circuit does not work I will try yours

Ok i tried my idea but the power fet needs + trigger and controls the dome light via ground so unless I have nothing else to do I might rewire my truck dome light circuit to get it to work I tried mike's idea also unfortunately the relay started to Buzz near the end cycle

What kind of relay are you using? A standard one that uses a coil? Or a solid state? When I tried this, I used a small one from radioshack, that runs off of 12VDC at 80ma, and it didn't do anything like that for me. I tried with a 63000uf cap, and it stayed pulled down for about a minute before the cap drained. I don't know what the buzzing would be, though. What size cap are you using?<p>Possibly something like a 555 timer triggered and reset by a dual pushbutton?