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fading car dome light

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lazynok

New Member
how could this be done? i read the thread on the "fading led" and it did not work. i tried hooking the dome light up in parallel and in a straight line(forgot what the other term was) with the capacitor. i also had the capacitor in a parallel infront of the light (capacitor and just a live wire) and it still did not work. when i hooked it up like the diagram in the FADING LED thread, my capacitor blew up into a ball of fire. i used a 1000uf, 100mfd, and 487mfd(blew up) capacitors. NOTE: i did not use any resistors for this because i did not know which ones to use. help please

i found this out... if i hook up the 10000uf capacitor up in line with the light... the light fades on really really slow. anyone know how to make it fade on kind of fast... and fade out slow? thanks (note: newbie)
 

Gene

New Member
Wow - what happened???? Let's try again

**broken link removed**

or maybe break it up....

**broken link removed**
circuits-diagrams/
carsimages/3.gif
 

lazynok

New Member
damn and i thought this was going to be easy... i can not find out how to wire the OFF switch... how do you do that to charge the cap? says something about that on the site **broken link removed** onic-circuits-dia grams.com/carsimages/carsckt3.shtml
 

lazynok

New Member
okay nevermind i undersatnd it. why is the site banned? it seams very informative..

also.. what is a VR1 and VR2? are they resistors..? or what
 

daviddoria

New Member
the "straight line" is called "series"

if you hook a capacitor and a LED in series, the light turns fully on, then dims (when the capacitor is fully charged it creates a "pseudo-open" in the circuit, so current can no longer flow). you might use a SPDT switch, with one of the paths through the capacitor, and one of the paths straight to the LED (through a resistor of course) so if you switch it "off" it dims to off, and if you switch it "on" it is simply on.

let me know if that needs clarification.

good luck
david
 

Gene

New Member
My appoligies. Since the restricted site begins with "This site contains lots of FREE electronic circuits (schematics) & do-it-yourself (DIY) circuit diagrams . . .", I thought they meant that the circuits were free [to use, to share, etc].

After reading the referenced old thread, in which people saying they represented the site owner's financial interest were complaining, I can easily see why the site has been restricted. Who needs that attitude? For that matter, who needs their schematics? There is certainly nothing special there.
 

lazynok

New Member
SPDT switch? i though those were relays.... clairify pleasee

also is there any reason why the diagram i drew up (below) will not work? and if it won't... why not? and if it does... what kind of capacitor and transister should i use? thanks much.. still learning...
 

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lazynok

New Member
also.... in the electro-circuits online place.. on the diagram it has these peices... called VR1 and VR2, with presets under on them. are they just normal 220k and 10k resistors? because i have never seen a resistor with 3 plugs coming out of it.
 

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daviddoria

New Member
VR is for variable resistor, also called potentiometer

there is indeed 3 leads on it, so you can set either way to 0.
 

lazynok

New Member
oh potentiometer. damn those things are big.. how am i to fit one of those in my car ceiling?? =[ do they make small ones?
 

Phasor

Member
do they make small ones?

Yes, they do. Sometimes called "skeleton" pots. Designed to be set once, and left alone after that. Typically only 0.25W or 0.125W power rating.
 

mechie

New Member
Series cap ?

Sebi
Can you check your diagram ... seems to me the switch will turn the light on but it will then fade out as the capacitor charges (in series with the resistor). Opening the switch will instantly kill the light.
This isn't quite what was wanted ?
 

daviddoria

New Member
also they make small pots, like surface mount... i dont know if you will want to use a screwdriver each time you want to change something though...

the ones i have are blue rectangular prisms with a gold screw on the end.
 

Sebi

Active Member
Thanks, Mechie! I've forgot the fade-out function. This cct. can work.
 

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Roff

Well-Known Member
Here's another circuit you can try. You can choose another MOSFET, so long as it has low enough ON resistance and can handle the current. If your dome light actually connects to ground instead of +12v (do you know for sure?), you can use a p-channel MOSFET and turn the circuit upside down.
In this circuit, the lamp voltage turns off with a linear ramp waveform, while in Sebi's, it will be an exponential waveform. Due to the nonlinear characteristics of lamps, I'm not sure which is better.
 

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