Help With Basic Electronic Circuit?

[85 Cutlass Brougham]

I have an idea for using LED's for my dome light, but want to take it a step further. I plan on running about 4 or 5 LED's in series, but I want them to fade out when the power is turned off rather than immediately going off. I figure that if I use a small capacitor in series with the LEDs , it will drain out in a few seconds through the LEDs thus giving me the desired effect. However, how do I go about this and what capacitor do I need? I have a basic knowledge of Ohm's law, and series and parallel circuits, but beyond that I am lost. The dome light circuit for the whole car I believe is parallel, and I have lights in the front foot wells as well as LED map lights in the rear view mirror. Any help or ideas are welcome.

 

[TURNA]

I don't think 4 or 5 LEDs by themselves would be bright enough, unless you are using some typle of reflector like in a small flashlight.

They make LED dome lights that are pretty cheap. I would start with one of them, being that they are already mounted/wired onto a board.

There are a bunch on ebay

http://shop.ebay.com/?_from=R40&_trksid ... Categories


You may be able to adapt something like this to make it work.


http://cgi.ebay.com/5-LED-FADING-DOTS-F ... 999.c0.m14



Or I am sure if you look around someone makes a "pre made" fading setup especialy since Halloween is comming.




If you already have a "regular" fading dome light maybe this would work

http://cgi.ebay.com/ebaymotors/High-Flu ... ccessories

or this

http://cgi.ebay.com/ebaymotors/BRAND-NE ... ccessories


Here are some links on how to make a fading led from scratch


http://metku.net/index.html?path=mods/c ... /index_eng

http://metku.net/index.html?path=mods/h ... /index_eng

http://forum.allaboutcircuits.com/showthread.php?t=2389

 

[shotgun]

Just for reference, I have a large capacitor (38k mfd 16vdc) for my MSD wired in parallel.

I have a small single bulb at my kill switch.It will start to fade and go off after about 10 seconds from when the kill switch is turned off.

The bulb is the only draw with the ign switch off.

 

[85 Cutlass Brougham]

I got my LED's in, but not my project board. I am hoping to play with this when that comes in early next week. As to why I would want to do this, well I am tired of crappy parts store bulbs that only last 6 months. I also do not have the little plastic thing that the contacts attach to in order to hold the bulb, so I thought why not make something cooler than stock to replace it with? I don't have a fading light yet, but I will be trying to figure it out in the next week or so. It's one of the last details I have left to build for the interior. I am going to try different colors of lights too, in order to experiment with lighting effects. I am bored and broke, so I need to fill my time somehow!

 

[nycutlass]

Superflux LED light 3 times brighter than a regular led might be the best one to use for what you doing

 

[85 Cutlass Brougham]

I found out something new about the LED's last night: They really can't take too much power. I have a cut down USB cable that I use to power some experiments off my laptop, and decided to try it on one of the LED's. It lit for a few seconds and burned out. Now, as everyone knows, USB is a regulated 5 volt power source (red and black wires, the others are for signal). The LED supposedly likes 3.3 volts, so I figured I was safe. Nope. Burned it right out.

I also bought some 16volt capacitors and a solderless breadboard off E-Bay last night for a few bucks. This way, I can try a few different configurations before I solder it all to a PC board. Again, I really don't know what I am doing, but as with most things in life I am willing to make an attempt and hope I do not maim myself in the process. Boredom and being broke make my mind go to funny places sometimes...

 

[nycutlass]

I found out something new about the LED's last night: They really can't take too much power. I have a cut down USB cable that I use to power some experiments off my laptop, and decided to try it on one of the LED's. It lit for a few seconds and burned out. Now, as everyone knows, USB is a regulated 5 volt power source (red and black wires, the others are for signal). The LED supposedly likes 3.3 volts, so I figured I was safe. Nope. Burned it right out.

I also bought some 16volt capacitors and a solderless breadboard off E-Bay last night for a few bucks. This way, I can try a few different configurations before I solder it all to a PC board. Again, I really don't know what I am doing, but as with most things in life I am willing to make an attempt and hope I do not maim myself in the process. Boredom and being broke make my mind go to funny places sometimes...

always use a resistor with a led i think 1.5 volt resister will do the trick i would use cheap leds for now befor the good leds....im sure you figured out that there is a positive and negtive side by now.fast question are you trying to use a stock housing with leds?one thing when dealing with leds is that you have a narrow range of power to deal with.Typically current is controlled using a resistor in series with the LED, or a current regulator circuit. Supplying more current to an LED increases its intensity, and reducing the current decreases its intensity. One way of dimming an LED is to use a variable resistor or a timed ic to dynamically adjust the current getting to the LED and therefore increasing or decreasing its intensity. This works very well when just one LED bulb is involved.