car LED power on after engine off

[mixtape]

Hello, I am looking to build a circuit for my car however I cannot figure it out on my own. I can describe what I want it to do any maybe someone can give me alittle info on it. From what I remember back in highschool electronics, this shouldn’t be too difficult. Thank you for your time.

Alright. I would like little blue LEDS that I place around or under the car to turn on when I shut off the engine and stay on for only 5 minutes. Ive seen it don’t before and I believe it uses a “relay” or something , yet I cannot remember how to do it. Somehow the circuit knows when the car’s accessories (I guess) are trigged off and on. I also need to know as much as possible for the job. I would like to use maybe 20 LED (few or less) and have them power off the car battery for the 5 minutes after I turn off the engine.

Thank you again for any help

-Paul

 

[dknguyen]

Is it possible to just use a large bank of capacitors to keep the LEDs on? When the car is on, the capacitors will slowly charge up (and the LEDs brightness will slowly increase). When the car turns off, the capacitors (not the car battery) power the LEDs until they become empty.

Your LEDs are probably much larger than what I am imagining, so a capacitor bank for 5 minutes of power is probably not practical.

You could use a relay or transistor with timing circuitry like a 555 timer. I do not know anything about cars, but I suspect you can tap into the power wire that is controlled by turning the key partway (to activate the car's electrical system).

 

[mixtape]

Is it possible to just use a large bank of capacitors to keep the LEDs on? When the car is on, the capacitors will slowly charge up (and the LEDs brightness will slowly increase). When the car turns off, the capacitors (not the car battery) power the LEDs until they become empty.

Your LEDs are probably much larger than what I am imagining, so a capacitor bank for 5 minutes of power is probably not practical.

You could use a relay or transistor with timing circuitry like a 555 timer. I do not know anything about cars, but I suspect you can tap into the power wire that is controlled by turning the key partway (to activate the car's electrical system).

Thank you, however if i use a capacitor it will charge/power on the LEDs while the car is on. In my state it is currently illegal to have blue lights/LEds on while the car driven. I want the LEds instantly on as soon as the key is turned off. I can get an accessory wire (yellow) and a power wire (red) also a ground (black) thru the stereo connections under my dash. How can i use a 555 timer and a relay to connect to the 3 connections.

thnk u

 

[mixtape]

i will probably have 2 of the following rods

**broken link removed**
24 INCH BLUE LED RODS w/21 LEDs
LEDS BLUE - 24" CAR LIGHT ROD -
Led technology w/21 individual LEDs
Works with any 12 volt power source.
Less then 1/2 amp draw
LEDs are clear when off
{2 variables - solid and chase - swichable}
Transformer built in

 

[justDIY]

a time delay circuit should be all you need ... check out the internet and google for lots of plans ... you'll use a relay, wired to your ignition terminal (off the keyswitch) ... once the terminal is turned off (key = off), the time delay circuit is energized and begins its countdown, turning the connected leds off after the time expires.

 

[mixtape]

thank you, i'll give it a shot