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how to install red blinking LED in a car

Discussion in 'Automotive Electronics' started by peppers, Apr 17, 2009.

  1. peppers

    peppers New Member

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    i am trying to install a red blinking LED in my car. I want it to blink when the car is off and turn off when the car is running. I bought a 5 volt DC 20mA 5mm blinking LED. someone also told me to buy a 1/4 watt 1k ohm 5% tolerance resistor. will this blow of i isntall it in the car that operates at 12v? what do i need to do so it dosent? i also noticed that when i hooked up the LED to a 9volt battery it blinks faster than i would like. how do i slow down the rate at which it blinks? i am new to this knd of stuff so please explain clearly. i am good at working and installing electronics that are already built such as car stereos and speakers, but i have never actually built anything out of scratch that is electric.
     
    Last edited: Apr 17, 2009
  2. miro_gt

    miro_gt New Member

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    dummy alarm system .. huh :)

    you'll need to connect that resistor in series with the LED and there you go, as simple as that.

    note however that with 1Kohm you'll be on the upper side of the usually used current for LEDs, so if it's too bright then try 2.2Khom resistor.

    you wont be able to regulate the blinking rate as you want, so go with the bright level that you like and the coresponding blinking rate for it.
     
  3. peppers

    peppers New Member

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    so the resistor will only regulate the brightness not the timing? the LED is 5 volts and the car is 12 volts. is that a problem? if not, explain. i dont want to burn down my car
     
  4. dave

    Dave New Member

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  5. miro_gt

    miro_gt New Member

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    the resistor will regulate both, but you cant regulate those separatelly.

    LEDs are not rated by voltage, but by current. A typical LED will produce bright light at about 10mA and therefor you put resistor as big as needed for the power supply that you have. In your case say 12V so with 1Khom resistor it sill supply 12mA current, which is fine for LED. However, the voltage in a car can be up to 14.5Volts due to the alternator that charges the battery, so you may end up with even more current going through the LED. That's why I said to try little bigger resistor.
     
  6. peppers

    peppers New Member

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    where can i get a holder for a 5 mm led that i can drill into my dashboard. i found a metal one at radio shack but i dont like it. where else can i get one?

    do u also know where i could get a 12v blinking led that way i would not have to mess with resistors or any of that stuff?
     
    Last edited: Apr 17, 2009
  7. miro_gt

    miro_gt New Member

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    you keep thinking about the voltage of the LED and you shouldn't. I just explained why. This is not a light bulb, it's a diod that happen to emit light.

    is putting one resistor that big of a deal ?

    about the holder - just drill a hole and put the LED from inside out, and ducktape it at the back if you wish, lol.
     
  8. SPDCHK

    SPDCHK Member

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    Did you buy a "Flashing LED" or a normal LED?

    You do get LED's shat flashes, i.s.o. just shining normally like the other ones does. To test the LED, simply put the 1K (or 2k2) resistor in series with one of the LED leads, and connect to the car battery. If it does not shine, turn the polarity around.

    If the LED shines continuously, you'll need to make the LED flash. There are many ways to do that. Simple 555 IC (and you can Google for that) or try this simple single transistor LED flasher
     
  9. Mikebits

    Mikebits Well-Known Member

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    He already stated that he purchased a flashing LED.
     
  10. SPDCHK

    SPDCHK Member

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    :D:D I thought he was swearing :D:D
     
  11. Mikebits

    Mikebits Well-Known Member

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    That is funny...lol :)
     
  12. Diver300

    Diver300 Well-Known Member

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    A flashing LED is an LED with a flashing circuit and current limiter built in. You shouldn't run it at any voltage other than its rated voltage and you can't change its frequency.

    A resistor in series won't drop the voltage when it turns off, so you will end up feeding it 12 V so it may burn out.

    The simplest circuit is a series resistor of 330 Ω and a 5.1 V zenner in parallel with the flashing LED, after the resistor.

    It is not very efficient as it will take about 20 mA whether the led is on or off.
     
  13. colin55

    colin55 Well-Known Member

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    5v flashing LEDs work from 3v to 12v.
    They already have a built in resistor to enable them to work on 5v, so if you want to limit the current when using 12v, just add a 330R resistor.
     
    Last edited: Apr 18, 2009
  14. peppers

    peppers New Member

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    is it ok to tap into the power for my stereo in order to power the led? reason being that is the only place where i know what wire is what. i would not know where else to tap in to.
     
  15. Mike_2545

    Mike_2545 Super Moderator

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    It would be best to fuse the tap that you make into your car radio.
     
  16. peppers

    peppers New Member

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    how do i determine what kind and size of fuse to use? i found a 12volt blinking LED, and how do i put it on? on the + or the - end of the LED?
     
    Last edited: Apr 18, 2009
  17. Mike_2545

    Mike_2545 Super Moderator

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    + or - does not matter, I would make the fuse around 500ma and put it as close to the tap as you physically can.
     
  18. peppers

    peppers New Member

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    do they sell those at radio shack?
     
  19. Mike_2545

    Mike_2545 Super Moderator

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    Last edited: Apr 18, 2009
  20. colin55

    colin55 Well-Known Member

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    The short lead of the flashing LED (the lead that has a small flat on the side of the LED) is the cathode and it goes to 0v (chassis). Add a 330R to the long lead and connect the other end of the 330R to any 12v point on the car that is active when the ignition is off.
    You don't need a fuse.
     
    Last edited: Apr 18, 2009
  21. forumlicker007

    forumlicker007 New Member

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    The goal is to energize a relay when the when ignition is ON. Use music system power to energize the relay and it'll switch off the LED. Anyway you've to find one always active 12V point directly from the battery to make it work. Connect LED through NC contact of relay.
     

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