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Using LED's in cars....Dropping Voltage

Discussion in 'Electronic Basics' started by King George, Mar 5, 2004.

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  1. King George

    King George Guest

    Goodday!

    I wanted to wire a warning light up in my dash board that tells me
    when my stereo is on or off. I know I need to reduce the car's
    voltage down to a lower voltage....Is it possible to just use a
    resistor to do this. Or do I have to go through the routine of
    stepping down transistors....and going from say 18 volts, to 15 to 12
    to 9 to 6 and then use a resistor?? Is there a faster and easier way
    to get a 5 volt power source off of a 12v line?? Thank you for any
    responses!

    King George
     
  2. Rutger6559

    Rutger6559 Guest

    I'd buy a 3 pin 5V regulator at Radio Shack, and put a resistor in
    series with the LED.

    12V car goes to 12V input on regulator
    gnd car goes to regulator gnd
    5V output pin of regulator goes to + pin of LED
    - pin of LED goes to resistor
    other end of resistor goes to car gnd.

    Someone may be able to provide an approx resistor value to use.

    Just my approach.

    Best of Luck!!

    Rick
     
  3. Rutger6559

    Rutger6559 Guest

    Forget the above. This'll just keep a LED on draining your battery!
    LOL! Sorry, I'm tired.
    This is the one line that is wrong. You need to replace the 12V car
    wire with a wire on the other side of your radio's power on switch.
    You'll need to look at the radio's wiring to find an appropriate one.
    Probably the power antenna remote connector.

    Again, just my $0.02.

    Sorry about the first post I made!

    Rick
     
  4. Why ? I mean isn't it a bit obvious if the stereo is ON or OFF, i.e. when
    it's ON, it's usually all lit up and making sounds.
    Yeh you can just use a resistor to drop the voltage to power an LED.
    If the car supply is going to 18V, that too high, this is usually caused
    by a faulty alternator/regulator.
    If you want a regulated 5V supply, a 7805 type regulator would do the job
    perfectly.
     
  5. King George

    King George Guest

    I wanted to wire a warning light up in my dash board that tells meI want a light like this because when I turn off my cd player i
    sometimes forget to turn off the stereo...which effctively drains the
    battery of my car. Yes, I know the simple solution would be to use
    the remote wire on my head unit, but i like have seperate control over
    my four amps (i dont always need them all on) so I have a switch
    panel. I want to add LED's so that I can see if, after I have turned
    my Head unit on, that I have also remembered to turn my stereo off.
    Basically, I am making lighted toggle switches, just in two pieces.
    and buring everything out? or can I use a resistor to limit the 14
    volts or so enough to safely operate the LED?
    regulated 5 volts, I would have to use more than just a 7805. The guy
    at active electronics said I would need to step the voltage down in
    three volts intervals to make sure that I am not going to burn out the
    7805. If thta is all it is, I have a whole bunch of those at home
    anyways....
     
  6. Don Bruder

    Don Bruder Guest

    regulated 5 volts, I would have to use more than just a 7805. The guy
    at active electronics said I would need to step the voltage down in
    three volts intervals to make sure that I am not going to burn out the
    7805. If thta is all it is, I have a whole bunch of those at home
    anyways....[/QUOTE]

    "The guy" doesn't know his ass from a hole in the ground. You were told
    wrong.
     
  7. bj

    bj Guest

    hi
    I hope this isn't going to annoy your neighbours too much, maybe
    your battery should go dead now and again ----however previous
    advice was crap. You can work an LED from any voltage you
    want as long as you limit the current or drop the excess voltage
    (however you want to look at it)
    For a 14 volt supply you're looking for about about 1000 ohms
    resistance in series.You can play about with that value for
    brightness

    bj
     
  8. Rutger6559

    Rutger6559 Guest

    I still say to use the 5V regulator. That way, if you ever want to
    add any other digital circuits to your car you've got a nice 5V line
    for the TTL logic.

    Check out:

    http://electronics.howstuffworks.com/digital-electronics4.htm

    for a nice description.

    HTH!

    Rick
     
  9. Gerry Cohn

    Gerry Cohn Guest

    Hi,

    Forget the 7805. Use 1K or 1K2 resistor and be done with it.
    If you ever want to add any other 'logic' into you car, you will need a much
    better quality power supply than just a 7805 anayway.
    A simple 7805 solution does nothing for many of the voltage spikes that you
    can encounter in an automitive electrical system. These
    would create absolute havoc for any 'logic' that may be powered in this way.

    HTH

    Gerry
     
  10. Rutger6559

    Rutger6559 Guest

    Hmm... Interesting point.

    Thanks!

    Rick
     
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