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Car Headlight Alarm

  1. May 25, 2013 #1
    Hello Guyz!

    First of all I am new here and I found this section to be appropriated for submitting my question.

    Well, I was Investigating on Car headlight Alarm and how it should sound a buzzer when the headlights are on?

    I have attached the circuit diagram aswell you might wanna have a look on it.

    I found this while i was searching for ideas. Now all I need is lots of suggestion from you guyz regarding to how it can be improved. such as; a pnp transistor has been used can it be improved with a comparator or with any other components?

    Are there any other components of this circuit which can be improved?

    How can I make it smaller? I have heard about the surface mount techniques as well as Integrated circuits which can make a circuit smaller But I don't have a clue how they work in reality?.

    So, I would really appreciate if you guyz could give me a helping hand please?

    Attached Files:

  2. jcsd
  3. May 25, 2013 #2


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    Do you want the alarm to sound whenever the headlights are on or just when they're on when the engine is not running? (That's the normal thing in cars, so you don't wander off in the day, leaving the lights on and flatten the battery).
  4. May 26, 2013 #3
    I want buzzer to sound when the headlights are on and engine is off. And when the engine and headlights both are on; nothing should happen.
  5. May 26, 2013 #4


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    So that circuit is about as simple as you can make it and should work well. Of course, if the alarm were to work the 'other way round' you could connect the buzzer straight from the ignition switch to the headlamp line - because the headlamp resistance would be very low and would allow the buzzer to operate without any fancy switching transistor. A capacitor (0.1uF) between base and emitter would ensure that interference spikes don't randomly blip the buzzer - motor cars have quite a high level of EMI.
    But you definitely couldn't rely on the ignition circuit being low enough resistance for the buzzer to work and you wouldn't want the ignition circuit supplied all the while - via the buzzer.
    Btw, why would you want this to be any smaller? A transistor and resistor don't take up much room. Surface mount is only necessary when you have loads of components to find room for. The three components can easily be mounted together and you could even wrap them in tape. The transistor and resistor would take up no more room than a wire junction.
  6. May 26, 2013 #5
    Can I have a circuit diagram please? As I am finding it very hard to draw on multisim.
  7. May 26, 2013 #6
    someone suggested me these ideas;
    But for this I need circuit diagrams as I am having difficulty in connecting this circuit in multisim.

    In this one i am lost in which rectifier to go for as there are many but I need one which can work on 12v & I need a circuit diagram for this one (please also mention which rectifier should i use as there are many rectifiers in multisim and most o them works with high voltages).

    I would really appreciate if you guyz could give me a helping hand please?
  8. May 26, 2013 #7


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    I assumed that, as you had already posted a suitable diagram, you wouldn't need one and understood what was going on. If you substitute the ignition switch for the second lamp switch, the circuit will work fine. When the ignition switch is off and the headlamp switch is on, the transistor is turned on and powers the buzzer. Under any other conditions, the transistor is off and will not power the buzzer. You can draw your diagram on a piece of paper. Learning CAD is another issue.

    I would not bother with a simulation for something as simple as this diagram. You probably need the construction practice! :smile:
    Simulation packages are all very well but they can make people sloppy because they rely on getting an answer rather than working out, for themselves, what the answer should be.

    Almost any (ordinary) rectifier you can lay your hands on will do the job of feeding your buzzer with 12V.
  9. May 26, 2013 #8
    Agreeing with Sophie - if you build it you will learn....I see no value in doing this in multisim - unless you are really concerned with learning about multisim.
  10. May 27, 2013 #9
    I have finally managed to get it work and it’s all because of your help and support. I really appreciate your hard work and hope you will continue to help guyz like me in the future too.
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