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Need help with car headlight alarm

Discussion in 'LEDs and Optoelectronics' started by, May 26, 2013.

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    May 25, 2013
    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.

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

    How can I make it smaller?

    Here is what someone suggested me;
    But for this I need circuit diagrams as I am having difficulty in connecting this circuit in multisim.

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

    Attached Files:

  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    Nov 28, 2011
    The circuit you posted is workable, but the transistor needs a protection diode between base and emitter to protect it against reverse base-emitter current, which can damage it. Something like a 1N914 connected with its anode to the base and cathode to the emitter will do this. Also, I don't recognise the part number D45H8. I would use a PNP transistor rated for at least 80V collector-emitter voltage (to deal with automotive load dump) and a few hundred milliamps, e.g. an MPSA56, MPSA92 or BF423. This circuit will subject the buzzer to a high DC voltage during load dump which could damage it.

    The suggestions you quoted are good. You can simplify the circuit by simply connecting the buzzer between the two headlights, with a diode in series with it. A 1N4004 would be suitable. You want the buzzer to sound when the headlight voltage is +12V and the accessory/engine voltage is 0V, so connect the headlight wire to the anode of the diode, connect the cathode of the diode (the end with the stripe) to the positive terminal of the buzzer, and connect the negative terminal of the buzzer to the accessory/engine bulb wire.

    This will also subject the buzzer to a high voltage during load dump. Look up load dump on Wikipedia for more information.

    May 25, 2013
    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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