Connecting car alarm to light circuitry

Discussion in 'The Projects Forum' started by Georacer, Sep 20, 2010.

  1. Georacer

    Thread Starter Moderator

    Nov 25, 2009
    A friend of mine has bought this car alarm system:

    He wants to connect the auxiliary output of the alarm to the lights, in order for them to flash I guess.

    The problem is that the AUX output is only 0.5V high (It's not written on the site, but I believe him). How can I control a 12V voltage with only 0.5 volts?

    He thought of a relay at first, but I don't think that there's a relay that switches on with only half a volt.

    My thougt is to use a transistor to activate the relay, or a power transistor to replace the relay altogether. However, I don't have any schematics in mind.

    Any thoughts or recommendations?
  2. tom66

    Senior Member

    May 9, 2009
    Modifying the lights could be dangerous. Imagine if your relay tries to turn the lights on and off while driving due to a short on your board. It could be bad.

    However, you could probably use a comparator to detect the 0.5V signal and drive a transistor/relay combination with the comparator output. A bit of a long winded way to do it, but it might work.
  3. Georacer

    Thread Starter Moderator

    Nov 25, 2009
    I don't think we run a risk of the lights turning off. The controlled relay will be connected in parallel with the light switch. If the latter is on, it stays on.

    That was a good one.
    Anyone else?
  4. Georacer

    Thread Starter Moderator

    Nov 25, 2009
    I just realised that this thread is off forum rules.

    I ask for a moderator to delete it at their own discretion.
  5. beenthere

    Retired Moderator

    Apr 20, 2004
    Given the intent of an alarm function and the headlamp relay being able to override, the flasher, it sounds like an acceptable topic.
  6. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    Reading up on the product, I don't think it is a 'relay' type output. I believe it is a PWM coded output port for one their 'patented' add on modules.