Auto sense when vehicle engine is running

Discussion in 'General Electronics Chat' started by dean williams, Jan 18, 2012.

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  1. dean williams

    Thread Starter New Member

    Jan 18, 2012

    I am looking for a circuit diagram and hope someone can help.

    I install 12 volt accessories into vehicles and use a simple device which connects to the live and earth power connections on the vehicle and when the engine is turned on, the device senses the current load change and generates a live feed on the output wire. Basically this device generates an ignition 12 volt feed by just connecting to the permanent battery connections on the vehicle. I use a lot of these devices and they cost me £10 each but i hope to be abe to make up my own to save some money.

    The other option would be to use a canbus adaptor which could sense when the revs are over 500 rpm and auto generate the ignition live. It may be worth pointing out that many late vehicles have canbus systems which makes it hard to find an ignition live on the vehicle anyway.

    I don't have much experience with designing circuits but i use to purchase electronic kits and build projects when i was at college.

    Any help or advice would be most welcome. I am happy to be referred to a paid service if anyone knows of a circuit designer who can help with this.


  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    and good bye to this thread. :(
  3. strantor

    AAC Fanatic!

    Oct 3, 2010
    What R!f@@ means to say is: Welcome to AAC! It is unfortunate, but automotive topics are banned on this site. We would be happy to help you with anything else though. This thread will be locked by a moderator soon.
  4. shortbus

    AAC Fanatic!

    Sep 30, 2009
    Why not tap into the daytime running light circuit? A relay that matches your current needs with the pull-in coil wired to the running lights would give you power when engine is running.
  5. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    Or just use the switched 12V ignition wire like everyone else in the world does.. Plus not all cars have daytime running lights.
  6. dean williams

    Thread Starter New Member

    Jan 18, 2012
    Thanks for your replies. Many new vehicles have canbus wiring so it's a pain to find the ignition wire and connect manually so most fitters just use the voltage switching adaptor when installing devices.

    Why are automotive threads not allowed?

  7. Wendy


    Mar 24, 2008
    Basically it has to do with the wide range of laws out there, and this being an international forum.

    For a while we restricted it to lights and ECU (pollution controls), but the number of odd requests meant moderators had to know about cars. Since this is an electronics forum good luck with that. The sites owner basically decided it was more hassle than it was worth. He is the one at risk is someone in this litigious USA decided to come after him.

    I can bias a transistor with the best of them, but I am not into cars. There are many forums that are however, so you have lots of choices.

    A side thought, then I will post the normal notice and close this thread. Many cars have lighter outlets whose power turns off when the car is off. This would be easy if your car has this feature. The fuse box is full of accessories that will power down as the car does.

    Now for the notice...

    The All About Circuits forum Administrative Team has elected not to host discussions of automotive electrical system modifications/enhancements due to safety concerns, the potential of legal ramifications and the possible circumvention of vehicle regulations at the state and federal level.

    This thread is against the AAC forum rules, Chapter 6, as seen here:

    Automotive modifications of any kind are strictly forbidden. Therefore, this thread will be closed.

    Please try to understand the reasons behind this action, and feel free to browse and use the forums.

    You might find answers to your questions in one of these forums:
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