Anti-hijacking car immobilizer

Discussion in 'Automotive Electronics' started by Joh Drinda, Sep 28, 2015.

  1. Joh Drinda

    Thread Starter New Member

    Jul 30, 2015
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    I found a simple enough immobilizer circuit, but I need some additional safety measures:
    The circuit shows a basic, automatic immobilizer, which stops car thieves or at least waste their time, searching for ...why the car doesn't start?
    Yet, that's not good enough, for if the thieves forced me to hand over the car's keys, I want them to get away for about 30 seconds and then the engine stops. I. o. W. I would need to add a simple delay.
    Is it possible to just use a bigger electrolytic condenser in the circuit or is it more complicated?
    I once had such a circuit, which allowed the car to start and run for about 40 seconds and then the engine stalled. The car then could be restarted and run only for about 10 seconds and the engine stalled. The 3rd time it could not be restarted anymore. That was good, because it confused the would be thief and was far enough for my safety, while I'll be busy contacting police.
    Car Immobilizer.JPG
     
  2. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Do you have a regular problem with getting car jacked? o_O
     
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  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Is your car insurer happy about modifying the car's electrics? You don't want your insurance invalidated.
     
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Just put the engine kill switch in and use a BIG red button with writing that says "DO NOT TOUCH".

    They can't resist such an obvious temptation and will disable the vehicle themselves. Direct latching through a dedicated battery connection will require the battery terminal to be disconnected to reset the relay.
     
  5. Joh Drinda

    Thread Starter New Member

    Jul 30, 2015
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    Yes, I get a Nissan seller workshop install this circuit. Most car electricians don't know much about electronics. Thus, this almost "non-electronic" circuit allows them to understand its function.
    Yet, whether I have regular problem with hijacking, insurance or the parish priest, is View attachment 92240 another question. Thanks for your concern...
    My problem is how to delay its immobilization?
    Here in St'go there are daily several cars hijacked by kids with pistols. I'm 73 young and will have to hand them the car keys.
    This morning I was thinking adding a big enough condenser (see circuit, below).
    2.jpeg
     
  6. Joh Drinda

    Thread Starter New Member

    Jul 30, 2015
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    The thing is... I want them to think the car stopped, because it has "one of many possible problems..."
    Your trap gives away that there's fool play involved and they may come back to me... to "pistolize"/ terrorize me or even kill me... so, it's better to play the stupid innocent... and helpless.
     
  7. Joh Drinda

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    Jul 30, 2015
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  8. Joh Drinda

    Thread Starter New Member

    Jul 30, 2015
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    No... it won't work, because that would keep the ignition on. I need some idea on how to momentarily fill the electrolytic condenser, which then gradually bleeds itself out and so, allowing a couple restarts.
     
  9. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Simplest way would be to use a relay that is always on and has a supercap in parallel with the coil power supply. Cutting the power by a switch would leave the capacitor powering the relay and it would soon unlatch. Only experiment would tell exactly how long it would last. Use bigger caps or smaller caps to change the time till it releases.
     
  10. DickCappels

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    Aug 21, 2008
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    cmartinez likes this.
  11. MrSoftware

    Active Member

    Oct 29, 2013
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    The biggest challenge I see, is how do you hit a timer button when someone has a gun in your face? Things probably won't go as smoothly as planned.

    I don't know what your budget or experience is, but here's an idea. For boats here they have wireless devices that you wear on your person. If anyone falls out of the boat (any device goes out of range), the engine is killed. You could do something similar, with a delay. Inside the car use something like an Arduino with a radio shield to control the kill switch. In your pocket keep a BlueTooth or ASK radio type device that just sends signals to the Arduino every few seconds. If the Arduino hasn't heard from the device in a minute or so, it could beep a few times (or flash one of the dashboard lights, etc...) then turn off the car.

    You would need an override button hidden somewhere, in case you're driving down the road and something goes wrong with the radio in your pocket. When it beeps, you have a few seconds to press the hidden override button to keep the car going another 30-60 seconds. This way you're not stranded. The bad guys won't know about the button so for them the car will just stop. This will also work if they try to jack you on the way TO your car, before you even get in it. If you're close by, the car will start for them and they can drive away.

    Now when you have a gun in your face, you have nothing to think about except how to stay alive. When you're out of range of the car, the kill timer starts automatically.

    If you want to stay with your plan; check into buying or making a delay release relay. You can do it yourself with a small relay and a very high capacity capacitor, but there must be a commercially available relay that already has this functionality. Good luck!
     
  12. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Here's one way to make a delayed switch-off device. Choice of good quality components and skill in construction are key to reliability and safety for this project.
    Immobiliser.PNG
     
  13. Joh Drinda

    Thread Starter New Member

    Jul 30, 2015
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    Thank you all for your helpful thoughts....
    I also did a lot of pondering and came up with this circuit idea. Please check it ....if it will work:
    22.JPG
    Or maybe I should replace this Cap with a timed RLY?
     
  14. Nykolas

    Member

    Aug 27, 2013
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    The way I see it:
    1) Your keys are taken away while you are outside the car
    2) Or you are inside, with the engine running.

    1) I believe you would want to start the 30 seconds after the car starts moving, sensing a signal from the ABS system or a custom built motion detector if the override is off or the hidden "OK" switch was/is not pushed.
    In 2) you most likely would be pulled out of the car. Engage a door switch to signal the "Disabler" to start at 1).

    This is a classic example for a flow chart! E

    PS: Where do you live? I don't wont to move there!
     
  15. Joh Drinda

    Thread Starter New Member

    Jul 30, 2015
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    Great idea, but how or when will the supercap be charged??
     
  16. Joh Drinda

    Thread Starter New Member

    Jul 30, 2015
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    It's far less complicated:
    The moment the driver's door is opened the the circuit turns off (i.e. is armed and the hidden button needs to be pressed or engine soon stops.)
     
  17. Joh Drinda

    Thread Starter New Member

    Jul 30, 2015
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    Simplest way would be to use a relay that is always on and has a supercap in parallel with the coil power supply.
    Yet, that requires to activate another switch, which removes the 12V positive supply so, that the supercap can bleed out.
     
  18. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    The circuit I suggested in post #12 is only practical for delays up to about 1 minute, because of capacitor leakage current. I'm thinking you would probably want a delay much longer than that; otherwise the bad guys will still be within easy walking distance of your house when the ignition cuts out!
    As for using a supercap, have you done the sums? A typical Bosch relay has a coil resistance of around 75 Ohms. If you parallel a supercap with that, a value of 1 Farad 12V (if such an animal exists) would hold 12 Coulombs when fully charged and take about 100 secs to discharge down to an assumed 3V drop-out point for the relay.
     
  19. Joh Drinda

    Thread Starter New Member

    Jul 30, 2015
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    Thank you for your helpful Info. That means, all would need is to increase the supercap. Please check my amended, latest circuit idea:
    Car-Immobi.JPG
     
  20. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Bearing in mind that a car's '12V' rail might be as high as 14V or so (even higher with load-dump spikes), have you identified a source of a suitable supercap? Have you considered how you will safely charge it?
     
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