Simple car theft prevention

[zachtheterrible]

So I locked my keys in my truck the other day (first time :lol: ). Fortunately I have this little window in the back of my truck that i can open and get my keys. This led me to realize just how easy it would be to get inside of my truck.

I would simply like to put a concealed small pushbutton and circuit in my truck that I have to push before turning the key, the point of this being that the would be theif would not know about it. When I hit the pushbutton, it will turn on an SCR for a 1/2 minute or so, and will allow the truck to start. This part of the project I need no help with.

My question is where to put this circuit, as I am not familiar with the ignition system of vehicles. It obviously needs to be in a place where it would not be bypassed by hotwiring the truck.

Thanks for your help :lol:

 

[Roboticinfo]

reply

Well you would want to add a enclosure when you make that and add a lock.

All you have to do is cover it up with a small project box from crapy radioshack a easy thing to do.

 

[Pommie]

Immobiliser switches are a little bit obvious as the car won't start and so the thief tries all swithes in an attempt to find it. Hiding it in the trunk may work but thieves tend to realise a kill switch is pressent and take revenge in some way- normally vandalism. As an allternative, a switch in the fuel pump wiring can be very effective. The car will start as normal and run for about 30 meters. The thief assumes there is something wrong with the car and abandons it.

Mike.

 

[zachtheterrible]

Pommie, I very much like that idea. Could you give me some idea as to where the fuel pump wire might be? I know how a car works but I don't have the practical knowledge of where everything is and what not :lol:

Well you would want to add a enclosure when you make that and add a lock.

All you have to do is cover it up with a small project box from crapy radioshack a easy thing to do.

The switch will be nearly impossible to find because it will be one of those tiny pushbutton switches like you see on VCRs and stereos, and it will be mounted in a very unobviuos spot. The circuitry will be hidden somewhere as well.

 

[john1]

Hi,

Not all vehicles use an electric fuel pump.
Most use a mechanical type.

But the principle of quitting after a short while
could easily be arranged with a simple timer circuit.

You can purchase small timer units for electrically heated window demisters,
it might be easier to use something ready-made
which is intended to be used in motor car wiring,
because vehicle electrics can impose very harsh conditions for electronics.

Best of luck with it, John

 

[David Bridgen]

Here's a variation on the theme

https://www.davidbridgen.com/imob.htm

 

[zachtheterrible]

Hey john, i would rather make this on my own, I love designing and building circuits, and this is a perfect excuse :lol:

I'm pretty sure that my car uses an electric fuel pump. I can hear it turn on when I turn the key towards ignition but don't actually start the truck.

it might be easier to use something ready-made
which is intended to be used in motor car wiring,
because vehicle electrics can impose very harsh conditions for electronics.

What will be harsh? The only thing that I can think of is that the voltage of the battery is definetly not a stable 12v, but varies quite a bit. This could easily be compensated for in my design.

I would realy like to know where the fuel pump is usually located on a truck. I have a chevy s10 if that helps

 

[john1]

Hi Zach,

The fuel pump would usually be fairly close to the fuel tank.
It could of course be anywhere between the tank and the engine,
but typically they are not made to suck, but to pressurise.

And if there is very little fuel in the tank,
one would still want the pump to deliver,
since it may not operate without any fuel in the pump,
then often the pump is near enough level with the base of the tank,
and close by.
Therefore even with only a small amount of fuel in the tank,
hopefully enough will enter the pump to allow it to deliver.

A pump in good condition will 'draw' fuel,
but may not work if it runs dry,
however even badly worn pumps will usually operate when primed.

The rough and spiky nature of vehicle electrics can be disastrous to
home-made electronic stuff unless it is taken into account.
And the battery could be anywhere from zero to fourteen volts,
this alone can be a problem for some circuits.

When 'jump-starting' a vehicle using a battery on another vehicle
there are many stories of charging systems giving problems afterwards.

My own routine when i have to 'jump-start' is as follows, born of many
painful breakdowns, i follow it carefully, and have had no problems
using it, or after using it, with either vehicle.

* both vehicles off.
* attach leads.
* start the host vehicle (the one that will run)
* let it run for a few minutes if possible (to put some charge into the client)
* attempt to start the client vehicle.
* If possible turn both off to remove leads, otherwise turn off host.

I feel this routine has on many occasions saved me problems,
which would previously have given me at least one or two further
problems with the charging systems.

Sorry i'm not familiar with a Chevrolet S 10
maybe someone will drop in with that info ...

Best of luck with it, John

 

[john1]

A forum for the Chevrolet S-10

https://www.s10forum.com/forum/

 

[zachtheterrible]

Thanx john, i was fiddling around a bit more and realized that my manual tells me which fuse and relay does which. There is a box under the hood called fuse and relays. I found this one relay that if disconnected will let the ignition try to start the truck, but the truck will not actually start, which gives the perfect illusion of a truck that does not work very well.

This way I won't have to worry about dry running my fuel pump or anything like that, cuz im sure that i would forget to push the button a couple of times when i first install it.

I am very sure of the answer to this question, but just want to make doubly sure. It is okay to hook up a 12 volt device directly to a car battery, right (excluding the crazy voltage range)? The battery won't push too much current through it or anything like that. The 12v device only pulls as much current as it needs. Just making sure :lol:

And thanks for that forum, im sure that it will come in very handy in the future

Thank you :lol:

 

[Dialtone]

Most car alarm systems have the ability to disable 2 main items.
1. The starter curcuit
2. The ignition circuit.

Most likely your S-10 has a spot where both can be disabled.

For the starter circuit, usually what is done is to splice a relay contact into the solenoid power lead. This keeps the starter from cranking the engine when the key is turned over.
As a secondary, they also insert another relay contact set into the power feed to the ignition module. If your has one of the new style modules, it is easy to locate the power lead and do just that.

As a bonus, you can also disable the fuel pump circuit by locating the inertia switch (disables the pump in the event of a crash) and inserting relay contacts there also.

Relays for all of the above are readily available at any auto parts store and the cost is around $10 each for some heavy duty ones, you just have to know what you are looking for. Most have a Normally open, Normally closed arrngement so you can wire the coil for either on or off.

Your best bet is to go down to Autozone and purchase a Haynes Manual for your vehicle (around $20). They have a wiring schematic section that covers just about everything. As a bonus, you now have other info to help you repair your truck and save some cash to boot.
Dialtone

 

[zachtheterrible]

Hi dialtone, yes that is the relay that i found. It said something about a solenoid. I measured with my ammeter and found that the electromagnet part of the relay only has about 160mA flowing through it, so it will be easy to control it with a cheap SCR that i have.

If all goes well, this project will be complete by the end of today :lol:

 

[mstechca]

how about sticking a button right underneath the gas pedal! LOL

then make it remote!

As soon as the thief breaks in, he'll be lucky to use it as a camping device, but when he wants to start the car, he could, BUT as soon as he wants to drive it away, he'll hear some crack, which means the button is pushed on the transmitter, and you will hear a continuous tone. Meanwhile, he will break your transmitter, and yet, the tone still keeps on going!

He think he got away with everything until you come in and do some <place swear word here> to him.

and be cautious when entering David's site, because if you click on a "." link under the links at the top, you will get an image that is meant for 18+ audiences only.

 

[zevon8]

One thing you can use for a switch that is not obvious, is the cigarette lighter. The coil has a very low cold resistance, and can be used as a switch.

 

[DirtyLude]

**broken link removed**

 

[ljcox]

One thing you can use for a switch that is not obvious, is the cigarette lighter. The coil has a very low cold resistance, and can be used as a switch.

I heard of someone that used the cigarette lighter as the trigger for the immobiliser. One day the car was stolen and was found about 400 metres away. The thief must gave been a smoker.

Len
[/quote]

 

[ljcox]

it might be easier to use something ready-made
which is intended to be used in motor car wiring,
because vehicle electrics can impose very harsh conditions for electronics.

What will be harsh? The only thing that I can think of is that the voltage of the battery is definetly not a stable 12v, but varies quite a bit. This could easily be compensated for in my design.

There are often high voltage spikes (as much as 150 Volt I'm told) that will destroy any electronics unless it is protected. There was a post in this forum about 1 or 2 weeks ago discussing how to protect electronics in cars. I can't recall the title of it.

I suggest you search for words such as alternator, car, spikes, etc.

Len

 

[zachtheterrible]

I did what you said len and found that there are quite a bit of voltage spikes.

I would imagine that my supply should probably be relatively smooth, seeing as I am using a capacitor to provide the time delay, and the AC component of the signal (noise) will pass right through the capacitor. Of course the supply doesn't have to be perfect.

I was thinking of using a choke in series with the circuit to take out the massive voltage spikes, and then an capacitor from + to - to take most of the noise out. How does that sound?

I don't think I need to get into regulators and zeners for this project.

 

[pike]

Hmm I never thought of that choke idea, good one.

It sounds fine with me, if the SCR fires when it shouldn't you could just put a voltage regulator or a zener-resistor filter to further smooth it out.

BTW: how old do you have to be in the US to have a drivers license?? I have one year to wait till i'm 16.

 

[Nigel Goodwin]

Hmm I never thought of that choke idea, good one.

It sounds fine with me, if the SCR fires when it shouldn't you could just put a voltage regulator or a zener-resistor filter to further smooth it out.

I would suggest that a relay would be more suitable than an SCR, and is more in keeping with car technology (and removes any PSU noise and spike problems). For that matter, why not just have a hidden toggle switch?.

BTW: how old do you have to be in the US to have a drivers license?? I have one year to wait till i'm 16.

I think it varies somewhat from state to state?, but in the UK you have to be 17 years old to have a licence, although you can have a moped at 16 years old (maximum 50cc, maximum 30 MPH, and an engine power measured in 'kitten power' rather than 'horse power'!).