Simple car theft prevention

[zachtheterrible]

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.

16 here as well. I think that the age varies from state to state though.

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?.

1. A toggle switch would be a bit of a pain because I would have to remember to turn it off each time I get out of the car. With my idea all I would have to do would be to press the tiny pushbutton switch and I would be good to go.
Why the SCR instead of a relay? I dunno, I guess I just like the idea of an SCR better 8)

EDIT: One question that I forgot to ask: Do I need chokes on both sides? + and - ??

 

[Nigel Goodwin]

EDIT: One question that I forgot to ask: Do I need chokes on both sides? + and - ??

No, just the positive, the negative is connected to chassis.

Assuming you need a choke at all?.

Bear in mind that this needs to be a very reliable and trustworthy device!, you don't want your engine dying on you at a vital moment!.

 

[jkmadsci]

I used to install car alarms, and its best to cut the starter wire because at some time the car will have engine problems. This way the car starts or dosent start and the alarm will never cause stalls or erratic operation.

 

[ljcox]

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.

The choke idea sounds good, but I've had no experience in this field.

However, the other post that I referred to used a series resistor and a shunt 16 Volt Zener. This post was replied to by someone with automotive knowledge. It may be worth your while to send him a PM.

Len

 

[zachtheterrible]

Bear in mind that this needs to be a very reliable and trustworthy device!, you don't want your engine dying on you at a vital moment!.

A very good point Nigel. That is why I am going to install a regular toggle switch on my circuit that will bypass the whole thing, just in case it somehow gets fried.

However, the other post that I referred to used a series resistor and a shunt 16 Volt Zener. This post was replied to by someone with automotive knowledge. It may be worth your while to send him a PM.

I will do that. EDIT: ljcox, I'm having some trouble tracking down the person who you said used a 16v zener. Do you know who it was?

 

[ljcox]

I think it may have been screech.

It was about 2 weeks ago. I'm having computer problems (virus protection suspect) so don't have the time at the moment to search myself.

Len

 

[zachtheterrible]

I found the person you were talking about, it was instruite. I PM'd him with some questions.

Instruite, here is the circuit I was talking about

 

[john1]

Hi Zach,

I should mention that with SCRs,
although the gate is the most usual method of turning it on,
they can also be turned on by voltage pulses across them.

There are comraratively few circuits that use that as a method
of turning them on, but it is an established method.

Cheers, John

 

[zachtheterrible]

I should probably ask this question here as well as asking instruite.

You can see on my schematic that there is a ground on either side of the SCR (one through the relay). The reason for this is that on both sides of the relay, I measure ground with my voltmeter. Will this not allow my SCR to work?

btw, thanx for the tip john :lol:

 

[john1]

i can see you've draw a little arrow.
with no 'legend' or letter by it....

ah i see now you mean ground or chassis,

briefly, yes you are correct, you will need the supply to it,
probably to the topmost of your little arrows.

John

 

[john1]

although i really don't think an electronic arrangement would be the best
solution.

Best of luck with it, John

 

[zachtheterrible]

Good news everyone (if anybody watches futurama you'll get that) :lol:

I have been informed that I don't even need to install a kill switch because my truck is already equipped with one sort of! My truck has a system that will disable the starter UNLESS the correct key is inserted into my truck. This means hotwiring is out of the question, and slamming a screwdriver and breaking the tumblers is also out of the question. Cool huh? 8)

 

[Oznog]

Mechanical pumps are not used as far as I know for any fuel injection systems. Unlike carbs with fuel bowls, fuel injection has to have pressure or it will not fire.

You have to look up the wiring for that vehicle to locate the fuel pump wiring. You will also want to find a convenient yet concealable point to splice it in. If you want to be really clever, add a dummy switch in a more obvious place or even use a couple of double pole switches that both have to be in the right position to start it.

Fuel pump shutoff switches have a LONG history. They are effective because they're done in such a nonstandard way it may be difficult to find. Unfortunately this means a system like that stock trunk switch you describe may be easy to bypass. For carb'ed vehicles it was neat because the guy goes to all the trouble to start it and once he's driven it a block he'd be too conspicuous trying to mess with getting it to work again (in most areas or times of day at least). Note that the sudden loss of power may be dangerous to you if you forget to turn the switch on, it will make power steering and power brakes VERY hard to operate. Doing this on an EFI may be less effective because it won't start in the first place, leaving the thief in a comfortable position to work on it and if he has any experience at all wiring past that switch is extremely simple compared with jacking the steering column.

I think the liability of having their hardware malfunction, potentially crashing the vehicle, is the main reason security systems don't do this so often.

If you were going to do something tricky with a timer for a delayed action on an EFI system, it could be effective and do something neat like give an audible siren a few sec before turning off the pump so you would figure out what was happening before getting screwed with losing power on the road. In this case, you need a switching element like a relay or a MOSFET.

I would recommend against an SCR. Any glitch in the current could shut it off and you might be on the highway at the time. Just a mechanical switch capable of holding the constant current of the pump will do the job.

 

[David Bridgen]

I found the person you were talking about, it was instruite. I PM'd him with some questions.
Instruite, here is the circuit I was talking about

Zach, the transistor should be an npn one.

Whatever the scr is switching should be connected between its anode and the 12V supply.

 

[kurnia.2]

What year of Chevy S10 do you have?
I might have an aftermarket wiring diagram.

I have some collections of US-version vehicle wiring diagrams (from early 80s to 96). If anyone happens to need one for whatever circuitry, just let me know.

 

[zachtheterrible]

I have a '99.

A wiring diagram would be sweet!

 

[kurnia.2]

I'll PM you. Due to copyright issue, it may not be suitable to put it on the forum.

I have the 98 Chevy S10 which, I think, will most likely be similar.

 

[kurnia.2]

Sorry, there is no options for attachment on PM.

Is it OK if I just put it on the forum?

 

[zachtheterrible]

You could email it to me: zachtheterrible@hotmail.com

Thanks so very much, this will be extremely helpful!

 

[kurnia.2]

Email sent!