FireDemonSiC

While standing here at work bored out of my mind on the wednesday morning sales floor, a crazy idea popped into my head for a capacitive discharge security system.

There have been numerous little bastards around my neighborhood that are known for going around all the cars at night at trying the door handles to see if the car is unlocked.

The idea I got was to put two metal contacts on the underside of each door handle very close together, but not touching and then shim the door handle away from the body. One + and one ground, so if anyone was to try and open the door while the system was armed, they'd get a decent wake up call.

Before anyone chimes in with any legal mumbo jumbo, I know all the risks of capacitive discharge, and would prefer to to incur the same, "DUDE YOUR GONNA KILL SOMEONE", responses I got when I tried to cook up a system like this to rig to my home PC's power button (Purely for the excitement of putting the project together in that application).

The only real problem I see with this idea is that capactiors bleed off rather quickly, and I'm afraid the continuous amounts of current needed to keep them charged would drain the battery. Obviously my knowledge is limited in this area. Anyone care to chime in and help?

camaronewbie

LOL SHOCKING!!!

I remember in the old days of points rather than HEI, we'd remove the little capacitor from the distributor system, rubberband the pigtail to the casing, and toss it at someone - they got a wake-up call when they caught it - that little sucker held like 50,000 volts or something crazy.

Maybe simply getting one of these old distributor capacitors and "mounting" it up under the door handle would do the trick - it would be small enough to fit - just don't let it touch the metal of the car. I'd think one time would be enough to ward off further attempts LOL.

As far as killing anyone, as I understand it - it's not the volts, it's the amps - and it takes a large unit to carry enough amps - so unless you were rigging something large somewhere hidden in the car, I wouldn't think you'd hurt anyone.

FireDemonSiC

You are correct about the amps. The only risk there is even as little as 100mA can stop a heart. But that's on a perfect day when the sun is shining and the person doesn't have any health complications. Even so, once you factor in things like Discharge rate of the capacitor and skin resistance, just because a capacitor is capable of holding say 200mA, doesn't mean that someone is going to recieve the full 200mA. I used to remember all the formulas and the resistance ohm's of human skin, but It's been a few years since I got into this stuff.

I was actually thinking of going to the photolab where I work and asking them for a few disposable cameras to rig the setup up with. Each capacitor in there is like 300VDC. I was thinking of doing two in parallel to each handle. I've been hit with 250VDC from a dispoasable camera circuit before. And I got hit in the worst way: One hand on the + the other hand touching the ground so the voltage actually passed through my body. Let's just say you won't be needing any coffee after that.

But again, the only thing that concerns me is the rate of discharge of the capacitors. Depending on what components you use, they like to bleed off slowly and I'm afraid the continuous charging might drain the battery over time. That's why I'm posting here hopefully maybe some of the audio enthusiasts can chime in and help.

Something else I'd also need would be a discharge circuit. Something that would short the capacitors to themselves with a fairly beefy resistor (again, can't remember what value I'm supposed to use) to immdiately discharge the capacitors once the system has been disarmed. I can conjure up all this stuff on my own, I'm just looking for an opinion of a reliable capacitor to use that can HOLD a charge for a long time.

The actual components to the system will be held inside the door. Only the actual contacts to pass on the electricity will be underneath the handle.

mos68x

You can build a small charging that won't take much power so that you could keep them charged. If it were me I'd do alternating contacts that you can't feel so that there is no way to miss them, but to also make a small button that you can press to disable the system so you can open the door.

FireDemonSiC

I got another simplified idea.

Instead of going to all the trouble of using capacitors and whatnot, what if I were buy two cheap autozone ignition coils, one for each door. Them with a switch of course, wire them to be constantly hooked to the battery. This way someone will get hit with 30,000volts and the circuit would only be completed when someone grabs the door handle.

Drawbacks?

DrummerDad

Why not use a pocket tazer? Already been engineered to be "heart safe", and it would only take 2 AA batteries.

Omega

iTrader: (1)

Im pretty sure there are some companies in Africa that do this kind of security system. There was also a spring loaded anckle breaker if I recall correctly. Abductions are rampant out there.

//<86TA>\\

iTrader: (14)

its a great way to get sued.

wouldnt smearing poo under the door latch be safer and easier

Rolling Thunder

Well the problem is this the way ignition coils work is there "charged" when current passes through the primary coil however when the power is removed it the collapsing magnetic field induces a large voltage in the secondary coil. So if you wanted to use a coil you would need to pulse it with a square wave. Capacitors wont work either im afraid although the shouldnt have much leakage at all if good if you charge a capacitor to 12 V all it will be able to do is belt out a 12V and im sure youve touched battery terminals befor and probably noticed not much of anything happened. A 300V capacitor means it has a maximum of 300V but will only be charged to whatever voltage is applied to it. I wouldnt be too worried about killing anyone as the human body has a fairly high resistance (if you have an ohm meter try grabbing each lead in your hands). Also that 1 tenth of an amp is the minimum current required to kill you if the current passed across your heart. Considering the plates would be side by side current would travel through your hand not across your heart. Just for example Ill crunch a few numbers to demonstrate my point. I happen to have an ohm meter handy and when i measure the resistance across my hand it comes out to be 1.5 mega ohms (1,500,000 ohms). Using ohms law to calculate the current that would result from getting hit with 12V (12V/1.5M ohms) the resulting current is 8 micro amps (.000008 A). This is roughly 1000 times less current than the minimum current required to stop someones heart and is not traveling across the heart anyways. Between the fact current has to travel in a path through something vital to do damage and be of sufficient quantity for a long enough duration I wouldnt be to worried as long as you kept things within reason and for a short duration. The problem is you have to step up the voltage substantially from your cars 12V and the most readily ways of doing that would require some kind of electrical circuit that would drain your battery. Unless you also rigged up a switch on your door handle it may run the battery down to the point it wont start if left on all night. I think your original plans of borrowing the guts from a disposable camera would work best (need more than just the capacitors). I wouldn't be worried about the drain of the capacitors themselves as theoretically the should allow no current to flow through them at all realistically there is some but it should be extremely extremely small. What draws the power is the circuitry to create these large voltages across the capacitors.

TheLegedaryErin

Just thinking like a low life who walks around testing door handles there would probaly be a fine line between yours being the car i want to avoid and the car that my enemy owns. I do like the idea and i have friends who have built stun guns and the such with parts from the flash off a disposable camara.

383RAT

Well just opinion but a shock would just probably make the person angry which would probably lead them to kicking your door, breaking your wind shield, or something along those lines. Just a passing thought I had while reading all this.

InfernalVortex

iTrader: (4)

Yeah I think if they managed to notice that you intentionally did it, they'd probably trash your car pretty bad at some point.

ownor

iTrader: (5)

+1, i'd be more worried about my car after shocking those little bastards. if they just try your door handle and it's locked, so what?
although i gotta say, this thread is really interesting and i really come to like the idea in itself

skinny z

Just hide in the bushes for a few nights and ambush the little bastards. You don't have to touch them. Just scare the crap out of them. They'll never know if you're hiding there the next time they come around.

FireDemonSiC

I too thought about the car being vandalized after they got a decent jolt. Only drawback I see with this idea, but none-the-less it will be a fun project.

el_muerte

I've often dreamt of such a system, especially after having vehicles broken into multiple times. I've concluded, however, that a better idea would be some sort of silent alarm that sends you an alert (maybe on your cell phone?) so you can come outside with a 2x4 or the Louisville Slugger.

Scorpner

iTrader: (4)

They make pagers for alarm systems. Just don't hook up the audible part and you're set. Probably still isn't worth going out there though.

Dr.NickRiviera

Depends on where you live. I'd run out of the house with my Mossberg in hand and i gaurantee they wouldn't screw with my car again.

z28 TPI

What about a transformer? I used to work in an arcade for like 8 years we had isolation transformers for the monitors. Anyways I took a 12vdc battery for a flash light hooked it up to the transformer, I did more than wake a few people up... Food for thought found a small transformer step up kind, hooked it up to a 9v battery, and then I hollowed out a book, connected the trans to the outer covers via aluminum foil, woke up my friends with that one. Enjoy.

FYRCHKN

Just cut the female end off of an extension cord, tie the hot leg to a clamp and the ground to a metal bar that you can stick into the dirt. Put the clamp on metal under the car, shove the metal bar into the dirt and plug in the cord. They'll only touch it once.

RSFreak

I used to think so too. Slept with my .45 close at hand. Never even heard the bastard who broke the window of my '85 Z and stole my stereo. Lucky for the thief I'm a heavy sleeper!

87WS6

iTrader: (1)

I had a similar thought. Take a taser apart and use it's probes to create contact strips on the under side of the door handle. Rig the switch to discharge the taser to the handle itself. When lifted the taser kicks on and anyone touching the door handle will only do it once. Tasers do not electrocute in the presense of water, are somewhat energy efficient and safe for use against most people. Obviously anyone with a heart condition could still be killed by one, but then again I doubt many people with heart conditions and pace makers go around trying to steel cars.

87WS6

iTrader: (1)

I keep a .45ACP caliber handgun on the nightstand. Unfortunately I'd never hear anything happening in the driveway unless they set off an alarm or something. Fortunately my thirdgens are garaged. My other vehicles aren't though.

RedRokkit

Best Idea EVER........

matthufham

iTrader: (5)

i have a radar sensor on mine, gives warning beeps when people walk by or peek in. i say shave your handles. that's my next plan.

mos68x

I've been thinking of shaving my handles myself, only one way in the car unless they want to break windows.

87v6Bird

iTrader: (1)

Although unfortunately I don't know how he did it, my father laughs about an uncle of mine who had his ignition coil wired into the car frame somehow. Whenever he was on the town square he would pretend to be asleep waiting on his wife and as people bumped into his car he'd get a good laugh watching their reaction to the shock they got. So it has been done before and definitely encourages you to not touch the car again.

Primetime91

iTrader: (15)

ALSO: Keeps the neighbors cat from leaving muddy pawprints all over your car lol

Firebat

iTrader: (7)

I wouldn't do this. What's the lowlife going to do after he gets shocked? Good chance he's going to get angry and kick your door panel in or throw a brick through the side window. One thing to have a lowlife, another thing to have a pissed off lowlife.

z28z34man

sitt in the bushes with a 12 gauge loaded with less than lethal first round ( possibility a flash bang but a flame thrower round would be cool ) an when they come and touch the door let off a shell i don't think they will want to steel in that neighborhood again