I once saw this device called a tap lock for cars. It was a type of microphone/vibration sw (I think) that sticks to the inside of your windscreen. It sits there waiting for you to tap out the correct code and would then unlock your car doors if the code was correct. Useful if you locked your keys in. I think it's useful if you want to get rid of the car key completely, and use it to unlock doors as well as fire up the ignition etc.

http://www.12voltshop.com/product.as...&parentcatid=0

Anyway I don’t want to buy 1 - And the microphone stuck to the windscreen seems a bit crude.

Would it be possible to build something similar using a touch switch (The keyhole on the drivers side is metal) and getting a PIC to handle the security code bit.

I guess what I'm asking is it possible to turn the key hole on my car into a reliable touch switch so I can drum a code into it to unlock the doors. (tap 3times - pause - tap 2times - pause - tap 4times -- unlock - anything else trips alarm/disables tap lock)

(Every time I look up touch switches I see the same stupid design with two piece of metal and you use your finger to short the two. I'm after a touch switch that works with just 1 piece of metal. I have a touch lamp like that. Even my living room dimmer is like that - so I know it possible.)

Thanks.

 

I doubt that your keyswitch is insulated from the body. That would seem to be a major problem.

__________________
Ron (aka Rube)

 

Thanks for the reply.

Well I'll test that tomorrow. (fingers crossed)

 

Hows about a capacitive touch switch? Mount in discretely behind glass somewhere... or behind some plastic trim

or, take what appears to be a simple blinking alarm light, but actually it's a bi directional LED... always watching for the correct morse-code like sequence to be flashed from say, a photon key chain light.

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Ok - you were right. It's not isolated from the rest of the car body. (There is continuity from it to the car cigarette lighter -ve)

So what does that mean? I can't turn it into a touch switch?

 

Interesting idea.

Well that's missing the point - Im trying to get rid of all keys and fobs. I already have a car alarm with engine start on a key fob. I like the idea of not carrying any key making it impossible to lose or misplace (which is a daily occurrence).

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What about insulating the key hole from the rest of the car? Perhaps paint the barrel? Or I can just take the key barrel off completely and replace it with a circular piece of metal - yes I think I will do that. So how do I make a touch switch from say a coin size piece of metal?

 

Reliability is obviously a major concern, from that point of view I wouldn't consider a touch switch, as they have never been at all reliable!.

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Oh dear. I did not want it to be obvious that there was any kind of switch there - that's why I was keen on the touch switch idea.

I could try to install some kind of microswitch to the door handle/rod inside, but might look like a right fool flapping the code into the door handle - might even be arrested.

What do you mean by unreliable? If I bash on it 3 times it might only register 2 times?

 

Does the switch have to work when the car is wet, in the pouring rain?
Or when it is covered in snow?
Or a layer of ice?

JimB

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Experience is directly proportional to the value of the equipment ruined.

 

I guess so - I take it touch switches are not good under those conditions?

Okay - lets scrap the idea of the touch switch (still interested in how to build one though).

Perhaps I should just copy the idea of the real tap switch that uses some kind of vibration switch but install it hidden on the driver's window inside the panelling.

What kind of switch could I use to pick up the vibrations of someone tapping on a window?
(Or might just buy the real thing as it seems to be on sale - but that's no fun)

 

still sounds a pretty risky endeavor to me, relying solely on a non mechanical switch

I dunno about your location, as it's not filled in, but both the cars I own ('94 and '06) require a key to unlock the transmission shift lever - how do you propose to get around that with a switch?

to take things a bit more on the wild side, you can implant yourself with an rfid tag, and put a reader inside the driver door handle area

__________________
If you don't have a planet, what good are gold bars?

want to contact me directly? gmail gordonthree
check out my project website: http://projects.dimension-x.net
Favorite numbers:
09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0

 

We don’t have transmission locks in the UK I think, but we do have steering locks. I will simply override it - I have done this to my old car. I simply took out a rectangular piece of metal out of the lock. Not sure if it will be that simple on my new car.

As for your rfid tag, interesting (I think there was a university prof in the UK who did just that). Im a bit squeamish - the thought of something like that under my skin make me uncomfortable. But I guess I could have it in a ring and wear that.(Still can be lost though). And the cost to build such a system? Actually it pretty hard to lose a ring unless u take it off - some people can't even take their rings off. I like this rfid - what is the cost?

Even better just use finger print recognition. But again the cost rules it out for me.

 

Is this capacitive touch switch more reliable than the other sort (bare metal)?

 

If your battery goes dead, and you don't have your key, how will you get the door open?

__________________
Ron (aka Rube)

 

i dont know how much rfid costs, but there are a ton of kits on google readers of various shapes and sizes, as well as different types of rfid tags. you'd want an implant or a hidden tag (stitch one into all your pants, hide one in your shoe, something like that), versus something like a ring or card that can be stolen

as for the capacitive touch switch, the manuf. would have you believe they're very reliable. I'm sure there are various failure modes, but I think roboust programming can take care of most of them.

Ron's concern about a flat battery is a pretty common failure that defeats just about any electronic method ... unless you build a separate power supply just for your security system, and then that's something to maintain

__________________
If you don't have a planet, what good are gold bars?

want to contact me directly? gmail gordonthree
check out my project website: http://projects.dimension-x.net
Favorite numbers:
09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0