touch switch.electronic lock

[RMIM]

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.

**broken link removed**

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.

 

[Roff]

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

 

[RMIM]

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

Thanks for the reply.

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

 

[justDIY]

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.

 

[RMIM]

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

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?

 

[RMIM]

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

Interesting idea.

Just DIY>> 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.<<

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?

 

[Nigel Goodwin]

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!.

 

[RMIM]

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!.

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?

 

[JimB]

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

 

[RMIM]

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

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)

 

[justDIY]

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

 

[RMIM]

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

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.

 

[RMIM]

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

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

 

[Roff]

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

 

[justDIY]

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

 

[Nigel Goodwin]

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.

Bear in mind, you would have to inform your insurance company of any modifications, and it's likely that such changes would void your insurance anyway!.

If you didn't tell them, and tried to make a claim, they would have a perfect write to refuse your claim!.

 

[RMIM]

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

If I did build this system and decided not to walk around with a key I would have a hidden key on the car. Magnetic hide away key boxes – maybe..

Nigel G: Bear in mind, you would have to inform your insurance company of any modifications, and it's likely that such changes would void your insurance anyway!.
If you didn't tell them, and tried to make a claim, they would have a perfect write to refuse your claim!.

LOL – true, but is this a law forum or electronics? No, you’re quite right, there is even the potential for this project to be extremely dangerous - if I did build it and the system fails at 70mph and the ignition decides to turn off.

Anyway I had no intension of messing with ignition and starter motor this year (if at all due to the risks of cut outs from an improperly design system), winters coming. My old car has a remote start I installed that works just fine. I disabled the steering lock and was planning to modify the remote start to stay on – never got round to it, plus thought about the danger of things failing.

I once drove a keyless Nissan Micra. U hand to keep a transceiver in your pocket (but there was no need to press any buttons). You still had to turn a mechanical switch to start the ignition and starter motor. But I think I remember the guy saying if the transceiver is away from the car for more that 15seconds the car engine would cut out – what if some brat kid decided to throw it out the window?


Im not planning to get myself in trouble with this project, the main aim of all of this is to learn electronics – this just seemed a fun way of doing it so rather than just reading a book on diodes/transistors etc. actually aiming for something.


I’ll try and ask another question and hope I get electronics advice rather than legal ones and suggestion of better ways to do things (because I just want to learn how to do it that way even if it not the best way for that particular project. Of course you can suggest a better way if you explain how to do that too.

Ok – Im very new to PICs, and staying on the theme of this electronic lock (lets forget about it being touch or whatever – lets say it’s a simple Push To Make) – how do I get it to recognise when the correct code is punched in. Say the code is tap2times – pause – tap1time – pause – tap3time. Just some general ideas and various commands that I need to use. (As for how much pic programming I know – very little. I did write something on my own. A 7seg display (fed by 7outputs on the PIC) that counts from 0 to 9 which advances by 1 every time you push a switch.)