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Car touch sensor!


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I want to make a sensor that is wires to the sheet metal of a car body that when touched can activate something such as a 555 or a piezo (to be determined later).

How do touch lamps work?
Can I apply this to a car body somehow?
Any ideas?

I don't want an alarm system to go off or anything but just a little beep or something to warn people my car is "smart" and not to be messed with.

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Hi Um,
Your idea of having the entire car as a touch sensor has problems:
1) Most touch sensors detect the effect of the 100pF of a human on a high frequency oscillator. The oscillator and the human are referenced to EARTH. So your circuit will need to have a ground strap under the car.
2) Most touch sensors use a tiny touch plate so that the small 100pF to EARTH of a human has an effect. If the entire car is the touch plate then it will already have a big effect to EARTH and the addition of the small capacitance of a human will be neglegible.

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The circuits are exactly the same when you remove the short of the sensor plate to the battery in the 1st one.

It won't work if you get close to the sensor plate. It works when the resistance of your body completes a connection from the sensor plate to the negative battery terminal.

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So will the first one work at all with that short in there?

Both the pages that had these, which were published (to the web) in different years, said if you got close (not touch) it would work.  Hmmmm?  They both are for connecting the circuit to a metal object such as a doorknob.

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