Touch Sensor

Hi all,

I'm looking to make a small circuit that can detect if it's in contact with skin. My goal is a bracelet/watch strap that can tell if its being worn by someone or not. Any ideas of where to start would be great. Thanks

I think the theory is based on skin capacitance.
I think the simplest of these type circuits take advantage of the potential between your body and the ground, which can be used to bias a mosfet, probably p-channel would work best here.

Another way of accomplishing what you are looking for might be motion sensing, usually when a watch is worn it moving around.

A few methods that come to mind:
Skin resistance - detected using simple current detector/amplifier
Body capacitance - detected using oscillator and either capacitive divider & measuring voltage or by checking the charge rate of the skin 'cap' compared to a reference cap
Body as antenna - use the body as an antenna and detect the rf signal (or even the 50Hz hum if worn inside/near powerlines).
Pressure sensor / mechanical switch - turns on when something pushes against it.

The skin resistance detection or body as antenna detection are simple to implement using a transistor