Capacitive touch sensor project

[carebare47]

Hello,

I am doing A-level electronics and have just started my coursework project. I wanted to try and design/build the kind of touch sensor that you can find on some lamps, where you come into contact with metal on the lamp and this turns the light on. I think that these work by sensing capacitence. I have looked online but can't seem to find much on this. Is there a simple-ish way of doing this, or is it not worth trying?

Many thanks,

Tom

 

[shrtrnd]

You can do it, but it's not a simple circuit, it'll take some parts.
For safety reasons (isolating yourself from the power outlet), you have to be pretty careful.
I figure there's a circuit available somewhere on Google, but I cheated when I did my
first one. I bought one from All Electronics Corp in California for $2. Then disassembled it,
and made a circuit I thought was more reliable (the one I bought was bare-minimum in
current and wattage capacity). Maybe somebody here will direct you to an available
circuit online.

 

[carebare47]

Managed to find a schematic that uses 12 NOT gates to generate a pseudo sine wave that excites an 'antenna'. When you touch the antenna it disrupts the signal slightly, the circuit detects this and is switching a LED through a MOSFET. It works, but it was too easy =P Think I am going to add PWM on with a 555 and use that to have different sound levels or something =) Thanks for the help, and any further advice/ideas will be welcome ^_^

 

[shrtrnd]

Hmmm, I never thought of an LED as a 'lamp' before.
Learned something new today.