This is the same technology used in those ovens that have the glass panel over the controls, but they use ICs. The principal is the same however, they both detect (I think) the small electrical signals that people give off and amplifies this to a useful level. If this is wrong correct me, but all I know is that this works.
(This design works great for LEDs. I am making a touch LED flashlight that runs off rechargeable batteries, but I am not sure what batteries to get yet.)
Step 1: Parts
-4 x 2N3906 PNP transistors or similar (note below about transistors)
-1 x 1N914 diodes
-1 x 10v 1000uF capacitor (keep the voltage below 10v / Caps rated voltage or it will
-1 x Barrel jack
-1 x 9v 300ma adapter
-1 x 120 Ohm resistor (Brown, red, brown)
-1 x Ceramic capacitor
-some shield wire (I don't use it because I don't have any but if you do use it!)
-some copper clad is nice to have but not needed
-ugly perf board
-Breadboard/protoboard are handy as well
-tin snips for copper clad and ugly perf board
*Note: The transistors I used are random transistors similar to 2N3906 but I live in Canada and can only get a package of transistors "similar" to 2N3906 so protoboards are good to test this out on. Mine are bi polar and let some electricity through one way all the time wether they are off or turned around let no electricity through when off. Test the different combinations to get the way that works best. 2N3906 should work fine in this circuit though I have not tried it.
Step 2: Circuit
The only reason the resistor is needed is because the last transistor always began to over heat after about five mins. but with the resistor there it does not overheat anymore. You could try a similar transistor to the 2N3906 but with better power ratings and the resistor would not be needed, but as I said earlier, probably, I live in Canada and the Source by Circuit City doesn't have a good selection so I have no choice. So if you live in the States (USA) or buy parts online (thats what I should probably do) then test different transistors.
I would also like to add in an indicator LED to the board that way it turns on whatever the load is as well as a visual que that it is working.
UPDATE! - The transistors are all 2N4403 except for the one connected to the resistor. It is a 2N3906. Also I think the arrows in schematic might be on the wrong side or pointing the wrong direction, but they are PNP transistors. I did label the Collector, Base and Emitter in the picture in case I did the symbol wrong.
Step 3: Solder
Also you can do a way better solder job then I can, probably.
Step 4: Done
one project that would be cool is to remove an on/off switch and replace it with a locking relay. You can buy small relays that are like pens, when they are switched on they snap closed and they lock and when they are switched again they unlock, then add in the touch sensor to control the coil of the relay.
Have fun and mess around with this design all you want. Also if anything is wrong in my Instructable, message me to fix it.