I would like to generate computer controlled touches on a capacitive touch screen (e.g. iphone) using the following setup: I have a conductive patch (size of finger) that I place on the touchscreen which is connected to a wire. When I touch the other end of the wire, it generates a touch at the location of the capacitive patch. However, also when I do make contact with the wire, it also generates a touch. I think this is because the wire (25cm) acts as an antenna and the capacitive signal is influenced by noise. I do not encounter this problem when the wire is shorter (e.g. 5cm).
My idea now is to place an electronic component close to the patch, which I can control digitally to connect/disconnect the wire (switch). So when the "switch" is open the wire is very short and will not generate a touch. When the "switch" is closed a touch will be generated because it is connected to the longer wire which generates a touch because of noise in the environment or/and the user is touching the end of the long wire. From my basic knowledge of electronics and transistors, I though that a transistor might be suitable as this can be as a switch that is controlled digitally. However, I did not come that far as I encountered the following problem using a PNP BC327:
I directly soldered the collector to the conductive patch that makes contact with the screen. When touching the screen with this setup (leaving the base and emitter disconnected) does not generate any touches. However, when connecting a loose wire to the base or emitter, a touch is generated without even controlling the transistor. I do not measure any conductivity between the Collector, Base, or Emitter using a multi-meter so I am very surprised that connecting these wires causes a change in capacitance on the collector.
Any help to beter understand this problem would be useful as well as input on other techniques on how to make the desired system/setup.