1. can i use like 2 thumbtacks next to each other just for a simple body contact touch switch?
2. is there a possibility of building a switch with just one thumbtack (or one nail or whatever) coming out of my case? i read about capacity sensing but didnt really get how to programm the arduino for this... and i read about "touching" the base of the transistor to have it passing through current from collector to emitter... would that work that easily?
3. using two thumbtacks as a body contact for analogue input, it worked with pull down, but not with pull up circuit! why is that?
4. can you "capsense" a distance? or is it just for on/off, and for distance sensoring, you have to use ultrasonic or infrared?
5. can i use a simple switch to switch between two sensors, one sensor at a time is chosen to run into one analog input, like this?
6. is there definitely no kind of danger using body contacts (two thumbtacks, one connected to 5v, one to GND and analog input pin)? i mean can any harm be done to the body concerning electromagnetic fields or whatever? could usb possibly draw more power over a short period of time? the arduino is connected to a computer constantly via usb. i dont have any clue, on the one hand people just say theres no danger at all, while others say "if you dont feel good about using body contacts and arduino, better dont do it"
7. i want to use a potentiometer to adjust the sensivity of an analog input...
You need a HIGH GAIN amplified input to read the small change that will occur when your finger
With high enough amplification and a some what unstable enough circuit, yes, you can do that. You need a circuit that is almost ready to "flip state" and just needs a little prodding. So, just a thumbtack by itself... unlikely to be any sort of reliable.
Works or does not work is likely due to transistor type (NPN versus PNP). Pull up / Pull down hardly matters... as long as you know WHY the pin state changes, you can make a logical decision (code) around it.
Yes, look at using a 4051 or maybe 4016... depends on what you can get you hands on and how you want to use them.
Your question cannot be answered because your circuit details are not disclosed. Including the value of the pull-up/down resistor(s)?
I can't tell what you are asking here? Please describe exactly what you are trying to do. I can't follow your proposed solution?
With high enough amplification