@ pwillard - at first thanks for answering!
You need a HIGH GAIN amplified input to read the small change that will occur when your finger
...hmm well but i tried this: i connected one thumbtack to 5v, the other to ground via 1M resistor and to analog-in...
the result was: having my fingers touching both thumbtacks a bit gave me a value of about 200, pressing harder did 400-600 and touching with a wet finger did like value 1000, which is nearly 100% of the 5v, isn't it?
why cant i do this with the digital pin, as well? i mean if values just go up to about 200, i could (software-wise) still convert the values to a boolean state, setting the threshold to 100 (above giving 1, beneath giving 0) or so!?
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.
could you explain that just a bit more? i'm no native english speaker, i'm sorry, i don't get what you mean by "prodding"
and what kind of a "flip state" circuit could that be
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.
(talking about two thumbtacks connected via finger working pull down, but not pull up)
okay... but i didnt use any transistor at all...
what i know is that i can flip things over easily and make a "LOW" a "1" and a "HIGH" a "0", so that my software gets "1" when pressed, talking about pull up. but it just works pull down, and i wonder why. people say pull down is not as safe and good working as pull up. is that right?
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.
(talking about simple switching)
what about a real simple switch?:
i'm fine with the rest of your answers, thank you! well, not totally true, but i'll come to one thing later on, and thats the danger of finger switching
@ KE7GKP - thanks to you too!
Your question cannot be answered because your circuit details are not disclosed. Including the value of the pull-up/down resistor(s)?
i'm talking about very easy circuits that are presented here:http://www.thebox.myzen.co.uk/Tutorial/Inputs.html
(in the middle of the page there are pictures of pull-up and pull-down switching)
i'm using 1M resistors.
is that still difficult to answer?
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?
hmm... its quite easy actually...lets see if i can describe it in a better way:
i have one arduino analog input left, the arduino sits inside a controller box with potis, buttons etc., but i want two analog-input-sensors to be selectable by a simple switch
... so i'm thinking about connecting the middle pin from the switch to analog-input-pin and to ground and one other pin is connected to the piezo and one is connected to the body contact (the minus or ground poles of piezo and bodycontact go into ground as well). so now i can switch between either the piezo signal going into the analog-input or the body-contact-"signal". is that wrong?
and now comes the most important part to me.
my question number 6 is asking: is there any danger using arduino usb-plugged and body contacts?
the first one said "NO DANGER", the second one said "there is most definitely a hazard"
now - what is true? could anyone explain it again to me so that i'm just really sure about this?
i don't want to use a shield like the JK-devices-shield, because i have only little space on the front plate of my controller.
what i have is: one thumbtack is connected to 5v, the other one is connected to ground via 1M resistor and to analog-input of the arduino.
the arduino is usb-connected to my macbook. i don't use any external power source.
if i put my fingers on the thumbtacks, what could happen then?
i'm sorry that i am not really getting the point of the danger, KE7GKP, i mean... 5v?
when does it go dangerous? at 5v and 40mA? or how much can arduino give out? 500mA and 5v max for a short time? (i think i read this somewhere)
PLUS: isnt there a difference between DC and AC? do i have DC here?
roll on, give me answers, please, and... THANKS for any!
i really appreciate your help as people i asked about this couldn't really help me and i want to go on with building
(its my first ever electronics project, and i'm very at the start, slowly getting to know about transistors, having understood like half of the resistor-ampere-voltage-relations)