A door opens and closes. A transistor turns off, or turns on partially (is linear) or turns on fully (is saturated).
There are thousands of different transistors because:
1) Maximum allowed voltage.
2) Maximum allowed current.
3) Maximum allowed dissipation (heating).
4) Maximum radio frequency.
5) Lowest maximum noise (a good signal to noise ratio).
Normally closed?
An idle bipolar or enhancement mode Mosfet transistor are turned off and does not conduct.
A bipolar transistor is turned on when it has base to emitter current which needs some base to emitter voltage.
A depletion mode Jfet is turned on when its gate to source voltage and current are zero.
You appear to think that transistors are similar to relays with NO and NC contacts. They're not. They will turn on (collector and emitter connected) when a current flows into the base. See wiki.
The length marked in green of approx. 90cm is an ISOLATED cable as an extension of the middle pin, which is not insulated at the end and comes into contact with metal there!
I think you mean "insulated"?
Insulation does not block capacitive pickup.
I've found an article that shows the module schematic; it is just a "hum detector" type device as I thought.
Anything that acts as an antenna connected to the input pin (transistor base) and picks up enough stray signal will trigger it.
(And insulated wire is fine as an antenna).
Also note it is a very crude touch switch not a metal detector! Anything conductive may trigger it - including damp materials or skin. If both you (holding it) and whatever it touches are at the same potential, it will not be triggered.
But there has to be direct contact between the base (antenna) and metal to trigger it so that it triggers a touch signal?!
Is it possible to adjust the sensitivity ev with resistors so that the stray signals are too weak to trigger the sensor, i.e. only if there is direct physical contact because then the capacity is much higher...???
No - touch it with your finger and it will trigger. It is NOT a "metal detector", that's what I keep trying to stress.
Anything conductive may trigger it, dependant on the surroundings.
Actual metal detectors use inductive sensing, with a coil driven by an oscillator and circuitry to detect the changes that being near metal has on the coil / magnetic field properties, not capacitive or hum pickup.
It senses electrical contact with anything conductive, that is not connected to the same circuit ground at the module, and is picking up "hum" or electrical noise from the environment.
Small, otherwise unconnected metal items would have no effect. eg. Coins.
If you were holding it and touched it to the base terminal lead, it be like touching it directly with your finger.
A large piece of metal or moderately long wire, that could act as an antenna touched it, that should also trigger it.
Anything that would cause strong hum or buzz if touched to an audio amplifier input should trigger it. Things that would not cause hum will not trigger it - as it works by sensing that same "hum" or buzz, just in a very crude and simplistic manner.
I only want to have the analog output of this metal body touch sensor ky-036 without LED.
What can I leave out of the diagram so that the sensor still works but can do without digital components?!...
Maybe you can mark in red what I can leave out
I only want to have the analog output of this metal body touch sensor ky-036 without LED.
What can I leave out of the diagram so that the sensor still works but can do without digital components?!...
Maybe you can mark in red what I can leave out