Hello everyone, thank you for reading,
digitalRead will detect state LOW on pin(INPUT_PULLUP) when we will stick wire
from pin(INPUT_PULLUP) to GND.
I made circuit with short cable like 100mm and 1 wall-switch(Bell, ring) one end connected to pin (INPUT_PULLUP) and second to GND
and it works as it should be i detect LOW when te circuit is closed and HIGH when it doesn't.
Then i made circuit with 10 wall-switches with common GND still with 100mm cable
and it works perfect as well.
then i lay the cable (copper wire 0,75 mm) each max long 10 m thro the hause and made a circuit with 10 wall-switches with common GND, ive made the measurement of resistance and it was ok as it should be. then i connected it to arduino and it works but sometimes when i click some switch digitalRead detect pin state LOW on other switch as well i cant sleep with that.
then i unpluged everything from arduino and then i connect short wire 100mm to pin(INPUT_PULLUP) and second end to common GND of that switches remeber this common gnd is not connected to gnd of arduino rhight now this circuit with switches is connected to nothing. and digitalRead sometimes return LOW when i stick cable from input_pullup to this common gnd of switches wich is not connected to gnd.
and my question is why arduino detecing LOW of pin(INPUT_PULLUP) in circuit wich is not connected to anything
sorry for my english, please help