Button FAQ: common mistake - button does NOT work as expected.

Using Arduino Introductory Tutorials
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Newbie usually runs into trouble when getting started with a button. A lot of people asked on the forum about the same issue.

To avoid this, newbie SHOULD pay attention to the following notes:

1. Floating input problem:
Symptom: the reading value from the input pin is not matched with the button's pressing state.
Cause: input pin is NOT used pull-up or pull-down resistor
Solution: Use pull-up or pull-down resistor. See Arduino Button (with pull-up/pull-down)

2. Chattering phenomenon
It should be considered in only some application that needs to detect exactly number of the pressing.
Symptom: Button is pressed one, but Arduino code detects several times.
Cause: Due to mechanical and physical issues, the state of the button (or switch) is quickly toggled between LOW and HIGH several times
Solution: Debounce. See Arduino Button Debounce

2

CORRECTION: change thread title, “If digitalRead() works, but not as you expected”
There is no ‘button’ functionality other than the button library.
Inputs may need to operate the way they do for applications other than ‘buttons’, perhaps you might explain detecting state-change and debouncing.

3

Hello IoT_hobbyist,

Excellent! This is a repeated frustration here, along with having 2 power supplies and not connecting the 0V from one to the other.
++Karma;

4

Maybe an image like this could be offered:

5

lastchancename:
CORRECTION: change thread title, “If digitalRead() works, but not as you expected”
There is no ‘button’ functionality other than the button library.
Inputs may need to operate the way they do for applications other than ‘buttons’, perhaps you might explain detecting state-change and debouncing.

Thank you for your correction.

You are absolutely correct in term of concept.
However, I would like to keep the title because It is familiar to newbie.

6

PerryBebbington:
Hello IoT_hobbyist,

Excellent! This is a repeated frustration here, along with having 2 power supplies and not connecting the 0V from one to the other.
++Karma;

Thank you,

I will make another FAQ about two power supplies.

7

larryd:
Maybe an image like this could be offered:

Thank you for the real image