Note: When not using the built-in pull-up resistor on a pin, you will need to add a pull-down or pull-up resistor yourself, depending on your type of switch. Most digital signals can be used without ...

Switches and push buttons need debouncing. It is straightforward to do this with software, using a library. The advantages of the Switch library are: External pull-up resistors are not required.

When reed switch is opened, pin 2 of Arduino goes high with the help of the pull-up resistor R2, and the alert signal is available through the piezo-speaker PZ1 (not an active piezo-buzzer). At the ...