Arduino now has an officially supported command-line interface. The project, called arduino-cli, is the first time that the official toolchain has departed from the Java-based editor known as ...

This sensor sits in line with the water line and contains a pinwheel ... The Arduino Sketch (code) uses the external interrupt (int 0) on Arduino’s digital pin 2 (D2). This is used to read the output ...

Also, in the setup() you can see this line attachInterrupt(0, count, LOW); that is used to attach an interrupt on pin 2. In our case Arduino UNO has 2 external interrupts: on pin 2 with ID 0 and on ...