const int buttonPin = 8; // the number of the pushbutton pin
      const int ledPin = 2; // the number of the LED pin
      // variables will change:
      int buttonState = 0; // variable for reading the pushbutton status
      void setup() {
         // initialize the LED pin as an output:
         pinMode(ledPin, OUTPUT);
         // initialize the pushbutton pin as an input:
         pinMode(buttonPin, INPUT);
      }
      void loop() {
         // read the state of the pushbutton value:
         buttonState = digitalRead(buttonPin);
         // check if the pushbutton is pressed.
         // if it is, the buttonState is HIGH:
         if (buttonState == HIGH) {
            // turn LED on:
            digitalWrite(ledPin, HIGH);
         } else {
            // turn LED off:
            digitalWrite(ledPin, LOW);
         }
      }
      

      Cpp language logoArduino - Connecting Switch

      arduino
      uno
      hardware
      ...

      Pull-down resistors are used in electronic logic circuits to ensure that inputs to Arduino settle at expected logic levels if external devices are disconnected or are at high-impedance. As nothing is connected to an input pin, it does not mean that it is a logical zero. Pull down resistors are connected between the ground and the appropriate pin on the device.

      An example of a pull-down resistor in a digital circuit is shown in the following figure. A pushbutton switch is connected between the supply voltage and a microcontroller pin. In such a circuit, when the switch is closed, the micro-controller input is at a logical high value, but when the switch is open, the pull-down resistor pulls the input voltage down to the ground (logical zero value), preventing an undefined state at the input.

      The pull-down resistor must have a larger resistance than the impedance of the logic circuit, or else it might pull the voltage down too much and the input voltage at the pin would remain at a constant logical low value, regardless of the switch position.

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