Use this code to connect a Toggle Flip Switch to an Arduin Pro Micro or Leonardo.

The pin to connect is Digital PIN 8 and GND

ON will output "a"

OFF will output "b"

Change if you like!

#include <Keyboard.h>

const byte switchPin = 8;
byte oldSwitchState = HIGH;  // assume switch open because of pull-up resistor
const unsigned long debounceTime = 10;  // milliseconds

void setup ()
  {
  Serial.begin (9600);
  pinMode (8, INPUT_PULLUP);
  }  // end of setup

void loop ()
  {
  Keyboard.begin();
  // see if switch is open or closed
  byte switchState = digitalRead (switchPin);
  
  // has it changed since last time?
  if (switchState != oldSwitchState)
    {
    oldSwitchState =  switchState;  // remember for next time 
    delay (debounceTime);   // debounce
    if (switchState == LOW)
       {
       Serial.println ("Switch closed.");
       Keyboard.press('a');
       delay(100);
       Keyboard.releaseAll();
       }  // end if switchState is LOW
    else
       {
       Serial.println ("Switch opened.");
       Keyboard.press('b');
       delay(100);
       Keyboard.releaseAll();
       }  // end if switchState is HIGH
    }  // end of state change
     
  // other code here ...
   
  }  // end of loop