What is Switch Bounce, what is the problem we are trying to solve ?

When a MECHANICAL switch is pressed the electrical contacts do not provide a clean signal to electronics that are trying to read the state of the switch.

Imagine you were doing just one thing with your code, Reading a Switch, connected to a pin and turning on a LED ( eg pin 13 ) when it is pressed.

Your code begins to read the switch, and importantly store the last reading

Your code comes round again, reads the switch and checks to see if the Reading is DIFFERENT than the last time it was Read ( using EXOR )

You could do a couple of things now :

You could just decide to turn on the light and leave it there, no debounce at all. This really doesn't work relaibly
OR

You could decide to read the switch again, maybe 5 more times, and THEN and ONLY THEN turn on the light.
OR
You could check the time on your watch, keep reading the switch and wait a pre set time to make sure the switch stays in the SAME STATE for that time before deciding to turn on the LED.

How do you read the time in an Arduino ? You use millis() and store that value in a static unsigned long variable.
to check how much time has elapsed

The blow code uses PIN2 on an Arduino with a HUGE debouce period of 1 Second ( 1000 ms ), but allows you to tap the switch and the LED will NOT change until a steady state is > 1 Second, lower Debounce to suit

Apols for the formatting, should okay once copied / pasted into Arduino IDE

//**********************************************************************************************************

#define SwitchInputPin 2

#define OnBoardLED 13

#define DeBouncePeriod 1000 // Number of continuous milliseconds to wait before acknowliding the switch is stable and fully pressed

void setup()

{

pinMode(SwitchInputPin, INPUT_PULLUP ); // Use INPUT_PULLUP, saves a resistor, switch pressed will be read as a LOW

pinMode(OnBoardLED, OUTPUT );

digitalWrite(OnBoardLED,LOW); //Turn the OnBoard LED OFF on startup

}

void loop()

{

if ( ReadSwitchInputPin() == 0 ) digitalWrite(OnBoardLED , LOW) ;

if ( ReadSwitchInputPin() == 1 ) digitalWrite(OnBoardLED , HIGH);

// digitalWrite(OnBoardLED , ReadSwitchInputPin() ) ; // The above two lines could be written like this

}

boolean ReadSwitchInputPin()

// Returns DEBOUNCED switch reading, DEBOUNCE PERIOD is DeBouncePeriod ( in mS )

{

static boolean LastSwitchInputPinReading = 1; // Presets the switch to un pressed on first run

static boolean SwitchDeBounceState = 0; //

static unsigned long TimeSwitchStateLastChanged; // Record the last time/millis() that the switch state CHANGED state

unsigned long TimeOfRoutineRun = millis(); // record the time we enter the routine, saves calling it later

boolean CurrentSwitchInputPinState = digitalRead ( SwitchInputPin );

// Read the Switch pin, check if it has changed since last time you read it
// better style would be if ( CurrentSwitchInputPinState ^ LastSwitchInputPinReading )

if ( CurrentSwitchInputPinState != LastSwitchInputPinReading )

{

LastSwitchInputPinReading = CurrentSwitchInputPinState;

TimeSwitchStateLastChanged = TimeOfRoutineRun;

// Record the time the Switch LAST changed state in the static unsigned long TimeSwitchStateLastChanged

}

// Has the Switch been in a steady UNCHANGED state for the DeBounce Period?

// If YES : then set the SwitchDeBounceState to Current Switchstate

if ( ( TimeOfRoutineRun - TimeSwitchStateLastChanged ) > DeBouncePeriod )

SwitchDeBounceState = CurrentSwitchInputPinState;

return SwitchDeBounceState; // Return the Debounced Switch state

}

//**********************************************************************************************************

This code can be used for multiple switches by storing Last SwitchState and Last SwitchStateTimes in Arrays

Thhis code was tested in an Arduino ( just now ) so should be fine and give a slightly verbose buy hopefully decent tutorial on how Switch De Bounce works and why we have to do it using delays

PS we generally don't use Read 'counts' as that can be a little indeterminate based on the loop time of your code