I have the following setup and sketch.

The problem is that when I click the button it works sometimes, but other times it executes On Off straight after On as if it's executing twice.

This is after pressing the button only 7 times:


I thought that was the whole point of a state machine? That it continues to execute the next state (not multiple times at random).

Very very confused with this one.

enter image description here

#include <FiniteStateMachine.h>
#include <Button.h>
#include <LED.h>

const byte NUMBER_OF_STATES = 2; //how many states are we cycling through?

//initialize states
State On = State(ledOn);
State Off = State(ledOff); 

FSM ledStateMachine = FSM(On);     //initialize state machine, start in state: On

Button button = Button(2, INPUT_PULLUP); //initialize the button (wire between pin 12 and ground)
LED led = LED(13);                 //initialize the LED
byte buttonPresses = 0;            //counter variable, hols number of button presses

void setup(){

//poor example, but then again; it's just an example
void loop(){
  if (button.uniquePress()){
    //increment buttonPresses and constrain it to [ 0, 1 ]
    buttonPresses = ++buttonPresses % NUMBER_OF_STATES;
    switch (buttonPresses){
      case 0: ledStateMachine.transitionTo(On); Serial.println("On"); break;
      case 1: ledStateMachine.transitionTo(Off); Serial.println("Off"); break;

//utility functions
void ledOn(){ led.on(); }
void ledOff(){ led.off(); }
//end utility functions

2 Answers 2


Maybe you need some sort of debouncing? There's a tutorial on the Arduino site that I think will sort your problem out.


It doesn't look like the state machine is a problem here. More likely it's a problem of the button bouncing, as you don't have any code or circuitry to guard against it.

A button is typically a very simple component which doesn't necessarily make/break connections cleanly. Sometimes it will have a brief intermittent connection, making it look like it's been pressed/released multiple times. This is referred to as bouncing.

There's lots of material online about debouncing, whether in hardware or software. The top answer here may help:

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