Friday, December 12, 2014

Trinket - Turning a LED on off with a switch

The Trinket is $6.95 micro controller from Adafruit that is compatible with the Arduino.

I followed the demo from the video: "Tutorial 02 for Arduino: Buttons, PWM, and Functions".

By pressing the button, the on board red led will be turned on or off.

  • The red wire provide power
  • The black wire is the ground
  • The green wire also is connected to the ground and pin 0. We will read from pin 0, the state of the button

One tricky thing, is that reading the value of the button is not stable or can bounce, see function GetButtonStateDebounced().
I tried to write a cleaner and clearer code than in the video.

    based on video Tutorial 02 for Arduino: Buttons, PWM, and Functions

    Torres Frederic 2014.12.12

void LedOn(int pin, boolean state) {

    digitalWrite(pin, state ? HIGH : LOW);

const int SWITCH_PIN                  = 0;
const int LED_PIN                     = 1;   // Red LED on the Trinket

boolean _buttonLastStateInLoop = false;
boolean _ledOn                 = false;

boolean IsButtonPressed() {

    return digitalRead(SWITCH_PIN) == HIGH;

// If we detect a change of button state between the current loop()
// function execution and the previous one, we wait and re reread 
// the value
boolean GetButtonStateDebounced(boolean lastState) {
    boolean state = IsButtonPressed();
    if (state != lastState) {
        state = IsButtonPressed();
    return state;

void setup() {

    pinMode(SWITCH_PIN, INPUT);
    pinMode(LED_PIN,    OUTPUT);

void loop() {

    boolean buttonPressed = GetButtonStateDebounced(_buttonLastStateInLoop);

    if (buttonPressed == true && _buttonLastStateInLoop == false) {

        _ledOn = !_ledOn;
    _buttonLastStateInLoop = buttonPressed;
    LedOn(LED_PIN, _ledOn);

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