ESTE: GPIO and External Interrupts - part 2

This experiment is part of this project.

Here we are going to build another experiment with an led and a push button, using the GPIO to consolidate concepts of interrupts. The exercise here proposed is to turn on a led always when a push button is pressed and off when the button is no longer pressed. To complete this experiment it is recommended to see at first the GPIO and External Interrupts - part 1 scripts.

Pseudo code

Let's begin with a solution. The pseudo code (actual coding is up to you) is below:

interrupt_source = 0;       //you can select two interrupt sources: 0 (pin 2) and 1 (pin 3)
led_state = LOW;              //state = 0, led is off; state = 1, led is on
debounce_limit = 200;       //limit time in ms between interrupts to debounce the electric signal
sensitivity = HIGH;         //select signal event that generates interrupt (SIGNAL_HIGH, SIGNAL_LOW, SIGNAL_CHANGE, RISING_EDGE, FALLING_EDGE)
button_state = LOW;           //to check exactly if it is happenig a RISING_EDGE or a FALLING_EDGE

int main(void) {
    while(1) {
        led_value(led_state);
    }
    return 0;
}     

void interrupt_handler(){
    if (debounce()){
        if (button_state == HIGH)
            led_state = HIGH;         //if the button is pressed, the led is on
        else
            led_state = LOW;          //if the button isn’t pressed anymore,  the led is off
    }
}

int debounce(){ 
    //debounce is the function responsible for stabilizing the interruption requests
 
    if( (now - time_last_accepted_interrupt) > debounce_limit) {
        time_last_accepted_interrup = now;
        return 1;
    }
    else
        return 0;
}

This pseudo-code always send a led_state to the led so that it atualizes his brightness acording to the states on and off. When the microcontroller detects a special “moment”, it will call the function specified to a certain type_interrupt (each type of interruption can call only one function or perform one determinated action). To truly perform the led_change() it is necessary to check if the debounce() was done correctly, because the debounce will treat all the calling signals to the interruption - commonly more then thousands calls for each second in a push button - so that they stay regular. After the treatment of the interrupt signals, it will be checked if the button is still pressed or not. If yes we turn the led on, if not the led will be turned off.

Schematic

Schematic of the circuit

Part List

• 1 LED
• 1 push button
• 1 10k ohm resistor to the button
• 1 220 ohm resistor to the led
• 1 Protoboard
• 5 copper wires (tinned) or jumpers

Assembly

Assembly of the circuit

Solutions

• C - AVR
• Arduino UNO

Tools

• AVR GCC and tools
• Arduino IDE