## Blinky

The classic, helloWorld of embedded programming. This program turns the LED on and off periodically.

### Initial steps:
- Create new project with project generator.
- Open the project folder in VSCode.
- Build the project by pressing the `build` button at the bottom and select the option with `arm-none-eabi`.
- Make sure the build exits with code 0.

<img src="https://c.l3n.co/i/OW219o.png" width="300">

### Basic Code:

``` C
int main()
{
    stdio_init_all();

    const uint OnBoardLED = PICO_DEFAULT_LED_PIN;
    gpio_init(OnBoardLED);
    gpio_set_dir(OnBoardLED, GPIO_OUT);
    while (true){
        gpio_put(OnBoardLED, true);
        sleep_ms(500);
        gpio_put(OnBoardLED, false);
        sleep_ms(500);
    }
}
```

#### Explanation:
`stdio_init_all()`: initialize stuff

`OnBoardLED = PICO_DEFAULT_LED_PIN`: Get the GPIO number of onboard LED. Remember: this is GPIO Number, NOT PIN NUMBER.

`gpio_init(OnBoardLED)`: Initialize that GPIO pin.

`gpio_set_dir(OnBoardLED, GPIO_OUT)`: Set GPIO direction (`GPIO_OUT` for writing and `GPIO_IN` for reading).

`while (true){}`: Super loop of the program

`gpio_put(OnBoardLED, true)`: Set `OnBoardLED` pin to `on` (`true` to turn on/set to high/voltage to VDD, `false` to turn off/set to low/voltage to GND)

Pico logic HIGH voltage is 3.3v and LOW voltage is 0v.

`sleep_ms(500)`: sleep for 500ms.

---

## Different Blinky

This makes the pico blink like a beacon, 2 short blinks followed by long delay. A `for` loop is used for repeating the short blink twice.

```c
for (int i = 0; i < 2; i++)
{
    gpio_put(OnBoardLED, true);
    sleep_ms(50);
    gpio_put(OnBoardLED, false);
    sleep_ms(100);
}
sleep_ms(500);
```

---

## External Blinky

This program blinks an LED connected to one of the GPIO(General Purpose Input/Output) ports.

For this example, I used Pin 20 == GP15. I connected a resistor to this pin and connected an LED in series with the resistor to the ground, as shown in the image below.

```c
const uint LEDPin = 15;
gpio_init(LEDPin);
gpio_set_dir(LEDPin, GPIO_OUT);
while (true)
{
    for (int i = 0; i < 2; i++)
    {
        gpio_put(LEDPin, true);
        sleep_ms(50);
        gpio_put(LEDPin, false);
        sleep_ms(100);
    }
    sleep_ms(500);
}
```

The only change here is in line 1, `PICO_DEFAULT_LED_PIN` is changed to `15`, to represent GP15. Remember: in the program, a GPIO pin is represented by the GP number and NOT by the pin number, as shown in the [Pico's Pinout](https://pico.pinout.xyz/).