Your First Circuit: Blinking an LED

The classic first microcontroller project: make an LED blink, on purpose, using nothing but a pin, a resistor, and a short delay loop.

Blinking an LED is the microcontroller world's equivalent of printing "Hello, World" — it's small enough to fully understand, but it proves every part of your toolchain and hardware setup is working end to end: the chip is programmed correctly, the oscillator is running, and your output pin is wired correctly.

The circuit is simple: connect an LED's longer leg (the anode) through a current-limiting resistor — typically a few hundred ohms — to a GPIO pin, and its shorter leg (the cathode) to ground. When the pin outputs a high voltage, current flows through the resistor and LED to ground, and the LED lights; when the pin outputs low, no current flows and the LED goes dark.

In software, the whole program is just three steps repeated forever: turn the pin on, wait, turn the pin off, wait. The "wait" is usually a simple software delay — a loop that does nothing useful except take a predictable amount of time — though later lessons on timers show a more precise way to time delays.

void main(void) {
    TRISB0 = 0;   // RB0 as output

    while(1) {
        LATB0 = 1;        // LED on
        __delay_ms(500);  // wait half a second
        LATB0 = 0;        // LED off
        __delay_ms(500);  // wait half a second
    }
}