Learn how to continuously turn on and off a simple LED; in other words, to blink a LED. The microcontroller used here is the PIC16F628A and you are going to use variables. A blinking LED can be used effectively as an indicator and in some cases as communication interface.

In a previous post called Hello World, a LED was simply turned on. This post is about blinking the LED (turn it on and off repeatedly), so the novelty here comes in software.

Before reading this, you will need to know how to setup MPLAB IDE and how to connect the PICkit to the microcontroller. If not, check them out first. Check out also another projects for beginners in 8-bit PIC microcontrollers.

Requirements for Blinking LED

Components and Devices

In this tutorial, all the components are Through Hole.

• PIC16F628A: 1 unit.
• LED, any size or color: 1 unit.
• Resistors:
  • 330Ω, 1/2 or 1/4W: 1 unit.

Tools and Machinery

• Breadboard: 1 unit.
• PICkit (3 or 4): 1 unit.
• AC/DC Power Adapter to 5V DC, with at least 500mA: 1 unit.
• Jumper or UTP Wires: various.

Schematics for Blinking LED

Schematic

A simple LED with the resistor is needed for this circuit. Just connect them to the pin RB3 as shown below. Use the same 330Ω resistor as the previous Hello World post.

Photo

A picture of the circuit was taken as reference.

Code for Blinking LED

Configuration() function

Just like the previous tutorial, we have to set the Configuration Bits. The exact code can be found below.

• Turn off:
  • The internal oscillator (FOSC) running at 4MHz.
  • Watchdog Timer (WDT).
  • Master Clear (MCLR).
• Turn on:
  • Power-Up Timer (PWRTE)
  • Brown-out Timer (BOREN).

The rest is unimportant for now.

Above main(), open a new function called config() and paste the following code:

config(){ // CONFIG
    #pragma config FOSC = INTOSCIO  // Oscillator Selection bits (INTOSC oscillator: I/O function on RA6/OSC2/CLKOUT pin, I/O function on RA7/OSC1/CLKIN)
    #pragma config WDTE = OFF       // Watchdog Timer Enable bit (WDT disabled)
    #pragma config PWRTE = ON       // Power-up Timer Enable bit (PWRT enabled)
    #pragma config MCLRE = OFF       // RA5/MCLR/VPP Pin Function Select bit (RA5/MCLR/VPP pin function is MCLR)
    #pragma config BOREN = ON       // Brown-out Detect Enable bit (BOD enabled)
    #pragma config LVP = OFF        // Low-Voltage Programming Enable bit (RB4/PGM pin has digital I/O function, HV on MCLR must be used for programming)
    #pragma config CPD = OFF        // Data EE Memory Code Protection bit (Data memory code protection off)
    #pragma config CP = OFF         // Flash Program Memory Code Protection bit (Code protection off)
    //More code comes after this line
}

config(){ // CONFIG

    #pragma config FOSC = INTOSCIO  // Oscillator Selection bits (INTOSC oscillator: I/O function on RA6/OSC2/CLKOUT pin, I/O function on RA7/OSC1/CLKIN)

    #pragma config WDTE = OFF       // Watchdog Timer Enable bit (WDT disabled)

    #pragma config PWRTE = ON       // Power-up Timer Enable bit (PWRT enabled)

    #pragma config MCLRE = OFF       // RA5/MCLR/VPP Pin Function Select bit (RA5/MCLR/VPP pin function is MCLR)

    #pragma config BOREN = ON       // Brown-out Detect Enable bit (BOD enabled)

    #pragma config LVP = OFF        // Low-Voltage Programming Enable bit (RB4/PGM pin has digital I/O function, HV on MCLR must be used for programming)

    #pragma config CPD = OFF        // Data EE Memory Code Protection bit (Data memory code protection off)

    #pragma config CP = OFF         // Flash Program Memory Code Protection bit (Code protection off)

    //More code comes after this line

}

Pinout Configuration

All PORTA is unused, therefore let's leave it as input (because it has higher impedance). Just the RB3 from PORTB is going to be used as output, therefore

TRISA=0b11111111; //They are unused, therefor leave them with '1'.
TRISB=0b11110111; //Only RB3 will be an output (therefore the '0'). Leave the rest of 1.
PORTA=0; //Clean the ports.
PORTB=0;

TRISA=0b11111111; //They are unused, therefor leave them with '1'.

TRISB=0b11110111; //Only RB3 will be an output (therefore the '0'). Leave the rest of 1.

PORTA=0; //Clean the ports.

PORTB=0;

Run it forever

After adding the configuration bits, remember to add the while to run the program forever.

while(1) {

}

while(1) {

​

}

Creating delay

Let's write some code that freezes the microcontroller temporally.

WHAT??!! Why would anybody want to make it STOP for a while? It is actually more useful than you might think.

For this tutorial specifically, we will need it to make the LEDs perceptible to the human eye. In fact, you don't freeze it, you just make the microcontroller to idle or do nothing for a small period of time.

Definition

There are many ways to make a processor to do nothing for a while. One of them is to make it count for a determined amount of time.

Declare the local variable x as integer.

int x;

int x;

Remember that integer can store values from -32,768 to 32,767. Let's make it count different values and let's find out empirically how many time in seconds this happens to be. Try for example: 100, 1000, 10000 and 32000. Let the program count from 0 to the values previously specified using while and x++.

x=0;
while(x<10000) x++;

x=0;

while(x<10000) x++;

​

When I tried out the 10000 value, the Blinking LED was turning on and off for about 3 times per second.

Blinking the LED

Now, you just have to give the command to turn the LED on:

PORTBbits.RB3=1; //LED On

PORTBbits.RB3=1; //LED On

and then turn the LED off:

PORTBbits.RB3=0; //LED Off

PORTBbits.RB3=0; //LED Off

Download the code of the Blinking LED

If you would like to see and read the whole code through, enter your name and e-mail in the form below to download the project. I promise that I won't send you spam; just relevant content to the blog. If you don't see any form below, please click here.

Testing the Blinking LEDs

If you don't know how to compile and code a project into a PIC microcontroller, follow this link to my tutorial.

If everything executed properly, you should see a message in the bottom of the Output window confirming that the programming process has been complete.

Next Chapter

The next series of posts will be related to transistor switching. Subscribe to the newsletter if you haven't already so you don't miss out!

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