Embedded Lab

Description

Today’s lab session is about binary counting LEDs. The binary 1 and 0 will be represented by turning LEDs on and off. You will make a 4-bit binary counter (using 4 LEDs) that counts from 0 to 15 (0000-1111 binary). The four LEDs are connected to RC0 through RC3 port pins of PIC16F688 with current limiting resistors (470? each) in series. A push button switch is connected to pin RC4 to provide input for the counter. The counter starts from 0, and increase by 1 every time the button is pressed. When the counter reaches 15 (all LEDs on), it will reset to 0 on the next press of the button.

Required Theory

You should be familiar with the digital I/O ports of PIC16F688 and their direction settings. If you are not, read Digital I/O Ports in PIC16F688. Read previous lab session (Lab 2: Basic digital input and output) to learn about reading inputs from a push button.

Circuit Diagram

The circuit diagram and its construction on the breadboard are shown in figures below. The PIC16F688 microcontroller uses its internal clock at 4.0 MHz.

Software

Define PORTC pins RC0-RC3 as output, and the pin RC4 as an input. Disable comparators (CMCON0=7), and configure all I/O pins as digital (ANSEL=0). Use Button() function to read input from the push button switch.

/*

 Lab 3: 4-bit up counter

 Internal Clock @ 4MHz, MCLR Enabled, PWRT Enabled, WDT OFF

 Copyright @ Rajendra Bhatt

 Nov 6, 2010

*/

// Define Tact switch @ RC4

 sbit Switch at RC4_bit;

// Define button Switch parameters

 #define Switch_Pin 4

 #define Switch_Port PORTC

 #define Debounce_Time 20  // Switch Debounce time 20ms

 unsigned short count;

 void main() {

 ANSEL = 0b00000000; //All I/O pins are configured as digital

 CMCON0 = 0x07 ; // Disbale comparators

 TRISC = 0b00010000; // PORTC all output except RC4

 TRISA = 0b00001000; // PORTA All Outputs, Except RA3

 count = 0;

 PORTC = count;

 do {

 if (Button(&Switch_Port, Switch_Pin, Debounce_Time, 0)) {

 if (!Switch) {

 count ++;

 if (count ==16) count =0;

 PORTC = count;

 }

 while (!Switch); // Wait till the button is  released

 }

 } while(1);  // Infinite Loop

}

Download HEX file

Output

The counter starts from 0 (all LEDs off), and is incremented by 1 on every button press. After it reaches 15, it overflows and takes the next value 0. This repeats forever.