Getting Started

Chapter 4: C Types, Operators, and Expressions

Cylon Eye Speed and Polarity Control

se to control the
polari y polarity I ean that we will
LED which will be off, or all the
LEDs off and the sweep LED on. We will control the polarity with the switch

this ample we will use the ~ bitwise operator to invert the LEDs on port D.

Open PortIO.c in Personal Notepad and save it as CylonEyes.c in a new directory
CylonEyes. Make the following changes to the main() function

// Cyl

#include <av

#inclu

int main (vo

{

ize the scroll delay_count

unsigned long delay_count = 10000;

a variable for the speed increase

unsigned long increase = 0;

ase = PINB;

polarity

127)

e -= 127;

ity = 1;

In this example we will use port B to input data that we will u
Cylon eye movement rate and the LED ty. B m
set either all the LEDs on except the sweep

connected to the port B pin 7, leaving the lower pins to allow us to set the speed
increase factor from 0 to 127.

In ex

onEyes.c

r/io.h>

de <avr/delay.h>

id)

// declare and initial

// declare

// declare a variable for the polarity

unsigned char polarity = 0;

// Init port pins

DDRB = 0x00; // set port B for input

DDRD = 0xFF; // set port D for output

while(1)

{

// read the switches

incre

// set the

if(increase >

{

increas

polar