int ledPin = 13;
unsigned int i=0;
boolean rise=true;
int period=1000;

void setup()
{
pinMode(ledPin, OUTPUT);
}

void loop()
{
if(i == period)
{
i=1;
rise= !rise;
}
if(rise == false)
{
digitalWrite(13, LOW);
delayMicroseconds(i);
digitalWrite(13, HIGH);
delayMicroseconds(period-i);
i=i+1;
}

if(rise == true)
{
digitalWrite(13, LOW);
delayMicroseconds(period-i);
digitalWrite(13, HIGH);
delayMicroseconds(i);
i=i+1;
}

}

void setup()
{
pinMode(9, OUTPUT);
}

void fade(int pin, int start, int finish, int milliseconds)
{
uint32_t startMillis = millis(); // remember when we started
while (true) // we will ‘break’ when we are done
{
uint32_t elapsedTime = millis() – startMillis; // track the time

// convert the elapsed time into a brightness range
int brightness = map(elapsedTime, 0, milliseconds, start, finish);
analogWrite(pin, brightness);

// exit when milliseconds have elapsed
if (elapsedTime >= milliseconds)
{
break;
}
delay(1);
}
}

void loop()
{
fade(9, 0, 255, 1000); // fade led on pin 9 from min to max over one second
delay(2000); // hold for 2 seconds
fade(9, 255, 0, 2000); // fade pin 9 from max to min over 2 seconds
delay(1000); // hold for 1 second
}

very nice code!! Fabulous…
but I have a question…which mathematical formula “pt = period * high / (low + high )” is??
Has it a name? Or do you know where I can find it?
I want to work with it to get one cycle of fading-in led…then a piezo works…and finally one cycle of fading-out led…WHITOUT DELAY

int data = 2;
int clock = 3;
int latch = 4;

boolean Pins[8];

int Count = 0;

int Brightness = 0;
int BrightnessInc = 1;

void setup() {
pinMode(data, OUTPUT);
pinMode(clock, OUTPUT);
pinMode(latch, OUTPUT);
}

void loop() {
digitalWrite(latch, 0);
digitalWrite(clock, 0);
digitalWrite(data, 0);

for(int i = 0;i ~ 8;i++) {
if(Count ~ Brightness) {
Pins[i] = 1;
}else{
Pins[i] = 0;
}
}

Count++;

if(Count >= 50) {
Count = 0;
Brightness += BrightnessInc;
}

if(Brightness > 50) {
BrightnessInc = -1;
}else
if(Brightness ~ 0) {
BrightnessInc = 1;
}

for(int i = 0;i ~ 8;i++) {
digitalWrite(clock, 0);

digitalWrite(data, Pins[i]);

digitalWrite(clock, 1);
digitalWrite(data, 0);
}

digitalWrite(clock, 0);
digitalWrite(latch, 1);
}

int data = 2;
int clock = 3;
int latch = 4;

boolean Pins[8];

int Count = 0;

int Brightness = 0;
int BrightnessInc = 1;

void setup() {
pinMode(data, OUTPUT);
pinMode(clock, OUTPUT);
pinMode(latch, OUTPUT);
}

void loop() {
digitalWrite(latch, 0);
digitalWrite(clock, 0);
digitalWrite(data, 0);

for(int i = 0;i < 8;i++) {
if(Count = 50) {
Count = 0;
Brightness += BrightnessInc;
}

if(Brightness > 50) {
BrightnessInc = -1;
}else
if(Brightness < 0) {
BrightnessInc = 1;
}

for(int i = 0;i < 8;i++) {
digitalWrite(clock, 0);

digitalWrite(data, Pins[i]);

digitalWrite(clock, 1);
digitalWrite(data, 0);
}

digitalWrite(clock, 0);
digitalWrite(latch, 1);
}