This project shows how to simply Fade-In and Fade-Out a LED by using delay function to control pulse width what is sometimes called Software PWM (Pulse Width Modulation). In our circuit a LED is connected to PB0 and it is made to Fade the LED In and Out alternately. The code is on Github, click here.
Parts Required
- ATtiny13 – i.e. MBAVR-1 development board
- Resistor – 220Ω, see LED Resistor Calculator
- LED
Circuit Diagram
Firmware
This code is written in C and can be compiled using the avr-gcc. More details on how compile this project is here.
#include <avr/io.h>
#include <util/delay.h>
#define LED_PIN PB0
#define DELAY_MAX (512)
#define DELAY_MIN (1)
#if DELAY_MAX < 1 || DELAY_MIN < 1
# warning "Value of DELAY_MAX and DELAY_MAIN should be from range <1, 2^16>"
#endif
#if !(DELAY_MAX > DELAY_MIN)
# warning "Value of DELAY_MAX should be greater then DELAY_MIN"
#endif
int
main(void)
{
uint16_t delay = DELAY_MIN;
uint8_t dir = 0;
/* setup */
DDRB = 0b00000001; // set LED pin as OUTPUT
PORTB = 0b00000001; // set LED pin to HIGH
/* loop */
while (1) {
PORTB &= ~(_BV(LED_PIN)); // LED off
_delay_loop_2(delay);
PORTB |= _BV(LED_PIN); // LED on
_delay_loop_2(DELAY_MAX - delay);
if (dir) { // fade-in
if (++delay >= (DELAY_MAX - 1)) dir = 0;
} else { // fade-out
if (--delay <= DELAY_MIN) dir = 1;
}
}
}