ATTINY85-LED-Boost.c

/*
 * ATTINY85-LED-Boost.c
 * Full article at
 * http://wp.josh.com/2017/03/20/blinking-blue-powering-a-3-7-volt-blue-led-from-a-2-4-volt-coin-cell-with-a-0-02-charge-pump
 * 
 */ 

#include <avr/io.h>

#define F_CPU 1000000       // 1MHz, default for 8MHz internal osc and clkdiv8

#include <util/delay.h>

int main(void)
{
       
    DDRB |= _BV(0);         // Pin 5 = Output
        
    while (1)               // Blink forever at about 5Hz (100ms oscillating, 100ms off)
    {
    
        // This top section oscillates pin 5 at about for about 100ms
        
        for(int i=0; i<10*100;i++ ) {       // Each loop pass takes about 100us, so this for() will take ~100ms
        
            // This is a 10KHz (50us high, 50us low) oscillator on pin 5 
            PORTB |= _BV(0); 
            _delay_us(50); 
            PORTB &= ~_BV(0);    
            _delay_us(50);
        }
        
        // This leaves pin 5 low for 100ms
        
        _delay_ms(100);
    }
}