ATtiny code to sense touch and flash an LED a few times

firefly.c

// Firefly
// An ATtiny13 connected to a bit of metal to detect touch
// and an LED which it can PWM.
//
// Sleep most of the time, wake up occasionally, if we're being touched
// then light up a bit.
//
// Adam Greig, July 2010

#include <avr/io.h>

inline void init_io() {
    // Set PB1 to be an output and everything else an input pulled high
    // (defined levels help save power)
    DDRB = (1<<PB1);
    PORTB = (1<<PB0) | (1<<PB2) | (1<<PB3) | (1<<PB4);
}

inline void deinit_io() {
    // Set all pins to input, and all but PB1 to be pulled high
    DDRB = 0;
    PORTB = (1<<PB0) | (1<<PB2) | (1<<PB3) | (1<<PB4);
}

inline void init_timer() {
    // Set for Fast PWM with TOP at 0xFF, set OC0B on compare match
    TCCR0A = (1<<COM0B1) | (1<<COM0B0) | (1<<WGM01) | (1<<WGM00);
    TCCR0B = (1<<CS00);
    OCR0B = 255;
}

inline void deinit_timer() {
    // Turn off the timer
    TCCR0A = 0;
    TCCR0B = 0;
    OCR0B = 0;
}

uint8_t lfsr;
uint8_t rand() {
    uint8_t feedback = lfsr & 1;
    lfsr >>= 1;
    if(feedback == 1)
        lfsr ^= 0xB8;
    return lfsr;
}

inline void init_rand() {
    // Read EEPROM address 0x00
    EEARL = 0x00;
    EECR = (1<<EERE);

    // Increment the value and use it as a random seed, special casing zero
    // as it produces all 0s for the pseudorandom sequence
    lfsr = EEDR;
    lfsr++;
    if(lfsr == 0)
        lfsr = 1;
    EEDR = lfsr;

    // Store the newly incremented value
    EECR = (0<<EEPM1) | (0<<EEPM0);
    EEARL = 0x00;
    EECR = (1<<EEMPE);
    EECR = (1<<EEPE) | (1<<EEMPE);
}

inline void clear_wdt() {
    // After the watchdog reset, clear it properly
    MCUSR = (0<<WDRF);
    WDTCR = (1<<WDE) | (1<<WDCE);
    WDTCR = 0;
}

inline void start_wdt() {
    // Set the watchdog timer to reset the system after eight seconds
    // and start it going
    WDTCR = (1<<WDE) | (1<<WDCE);
    WDTCR = (1<<WDE) | (1<<WDP3) | (1<<WDP0);
}

inline void sleep() {
    // Enable sleeping and set us up for power down mode, then sleep
    MCUCR = (1<<SE) | (1<<SM1);
    asm("SLEEP");
}

void init() {
    // Clear watchdog reset flag
    clear_wdt();

    // Turn off the analogue comparator to save power
    ACSR = (1<<ACD);

    // Initialise I/O ports
    init_io();

    // Initialise timer for fast PWM
    init_timer();

    // Initialise the rand() system
    init_rand();
}

void deinit() {
    // Turn off timer
    deinit_timer();

    // Turn off I/O
    deinit_io();

    // Start the watchdog to wake us up in 8 seconds
    start_wdt();

    // Go to sleep
    sleep();
}

uint8_t touched() {
    // Set PB4 to output and ground it
    DDRB = (1<<PB1) | (1<<PB4);
    PORTB = (1<<PB0) | (1<<PB2) | (1<<PB3);
    // Set PB4 to input and enable pullup
    DDRB = (1<<PB1);
    PORTB = (1<<PB0) | (1<<PB2) | (1<<PB3) | (1<<PB4);
    // See if it's charged
    asm("nop \r\n nop");
    return !(PINB & (1<<PB4));
}

volatile inline void delay() {
    asm("nop \r\n nop \r\n nop \r\n nop \r\n nop \r\n");
}

void fade_in() {
    uint16_t i;
    uint8_t j;
    for(i=65280; i>12800; i--) {
        OCR0B = i >> 8;
        for(j=0; j<10; j++)
            delay();
    }

    OCR0B = 50;
}

void light() {
    uint16_t i;
    uint16_t imax = rand() << 2;
    uint8_t j;
    for(i=0; i<imax; i++)
        for(j=0; j<255; j++)
            delay();
}

void fade_out() {
    uint16_t i;
    uint8_t j;
    for(i=12800; i<65280; i++) {
        OCR0B = i >> 8;
        for(j=0; j<10; j++)
            delay();
    }
    OCR0B = 255;
}

void dark() {
    uint16_t i;
    uint16_t imax = rand() << 4;
    uint8_t j;
    for(i=0; i<imax; i++)
        for(j=0; j<255; j++)
            delay();
}

int main() {
    // Initialise sub-systems
    init();
 
    // Check for capacitance, if found, light up
    while(touched()) {
        uint16_t i;
        uint8_t imax = rand() >> 4;
        for(i=0; i<imax; i++) {
            fade_in();
            light();
            fade_out();
            dark();
        }
    }

    // Turn everything off and go to sleep
    deinit();

    return 0;
}