// Puts MCU to sleep for specified number of seconds using
// WDT to wake every second and track number of seconds
void sleep(uint8_t s)
{
    uint8_t i;
    sleep_interval = 0;
    while (sleep_interval < s) {
        set_sleep_mode(SLEEP_MODE_PWR_DOWN);
        wdt_reset();
        sleep_mode();
    }
}