Digispark Power Save

Disable analog-to-digital conversion

To safe power you can deactivate function you don't use:

ADCSRA = 0; // Disable analog-to-digital conversion

Power down & button wakeup

This example shows how to let the ATTiny go to sleep and letting it wake up with an interrupt for a button state change:

// The pin to use in the interupt
#define PIN_I 0

bool _sleeping = false;
bool _goAsleep= false;

void setup() {
  /*************************\
  ** Prepare pin interrupt **
  \*************************/
  // Disable interrupts
  cli();
  // Enable interrupt handler (ISR) for PIN_I (PCINT1)
  PCMSK |= (1 << PIN_I);
  // Enable PCINT interrupt in the general interrupt mask
  GIMSK |= (1 << PCIE);
  // Set pin as input pin - has dedecated pullup
  pinMode(PIN_I, INPUT);
  // Last line of setup - re-enable interrupts
  sei();
}

ISR(PCINT0_vect) {
  // Handle only falling edges
  if (digitalRead(PIN_I) == LOW) {
    if (_sleeping) {
      // Interrupt while sleeping
      _sleeping = false;
      MCUCR&=~(1<<SE); // Disabling sleep mode
    } else {
      // Interrupt while awake -> flag sleep request
      _goAsleep = true;
    }
  }
}

void fallAsleep() {
  _sleeping = true;
  // Enabling sleep mode and powerdown sleep mode
  MCUCR|=(1<<SM1);
  // Enabling sleep enable bit
  MCUCR|= (1<<SE);
  // Sleep instruction to put controller to sleep
  __asm__ __volatile__ ( "sleep" "\n\t" :: );
}

void loop() {
  if (_goAsleep) {
    _goAsleep = false; // handled
    fallAsleep();
  }
}

Power down extreme

// Disable interrupts
cli(); 

// Reduce the clock frequency to conserve power
clock_prescale_set(clock_div_128);

// Disable all modules
power_all_disable();
set_sleep_mode(SLEEP_MODE_PWR_DOWN);

// Disable the ADC
ADCSRA &= ~ bit(ADEN); 

power_all_disable();

sleep_enable();
sleep_bod_disable();
sleep_cpu();