SMOLSAT-1 Microcontroller Code

smolsat_1.c

#include <avr/sleep.h>
#include <avr/wdt.h>

const int PIN_LED = 0;

// ADCSRA disables ADC, saves ~230uA
// set_sleep_mode(SLEEP_MODE_PWR_DOWN) powers down everything and wakes
// up from WDT.
void setup() {
  pinMode(PIN_LED, OUTPUT);
  ADCSRA &= ~(1<<ADEN);
  set_sleep_mode(SLEEP_MODE_PWR_DOWN);
  sleep_enable();
}

// watchdog_counter++;
ISR(WDT_vect) {
}

void loop() {
  setup_watchdog(8);
  sleep_mode();
  fade();
}

// Sets the watchdog timer to wake us up, but not reset
// 0=16ms, 1=32ms, 2=64ms, 3=128ms, 4=250ms, 5=500ms
// 6=1sec, 7=2sec, 8=4sec, 9=8sec
// From: http://interface.khm.de/index.php/lab/experiments/sleep_watchdog_battery/
void setup_watchdog(int timerPrescaler) {
  // Limit incoming amount to legal settings
  if (timerPrescaler > 9 ) timerPrescaler = 9;

  byte bb = timerPrescaler & 7; 
  //Set the special 5th bit if necessary
  if (timerPrescaler > 7) bb |= (1<<5); 

  // This order of commands is important and cannot be combined
  // Clear the watch dog reset
  MCUSR &= ~(1<<WDRF); 
  // Set WD_change enable, set WD enable
  // Set new watchdog timeout value
  WDTCR |= (1<<WDCE) | (1<<WDE); 
  WDTCR = bb; 
  // Set the interrupt enable, this will keep unit from resetting after each int
  WDTCR |= _BV(WDIE); 
}

void fade() {
  int brightness = 0;
  int fadeAmount = 5;

  while(true) {
    brightness = brightness + fadeAmount;
    analogWrite(PIN_LED, brightness);
    if (brightness >= 255) {
      fadeAmount = -fadeAmount;
    }
    delay(30);
    if (brightness <= 0) {
      break;
    }
  }
}